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UBC Theses and Dissertations

Performance evaluation of the integration of voice and data in a high-speed local area computer network… Lee, Jackson Ying-Kin 1987

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PERFORMANCE EVALUATION OF THE INTEGRATION OF VOICE AND DATA IN A HIGH-SPEED LOCAL AREA COMPUTER NETWORK THE EXPRESSNET by JACKSON YING-KIN LEE B.A.Sc, The University of New Brunswick, 1984 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of E l e c t r i c a l Engineering) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October 1987 @ Jackson Ying-Kin Lee, 1987 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C o lumbia, I agree t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s o r her r e p r e s e n t a t i v e s . I t i s un d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . DEPARTMENT OF ELECTRICAL ENGINEERING The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date : O c t o b e r , 1987 ABSTRACT A h i g h - s p e e d l o c a l a r e a c o m m u n i c a t i o n n e t w o r k . — t h e E x p r e s s n e t — i s i n v e s t i g a t e d i n t h i s t h e s i s w i t h r e g a r d t o v o i c e and d a t a t r a n s m i s s i o n s . P e r f o r m a n c e c r i t e r i a , s u c h as c h a n n e l u t i l i z a t i o n s , d e l a y c h a r a c t e r i s t i c s , and queue l e n g t h s a r e d e t e r m i n e d f r o m c o m p u t e r s i m u l a t i o n and n u m e r i c a l c a l c u l a t i o n a p p r o a c h e s . The p r o t o c o l i s p a r t i c u l a r l y s u i t a b l e f o r t h e t r a n s m i s s i o n o f p a c k e t i z e d v o i c e as i t i s a b l e t o g u a r a n t e e a n u p p e r b o u n d on t h e t r a n s m i s s i o n d e l a y f o r e a c h p a c k e t . The n e t w o r k u n d e r s t u d y t h u s w i l l f i n d m a j o r a p p l i c a t i o n i n f u t u r e o f f i c e a u t o m a t i o n , w h e r e l a r g e amoun t s o f v o i c e w i l l be i n t e g r a t e d w i t h d a t a . TABLE OF CONTENTS LIST OF ILLUSTRATIONS V GLOSSARY OF SYMBOLS X ACKNOWLEDGMENTS x i i 1. INTRODUCTION 1 1.1 ISDN 1 1.2 Organization of Thesis 4 1.3 Integration of Voice and Data i n Packet-switched Networks 5 1.3.1 Advantages 5 1.3.2 Performance C r i t e r i a for Data and Voice T r a f f i c .. 6 1.3.3 Transmission Procedures of Packetized Voice and Data 8 1.3.4 Channel Access Protocols 9 1.4 Scope of Thesis 11 1.4.1 Broadcast Systems, Round Robin Schemes, and Expressnet 11 1.4.2 Basic Assumptions and Performance Measures of Interest 13 2. TRANSMISSION OF DATA PACKETS IN EXPRESSNET 16 2.1 General Description of Expressnet 16 2.2 Assumptions Used in Simulation Model for Data Protocol 18 2.3 Summary of Results 20 2.3.1 Analysis of Results for Single Buffer Case 20 2.3.2 Analysis of Results for I n f i n i t e Buffer Case .... 32 3. TRANSMISSION OF VOICE PACKETS IN EXPRESSNET 36 3.1 Voice Protocol 36 3.1.1 General Requirement of Voice T r a f f i c 36 3.1.2 A r r i v a l Pattern of Voice Packets and Transmission Mechanism 38 3.2 Assumptions Used i n Simulation Model for Voice Protocol 39 3.3 Analysis of Results 43 3.4 C a l l Estimation Implementation 54 3.4.1 Introduction 54 3.4.2 Control Mechanism 56 3.4.3 Analysis of Results 58 4. INTEGRATION OF VOICE AND DATA IN EXPRESSNET 66 4.1 Introduction 66 4.2 Features of the Proposed Network Configuration 66 4.3 Proposed Packet Transmission Protocols 68 4.4 Summary of Results 71 4.4.1 Analysis of Results for VDl 72 4.4.2 Analysis of Results for VD2 78 4.4.3 Analysis of Results for VD3 88 5. COMPARISON OF THE DIFFERENT PROTOCOLS 100 6. CONCLUSIONS 107 APPENDICES Al C l a s s i f i c a t i o n of Data Performance Parameters 112 A2 C l a s s i f i c a t i o n of Voice Performance Parameters 112 B Transmission Mechanism of Expressnet 113 CI Flowchart for Main Program (Data, Voice) 119 C2 Flowchart for BOTRAIN (Data) 120 C3 Flowchart for CHECKSERVE (Data) 121 C4 Flowchart for VOICEGENERATE (Voice) 122 C5 Flowchart for BOTRAIN (Voice, with Discarding of Packets). .123 REFERENCES LIST OF ILLUSTRATIONS Page 1.1 Conceptual view of ISDN connection features 3 1.2 An integrated d i s t r i b u t e d communications architecture .... 3 1.3 Block diagram of integrated voice/data packet transmission system 10 1.4 Block diagram of multiple access schemes 12 2.1 Block diagram of Expressnet 17 2.2 Transmission procedure of Expressnet 19 2.3 U t l vs I AT, N = 20 23 2.4 Mean queue length vs U t l , N = 20 23 2.5 Mean wait time vs U t l , N = 20 25 2.6 Variance of wait time vs U t l , N = 20 25 2.7 U t l vs N, I AT « 12.5 27 2.8 Mean queue length vs U t l , IAT = 12.5 27 2.9 Mean wait time vs U t l , IAT = 12.5 29 2.10 Variance of wait time vs U t l , IAT = 12.5 29 2.11 U t l vs N, IAT • 12, 12.5 30 2.12 Mean queue length vs U t l , IAT = 12, 12.5 30 2.13 Mean wait time vs U t l , IAT » 12, 12.5 31 2.14 Variance of wait time vs U t l , IAT = 12, 12.5 31 2.15 U t l vs N, IAT • 28 34 2.16 Mean queue length vs N, IAT = 28 34 2.17 Mean wait time vs N, IAT = 28 35 2.18 Variance of wait time vs N, IAT = 28 35 3.1 Packet speech model 40 Page 3.2 Maximum ETE delay requirement 40 3.3 Voice transmission i n Expressnet 42 3.4 U t l vs N, V1/V2 46 3.5 Mean queue length vs U t l , V1/V2 46 3.6 Mean wait time vs U t l , V1/V2 47 3.7 Variance of wait time vs U t l , V1/V2 47 3.8 Mean queue length vs U t l , VI 48 3.9 Mean queue length vs U t l , V2 48 3.10 Mean t r a i n s i z e vs U t l , V1/V2 50 3.11 Variance of t r a i n size vs U t l , V1/V2 50 3.12 PDLP vs U t l , V1/V2 51 3.13 PDLP vs N, V1/V2 51 3.14 Markov chain for V2 protocol 52 3.15 Model for an active voice source •••• 53 3.16 VPDR vs U t l , V1/V2 55 3.17 VPDR vs N, V1/V2 55 3.18 C a l l a r r i v a l s and d i s t r i b u t i o n on-off model 56 3.19 Actual vs estimated # active stations , of. = 0.1 59 3.20 Actual vs estimated # active stations , Ot = 0.5 59 3.21 Actual vs estimated # active stations = 0.9 60 3.22 U t l vs N , the o r e t i c a l / simulation 60 3.23 U t l vs N , d i f f e r e n t oC 63 3.24 Mean wait time, mean queue length vs N 63 3.25 Variance .of wait time vs N 64 3.26 % packet discarded, blocking p r o b a b i l i t y vs N 64 Page 3.27 % packet discarded vs blocking pr o b a b i l i t y % 65 3.28 % packet discarded vs blocking pr o b a b i l i t y % 65 4.1 Configuration of integrated V/D Expressnet 67 4.2 Utl vs N, VD1, I AT = 12 73 4.3 Mean queue length vs U t l , VDl, I AT = 12 73 4.4 Mean wait time vs U t l , VDl, I AT = 12 74 4.5 Variance of wait time vs U t l , VDl, I AT = 12 74 4.6 Mean t r a i n s i z e vs U t l , VDl, I AT = 12 75 4.7 Variance of t r a i n size vs U t l , VDl, I AT = 12 75 4.8 PDLP vs U t l , VDl, I AT = 12 76 4.9 PDLP vs N, VDl, I AT = 12 76 4.10 U t l vs I AT, VDl, N = 14 77 4.11 Mean queue length vs I AT, VDl, N = 14 77 4.12 Mean wait time vs I AT, VDl, N = 14 79 4.13 Variance of wait time vs I AT, VDl, N = 14 79 4.14 Mean t r a i n size vs I AT, VDl, N = 14 80 4.15 Variance of t r a i n size vs I AT, VDl, N = 14 80 4.16 Utl vs N, fixed I AT, K d a t a , if 81 4.17 Mean queue length vs U t l , fixed I AT, K d a f c a , ^ 81 4.18 Mean wait time vs U t l , fixed IAT, K d a t a , *f 82 4.19 Variance of wait time vs U t l , fixed IAT, K d a f c a , Y 82 4.20 Mean t r a i n size vs U t l , fixed IAT, K d a t a , <f 83 4.21 Variance of t r a i n size vs U t l , fixed IAT , K d a t a » ^ 8 3 4.22 % D, V pks discarded vs U t l , fixed IAT, K d a t a , <f 84 4.23 % d e l a y e d v o i c e p a c k e t s vs U t l , f i x e d IAT, K d a t a » 8 4 4.24 U t l vs Y ' v a r y i n g K d a t a , f i x e d IAT , N 85 4.25 Mean queue l e n g t h vs <^  , v a r y i n g K d a t a » f i x e d IAT, N ....... 85 4.26 Mean w a i t t i m e vs <X , f i x e d K, ^ , IAT , N 86 1 d a t a 4.27 V a r i a n c e o f w a i t t i m e vs Cf f i x e d K, ^ , IAT; N 86 1 d a t a 4.28 Mean w a i t t i m e vs , v a r y i n g K d a t a ' f i x e d IAT, N 87 4.29 V a r i a n c e o f w a i t t i m e vs , v a r y i n g K d a t a » f i x e d IAT, N .... 87 4.30 Mean t r a i n s i z e vs , v a r y i n g K d a t a » f i x e d IAT, N 89 4.31 V a r i a n c e o f t r a i n s i z e vs , v a r y i n g K d a t a » f i x e d IAT, N ... 89 4.32 % Data p a c k e t s d i s c a r d e d v s f , v a r y i n g K d a t a » f i x e d IAT, N .... 90 4.33 % V o i c e p a c k e t s d i s c a r d e d vs ^ , v a r y i n g K d a t a » f i x e d IAT, N ... 90 4.34 % D, V p a c k e t s d i s c a r d e d vs , f i x e d K d a t a » f i x e d IAT, N — °.i 4.35 % d e l a y e d V pks(PDLP) vs <f ,varying K , f i x e d IAT, N & HoiawoH w  Y ,varying d a t a , f i x e d 91 4.36 % d a t a t r a n s m i t t e d vs ^  , v a r y i n g K d a t a » f i x e d IAT, N 92 j j v a r y i n g „ d a t a , 4.38 U t l vs N, f i x e d K d a t a , , IAT 94 4.37 % v o i c e t r a n s m i t t e d vs v a r y i n g K, , f i x e d IAT, N 92 d a ' 7 'eue l e n g t h vs N, f i x e d K 4.39 Mean queue l e n g t h vs N, f i x e d K d a t a » *f > I A T 94 4.40 Mean w a i t time vs N, f i x e d K d a f c a , (f , IAT 95 4.41 V a r i a n c e o f w a i t time vs N, f i x e d K d a t a » > I A T 95 4.42 Mean w a i t t i m e o f v o i c e pks vs N, f i x e d K d a f c a , , IAT 96 4.43 V a r i a n c e o f w a i t time of v o i c e pks vs N , f i x e d K d a t a ' ^ > IAT.. 96 4.44 Mean t r a i n s i z e vs N , f i x e d K d a t a # < I A T 97 4.45 V a r i a n c e o f t r a i n s i z e vs N, f i x e d K d a t a > , IAT 97 4.46 % Data, V o i c e T r a n s m i t t e d vs N, f i x e d K d a t a » » I A T 98 4.47 % V o i c e p a c k e t s d i s c a r d e d vs N , f i x e d K d a t a , <y/ IAT 98 vi i i P a 9 e 4.48 Prob. d a t a t x / d e l a y e d vs N, f i x e d K d a t a , <p , I AT 99 4.49 Prob. d a t a d e l a y e d vs N, f i x e d K d a t a , (f , I AT 99 5.1 U t l vs N 102 5.2 Mean queue l e n g t h vs N 102 5.3 Mean w a i t time of d a t a p a c k e t s vs N 103 5.4 V a r i a n c e of w a i t time o f d a t a p a c k e t s vs N 103 5.5 Mean w a i t time of v o i c e p a c k e t s vs N 104 5.6 V a r i a n c e o f w a i t time o f v o i c e p a c k e t s vs N 104 5.7 Mean t r a i n s i z e vs N 105 5.8 V a r i a n c e o f t r a i n s i z e vs N 105 5.9 % v o i c e p a c k e t s d i s c a r d e d vs N 106 5.10 % d e l a y e d v o i c e p a c k e t s vs N 106 B l G l o b a l t i m i n g diagram o f E x p r e s s n e t 117 B2 F l o w c h a r t f o r the E x p r e s s n e t a c c e s s p r o t o c o l 118 GLOSSARY OP SYMBOLS N t o t a l number of s t a t i o n s connected to the cab l e or net wo r k C t o t a l a v a i l a b l e channe l c a p a c i t y (Mbps) B s i z e o f data packets ( b i t s ) v p ropaga t i on v e l o c i t y of s i g n a l s i n a c o a x i a l cab le (km/s ec) Lc l e n g t h of c ab l e (km) ^ a r r i v a l r a t e of data packets (packets I s l o t ) IAT mean l n t e r a r r i v a l t ime of data packets (seconds) t one-way p ropaga t i on de l ay ( seconds ) *^ "C p r o p a g a t i o n de l ay i n c o n n e c t i o n cab l e (seconds) T t r a n s m i s s i o n time of a packet (seconds) t t ime taken to detect presence or absence of c a r r i e r ^ (seconds) T locom d u r a t i o n of l ocomot ive (seconds) a r a t i o between one-way p ropaga t i on de lay and the packet t r a n s m i s s i o n t ime SIM s i m u l a t i o n ( r e s u l t s ) TH t h e o r e t i c a l ( r e s u l t s ) U t l ( f ) channe l u t i l i z a t i o n mean queue l eng th of sy s t em, mean number of packets w a i t i n g i n the system Q*2 mean number of packets i n the sys tem, i n c l u d i n g the one be ing se rved X t r a n s m i s s i o n pe r i od of a p acke t , i n c l u d i n g overhead be fore each t r a n s m i s s i o n to determine 1 which user gets access to the c h a n n e l , preamble t r a n s m i s s i o n t i m e , and data t r a n s m i s s i o n time (seconds) Y the t ime that the channe l becomes i d l e be fore rounds ( i n t e r r o u n d overhead) (seconds) D n network t r a n s i t t ime of a b i t ( seconds) D v maximum t o l e r a b l e d e l a y o f an i n d i v i d u a l b i t , d e f i n e d as t h e l a p s e o f t i m e f r o m t h e moment t h e b i t i s p r o d u c e d t o t h e t i m e when i t i s s u c c e s s f u l l y t r a n s m i t t e d t o t h e r e c e i v e r ( s e c o n d s ) B v number o f b i t s i n a f u l l v o i c e p a c k e t T f p a c k e t f o r m a t i o n t i m e i n o r i g i n a t i n g . t e r m i n a l o r p a c k e t i z a t i o n t i m e o f B v b i t s ( s e c o n d s ) W mean o v e r a l l w a i t i n g t i m e ( s e c o n d s ) Wq mean w a i t i n g t i m e o f d a t a p a c k e t s ( s e c o n d s ) Wy mean w a i t i n g t i m e o f v o i c e p a c k e t s ( s e c o n d s ) G~w2 v a r i a n c e o f o v e r a l l w a i t i n g t i m e o f p a c k e t s ^ W p ^ v a r i a n c e o f w a i t i n g t i m e o f d a t a p a c k e t s ^*Wy2 v a r i a n c e o f w a i t i n g t i m e o f v o i c e p a c k e t s Tz mean t r a i n s i z e ^""TZ^ v a r i a n c e o f t r a i n s i z e PDLP p e r c e n t a g e o f v o i c e p a c k e t s d e l a y e d more t h a n 20 ms VPDR p e r c e n t a g e o f p a c k e t s t h a t a r e t o be d i s c a r d e d i f t h e y a r e t o i n c u r a d e l a y more t h a n t h e t i m e t a k e n t o t r a n s m i t a f u l l v o i c e p a c k e t p g t f u l l f u l l s i z e o f v o i c e p a c k e t , g i v e n by p g t f u l l • D n / ( B v / C ) Njnax maximum number o f v o i c e u s e r s s u p p o r t a b l e ( C / C v ) s u c h t h a t t h e l o n g e s t d e l a y e x p e r i e n c e d by e a c h b i t i s g u a r a n t e e d t o be l e s s t h a n D n B v ( l ) l e n g t h o f v o i c e p a c k e t o c c u p i e d by o v e r h e a d B v ( 2 ) l e n g t h o f v o i c e p a c k e t c o n s i s t i n g o f a c t u a l i n f o r m a t i o n b i t s N t number o f v o i c e s t a t i o n s t h a t c a n be a c c o m m o d a t e d by s y s t e m s u c h t h a t t h e maximum t o l e r a b l e n e t w o r k d e l a y (20 ms) i s n o t e x c e e d e d a t a n y t i m e C v b i t r a t e o f t h e v o c o d e r i n t h e o r i g i n a t i n g v o i c e t e r m i n a l ( k b p s ) T v t r a n s m i s s i o n t i m e o f a p a c k e t i n t h e c h a n n e l ( s e c o n d s ) , g i v e n by B v / C \ c a r r i v a l r a t e o f v o i c e c a l l s , i n c a l l s / m i n u t e ACKNOWLEDGEMENTS The a u t h o r w i s h e s t o e x p r e s s h i s s i n c e r e g r a t i t u d e t o h i s s u p e r v i s i n g p r o f e s s o r , B r . H .W. L e e , f o r h i s u n e n d i n g p a t i e n c e , i n v a l u a b l e g u i d a n c e , a n d m e t i c u l o u s s u p e r v i s i o n t h r o u g h o u t t h e c o u r s e o f t h e p r o j e c t . A l s o t o be e x p r e s s e d a r e t h e a u t h o r ' s s e n t i m e n t s o f a p p r e c i a t i o n and a f f e c t i o n t o w a r d s h i s p a r e n t s , M r . a n d M r s . C . C . L e e , whose l o v e and c o n t i n u o u s s u p p o r t h e l p e d make t h e c o m p l e t i o n o f t h i s t h e s i s p o s s i b l e . G r a t e f u l a c k n o w l e d g e m e n t i s g i v e n t o t h e a u t h o r ' s d e v o t e d f r i e n d s , M r . I . L . S o e h a r j o n o a n d M i s s B . R o b l e s , f o r t h e i r c o n s t a n t e n c o u r a g e m e n t , p a r t i c u l a r l y t o M i s s R o b l e s f o r p r o o f r e a d i n g t h e p a p e r . The a u t h o r a l s o e x t e n d s h i s t h a n k s t o M s . R a c h e l R o u s s e a u f o r t y p i n g t h e t h e s i s . 1. INTRODUCTION 1.1 ISDN I t i s now w i d e l y r e c o g n i z e d t h a t t h e " I n t e g r a t e d S e r v i c e s D i g i t a l N e t w o r k ( I S D N ) " c o n c e p t i s p r o v i d i n g a u s e f u l f r a m e w o r k f o r t h e d e v e l o p m e n t o f f u t u r e t e l e c o m m u n i c a t i o n s n e t w o r k s and s e r v i c e s . An ISDN c a n be r e g a r d e d as a g e n e r a l - p u r p o s e , i n t e l l i g e n t d i g i t a l n e t w o r k c a p a b l e o f s u p p o r t i n g ( o r i n t e g r a t i n g ) a w i d e r a n g e o f s e r v i c e s ( v o i c e and n o n - v o i c e ) u s i n g a s m a l l s e t o f s t a n d a r d m u l t i p u r p o s e u s e r - n e t w o r k i n t e r f a c e s and d i g i t a l t r a n s m i s s i o n l i n k s . [ I S D N 1-3] The m a j o r a r g u m e n t i n f a v o u r o f d i g i t a l t e c h n o l o g y i s t h a t t h e t r a n s f e r o f d i g i t a l i n f o r m a t i o n i s l e s s s e n s i t i v e t o n o i s e , c r o s s t a l k , and d i s t o r t i o n t h a n t h a t o f a n a l o g d a t a . F a d e d s i g n a l s c a n a l s o be r e g e n e r a t e d w i t h o u t i n t r o d u c i n g c u m u l a t i v e d e g r a d a t i o n s . As t h e common c a r r i e r n e t w o r k e v o l v e s t o a p r e d o m i n a n t l y d i g i t a l b a c k b o n e p l a n t , t h e n e t w o r k p r o c e s s i n g f u n c t i o n s a r e a b l e t o d y n a m i c a l l y a l l o c a t e p o r t i o n s o f t h e c a p a c i t y t o s u p p o r t an a r r a y o f f u n c t i o n a l l y i n d e p e n d e n t n e t w o r k s and f a c i l i t i e s , c l o s e l y t a i l o r e d t o i n d i v i d u a l u s e r c h a r a c t e r i s t i c s . The f u l l c o m p l e m e n t o f c o m m u n i c a t i o n f a c i l i t i e s w o u l d c o m p r i s e v o i c e , d i g i t a l d a t a , image ( f a c s i m i l e ) , and v i d e o c o m m u n i c a t i o n s . T h e s e f u n c t i o n s w o u l d be i n t e g r a t e d i n t o a n e t w o r k w i t h a n o v e r a l l c a p a b i l i t y as d e p i c t e d i n F i g u r e 1 . 1 . [ I S D N 2] H i g h - c a p a c i t y , h i g h - q u a l i t y c o m m u n i c a t i o n c h a n n e l s , l a r g e l y o v e r s a t e l l i t e f a c i l i t i e s , o r by r a d i o m e a n s , p r o v i d e t h e m a j o r l o n g h a u l c omponen t o f t h e d i s t r i b u t e d a r c h i t e c t u r e ( F i g u r e 1 . 2 ) . [ I S D N 1] The p r i n c i p a l b e n e f i t s t o t h e u s e r c a n be e x p r e s s e d i n t e r m s o f economy and f l e x i b i l i t y . The u l t i m a t e o b j e c t i v e s o f i n t e g r a t i o n a r e t o a c c o m m o d a t e v a r i o u s e x i s t i n g and new d e v i c e s , p r o v i d e a w i d e r a n g e o f f l e x i b i l i t y and v e r s a t i l i t y t o t e r m i n a l c o n n e c t i v i t y , and r e a l i z e t h e e c o n o m i e s o f e q u i p m e n t c o m m o n a l i t y , l a r g e - s c a l e i n t e g r a t i o n , h i g h e r r e s o u r c e u t i l i t y , and c o m b i n e d n e t w o r k o p e r a t i o n s , m a i n t e n a n c e , a n d a d m i n i s t r a t i v e p o l i c i e s . A c t i v i t i e s c u r r e n t l y u n d e r way a r e l e a d i n g t o t h e d e v e l o p m e n t o f w o r l d w i d e I S D N . A number o f s t a n d a r d o r g a n i z a t i o n s a r e i n v o l v e d i n v a r i o u s a s p e c t s o f I S D N , w i t h CCITT b e i n g t h e m a j o r c o n t r o l l i n g b o d y . Among t h e f u l l I SDN c o n t e x t , t h i s t h e s i s d e a l s p r i m a r i l y w i t h t h e s e c t i o n on t h e i n t e g r a t i o n o f p a c k e t i z e d v o i c e and d a t a i n a l o c a l a r e a n e t w o r k , w i t h e m p h a s i s on v o i c e t r a n s m i s s i o n and p r o t o c o l s . Telephone}. Customer ISDN Interface 1 Customer ISDN Interface 2 Data [Terminal^ Customer ISDN face i D i g i t a l pipes (PBXh ISDN Central Office Subscriber loop and ISDN channel structures Local Area Network (LAN) Packet-switched network C i r c u i t -switched network Other networks Data bases Other services Figure 1.1 Conceptual view of ISDN connection features CBX+ SATELLITE E. S. LOCAL NETWORK E.S. = EARTH STATION PBX = PRIVATE BRANCH EXCHANGE CBX = COMPUTERIZED PBX CUSTOMER CONTROLLER+E.S. LOCAL NETWORK F i g u r e 1.2 An i n t e g r a t e d d i s t r i b u t e d communications a r c h i t e c t u r e M o r e o v e r , i t i s a s s u m e d t h a t t h e d i f f e r e n t u s e r nodes i n t h e c o m m u n i c a t i o n e n v i r o n m e n t a r e s t a t i o n a r y . F o r i n f o r m a t i o n o n t h e i n t e g r a t i o n o f v o i c e and d a t a on s a t e l l i t e and m o b i l e r a d i o t r a n s m i s s i o n , t h e r e a d e r i s u r g e d t o r e f e r t o r e f e r e n c e s u n d e r t h e "MOB" h e a d i n g . 1.2 O r g a n i z a t i o n of T h e s i s The o r g a n i z a t i o n o f t h i s r e p o r t i s as f o l l o w s . M o t i v a t e d by ISDN d e v e l o p m e n t s d i s c u s s e d i n S e c t i o n 1 . 1 , S e c t i o n 1.3 h i g h l i g h t s g e n e r a l t r a n s m i s s i o n a s p e c t s o f i n t e g r a t i o n o f v o i c e a n d d a c a . T h i s p a r t c o v e r s p o t e n t i a l b e n e f i t s , p e r f o r m a n c e c r i t e r i a , t r a n s m i s s i o n p r o c e d u r e s , and c h a n n e l a c c e s s p r o t o c o l s . The s c o p e o f t h i s t h e s i s i s t h e n p r e s e n t e d i n S e c t i o n 1 . 4 , i n w h i c h a b r i e f i n t r o d u c t i o n t o t h e E x p r e s s n e t a n d v a r i o u s a s s u m p t i o n s a r e i n c l u d e d . S e c t i o n 2 d e a l s w i t h t h e d a t a p r o t o c o l s o f t h e E x p r e s s n e t a n d p r o v i d e s d e s c r i p t i o n on t h e g e n e r a l t r a n s m i s s i o n m e c h a n i s m . S i m u l a t i o n r e s u l t s i n f o r m o f g r a p h s a r e a p p e n d e d a t d i f f e r e n t p l a c e s w i t h i n t h e s e c t i o n . S e c t i o n 3 i s d e v o t e d t o t h e o p e r a t i o n o f t h e v o i c e t r a n s m i s s i o n a l g o r i t h m s . The d e s c r i p t i o n s o f t h e i n t e g r a t e d v o i c e a n d d a t a p r o t o c o l s o c c u p y S e c t i o n 4 . S e c t i o n 5 d raws a c o m p a r i s o n among t h e v a r i o u s p r o t o c o l s . A l l t h e s e s e c t i o n s o b s e r v e t h e f o r m a t e m p l o y e d i n S e c t i o n 2 . A d i s c u s s i o n on t h e s i m u l a t i o n r e s u l t s , f u t u r e t r e n d s , and p o s s i b l e r e s e a r c h a r e a s a r e p r o v i d e d i n S e c t i o n 6, w h i c h s u m m a r i z e s t h e w h o l e t h e s i s . I n c o n j u n c t i o n w i t h i n t e r p r e t a t i o n s o f r e s u l t s , d i a g r a m s a r e p r e s e n t e d w h e r e v e r t h e a u t h o r deems a p p r o p r i a t e . A g l o s s a r y o f s y m b o l s , a l i s t o f i l l u s t r a t i o n s , as w e l l as a b i b l i o g r a p h y s e c t i o n a r e a l s o i n c l u d e d f o r t h e c o n v e n i e n c e o f t h e r e a d e r . 1.3 I n t e g r a t i o n o f V o i c e and Data i n Packe t - Sw i t ched Networks 1.3.1 Advantages The r e c e n t r a p i d g r o w t h o f d i g i t a l c o m p u t e r c o m m u n i c a t i o n n e t w o r k s h a v e made i t p o s s i b l e t o use t h e e x i s t i n g c o m p u t e r d a t a c o m m u n i c a t i o n t e c h n o l o g y f o r s p e e c h c o m m u n i c a t i o n . B o t h s i l e n t p e r i o d s and l ow b i t r a t e o f s p e e c h m o t i v a t e t h e c o n s i d e r a t i o n o f p a c k e t i z e d v o i c e . A p a c k e t - s w i t c h e d i n t e g r a t e d d i g i t a l v o i c e and d a t a c o m m u n i c a t i o n n e t w o r k s y s t e m i s i n t e r e s t i n g b e c a u s e i t o f f e r s t h e f o l l o w i n g p o t e n t i a l b e n e f i t s : - e c o n o m i c a l b e c a u s e s w i t c h i n g and t r a n s m i s s i o n r e s o u r c e s a r e s h a r e d - e n h a n c e d s e r v i c e s f o r u s e r s who r e q u i r e a c c e s s t o b o t h v o i c e and d a t a c o m m u n i c a t i o n s f l e x i b l e i n t e r n e t w o r k i n g a l l o w s i n t e r c o m m u n i c a t i o n among v o i c e u s e r s on d i f f e r e n t t y p e s o f n e t w o r k s e f f i c i e n t c h a n n e l u t i l i z a t i o n by t r a n s m i t t i n g o t h e r v o i c e and d a t a p a c k e t s d u r i n g s i l e n c e i n t e r v a l - a l l o w s c o n v e n i e n t a c c o m m o d a t i o n o f v o i c e t e r m i n a l s w i t h d i f f e r e n t r a t e s and d a t a f o r m a t s o n l y t h e r e q u i r e d c h a n n e l c a p a c i t y i s u s e d t o t r a n s m i t r a t h e r t h a n a f i x e d m in imum b a n d w i d t h i n c r e m e n t t y p i c a l l y u s e d i n c i r e u i t - s w i t c h e d n e t w o r k s - s e c u r i t y t e c h n i q u e s c a n be a p p l i e d t o d i g i t i z e d v o i c e - v a r i a b l e - b i t - r a t e v o i c e t r a n s m i s s i o n t e c h n i q u e s a r e p o s s i b l e , e i t h e r t o r e d u c e a v e r a g e e n d - t o - e n d b i t r a t e o r d y n a m i c a l l y a d a p t v o i c e b i t r a t e t o n e t w o r k co nd i t i o n s , and - f l e x i b i l i t y i n c o p i n g w i t h t h e c h a n g i n g t r a f f i c p a t t e r ns 1.3.2 Performance C r i t e r i a for Data and V o i c e T r a f f i c To f a c i l i t a t e d e s i g n and e v a l u a t i o n o f d i f f e r e n t n e t w o r k c o n f i g u r a t i o n s , i t i s e s s e n t i a l t o d e f i n e a s e t o f p e r f o r m a n c e c r i t e r i a w h i c h w o u l d p r o v i d e , i n a c o n c r e t e m a n n e r , a b e t t e r v i e w o f r e l a t e d i s s u e s and p o s s i b l e t r a d e o f f s b e t w e e n r e s o u r c e s u t i l i z a t i o n and p e r f o r m a n c e e x p e c t a t i o n . E x t e n s i v e w o r k has b e e n c a r r i e d o u t i n r e c e n t y e a r s i n t h i s a r e a . [PFM 1] G r u b e r [PFM 1] a d d r e s s e d t o p - d o w n , e n d - t o - e n d u s e r -o r i e n t e d p e r f o r m a n c e r e q u i r e m e n t s f o r v o i c e and d i g i t a l d a t a s e r v i c e s . A c c o r d i n g t o G r u b e r , p e r f o r m a n c e c r i t e r i a c a n be c l a s s i f i e d as b e i n g e i t h e r t r a n s m i s s i o n - o r i e n t e d o r s e r v i c e -o r i e n t e d . F a l l i n g u n d e r e a c h c a t e g o r y a r e q u a l i t y , d e l a y , and a v a i l a b i l i t y c o n s i d e r a t i o n s . A s u b s e t o f t h e d a t a / v o i c e p e r f o r m a n c e p a r a m e t e r s a r e t a b u l a t e d i n A p p e n d i x A . B a s i c a l l y , e v a l u a t i o n c r i t e r i a f o r p e r f o r m a n c e o f s w i t c h e s a n d n e t w o r k s t h a t c a r r y b o t h v o i c e and d a t a a r e p r i m a r i l y t h e same as t h a t f o r s e p a r a t e n e t w o r k s . One d i f f e r e n c e i s t h a t t h e v a r i o u s p e r f o r m a n c e c r i t e r i a must be s a t i s f i e d s i m u l t a n e o u s l y f o r d i f f e r e n t v o i c e and d a t a t r a f f i c m i x t u r e s . P e r f o r m a n c e c r i t e r i a i n c l u d e t h e e v a l u a t i o n o f d e l a y s , a s s e s s m e n t o f s y s t e m t r a f f i c h a n d l i n g c a p a c i t i e s , t h r o u g h p u t , t r a n s m i s s i o n c a p a c i t y s p e n t o n c o n t r o l o v e r h e a d , and a n a l y s i s o f b l o c k i n g and e x p e c t e d w a i t i n g t i m e . The p e r f o r m a n c e c r i t e r i a a r e a p p l i e d t o e a c h t y p e o f t r a f f i c . Among t h e v a r i o u s p a r a m e t e r s d i s c u s s e d i n G r u b e r ' s p a p e r d e l a y a n d e r r o r p e r f o r m a n c e a r e t h e most c r u c i a l ones t o be c o n s i d e r e d i n an i n t e g r a t e d v o i c e and d a t a n e t w o r k . F o r t h e v o i c e t r a n s m i s s i o n c a s e , n o i s e has l e s s d e t r i m e n t a l e f f e c t o n v o i c e i n t e l i g i b i l i t y t h a n i t does o n d a t a . T h e r e f o r e e r r o r c r i t e r i a f o r v o i c e need not be as s t r i n g e n t as t h a t f o r d a t a . H o w e v e r , d e l a y i n d e l i v e r y o f r e a l t i m e v o i c e a b o v e a c e r t a i n t h r e s h o l d m i g h t c a u s e a n n o y a n c e f r om t h e u s e r ' s p o i n t o f v i e w . On t h e o t h e r h a n d , d a t a s i g n a l s r e q u i r e c o n s i d e r a b l y b e t t e r e r r o r p e r f o r m a n c e t h a n v o i c e b u t a r e no t as c o n c e r n e d a b o u t t r a n s m i s s i o n d e l a y . I n v i e w o f t h e a b o v e , t h e p r o b l e m o f i n t e g r a t e d n e t w o r k d e s i g n r e q u i r e s t h e d e t e r m i n a t i o n o f m in imum c o s t n e t w o r k r e s o u r c e s ( n o d e s , l i n k s , c a p a c i t i e s ) w h i c h s a t i s f y a v e r a g e e n d - t o - e n d ( E T E ) d e l a y f o r p a c k e t - s w i t c h e d t r a f f i c and r e l i a b i l i t y c o n s t r a i n t s . T h u s , t h e d e s i g n p r o b l e m i n c l u d e s t h e s u b p r o b l e m s o f c a p a c i t y a s s i g n m e n t , r o u t i n g , and t o p o l o g i c a l des i g n . 1.3.3 T r a n s m i s s i o n Procedures o f P a c k e t i z e d Vo i ce and Data S i n c e much wo rk has b e e n done on t h e t r a n s m i s s i o n o f d a t a o n P a c k e t S w i t c h e d ( P S ) n e t w o r k s , t h e e m p h a s i s o f t h e f o l l o w i n g d i s c u s s i o n w i l l be o n v o i c e c o m m u n i c a t i o n , w i t h o c c a s i o n a l r e f e r e n c e t o d a t a t r a f f i c . The t e r m p a c k e t i z e d v o i c e means d i g i t i z e d v o i c e c a r r i e d i n t h e f o r m o f p a c k e t s o v e r a p a c k e t s w i t c h e d c o m m u n i c a t i o n n e t w o r k . T h i s t e r m u s u a l l y i m p l i e s r e a l - t i m e c o n v e r s a t i o n s b e t w e e n two p e r s o n s a t g e o g r a p h i c a l l y d i s p e r s e d l o c a t i o n s . M a j o r p e r f o r m a n c e c r i t e r i a as a p p l i e d t o v o i c e a r e : - v o i c e q u a l i t y , i n c l u d i n g d e l a y p e r f o r m a n c e , p r o b a b i l i t y o f l o s s o f c a l l s , p r o b a b i l i t y o f c l i p p i n g QPV 1-5, VN 1-2 3 - t h r o u g h p u t , and r e l i a b i l i t y . Other a spects In t h i s branch of communication i n c l u d e : bu f f e r s i z i n g of a Packet Vo ice Rece iver (PVR) [PVR 1-2] - o p t i m a l packet l e n g t h - t r a f f i c models (queueing a n a l y s i s ) - impact o f e r r o r s , and v o i c e s t o r a g e . The b a s i c scheme for packet v o i c e t r a n s m i s s i o n i nc ludes v o i c e encod ing , p a c k e t i z a t i o n , t r a n s m i s s i o n , packet reassembly , and b u f f e r i n g fo l lowed by decoding and p l a y i n g back [PVR 2] ( F i g u r e 1 .3 ) . [MOB 2 ,3 , SW 1, PVR 1, VDN 1] 1.3*4 Channel Access P r o t o c o l s With regard to the i n t e g r a t i o n of v o i c e and data in a l o c a l area network, the most important area to be cons ide red is the e s t ab l i shment of a p p r o p r i a t e channe l access p r o t o c o l s or s c h e d u l i n g schemes. Th i s t h e s i s d e s c r i b e s a m u l t i p l e x e d t r a f f i c from s e v e r a l users and d i f f e r e n t a p p l i c a t i o n s on the same b a n d w i d t h - l i m i t e d c h a n n e l . In order to ach ieve a h igher u t i l i z a t i o n , i t i s necessary t h a t a m u l t i - a c c e s s scheme be r e s p o n s i v e to the p a r t i c u l a r c h a r a c t e r i s t i c s o f each t y p e o f t r a f f i c , v o i c e , and d a t a . For data t r a f f i c , much r e s e a r c h has been done on m u l t i p l e access methods and many of the proposed schemes have been SP SRC DIGITAL DATA TRANSMITTER TERMINAL VOICE ENCODING PACKETIZATION f i l t e r A/D CODEC (vocoder) SAD Packet-i z e r TRANSMISSION 'NETWORK" with s tochast ic behaviour ( l i n k s , queues, switching devices ) -may include store-and-forward I* Processing delay Packet loading time 135 ms Rad l o^b l e^SAT j Network t l en t time DIGITAL DATA RECEIVER TERMINAL DEOOOINQ rece iver queue D/A CODEC (decoder) PSCKET PFAQgCTmi.V * BUFFER TNT. spkr m Receiving t  t rans- buffer delay »e U 1*0 ms Processing delay 150 ms 5 ms o I Effects o f excessive delay Figure 1.3 t r a n s i t queue trimming Network nodes d iscard packets Block Diagram of Integrated Voice/Data Packet Transmission System Receiver d iscard packets i f "too l a t e " Packet format: at point A CUT] at point B I H [ TSJ SP S/H: Sample & Hold SP : Speech SRC: Source Spkr: Speaker H : Header Timestamp Data S a t e l l i t e fev?ty Detector TS : i m p l e m e n t e d i n a c t u a l n e t w o r k s ; a n e x a m p l e o f t h i s i s t h e p o p u l a r E t h e r n e t , m a k i n g use o f t h e CSMA/CD p r o t o c o l . H o w e v e r , as t h e a p p l i e d l o a d i n c r e a s e s , o r i n c a s e s where t h e p r o p a g a t i o n d e l a y i s r e l a t i v e l y l a r g e , t h e p e r f o r m a n c e o f c o n v e n t i o n a l s chemes p r o v e s t o be u n s a t i s f a c t o r y , e s p e c i a l l y when v o i c e t r a f f i c i s i n v o l v e d . As a r e s u l t , many new p r o t o c o l s h a v e b e e n p r o p o s e d i n a n a t t e m p t t o i m p r o v e n e t w o r k p e r f o r m a n c e w h i l e s a t i s f y i n g t r a f f i c r e q u i r e m e n t s o f e a c h c l a s s . ( F i g u r e 1.4) I t i s t h e p u r p o s e o f t h i s t h e s i s t o l o o k i n t o t h e p e r f o r m a n c e o f a new n e t w o r k p r o t o c o l , t h e E x p r e s s n e t , i n a n i n t e g r a t e d v o i c e and d a t a e n v i r o n m e n t . 1.4 Scope o f T h e s i s 1.4.1 Broadcast Systems, Round Robin Schemes, and Expressnet The c o m m u n i c a t i o n a r c h i t e c t u r e o f i n t e r e s t i n t h i s t h e s i s i s b r o a d c a s t i n g . B r o a d c a s t s y s t e m s c a n be c l a s s i f i e d as e i t h e r b i d i r e c t i o n a l o r u n i d i r e c t i o n a l . I n t h e f o r m e r c a s e , B i d i r e c t i o n a l B r o a d c a s t S y s t e m s ( B B S ) , s u c h as E t h e r n e t , a l l t h e c o m m u n i c a t i n g d e v i c e s a r e c o n n e c t e d t o a common c a b l e o n w h i c h t r a n s m i s s i o n s i g n a l s p r o p a g a t e i n b o t h d i r e c t i o n s . I n t h e l a t t e r c a s e , c ommon ly r e f e r r e d t o as U n i d i r e c t i o n a l B r o a d c a s t S y s t e m s ( U B S ) , t r a n s m i s s i o n s i g n a l s a r e f o r c e d t o f l l E D SCHEMES I B M FPHA STOMA CDMA WW AfTKOACHESt-(CUHVUI110WAL) MULTIPLE ACCESS TECmfiqPES PTKAKIC SCHEMES CXWTEWTIOH SCHEMES  (KANPOH ACCESS) COOHPIKATEP SCHEMES TPRB S1AU1EU C8MA  ALOHA ALOTtA r o t x rwc ttSEHVATIOK COWTHCT-TnZE TECnKIQPES ( • • « . AT . M t . t O . MSAP )  THEE ALGORITHM PSMA F i g u r e 1 . 4 B l o c k diagram o f m u l t i p l e a c c e s s schemes p r o p a g a t e i n o n l y one d i r e c t i o n o f t h e c a b l e . E x a m p l e s o f p r o t o c o l s u s e d f o r t h i s c o n f i g u r a t i o n a r e Round R o b i n (RR) p r o t o c o l s [TH 9] and t h e i r v a r i a t i o n s , s u c h as E x p r e s s n e t and Fas n e t . The c o n v e n t i o n a l RR s chemes a l l o w t h e u s e r s t o s e n d o n l y one p a c k e t a t a t i m e . I t has a f i x e d o v e r h e a d f o r e a c h p a c k e t . E a c h s u b s c r i b e r , i n a p r e s c r i b e d o r d e r , i s g i v e n a c h a n c e t o t r a n s m i t ; i t t r a n s m i t s i f i t has a m e s s a g e r e a d y and d e c l i n e s i f i t has n o t . T h i s s u b s c r i b e r w i l l not be g i v e n a s e c o n d c h a n c e b e f o r e a l l o t h e r s u b s c r i b e r s have had t h e i r c h a n c e . The theme o f t h i s t h e s i s i s t h e E x p r e s s n e t , as p r o p o s e d by T o b a g i . [TH 1-4, 7 - 8 ] 1.4.2 B a s i c A s s u m p t i o n s and P e r f o r m a n c e Measures o f I n t e r e s t As m e n t i o n e d e a r l i e r i n S e c t i o n 1 . 3 , d e l a y c h a r a c t e r i s t i c s a n d e r r o r p e r f o r m a n c e s a r e t h e m a j o r i s s u e s i n v o l v e d i n an i n t e g r a t e d v o i c e and d a t a n e t w o r k ( L A N o r L H N ) . T h i s t h e s i s c o n c e n t r a t e s on t h e m e a s u r e m e n t o f t h e f o r m e r c r i t e r i o n , n a m e l y d e l a y c h a r a c t e r i s t i c s , e s p e c i a l l y f o r t h e v o i c e t r a n s m i s s i o n c a s e , w h e r e i t p l a y s an i m p o r t a n t r o l e i n n e t w o r k d e s i g n . S p e c i f i c a l l y , t h e r e l a t i o n s h i p b e t w e e n p a c k e t d i s c a r d i n g p e r c e n t a g e s and number o f s t a t i o n s i n t h e n e t w o r k i s i n v e s t i g a t e d . C a l l b l o c k i n g p r o b a b i l i t i e s a r e a l s o e x a m i n e d . O w i n g t o t h e f a c t t h a t t h e E x p r e s s n e t c o n f i g u r a t i o n i s s e r v i n g a l o c a l a r e a n e t w o r k , e r r o r s due t o i m p e r f e c t i o n s o f p h y s i c a l t r a n s m i s s i o n f a c i l i t i e s t e n d t o be s u f f i c i e n t l y s m a l l and c a n be c o n s i d e r e d n e g l i g i b l e . I n o t h e r s c h e m e s , a p o s s i b l e s o u r c e o f e r r o r w o u l d a r i s e f r o m c o l l i s i o n s o f p a c k e t s . H o w e v e r , t h e E x p r e s s n e t makes u s e o f a c o n f l i c t - f r e e m u l t i p l e a c c e s s p r o t o c o l and h e n c e t h e r e i s no c o l l i s i o n o f p a c k e t s . B a s e d on t h e s e a s s u m p t i o n s , t h e e r r o r a s p e c t o f V/D t r a n s m i s s i o n i s i g n o r e d and t h e m a i n t h r u s t o f t h e t h e s i s r e s t s o n t h e i n v e s t i g a t i o n o f d e l a y p e r f o r m a n c e o f t h e i n t e g r a t e d n e t wo r k . As f o r t h e g e n e r a l e n v i r o n m e n t o f t h e s i m u l a t i o n s t u d y , i t i s a s s u m e d t h a t t h e d a t a p a r t o f t h e i n p u t l o a d i s a l r e a d y i n d i g i t a l f o r m . W i t h r e g a r d t o v o i c e , t h e s p e e c h i n p u t was a s s u m e d t o h a v e , p r i o r t o t r a n s m i s s i o n , b e e n p r o p e r l y f i l t e r e d , s u b j e c t e d t o v o i c e c o d i n g p r o c e s s e s , and t h e r e s u l t i n g b i t s p a c k e t i z e d o n l y d u r i n g t a l k s p u r t d u r a t i o n s . R e c e i v e r b u f f e r i n g o p e r a t i o n , d e c o d i n g f u n c t i o n s , and p l a y b a c k s chemes have a l r e a d y b e e n i m p l e m e n t e d f o r d e l i v e r y o f s p e e c h t o t h e l i s t e n e r . The t a s k a t hand i s t o s p e c i f y a n e t w o r k p r o t o c o l t h a t c a n a c c o m m o d a t e d a t a t r a f f i c on t o p o f v o i c e t r a n s m i s s i o n on t h e same n e t w o r k , w i t h o u t v i o l a t i n g t h e b a s i c v o i c e d e l a y r e q u i r e m e n t . The g o a l s o f t h e t h e s i s a r e t o e x a m i n e t h e c h a n n e l u t i l i z a t i o n , d e l a y p e r f o r m a n c e , mean queue l e n g t h , and p a c k e t d i s c a r d r a t e o f t h e E x p r e s s n e t - - a h i g h - s p e e d l o c a l a r e a n e t w o r k t h a t i s deemed a p p r o p r i a t e f o r i n t e g r a t e d v o i c e and d a t a t r a n s m i s s i o n a p p l i c a t i o n s . 2. TRANSMISSION OF DATA PACKETS IN EXPRESSNET 2.1 Genera l D e s c r i p t i o n o f Expressnet E x p r e s s n e t i s a hi g h - p e r f o r m a n c e l o c a l a r e a communication network c o m p r i s i n g of an outbound c h a n n e l and an inbound c h a n n e l on which a p l u r a l i t y o f s t a t i o n s a r e co n n e c t e d . ( F i g u r e 2.1) S t a t i o n s t r a n s m i t on t h e outbound c h a n n e l and r e c e i v e on the inbound c h a n n e l . To a c h i e v e b r o a d c a s t communication, t h e inbound c h a n n e l i s l i n k e d t o t h e outbound channel v i a a c o n n e c t i o n c a b l e so t h a t a l l s i g n a l s t r a n s m i t t e d on the outbound c h a n n e l are d u p l i c a t e d on t h e inbound c h a n n e l . In o r d e r t o t r a n s m i t on t h e bus, s t a t i o n s u t i l i z e a d i s t r i b u t e d a c c e s s p r o t o c o l . They make use of a c o n f l i c t - f r e e round r o b i n s c h e d u l i n g scheme. T r a n s m i t t e r s i n the outbound c h a n n e l a r e o f t h e u n i d i r e c t i o n a l t y p e , r e n d e r i n g t h e E x p r e s s n e t a u n i d i r e c t i o n a l b r o a d c a s t bus a r c h i t e c t u r e (UBS). The communication medium may be a t w i s t e d p a i r , a c o a x i a l c a b l e , an o p t i c a l f i b r e , o r a waveguide. T h i s c h a n n e l a c c e s s p r o t o c o l y i e l d s h i g h e r t r a n s m i s s i o n e f f i c i e n c y t h a n c o n v e n t i o n a l Round Robin (RR) schemes even when the end-to-end p r o p a g a t i o n d e l a y i s a s i g n i f i c a n t f r a c t i o n o f , or even l a r g e r t h a n , the t r a n s m i s s i o n time of a p a c k e t . The major s t r e n g t h of E x p r e s s n e t l i e s i n i t s a b i l i t y t o p r o v i d e an upper bound on the network t r a n s i t d e l a y e x p e r i e n c e d PROPAGATION DELAY t INBOUND CHANNEL prop. delay inj Connection Cable TRAIN OUTBOUND CHANNEL TX connection cable RX I 2 Most Upstream Station Figure 2.1 Block diagram of Expressnet T X . TRANSMIT RX : RECEIVE N Most Downstrean Station by a p o t e n t i a l p a c k e t . T h i s o u t s t a n d i n g f e a t u r e makes t h e E x p r e s s n e t an a t t r a c t i v e s y s t e m t o be c o n s i d e r e d f o r i n t e g r a t i o n o f v o i c e and d a t a i n a l o c a l a r e a o f f i c e e n v i r o n m e n t . D e t a i l e d d e s c r i p t i o n s o f t h e t r a n s m i s s i o n m e c h a n i s m a r e f o u n d i n T o b a g i . [TH 1-4] A h i g h l i g h t o f t h e m a j o r p r o c e d u r e s u s e d i n b a s i c p a c k e t t r a n s m i s s i o n c a n be f o u n d i n A p p e n d i x B . 2.2 Assumptions Used i n S i m u l a t i o n Model fo r Data P r o t o c o l The f o l l o w i n g a r e a s s u m p t i o n s made i n t h e a c t u a l s i m u l a t i o n s : ( a) Non-gated s e q u e n t i a l s e r v i c e d i s c i p l i n e (NGSS) i s the v e r s i o n t o be implemented. ( F i g u r e 2.2) ( b ) The e r r o r a s p e c t i s n o t c o v e r e d i n t h i s t h e s i s . ( c ) I n t h e f i r s t p a r t , e a c h s t a t i o n p o s s e s s e s a s i n g l e b u f f e r f o r t h e p u r p o s e o f p a c k e t s t o r a g e . The r e s u l t s o b t a i n e d a r e l a t e r c o m p a r e d t o and v e r i f i e d by l i t e r a t u r e v a l u e s . R e s u l t s on t h e p e r f o r m a n c e o f t h e i n f i n i t e - b u f f e r c a s e a r e a l s o o b t a i n e d • (d ) The d u r a t i o n o f t h e l o c o m o t i v e i s v e r y s m a l l and i s t a k e n t o be 1% o f t h e f u l l p a c k e t t r a n s m i s s i o n t i m e T , i . e . , T l o c o m = 0 . 0 1 T . (e ) The p a c k e t o r t h e t r a n s m i s s i o n u n i t i s o f f i x e d l e n g t h . ( f ) The p r e a m b l e , a s s u m e d t o be much s m a l l e r t h a n t h e i n f o r m a t i o n s e c t i o n o f t h e p a c k e t t o be t r a n s m i t t e d , i s P a c k e t s a r r i v a l s a r e m o d e l l e d by a P o i s s o n p r o c e s s , w i t h A. d e n o t i n g the a r r i v a l r a t e o f p a c k e t s and IAT d e n o t i n g the i n t e r a r r i v a l t i me of p a c k e t s . s t a t i o n wi th lower index has packet to t ransmit there fore s t a t i o n 6 aborts t x s t a t i o n of lowest index can complete t ransmiss ion the s ing l e a v a i l a b l e buf fer occupied, packet d iscarded NON-GATED SERVICE DISCIPLINE(NGSS) have to wai t u n t i l the next round to have a to t ransmi t Packet a r r i v a l s Ac tua l Tx i n Channel dura t i on t r a i n Transmission Accept Packet Abort TX / Discard S ta t i on A r r i v a l s in terming le together ; A r r i v a l of one packet i n 1 s t a t i o n t r i g g e r s next a r r i v a l i n same s t n F i g u r e 2.2 T r a n s m i s s i o n p r o c e d u r e of E x p r e s s n e t i g n o r e d . (g) The c a r r i e r d e t e c t o r is p l aced ve ry c l o s e to the c h a n n e l . T h e r e f o r e , the time t<j r e q u i r e d for d e t e c t i o n of c a r r i e r i s i n f i n i t e s i m a l . (h) P o i s s o n d i s t r i b u t i o n of a r r i v a l of data p a c k e t s , i . e . , i n t e r a r r i v a l t imes of data p a c k e t s , are e x p o n e n t i a l l y d i s t r i b u t e d . ( i ) The medium of communication is the c o a x i a l c a b l e , v i t h the v e l o c i t y of p ropaga t i on of s i g n a l taken to be 2/3 o f the v e l o c i t y of l i g h t i n f r e e space . 2.3 Summary o f R e s u l t s 2 . 3 . 1 A n a l y s i s o f R e s u l t s f o r S i n g l e Bu f f e r Case F i r s t of a l l , s e v e r a l parameters are de f ined and a s s i gned s p e c i f i c va lues so that the r e s u l t s can be compared w i t h f i g u r e s ob ta ined from l i t e r a t u r e . The q u a n t i t y " a " , which i s the r a t i o between the p ropaga t i on de lay and the packet t r a n s m i s s i o n time T , i s set to be u n i t y , i . e . , Lc / v Lc C T B / C V B L e n g t h o f c a b l e (256 km) / V e l o c i t y o f p r o p a g a t i o n o f s i g n a l g a = i n c o a x i a l c a b l e (2 * 10 m/s) Number o f b i t s i n one p a c k e t / C h a n n e l c a p a c i t y (1 Mbps ) ( 1280 b i t s ) Ut i l l z a t I o n I n i t i a l l y , i t i s a s s u m e d t h a t t h e r e i s a t o t a l o f 20 s t a t i o n s a l o n g t h e o u t b o u n d c a b l e , y i e l d i n g a maximum p o s s i b l e c h a n n e l u t i l i z a t i o n f a c t o r o f 0 . 9 0 8 6 , as shown by t h e f o l l o w i n g c a l c u l a t i o n : max U t l max (N) * (T) — T o t a l t ime r e q u i r e d f o r t r a n s m i s s i o n o f Propagat ion de l ay a l l (20) packets 1 (20) * ( 1 + 0.0) + (1.0+1.0+0.0) + 0.01 0.9086 The a v e r a g e n e t w o r k t h r o u g h p u t ( u t i l i z a t i o n ) f o r a g i v e n v a l u e o f d a t a a r r i v a l r a t e A. i s g i v e n by * p = Ut 1 = t i m e u s e d f o r t r a n s m i t t i n g i n f o r m a t i o n l e n g t h o f t r a i n n T n X + Y w h e r e X i s t h e t r a n s m i s s i o n p e r i o d o f a p a c k e t , i n c l u d i n g o v e r h e a d , p r e a m b l e a n d d a t a t r a n s m i s s i o n t i m e ; Y i s t h e i n t e r r o u n d o v e r h e a d . where n Pn p r o b a b i l i t y that there are n packet t r a n s m i s s i o n s i n a round From F i gu r e 2.3 i t can be i n f e r r e d that as the i n t e r -a r r i v a l t ime i n c r e a s e s , the u t i l i z a t i o n g r a d u a l l y d r o p s . Th i s can be accounted for by the fact that as the number of t r a n s -m i s s i ons i n a t r a i n d e c r e a s e s , the e f f e c t of the p ropaga t i on de l ay becomes more p rominent , thus dec r ea s ing the o v e r a l l e f f e c t i v e n e s s of the sys tem. It can a l s o be seen that a s \ - > c o , n"—* N and the throughput reaches a maximum g iven by NT/(NX + Y) . To ensure s t a b l e network o p e r a t i o n , the norma l i zed in s tan taneous system load NX must be ma inta ined below u n i t y . To tha t e f f e c t , the a r r i v a l r a t e X i s r e s t r i c t e d i n order to a v o i d system ove r l oad due to e x c e s s i v e ou t s t and ing packets at any one t i m e . The c o n s t r a i n t i s determined as f o l l o w s : N(T + + * c + ttf) + Tlocom NT o < X m a x < T packets / sec N(T + %) + (t + * c + tjj) + Tlocom 0.0 20.0 40.0 Interarr iva l T ime (IAT) Figure 2.3 U t l vs IAT, N = 20 Channel Uti l ization (Utl) Figure 2.4 ( d e s c r i p t i o n on p.26) Mean queue length vs U t l , N=20 T h e r e f o r e , t h e i n t e r a r r i v a l t i m e ( I A T ) has t o be g r e a t e r t h a n , o r a t l e a s t e q u a l t o , t h e r e c i p r o c a l o f A . m a x . D e l a y C h a r a c t e r i s t i c s The e x p e c t e d w a i t i n g t i m e and v a r i a n c e o f t h e w a i t i n g t i m e a r e g i v e n by [TH 2,5,6] W - E [ w ] . £ n pr L J n n = 1 n e A. C(n-l)X+Y] _ x -w2 = Var w = E [ W 2 ] - ( E[W] ) 2 respectively , w h e r e T2\ 1 A Dn-DX+Y] e ^ ( n - 1 , X + Y ] Q ( n - l ) X + Y - 2 A ] + 2 E Iw 1= > n p • • Upon e x a m i n i n g F i g u r e 2 . 5 , one c a n o b s e r v e t h a t t h e average p a c k e t d e l a y i n c r e a s e s as u t i l i z a t i o n i n c r e a s e s and i s b o u n d e d f r o m a b o v e by t h e f i n i t e v a l u e a t t a i n e d a t s a t u r a t i o n , i . e . , when X - * C O . T h i s maximum d e l a y i s N(T + t^j) + * + * c + + T l o c o m * (N + 2a )T s l o t s . As f o r t h e v a r i a n c e o f t h e d e l a y ( F i g u r e 2 . 6 ) , i t c a n be s e e n t h a t as \+OD , t h e v a r i a n c e a p p r o a c h e s z e r o . I n e a c h r o u n d , e a c h s t a t i o n w i l l have a p a c k e t t o s e n d , r e n d e r i n g e a c h t r a i n a f u l l c y c l e , c o n s i s t i n g o f t r a n s m i s s i o n s f r o m e a c h and €||_ e l-c CO co ^ CO C CO 3S o SIM : s i m u l a t i o n TH : t h e o r e t i c a l 0.3 0.58 0.86 Channel Utilization (Utl) Figure 2.5 Mean wait time vs U t l , N=20 CVJ CO (U CM CO CM 0) o c co CO > o o 0.3 0.58 0.86 Channel Utilization Figure 2.6 0w*vs U t l , N=20 (Utl) e v e r y s t a t i o n . I n o t h e r w o r d s , a l l r o u n d s a r e o f f u l l l e n g t h and t h e p a c k e t d e l a y becomes d e t e r m i n i s t i c and e q u a l s t o N(T + t j ) + p r o p a g a t i o n d e l a y . Thus we have a c a s e i n w h i c h t h e v a r i a n c e i n c u r r e d i n t h e n e t w o r k t r a n s m i s s i o n i s h i g h e s t f o r t h r o u g h p u t c l o s e t o n e t w o r k c a p a c i t y , w h i l e a t n e t w o r k c a p a c i t y t h e v a r i a n c e a s s u m e s t h e v a l u e z e r o . The s i m u l a t i o n r e s u l t s r e s e m b l e t h o s e f r o m l i t e r a t u r e t h r o u g h f o r m u l a e v a l u a t i o n . Mean Queue L e n g t h F i g u r e 2 . 4 shows t h e r e l a t i o n s h i p b e t w e e n t h e mean queue l e n g t h o f t h e s y s t e m and t h e c h a n n e l u t i l i z a t i o n . i s f o u n d t o be a p p r o x i m a t e l y one l e s s t h a n 0,2* The f o r m e r r e c o r d s t h e number o f u s e r s i n t h e queue a w a i t i n g t r a n s m i s s i o n , w h i l e t h e l a t t e r m a i n t a i n s an a c c o u n t o f t h e t o t a l number o f u s e r s i n t h e s y s t e m , i n c l u d i n g t h e one c u r r e n t l y i n v o l v e d i n t h e t r a n s m i s s i o n p r o c e s s . I t c a n be s e e n t h a t as X i n c r e a s e s t h e mean queue l e n g t h Q 2 a p p r o a c h e s (N + ty) + ^ + t c + t^, + T l o c o m = (N + 2a )T s l o t s , w h i c h i s t h e same as W. V a r i a t i o n o f Number o f S t a t i o n s a t F i x e d I n t e r a r r i v a l T i m e As t h e number o f s t a t i o n s g r a d u a l l y i n c r e a s e s , t h e u t i l i z a t i o n i n c r e a s e s u n t i l t h e s y s t e m r e a c h e s s a t u r a t i o n . ( F i g u r e 2 . 7 ) The mean w a i t i n g t i m e , v a r i a n c e o f t h e w a i t i n g t i m e , and t h e mean queue l e n g t h a r e f o u n d t o be i n c r e a s i n g , as t h e number o f s t a t i o n s (N) i n c r e a s e s . »—' GO C o CO in N o , CM c c ce A o u d 1— i i i A SIM. — / \ RESULTS -/ \ / TH. — y / RESULTS -: I A T - 1 2 . 5 " I i I _ J 0.0 Number F i g u r e 2.7 16.0 32.0 of Stations (N) U t l vs N, IAT = 12.5 0.3 0.58 0.86 Channel Uti l ization (Utl) Figure 2.8 Z vs U t l , IAT =12.5 The s l ope of the curve becomes I n c r e a s i n g l y s teeper as the channe l u t i l i z a t i o n becomes h i g h e r . (F igures 2 .8 -2 .10 ) V a r i a t i o n of I n t e r a r r i v a l Time F i g u r e s 2 .11 -2 .14 demonstrate that a lower ing i n i n t e r a r r i v a l t imes w i l l b r i n g about increases i n channe l u t i l i z a t i o n , mean, and v a r i a n c e of wa i t ing t imes , as v e i l as the mean queue l e n g t h . F lowchar t s for data p r o t o c o l can be found in Appendix C. lit 2 0) g C CO £ o o 0.3 0.58 0.86 Channel Util ization Figure 2.9 w" vs U t l , IAT = 12.5 (Utl) CM CD E +J> CM • ^  CO CO O C CO > 0.3 Channel 0.58 0.86 Util ization (Utl) Figure 2.10 f~v vs U t l , IAT = 1 2 . 5 £3 Oi O C o c c ^ CO U 6 0.0 14.0 28.0 Number of Stations (N) Figure 2.11 U t l vs N, IAT = 12,12.5 inTco G ^ 0) C CO 0.3 0.58 0.86 Channel Uti l ization (Utl) Figure 2.12 Q vs U t l , IAT = 12, 12.5 l i s g > — " CD E r - 1 1 0 CO co ^ CD c co 2 o o 0.3 0.58 0.86 Channe l Uti l ization (Utl) Figure 2.13 W vs U t l , IAT = 12, 12.5 t . ^^ ^^  • CD £ • i—« CO CO ° 2 0) O G CO "~' o CO d CC 0.3 > u.J 0.58 0.86 Channel Uti l ization (Utl) rxyure 2.14 vs U t l , IAT=12, 12.5 2.3.2 A n a l y s i s o f R e s u l t s f o r I n f i n i t e B u f f e r Case In t h i s c a s e , t h e b u f f e r s i n each s t a t i o n have i n f i n i t e c a p a c i t y and a r e thus c a p a b l e of s t o r i n g a l l d a t a p a c k e t s which a r r i v e a t the s t a t i o n . The mean i n t e r a r r i v a l time of p a c k e t s ( o f s i z e 1280 b i t s ) i s assumed t o be 28 s l o t s ( i . e . , 28 * 1280/1000000) or 0.035 seconds. The i d e a of u s i n g t h i s f i g u r e i s t o examine the performance of t h e network under moderate l o a d . For t h i s v a l u e o f t h e i n t e r a r r i v a l r a t e , i t was found t h a t w i t h 22 s t a t i o n s , t h e c h a n n e l u t i l i z a t i o n approached 0.8, whereas the u t i l i z a t i o n f i g u r e d e c l i n e d t o about 0.65 when the number of s t a t i o n s was o n l y about 18. ( F i g u r e 2.15) The mean queue l e n g t h ranged from about 4 t o about 8 as t h e number of s t a t i o n s grew from about 17 t o 22. T h i s i n d i c a t e s t h a t more p a c k e t s were a w a i t i n g t r a n s m i s s i o n when the b u f f e r s a r e o f i n f i n i t e c a p a c i t y . ( F i g u r e 2.16) The mean and v a r i a n c e of t h e w a i t i n g t ime r i s e a c c o r d i n g l y w i t h i n c r e a s e i n number of s t a t i o n s i n t h e system. Once a g a i n , t h e mean w a i t i n g t ime b e a r s a c l o s e r e l a t i o n s h i p t o t h e mean queue l e n g t h which i n d i c a t e s t h e number of o u t s t a n d i n g p a c k e t s a w a i t i n g t r a n s m i s s i o n . ( F i g u r e 2.17) The v a r i a n c e o f t h e w a i t i n g t ime d i s p l a y s a s t e e p s l o p e , r e f l e c t i n g t h e f a c t t h a t w a i t d u r a t i o n becomes more u n p r e d i c t -a b l e f o r i n c r e a s i n g number o f s t a t i o n s . ( F i g u r e 2.18) I t c a n be e x p e c t e d t h a t a b u f f e r i n g o f t h e v a r i o u s p a c k e t s l e a d s t o i n c r e a s e d w a i t i n g t i m e f o r i n d i v i d u a l p a c k e t s s i n c e a p a c k e t i n a s t a t i o n has t o w a i t f o r t r a n s m i s s i o n o f a l l t h e p r e c e d i n g p a c k e t s b e f o r e i t c a n have a c h a n c e t o t r a n s m i t . T h u s , as t h e number o f s t a t i o n s o r t h e l o a d i n c r e a s e s , t h e number o f o u t s t a n d i n g p a c k e t s w i l l i n c r e a s e q u i c k l y and f l o o d t h e n e t w o r k . •ft c o G o « ee ° ha = 2 Cv C C m CO CD U i 1 1 1 1 r I n f i n i t e buffer case IAT = 28 J I I L 16.0 18.28 20.57 22.85 Numbe r of Stat ions (N) F i g u r e 2 .15 U t l vs N . IAT = 28 i 1 1 1 1 r be C w CV CD 0> CP c o P » Of c 16.0 18.28 20.57 22.85 N u m b e r _pf Stat ions (N) F i g u r e 2.16 Q vs N, IAT = 28 o Cvi 6 h 2 h Qi) C — o «• C ea 5 5 * 16.0 18.28 20.57 22.85 Number of Stations (N) F i g u r e 2.17 *W vs N, IAT = 28 i s « 5 o h 18.0 1828 20.57 22.85 Number of Stations (N) F i g u r e 2.18 P"w*vs N, IAT * 28 3 . TRANSMISSION OF VOICE PACKETS IN EXPRESSNET 3.1 Vo i ce P r o t o c o l 3 . 1 . 1 Genera l Requirement o f V o i c e T r a f f i c I n c o n t r a s t t o d a t a t r a f f i c , whe r e d e l a y i n t r a n s m i s s i o n i s n o t a c r u c i a l d e s i g n f a c t o r , t h e e x p e c t e d m e s s a g e d e l a y i s t h e most i m p o r t a n t c r i t e r i o n t o be c o n s i d e r e d i n v o i c e c o m m u n i c a t i o n s i n c e i t a f f e c t s t h e q u a l i t y o f r e a l - t i m e i n t e r a c t i v e s p e e c h s i g n i f i c a n t l y . The t o t a l e n d - t o - e n d ( E T E ) d e l a y i s m e a s u r e d f r om t h e i n s t a n t a s p e e c h p a r c e l i s a b o u t t o be g e n e r a t e d t o t h e moment when i t i s p l a y e d t o t h e l i s t e n e r a t t h e r e c e i v e r e n d . The ETE d e l a y i s c o m p o s e d o f t h e f o l l o w i n g c o m p o n e n t s : 1. o r i g i n a t i n g t e r m i n a l d e l a y , made up o f p r o c e s s i n g and p a c k e t i z a t i o n d e l a y s ; 2 . n e t w o r k d e l a y , c o m p r i s i n g o f n o d a l q u e u e i n g d e l a y , s w i t c h i n g d e l a y , as w e l l as t r a n s i t i o n t i m e on t h e i n t e r n o d a l l i n k s w h i c h i n c l u d e s t r a n s m i s s i o n t i m e and p r o p a g a t i o n d e l a y s ; 3. . d e l a y a t t h e r e c e i v i n g e n d , d e p e n d i n g on t h e s o r t o f p l a y b a c k s chemes e m p l o y e d ; and 4 . o t h e r p r o c e s s i n g d e l a y s . £pV, VN, PVR ] The human l i s t e n e r i n a c o n v e r s a t i o n has l i m i t e d t o l e r a n c e t o t h e a v e r a g e d e l a y and t h e f l u c t u a t i o n o f d e l a y . S u b j e c t i v e e v a l u a t i o n s i n d i c a t e d t h a t an e n d - t o - e n d d e l a y o f up t o 300 ms i s q u i t e a c c e p t a b l e i n t h e s e n s e t h a t t h e q u a l i t y d e g r a d a t i o n s t h u s i n c u r r e d a r e h a r d l y n o t i c e a b l e , w h i l e a h i g h e r d e l a y f i g u r e c a n c a u s e a n n o y a n c e o n t h e p a r t o f t h e l i s t e n e r . The d e l a y v a r i a n c e i s a l s o o f i m p o r t a n c e b e c a u s e t h e r e c e i v e r node has t o p r o v i d e a c o n t i n u o u s s t r e a m o f b i t s t o t h e v o c o d e r . T h a t i s , t h e v a r i a t i o n s i n t h e p a c k e t a r r i v a l t i m e s have t o be s m o o t h e d o v e r by t h e r e c e i v e r . T h i s i s done b y d e l a y i n g t h e p a c k e t s i n t h e r e c e i v e r ' s b u f f e r . I f t h e r e c e i v e r c o m p l e t e s p l a y i n g a p a c k e t t o t h e u s e r w h i l e t h e s u c c e e d i n g p a c k e t has n o t a r r i v e d y e t , t h e r e c e i v e r i s f o r c e d t o e m i t a n o t h e r s i g n a l , s u c h as n o i s e o r s i l e n c e . T h i s , o f c o u r s e , c a u s e s d e g r a d a t i o n s o f s p e e c h q u a l i t y . The s m a l l e r t h e v a r i a t i o n o f d e l a y , t h e b e t t e r t h e r e c e i v e r b u f f e r c a n be managed t o p r o v i d e t h e v o c o d e r w i t h t h e d e s i r e d c o n t i n u i t y . A p a c k e t w i t h t o o much d e l a y has m i s s e d t h e p l a y b a c k t i m e a n d i s e f f e c t i v e l y l o s t . T h u s , i t i s common m e a s u r e t o d i s c a r d p a c k e t s w h i c h w o u l d i n c u r e x c e s s i v e d e l a y s . A n o m a l i e s l e s s t h a n 50 ms i n d u r a t i o n t e n d t o go u n n o t i c e d by t h e human h e a r i n g p r o c e s s . I n f a c t , i t was r e commended t h a t p a c k e t l e n g t h o f 10-50 ms o f s p e e c h i n t e l l i g i b i l i t y c o u l d o n l y be m i n i m a l l y a f f e c t e d by l o s t p a c k e t s . T h e r e i s an i m p o r t a n t t r a d e o f f b e t w e e n n e t w o r k d e l a y p e r f o r m a n c e and l o s t v o i c e p a c k e t r a t e . To m a i n t a i n good s p e e c h q u a l i t y , i t i s n e c e s s a r y t o k e e p t h e p a c k e t d i s c a r d r a t e b e l o w 1 t o 2%. £ CALL 2 ] 3 . 1 . 2 A r r i v a l P a t t e r n of V o i c e Packets and T r a n s m i s s i o n  Mechanism A p o p u l a r m o d e l f o r v o i c e t r a f f i c a n a l y s i s i s t h e M a r k o v i a n m o d e l o f i n t e r a c t i v e t e l e p h o n e s p e e c h c o m p r i s i n g o f a l t e r n a t e t a l k s p u r t and s i l e n c e p e r i o d s , t h e mean o f t h e t a l k s p u r t d u r a t i o n m a k i n g up a b o u t 40% o f t h e c o n v e r s a t i o n l e n g t h . ["MUX 1 , SPCH 2] I n p a c k e t i z e d v o i c e n e t w o r k s , i n t e l l i g i b l e s p e e c h i s t r a n s m i t t e d a t h i g h r a t e s , r a n g i n g f r o m 1000 bps t o 64 k b p s . The l a t t e r f i g u r e i s o b t a i n e d f r o m d i g i t i z i n g o r d i n a r y t e l e p h o n e s p e e c h ( w i t h b a n d w i d t h o f a p p r o x i m a t e l y 4 KHz ) u s i n g a c o n v e n t i o n a l 8 - b i t PCM scheme a t a s a m p l i n g f r e q u e n c y o f 8 K H z . The h i g h r a t e v o i c e y i e l d s h i g h s p e e c h q u a l i t y i n t h a t i t i s l e s s s u s c e p t i b l e t o e n v i r o n m e n t a l d e g r a d a t i o n s b e c a u s e o f t h e h i g h l e v e l o f r e d u n d a n c y i n h e r e n t I n t h e c o d e d s p e e c h . F o r t h e v o i c e t r a n s m i s s i o n s e c t i o n o f t h e t h e s i s , t h e p e r f o r m a n c e o f E x p r e s s n e t i s e v a l u a t e d f o r c a s e s w i t h and w i t h o u t t h e d i s c a r d i n g o f p a c k e t s . I n s t e a d o f a n e x p o n e n t i a l d i s t r i b u t i o n o f i n t e r a r r i v a l t i m e s f o r a l l p a c k e t s , as i n t h e D a t a t r a n s m i s s i o n c a s e , t h e s i t u a t i o n h e r e i s t o be c o n s i d e r e d f r o m two p o i n t s o f v i e w , t h e g l o b a l v i e w and t h e l o c a l s t a n d p o i n t ( i . e . , a t e a c h s t a t i o n ) . F rom a g l o b a l v i e w p o i n t , when a s u f f i c i e n t l y l a r g e number o f v o i c e s o u r c e s (>^  10) a r e m u l t i p l e x e d , t h e d i s t r i b u t i o n o f i n t e r a r r i v a l t i m e s o f t a l k -s p u r t o r s i l e n c e p e r i o d s c l o s e l y r e s e m b l e t h a t o f a n e x p o n e n t i a l d i s t r i b u t i o n . H o w e v e r , i f one l o o k s a t a p a r t i c u l a r s t a t i o n , t h e n t h e a r r i v a l o f p a c k e t s becomes a d e t e r m i n i s t i c p r o c e s s . New v o i c e p a c k e t s a r e g e n e r a t e d by a t e r m i n a l a t r e g u l a r i n t e r v a l s . The i n t e r v a l e q u a l s t h e p a c k e t l e n g t h as l o n g as a t a l k s p u r t i s i n p r o g r e s s . The t r a n s m i s s i o n m e c h a n i s m i n v e s t i g a t e d i s t h e n o n - g a t e d mode o f t r a n s m i s s i o n o f t h e E x p r e s s n e t . 3 . 2 Assumptions Used i n S i m u l a t i o n Model for V o i c e P r o t o c o l B a s i c a l l y , t h e a s s u m p t i o n s i n t h e D a t a s e c t i o n a r e s t i l l v a l i d as f a r as t h e t r a n s m i s s i o n m e c h a n i s m i s c o n c e r n e d . H o w e v e r , a few i t e m s p e r t a i n i n g t o t h e c h a r a c t e r i s t i c s o f v o i c e t r a f f i c a r e t o be a d d e d t o t h e l i s t : ( a ) R e a l - t i m e s p e e c h (as i n t e l e p h o n e c o n v e r s a t i o n ) i s t h e v o i c e t y p e o f t r a f f i c o f i n t e r e s t . (b ) I t i s a s s u m e d t h a t v o c o d e r s d i g i t i z e v o i c e a t some c o n s t a n t r a t e o f C v , w h e r e C v i s s e t t o be 64 K b p s . ( c ) S p e e c h d e t e c t i o n p r o c e s s had a l r e a d y b e e n c a r r i e d o u t a n d t h a t d u r i n g t a l k s p u r t p e r i o d s , b i t s a r e g r o u p e d t o f o r m p a c k e t s o f s i z e B v , w h i c h a r e t o be t r a n s -m i t t e d i n t h e n e t w o r k t o t h e d e s t i n a t i o n v o c o d e r , as d e p i c t e d i n F i g u r e 3 . 1 . (d ) F i g u r e 3 . 2 d e s c r i b e s t h e a s s u m p t i o n o n t h e a p p r o x i -mate maximum d e l a y r e q u i r e m e n t f o r t h e v a r i o u s c o m p o n e n t s o f t h e t o t a l e n d - t o - e n d d e l a y . - AO -: speech d e t e c t i o n time t _ : speech d e t e c t i o n hangover time e Speech Speech D e t e c t o r Encoding P a c k e t i z a t i o i * F i g u r e 3 . 1 P a c k e t s p e e c h m o d e l [ M O B 5] Voice Source Packet i zat ion Delay-Processing Delay Network T r a n s m i s s i o n -Delay D Receiver Buffering Delay Y — * Process ing r- Delay Voice Des t ina t i on 100ms 20ms 20ms 150 ms 5 ms D V 295 ms ( < . 300ms ) n F i g u r e 3 . 2 Maximum ETE d e l a y r e q u i r e m e n t The o b j e c t i v e o f t h e v o i c e s e c t i o n i s t o d e v i S e a p r o t o c o l f o r v o i c e c o r a m u n i c a t i o n so t h a t t h e t r a n s m i s s i o n t i m e o f i n d i v i d u a l p a c k e t s does not e x c e e d 20 ms• (e ) S t a t i s t i c a l i n d e p e n d e n c e b e t w e e n t a l k s p u r c s i s g u a r a n t e e d . D u r a t i o n s o f t a l k s p u r t and s i l e n c e p e r i o d s a r e e x p o n e n t i a l l y d i s t r i b u t e d w h i l e t h e means o f t h e i r d i s t r i b u t i o n s a r e 1.4 a n d 2 . 0 s e c o n d s r e s p e c t i v e l y . T h e s e f i g u r e s a r e t a k e n f r o m r e s u l t s by B r a d y [SPCH 3] f o r m a l e s p e a k e r s c a r r y i n g o n c a s u a l c o n v e r s a t i o n w h i l e t h e s p e e c h a c t i v i t y d e t e c t o r (SAD) i s o p e r a t i n g T a l k s p u r t d u r a t i o n s a r e t h u s a b o u t 40% o f t h e t a l k e r ' s a c t i v i t y . ( f ) P a c k e t s a r e g e n e r a t e d o n l y d u r i n g t a l k s p u r t i n t e r v a l s , a s shown i n F i g u r e 3 . 3 . Two m a j o r c o n s t r a i n t s have t o be s a t i s f i e d : ( i ) The n e t w o r k t r a n s i t t i m e has t o be s m a l l e r t h a n o r e q u a l t o t h e p a c k e t f o r m a t i o n t i m e so t h a t t h e s y s t e m i s no t o v e r l o a d e d . T h e r e f o r e , i t i s r e q u i r e d t h a t T f > D n « ( i i ) The sum o f t h e p a c k e t i z a t i o n t i m e and t h e n e t w o r k t r a n s i t t i m e c a n n o t e x c e e d t h e maximum t o l e r a b l e d e l a y o f a b i t , i . e . , T f + D n < D v . Thus N m a x o c c u r s when T f = D n = D v / 2 , w h i l e t h e o p t i m u m B v ( 2 ) i s g i v e n by (Dv/2) * C v « A c c o r d i n g t o t h e E x p r e s s n e t * l e n g t h o f v o i c e p a c k e t c a r r y i n g a c t u a l i n f o r m a t i o n b i t s Packet A r r i v a l s 1 s ta t i on 1 w////////////m///////////,\m packet generation time : 20ms = 1230 bits/packet at Cy= 64kbps TIME s ta t i on 2 77777m i — mean of ta lkspurt durat ion » 1.4 second mean of s i lence duration = 2.0 second i Ml TIME s ta t i on 3 SILENCE packet a r r i v a l TIME TALKSPURT l i s t a t i on 4 v///////////M//////////////m///\ , i r n T I K E " 1280 b i t s C bps 1280/c seconds• Transmission Channel ' r fH-periodic a r r i v a l s i | of voice packets i . w i th in a ta lkspurt r' non-gated service d i s c i p l i n e 1 3 • • • TIME REALSTART Tlocom F i g u r e 3.3 V o i c e t r a n s m i s s i o n i n E x p r e s s n e t p r o t o c o l , D n has a v a l u e of N(T^ + t d ) + ( t + t c + t d ) + Tlocom. I g n o r i n g t , and Tlocom, N can be f o r m u l a t e d as N = 3 ^ d ~ max max (1) (D * C)/(2B + D C ) , where N i s the maximum number o f v o i c e v v v v max u s e r s s u p p o r t a b l e such t h a t the l o n g e s t d e l a y e x p e r i e n c e d by each b i t i s gua r a n t e e d t o be l e s s than D . I f t h e overhead b i t s a r e r n a l s o i g n o r e d , then the e x p r e s s i o n reduces t o N = C/C . ^ ^ max v For our purpose , i t i s assumed t h a t t h e p a c k e t i z a t i o n time i s 20 ms. The sour c e codes t h e b i t s a t a r a t e o f 64 kbps, i . e . , t h e number o f b i t s per p a c k e t i s B v = T^ * C v = 20 ms * 64 kbps = 1280 b i t s . I n summary , D n has t o s a t i s f y t h e f o l l o w i n g r e l a t i o n s h i p : D = N (T + t , ) + ( < f c + t r + t , ) + Tlocom n max v d w t d = N (B /C + t,) + +1L + t,) + Tlocom max v d nt d 4 T f = 20 ms 3.3 A n a l y s i s of R e s u l t s A major q u a n t i t y i n v o l v e d i n t h e a n a l y s i s i s t h e number o f s t a t i o n s t h a t can be accommodated such t h a t the maximum t o l e r a b l e d e l a y i s not exceeded a t any t i m e . The d e t e r m i n a t i o n o f t h i s v a l u e i s e x e m p l i f i e d by t h e f o l l o w i n g c a l c u l a t i o n : (p.44) 1 : T i s t h e t r a n s m i s s i o n o f a p a c k e t on the c h a n n e l v ^ 2 : Bv^.^^ i s t n e l e n g t h of p a c k e t o c c u p i e d by overhead N t - D n / ( B V / C ) 20 m s / ( 1 2 8 0 b i c s / 1 Mbps ) - 1 5 . 6 2 5 T h i s i s a l s o t h e f i g u r e f o r t h e f u l l p a c k e t g e n e r a t i o n t i m e " p g t f u l l " ( i n s l o t s ) , s i n c e t h e p a c k e t t r a n s m i s s i o n t i m e T i s n o r m a l i z e d t o be o n e . We a r e i n t e r e s t e d i n f i n d i n g ou t how many o f t h e s e T * s c a n be p a c k e d i n t o one p a c k e t g e n e r a t i o n t i m e i n t e r v a l , h e n c e t h e d e t e r m i n a t i o n o f N t • The k e y p o i n t i n t h i s o p e r a t i o n i s t h e f a c t t h a t t h e a c t u a l c h a n n e l c a p a c i t y i s much h i g h e r t h a n t h e v o c o d e r r a t e . An e x a m p l e o f t h e s y s t e m w o u l d be a 1 Mbps c h a n n e l s u p p o r t i n g t r a n s m i s s i o n s f r o m numerous v o c o d e r s o p e r a t i n g a t 64 k b p s . The i d e a i s t h a t as l o n g as N i s l e s s t h a n o r e q u a l t o N t , i t i s g u a r a n t e e d t h a t t h e D n c o n s t r a i n t i s no t v i o l a t e d . To move one s t e p f u r t h e r , one c a n e x p l o i t t h e f a c t t h a t i n a c a s u a l c o n v e r s a t i o n , a s p e a k e r i s a c t i v e f o r m e r e l y 40% o f t h e t i m e . By s a c r i f i c i n g a t i n y f r a c t i o n o f t h e f u l l t a l k s p u r t , v a r i o u s o t h e r s t a t i o n s c a n be a t t a c h e d t o t h e s y s t e m , w i t h m i n o r d e g r a d a t i o n o f s p e e c h q u a l i t y . T h i s c a n be i m p l e m e n t e d as d i s c a r d i n g o f p a c k e t s . The o b j e c t i v e i s t o d e t e r m i n e t h e maximum number o f s t a t i o n s t h a t c a n be s u p p o r t e d by t h e s y s t e m s u c h t h a t t h e p a c k e t d i s c a r d r a t e i s w i t h i n t o l e r a b l e l i m i t s . As m e n t i o n e d e a r l i e r , i t was r e p o r t e d t h a t a p a c k e t l o s s p e r c e n t a g e o f 1 t o 2% i s q u i t e a c c e p t a b l e f o r v o i c e c o m m u n i c a t i o s [CALL 2 ] . The r e s t o f t h i s s e c t i o n i s o r g a n i z e d i n t o two s u b s e c t i o n s d e s c r i b i n g p e r f o r m a n c e o f t h e two c a s e s , n a m e l y : ( V I ) T r a n s m i s s i o n W i t h o u t D i s c a r d i n g o f P a c k e t s , and (V2 ) T r a n s m i s s i o n W i t h D i s c a r d i n g o f P a c k e t s i f t h e p o t e n t i a l d e l a y s t h a t w o u l d be i n c u r r e d a r e l a r g e r t h a n t h e t i m e r e q u i r e d t o g e n e r a t e a p a c k e t . ( V I ) T r a n s m i s s i o n W i t h o u t D i s c a r d i n g o f P a c k e t s The c h a n n e l u t i l i z a t i o n c a n be o b s e r v e d i n c r e a s i n g r a p i d l y as t h e number o f s t a t i o n s i n c r e a s e s ( F i g u r e 3 . 4 ) . As t h e s y s t e m a p p r o a c h e s s a t u r a t i o n , t h i s i n c r e a s e l e v e l s o f f and f i n a l l y s e t t l e s t o i t s s t e a d y s t a t e v a l u e . The means o f t h e d e l a y s ( F i g u r e 3 . 6 ) a l s o m a n i f e s t s i m i l a r b e h a v i o u r s as t h o s e o b s e r v e d i n t h e D a t a c a s e . One c a n s e e t h a t an i n c r e a s e i n c h a n n e l u t i l i z a t i o n i n t u r n i n c r e a s e s t h e a v e r a g e d e l a y . H o w e v e r , t h e r e e x i s t s an u p p e r b o u n d f o r t h e d e l a y , t h e e x p r e s s i o n o f w h i c h i s (N + + ( t + t c + * d ^ + T l o c o m o r (N + 2a )T s l o t s . I t c a n be i n f e r r e d t h a t an i n c r e a s e i n c h a n n e l u t i l i z a t i o n c a u s e s a c o r r e s p o n d i n g i n c r e a s e i n t h e v a r i a n c e o f t h e d e l a y , w i t h t h e c u r v e b e c o m i n g s h a r p e r as t h e u t i l i z a t i o n a p p r o a c h e s u n i t y ( F i g u r e 3 . 7 ) . The mean queue l e n g t h ( F i g u r e 3 . 8 ) i s f o u n d t o c l o s e l y m a t c h t h a t o f t h e mean w a i t i n g t i m e and t h e mean number i n t h e s y s t e m i s one more t h a n t h a t o f t h e mean queue l e n g t h . CO o o N 6 1 1 1 1 - Y* — - A 2 — 1 I 1 1 CO _ CvJ d) © C C CO 5.0 29.0 53.0 Number of Stations Figure 3.4 U t l vs N, V1/V2 (N) O 0.0 0.4 0.8 Channel Util ization (Utl) Figure 3.5 Q vs U t l , V1/V2 0.0 0.4 0.8 Channel Uti l ization (Utl) Figure 3.6 Mean wait time vs U t l , V1/V2 C\J CO CM — • o co CM CO * U O c CO CO > 0.0 0.4 0.8 Channel Util ization (Utl) Figure 3.7 f\ix vs. U t l , V1/V2 3 •2 U v, bi) C w - 3 CMc CC T 1 1 r o I 1 0.0 0.4 0.8 Channel Util ization (Utl) Figure 3.8 Mean queue length vs U t l , VI c cc o 0.0 0.4 0.8 Channel Uti l ization Figure 3.9 *Q VS U t l , V2 (Utl) As f o r t h e mean t r a i n s i z e , t h e r e s u l t s i n F i g u r e 3 . 1 0 show t h a t as t h e c h a n n e l u t i l i z a t i o n e x c e e d s 0 . 8 7 , t h e mean t r a i n s i z e i s a p p r o x i m a t e l y g i v e n by Tz = 0 . 4 N . T h i s i s r e a s o n a b l e b e c a u s e t a l k s p u r t s o c c u p y o n l y a b o u t 40% o f a p e r s o n ' s s p e e c h i n a n o r m a l t e l e p h o n e c o n v e r s a t i o n . The v a r i a n c e o f t h e t r a i n s i z e c a n be o b s e r v e d i n c r e a s i n g as t h e s y s t e m becomes more h e a v i l y l o a d e d . H o w e v e r , a t a c e r t a i n p o i n t , t h e c u r v e a b r u p t l y d e c l i n e s f r o m i t s c l i m a x and f a l l s o f f q u i t e r a p i d l y . T h i s i s b e c a u s e as t h e u t i l i z a t i o n a p p r o a c h e s u n i t y , e v e r y s t a t i o n i s t r a n s m i t t i n g a p a c k e t i n e a c h r o u n d ( t r a i n ) and t h e t r a i n s i z e becomes more p r e d i c t a b l e . ( F i g u r e 3 . 1 1 ) I f 15 o r more s t a t i o n s w i t h l o w e r i n d i c e s have p a c k e t s t o be p l a c e d on t h e c h a n n e l f o r d e l i v e r y t o t h e d e s t i n a t i o n v o c o d e r , some s t a t i o n s may h a v e t o w a i t f o r more t h a n 20 ms ( t h e maximum t o l e r a b l e d e l a y ) f o r a c h a n c e t o t r a n s m i t . T h i s h y p o t h e s i s i s s u b s t a n t i a t e d by t h e f i g u r e s f o u n d i n t h e g r a p h s p l o t t i n g t h e r e l a t i o n s h i p b e t w e e n p e r c e n t a g e o f d e l a y e d p a c k e t s ( P D L P ) and t h e number o f s t a t i o n s (N) as w e l l as t h e c h a n n e l u t i l i z a t i o n ( F i g u r e 3 . 1 2 a n d 3 . 1 3 r e s p e c t i v e l y ) . One c a n s e e t h a t PDLP i n c r e a s e s f r o m z e r o a f t e r t h e number o f s t a t i o n s e x c e e d s 1 5 . (V2 ) T r a n s m i s s i o n W i t h D i s c a r d i n g o f P a c k e t s I n t h i s c a s e , p a c k e t s a r e d i s c a r d e d i f t h e d e l a y i s l a r g e r t h a n T f = 20 m s . The c h a n n e l u t i l i z a t i o n i s f o u n d t o be i 1 1 r 0.0 0.4 0.8 Channel Uti l ization (Utl) Figure 3.10 Tz VS U t l , V1/V2 0.0 0.4 0.8 Channel Util ization (Utl) Figure 3.11 0*Tz* vs U t l , V1/V2 0.0 0.4 0.8 Channel Uti l ization (Utl) F igu re 3.12 PDLP vs U t l , V1/V2 Q CM Pu CL> CO Q u P h q 0.0 20.0 40.0 Number of Stations F igu re 3.13 PDLP vs N, V1/V2 (N) s l i g h t l y lower than that in the VI case. (Figure 3.4) The means of the waiting times are smaller than those i n the VI case. (Figure 3.6) As for the variance of the delay, i t i s observed to be comparable to that of the VI case at low u t i l i z a t i o n . (Figure 3.7) When more stations are attached to the system, some packets may be discarded and hence the delays are more predictable, i . e . , less v a r i a b l e . Similar arguments hold for the mean queue lengths. (Figure 3.5 and 3.9) The mean t r a i n s i z e i s s l i g h t l y less than that i n the VI case. (Figure 3.10) The variance of the t r a i n s i z e increases as the channel u t i l i z a t i o n increases. (Figure 3.11) In f a c t , the protocol can be modelled by a 1-D Markov chain. (Figure 3.14) Talkspurt and silence durations are assumed to be exponential random variables. The rate of a r r i v a l of talkspurts i s proportional to N-k, which i s the number of offhook users not currently i n talkspurt ; while the rate of departure of talkspurt i s proportional to k, the current number of active talkspurts. (N -k+1)^ (N-k)X, y , ( k + i ^ t , ?n = Mean silence duration yH, = Mean talkspurt duration Figure 3.14 Markov chain for V2 protocol M^UX l ] ( T a l k s p u r t / s i l e n c e m o d e l ) The aode l for an a c t i v e v o i c e source Is I l l u s t r a t e d In F i g u r e 3 . 1 5 . P Q Q and P Q f f are t r a n s i t i o n p r o b a b i l i t i e s In the Markov t r a n s i t i o n m a t r i x . F i g u r e 3 .15 Model for an a c t i v e v o i c e source [CALL 1] The packet d i s c a r d i n g r a t e (VPDR) i s app rox imate ly g i v en by the e q u a t i o n be low, whose form bears a s t r i k i n g resemblance to the f r a c t i o n a l speech l o s s e q u a t i o n o f a Time Assignment Speech I n t e r p o l a t i o n (TASI) s y s t em. [SPCH 1-2] V P D R P [j:otal # of packet a r r i v a l s = k^] = f ( k, N, P ) on R e s u l t s f o r t h i s p a r t i s shown i n F i g u r e s 3 . 1 6 a n d 3 . 1 7 . The p a c k e t d i s c a r d i n g r a t e i s f o u n d t o i n c r e a s e s l o w l y i n s t e p w i t h i n c r e a s e i n t h e number o f s t a t i o n s i n t h e s y s t e m . T h i s c a n be o b s e r v e d u n t i l N = 2 8 , b e y o n d w h i c h VPDR i n c r e a s e s more r a p i d l y , h i n t i n g e x c e s s i v e l o a d on t h e s y s t e m . I t c a n be o b s e r v e d t h a t f o r a 1% p a c k e t d i s c a r d r a t e , t h e number o f s t a t i o n s t h a t c a n be s u p p o r t e d i s a b o u t 2 8 . The d i s c a r d r a t e b e comes 2% when 31 s t a t i o n s a r e a t t a c h e d t o t h e s y s t e m . F l o w c h a r t s f o r v o i c e p r o t o c o l s c a n be f o u n d i n A p p e n d i x C . 3.4 C a l l E s t i m a t i o n Implementat ion 3 . 4 . 1 I n t r o d u c t i o n F o r i n t e r a c t i v e t e l e p h o n e c o n v e r s a t i o n s , i t c a n be a s s u m e d t h a t e a c h t e l e p h o n e o f f e r s 0 . 2 5 E r l a n g s o f t r a f f i c [CALL 2] i n p e a k o f f i c e h o u r s . I n t h e m o d e l u s e d , i t i s a s s u m e d t h a t t h e r e i s a c a l l e v e r y 12 m i n u t e s ( i . e . , t h e a r r i v a l r a t e o f c a l l X c = 1 c a l l / 1 2 m i n u t e s ) . The c a l l a r r i v a l s a r e g o v e r n e d by a n e x p o n e n t i a l d i s t r i b u t i o n [SW 2 ] . F u r t h e r m o r e , t h e d u r a t i o n o f c a l l s i s e x p o n e n t i a l l y d i s t r i b u t e d w i t h mean 3 m i n u t e s . 1 / I A T C A L L A c = - 1/12 = 1/4 = 0 . 2 5 E r l a n g s / A C 1 / D U R C A L L 1 / 3 p = 0 . 2 5 f o r e a c h s t a t i o n Q CM P u ^ CO 0) cu cvi CO CJ <«• in 1 1 1 1 1 j — SIM. 1 — RESULTSi y 1 1 0.0 0.4 0.8 Channel Uti l ization (Utl) Figure 3.16 VPDR vs U t l , V1/V2 0.0 14.4 28.8 Number Of Stations (N) F igu re 3.17 VPDR vs N, V1/V2 The s i t u a t i o n i s depicted i n Figure 3-18. Current C a l l duration of c a l l exponentially d i s t r i b u t e d with mean 3 minutes : DUR_,T T = 3 minutes CALL exponential d i s t r i b u t i o n of c a l l a r r i v a l s , with a mean of 12 minutes,i.e., I A T C A L L = 12 minutes Next C a l l representing the mean i n t e r a r r i v a l time of a c a l l CALL ARRIVALS AND DISTRIBUTIONS A [mux l ] = C a l l a r r i v a l rate = Mean c a l l duration CALL ON-OFF MODEL Figure 3.18 C a l l a r r i v a l s and d i s t r i b u t i o n s , on-off model 3.4.2 Control Mechanism In the model, there are two level s of control of voice transmission, namely, (i) C a l l Entry Level : c a l l s are rejected i f the channel i s o v e r - u t i l i z e d . ( i i ) Packet Level : a packet i s discarded i f the waiting time i s equal to or i n excess of 20 ms. The d i s t r i b u t e d c a l l - b l o c k i n g mechanism described i n (i) works as follows. A c a l l which arrives at a station i s blocked with a prob a b i l i t y of (1-p), where p i s given by where •)f i s a constant p g t f u l l Is the maximum number of s t a t i o n s a l lowed to guarantee zero packet d i s c a r d and c a l l b l o c k i n g r a t e s Nj i s g i v en by Nj - ( l - * ) N j _ ! + c d L j / 0 . 4 ; L j • a c t u a l l eng th of prev ious t r a i n N-i/(DURCALL * * * 8 t h e e s t imated number of a c t i v e v o i c e c a l l s The purpose o f t h i s s e c t i o n i s to implement a c a l l e s t i m a t i o n scheme Into the v o i c e t r a n s m i s s i o n aspect of E x p r e s s n e t . Channel u t i l i z a t i o n , mean and v a r i a n c e of wa i t i ng t i m e s , c a l l b l o c k i n g p r o b a b i l i t y , and packet d i s c a r d r a t e are performance measures of i n t e r e s t . The idea is to dev i se a dynamic c o n t r o l scheme to r e g u l a t e the amount of t r a f f i c in the system by making use of s e v e r a l parameters (number of s t a t i o n s , s i z e of p rev ious t r a i n , e t c . ) to ach ieve a d e s i r e d l e v e l of per formance. 3 . 4 . 3 A n a l y s i s o f Re su l t s The s i m u l a t i o n t i m e f o r t h e p r o g r a m i s 6 h o u r s , w i t h V s e c * t o be 4 . 0 2 . T h r e e d i f f e r e n t v a l u e s o f «C, n a m e l y cC = 0 . 1 , 0 . 5 , a n d 0 . 9 a r e u s e d i n t h e s i m u l a t i o n . The e f f e c t i v e n e s s o f t h e i n d i v i d u a l c a s e s a r e d e m o n s t r a t e d i n F i g u r e s 3 . 1 9 , 3 . 2 0 , and 3 . 2 1 r e s p e c t i v e l y . They p r o v i d e s n a p s h o t s o f t h e e n t i r e s i m u l a t i o n p r o c e s s . I t c a n be s e e n f r o m F i g u r e 3 . 1 9 t h a t i n t h e ot = 0 . 1 c u r v e t h e e s t i m a t e d number o f a c t i v e s t a t i o n s m a t c h e s c l o s e l y w i t h t h e a c t u a l v a l u e t h r o u g h o u t t h e r u n . D e v i a t i o n s f r om t h e a c t u a l v a l u e s a r e a b o u t + 1, as c a n be o b s e r v e d f r o m t h e d i a g r a m . M o r e o v e r , t h e t r a n s i t i o n f r o m 16 t o 17 i s a s m o o t h p h e n o m e n o n . H o w e v e r , f o r = 0 . 9 , t h e c u r v e p r o d u c e s a f a i t h f u l r e p l i c a f o r a c t u a l v a l u e s o f 1 0 , b u t s u f f e r s r e l a t i v e l y s e v e r e f l u c t u a t i o n s a t t h e t r a n s i t i o n o f number o f a c t i v e s t a t i o n s f r o m 10 t o 1 1 . The s e t o f p o i n t s on t h e c u r v e oC = 0 . 5 e x h i b i t e d c h a r a c t e r i s t i c s w h i c h l i e b e t w e e n t h e oi. = 0 . 1 a n d at = 0 . 9 c a s e s . H e n c e , oL = 0 . 1 i s t h e more f a v o u r a b l e e s t i m a t o r f o r t h e number o f a c t i v e s t a t i o n s . T h i s i n d i c a t e s t h a t s m a l l e r i s p r e f e r a b l e i n s a t i s f y i n g t h e c r i t e r i a o f e s t i m a t o r p r e c i s i o n . I n a l l t h e t h r e e c a s e s m e n t i o n e d , t h e e s t i m a t e d v a l u e s s e emed to be h i g h e r t h a n t h e a c t u a l ones on a v e r a g e . T h i s i n * *y = 4 . 0 2 : t h i s one was c h o s e n among o t h e r s b e c a u s e i t y i e l d s s a t i s f a c t o r y p e r f o r m a n c e Rot of Actual vs Estimated jj Active Stations for oC = 0.1 o < so r» »H 27¬26¬25¬24¬23¬22¬21¬20¬19¬18¬17¬* -O -M • U -Q -« • » • • H t 7 Estimated Actual \ i i — i — i — i — i — i — i * i — t i i t 0 S B O 20 » JO 35 40 45 SO 55 M * 5 70 7$ Veins F i g u r e 3.19 A c t u a l vs e s t i m a t e d # a c t i v e s t a t i o n s , OC .1 Plot of Actual vs Estimated ff Active Stations for oC = 0.5 o — | — i i i — i — i i i — i — r — i — i — i i i — i i i i V fi 20 25 U 35 40 45 50 55 « 0 65 70 75 B0 IS f 0 15 100 Trains F i g u r e 3.20 A c t u a l vs e s t i m a t e d # a c t i v e s t a t i o n s = 0.5 Plot of Actud vs Estimated ff Active Stations for c(. = 0.9 30 - , 28 27 26 25 24 23 22 21 20 19 te 17-1 K « 14 13 12 11 to * a 7 V 4 c o o Estimated Actual - i—i—i—r - 1 1 1 1 1 1 5 » B 20 25 30 35 40 45 50 55 M SS 70 75 >oins F i g u r e 3.21 A c t u a l vs e s t i m a t e d # a c t i v e s t a t i o n s , oC 0 . 9 F i g u r e 3.22 U t l vs N, t h e o r e t i c a l / s i m u l a t i o n t u r n imp l i e s that the percentage of vo i ce c a l l s b locked is s l i g h t l y h igher than n e c e s s a r y . I f * V can be ad justed to a lower v a l u e , one can expect the es t imated va lues to come c l o s e l y to the a c t u a l f i g u r e s , w i th the outcome of even b e t t e r per fo rma nc e . F i g u r e 3.22 serves to v e r i f y that the program i s pe r fo rming i t s j o b . It shows that the s imu l a t ed u t i l i z a t i o n va lues l i e i n c l o s e p r o x i m i t y to the p r e d i c t e d ones , a c c o r d i n g to the f o rmu l a : DUR N t a l k s p u r t d u r a t i o n U t l = ia.ui, + A , I A T C A L L p g t f u l l t a l k s p u r t s i l e n c e d u r a t i o n d u r a t i o n w i t h t h e assumption t h a t t h e b l o c k i n g p r o b a b i l i t y i s z e r o . F i g u r e s 3 . 23 , 3 .24 , and 3.25 i l l u s t r a t e that f , w, and (7"w^ i n c r e a s e at s teady ra tes as N i n c r e a s e s , w i th the ot - 0.9 curve y i e l d i n g h ighest va lues for a l l N. Th i s is not unexpected because g r e a t e r va lues of ©C d i s p l a y l e s s p r e d i c t i o n a c c u r a c y . F i g u r e 3.24 a l s o conf i rms the v a l i d i t y of the program for i t shows that the mean w a i t i n g t ime exceeds the mean queue l eng th by app rox imate ly one . The behav iours of Packet D i s c a r d i n g Rate (PkDis) and B l o c k i n g P r o b a b i l i t y (PB) can be observed i n F i g u r e 3 . 2 6 . F i g u r e 3.27 and F i g u r e 3.28 i n t u r n examine t h e i r t r a d e o f f s . In g e n e r a l , both measures amounted to more than 1% fo r N « 75 or h i g h e r . The oi - 0.9 case aga in produces l a r g e r va lues fo r P B . T h i s phenomenon c a n be e x p l a i n e d by t h e f l u c t u a t i o n s i n e s t i m a t e d v a l u e s . F o r s a t i s f a c t o r y c h a n n e l u t i l i z a t i o n p e r f o r m a n c e , s u b j e c t e d t o t h e s t r i n g e n t p a c k e t d i s c a r d i n g and c a l l b l o c k i n g c o n s t r a i n t s , a n o p t i m u m r a n g e o f 65 t o 70 s t a t i o n s i s r ecomme n d e d . Plot of Utilization vs Number of Stations 0.50-0.45-0 .40-0.33-c 0 .30-. g o 0 .25-5 0 .20-o.ts-o.n-0.05-0 .00-10 1 1 1— 20 30 40 50 60 Number of Stations N so 70 •o Legend alpha = 0.1 X alpha = 0.5 • alpha = 0.9 —I 90 F i g u r e 3.23 U t l vs N, d i f f e r e n t < Plot of Mean Wait Time, Mean Queue Length vs N lo I at 2.4-" i 18¬16¬14¬12¬0.8¬0.6¬0.4¬0.2-0L = 0.1 Legend A w afcho - 0.1 x w dpho - 0.5 O W ofrho « 0.9 • 0 otpho = 0.1 • 0 dfcho = 0.5 « 0 dyhc - 0.9 -r 20 30 40 50 60 Number of Stations N T 40 1¬50 F i g u r e 3.24 Mean w a i t t i m e , mean queue l e n g t h vs N Rot of Variance of Wait Time vs Number of Stations 5.5 A 0 » 20 30 40 SO 60 70 BO 90 Number of Stations N F i g u r e 3.25 V a r i a n c e o f w a i t time vs N Rot of % Packet Discarded, Blocking Probability vs N L6n 1.4 Number of Stations N F i g u r e 3.26 %packet d i s c a r d e d , b l o c k i n g p r o b a b i l i t y vs N Plot of % Pocket Discarded vs Blocking Probability% 7, Pocket Discarded F i g u r e 3.27 % pac k e t d i s c a r d e d vs b l o c k i n g p r o b a b i l i t y % Plot of % Pocket Discarded vs Blocking Probability% 1 0 J o j§ 0.4 0.2-N = 80 N = 35 Legend A N « I * K N t ] S 0 N • ( 0 • N = 70 1 N • SO I I I I I I 1— 0.2 0.4 0.6 0.6 I L2 14 X Pocket Discorded F i g u r e 3.28 % pac k e t d i s c a r d e d vs b l o c k i n g p r o b a b i l i t y % 4 . INTEGRATION OF VOICE AND DATA IN EXPRESSNET 4.1 I n t r o d u c t I o n I n r e c e n t y e a r s much r e s e a r c h has b e e n c a r r i e d o u t t o i n v e s t i g a t e t h e p e r f o r m a n c e o f i n t e g r a t e d v o i c e / d a t a t r a n s -m i s s i o n s y s t e m s . [VDN 1, CALL 1] The m a j o r c o n s t r a i n t s t h a t have t o be s a t i s f i e d i n c l u d e : i ) d e l a y c o n s t r a i n t s f o r v o i c e p a c k e t s , and i i ) m in imum b a n d w i d t h r e q u i r e m e n t f o r d a t a . I t i s d e s i r a b l e t o a c c o m p l i s h a n e t w o r k t h a t c a n p r o v i d e t h e b a n d w i d t h r e s e r v e d f o r d a t a on c o n t i n u o u s b a s i s . I t i s a l s o r e q u i r e d t h a t t h e p r o t o c o l s be d y n a m i c i n a l l o c a t i n g b a n d w i d t h t o v o i c e and d a t a a p p l i c a t i o n s . The m a i n p u r p o s e o f t h i s s e c t i o n i s t o d e v i s e a l o c a l a r e a n e t w o r k p r o t o c o l . Such a p r o t o c o l must be a b l e t o s u p p o r t a c e r t a i n number o f v o i c e and d a t a t e r m i n a l s , and y i e l d r e a s o n a b l e c h a n n e l u t i l i z a t i o n f a c t o r , w h i l e o b s e r v i n g t h e d e l a y c o n s t r a i n t o f v o i c e t r a f f i c . 4.2 Fea tures o f the Proposed Network C o n f i g u r a t i o n The c o n f i g u r a t i o n u n d e r i n v e s t i g a t i o n i s t h e E x p r e s s n e t b r o a d c a s t bus t o p o l o g y . I t i s a s sumed t h a t t h e r e i s a number o f v o i c e and d a t a s t a t i o n s , a l t e r n a t i n g i n p o s i t i o n , a l o n g t h e f u l l l e n g t h o f t h e c o a x i a l c a b l e , as shown i n F i g u r e 4 . 1 . PROPAGATION DELAY c INBOUND CHANNEL prop, delay Connection Cable f t TRAIN S ' + KM OUTBOUND CHANNEL TX RX I Host Upstream Station D : Data Terminals V : Voice Terminals 2 3 4 N Most Downstream Station TX : TRANSMIT RX : RECEIVE F i g u r e 4.1 C o n f i g u r a t i o n of i n t e g r a t e d V/D E x p r e s s n e t The program models bu r s t of i n t e r a c t i v e data a r r i v a l s as a Po i s s on p r o c e s s , wh i l e p r o v i d i n g e x p o n e n t i a l l y d i s t r i b u t e d t a l k s p u r t and s i l e n c e du ra t i ons for r e a l time te l ephone c o n v e r s a t i o n s on the part of the v o i c e u s e r s . The vo i ce input i s assumed to be coming from a s i n g l e c a l l . A t y p i c a l t r a i n c o n s i s t s of a mixture of v o i c e and data p a c k e t s . It i s f u r t h e r assumed that the s i z e of a data packet i s i d e n t i c a l to that of a f u l l - s i z e v o i c e packe t , i . e . 1280 b i t s . 4.3 Proposed Packet T r a n s m i s s i o n P r o t o c o l s T h r e e p r o t o c o l s a r e i n v e s t i g a t e d i n t h i s s e c t i o n o f t h e t h e s i s : VD 1, V D 2 , and V D 3 . T r a n s m i t - w h e n - R e a d y (TWR) P r o t o c o l (VD1) R e g a r d l e s s o f t h e t y p e o f t e r m i n a l s i t s u p p o r t s , i f a s t a t i o n has a p a c k e t t o s e n d , i t t r a n s m i t s t h e p a c k e t w h e r e v e r i t s t u r n c o m e s . S u c h t r a n s m i s s i o n o c c u r s i r r e s p e c t i v e o f t h e p o t e n t i a l d e l a y t h a t a p a c k e t may i n c u r d u r i n g t h e t r a n s -m i s s i o n . The s i z e o f t h e b u f f e r o f e a c h s t a t i o n i s a s sumed t o be o n e . T r a n s m i t - D a t a o n a D i s c a r d B a s i s ( TPS ) P r o t o c o l (VD 2) I n t h i s c a s e , a v o i c e s t a t i o n t r a n s m i t s w i t h p r o b a b i l i t y p w h e n e v e r i t s t u r n c o m e s . F o r a d a t a s t a t i o n t h e c o r r e s p o n d i n g t r a n s m i s s i o n p r o b a b i l i t y i s q , where p and q a r e d e t e r m i n e d by e x p r e s s i o n s g i v e n b e l o w . A v o i c e o r d a t a s t a t i o n d i s c a r d s i t s p a c k e t w i t h p r o b a b i l i t y 1-p a n d 1-q r e s p e c t i v e l y . E a c h s t a t i o n i s a s s u m e d t o have a s i n g l e b u f f e r ( o f s i z e 1) t o h o l d a p a c k e t w h i c h i s a w a i t i n g t r a n s m i s s i o n . T r a n s m i t - D a t a o n a D e l a y B a s i s (TDL) P r o t o c o l (VD3) As i n T D S , e a c h s t a t i o n c o m p u t e s t h e a p p r o p r i a t e t r a n s -m i s s i o n p r o b a b i l i t y and t r a n s m i t s a c c o r d i n g l y . A v o i c e s t a t i o n d i s c a r d s w i t h p r o b a b i l i t y 1 - p . H o w e v e r , t h e b u f f e r s i z e o f a data s t a t i o n i s assumed to be i n f i n i t e . Thus , data t r a n s m i s -s i o n can be r e a l i z e d on a de l ay b a s i s . Th i s imp l i e s that i n case a data packet i s p r o h i b i t e d from t r a n s m i t t i n g , i t i s p l aced as the f i r s t element i n the queue for the s t a t i o n as the next outgo ing p a c k e t . Future a r r i v a l s to the same s t a t i o n have to j o i n the queue and wait i n l i n e . The d e t e r m i n a t i o n of the va lues of p and q is based on a channe l u t i l i z a t i o n e s t i m a t i o n scheme which c o n s i s t s o f measur ing the l eng th of the prev ious t r a i n and the aggregate number of v o i c e and data t r a n s m i s s i o n s i n the p rev ious r ound . With t h i s e s t i m a t i o n mechanism, the va lues of p and q are g i ven by : , ,/i max - -max P d - min ( Y • w w * • « ( « ) . 1 ) / i A Lmax + Y ^max qj- min ( If . W max ( . * ) , 1 ) where p i • p r o b a b i l i t y of t r a n s m i t t i n g a v o i c e packet in the j t h t r a i n q4 • p r o b a b i l i t y of t r a n s m i t t i n g a data packet In the j t h t r a i n (f - O v e r a l l Sca le Fac to r W. W wdd Voice Factor (set to 1.0 ) = Data Factor in 3th train K d a t a BF max L T J - 1 N S m a x N v j - 1 = min ( m max + Kdata * N S rr max max D a t a W e i g h i n g F a c t o r ' B a s e f a c t o r ( p r e v e n t f r a c t i o n f r o m g o i n g t o i n f i n i t y i n c a s ~ ~ u ~ J 4 -o n l y o f l o c o m o t e t h e p r e v i o u s t r a i n c o n s i s t s t i v e) Maximum L e n g t h o f T r a i n ( e x c l u d i n g p r o p a g a t i o n d e l a y ) L e n g t h o f t h e ( j - l ) 1 p r o p a g a t i o n d e l a y t h T r a i n , i n c l u d i n g Maximum Number o f S t a t i o n s c o n n e c t e d t o t h e c a b l e s u c h t h a t t h e d e l a y i n c u r r e d i n t r a n s m i s s i o n o f any p a c k e t i s g u a r a n t e e d t o be l e s s t h a n 20 ms T o t a l Number o f V o i c e T r a n s m i s s i o n s i n t h e ( j - l ) * h T r a i n T o t a l Number o f D a t a T r a n s m i s s i o n s i n t h e ( j _ ! ) t h T r a i n , 1 ) W i t h t h i s m e c h a n i s m , i f t h e p r e v i o u s t r a i n i s s h o r t , v o i c e a n d d a t a s t a t i o n s t r a n s m i t w i t h h i g h p r o b a b i l i t y . I f t h e l e n g t h o f t h e p r e v i o u s t r a i n i s l o n g , t r a n s m i s s i o n f r om v o i c e a n d d a t a s t a t i o n s a r e d i s c o u r a g e d . D a t a s t a t i o n s a r e g r a n t e d l o w e r p r i o r i t y t h a n v o i c e s t a t i o n s i n t h a t Wjj(j n e v e r e x c e e d s W vv a r e : A d v a n t a g e s o f t h i s n e t w o r k p r o t o c o l and t h e c o n f i g u r a t i o n a . S i m p l i c i t y i n i m p l e m e n t a t i o n : - s o p h i s t i c a t e d c e n t r a l c o n t r o l l e r i s not r e q u i r e d - i d e n t i c a l p r o c e d u r e s o f t r a n s m i s s i o n i n e a c h t r a i n f o r e a c h s t a t i o n b . H i g h c h a n n e l u t i l i z a t i o n : - T r a i n t y p e i n d i c a t o r , u s e d i f d i f f e r e n t t y p e s o f t r a i n s a r e e m p l o y e d by t h e s y s t e m , i s no t r e q u i r e d . Thus o v e r h e a d due t o d i f f e r e n t t r a i n t y p e s i s e l i m i n a t e d . - The l a r g e r t h e number o f s t a t i o n s c o n n e c t e d t o t h e s y s t e m , t h e s m a l l e r t h e e f f e c t o f t h e p r o p a g a t i o n d e l a y . c . V o i c e d e l a y r e q u i r e m e n t s a t i s f i e d : - By d i s c a r d i n g s m a l l amount o f p a c k e t s , t r a i n s i z e p r e v e n t e d f r o m b e i n g e x c e s s i v e l y l ong> - By u t i l i z i n g the round r o b i n s t y l e of t r a n s m i s s i o n , a maximum v a l u e o f the d e l a y i s g u a r a n t e e d ; - By r e s t r i c t i n g t o t a l number o f s t a t i o n s c o n n e c t e d to the s y s t e m . d . P r i o r i t y s y s t e m p o s s i b l e : - P r i o r i t y i n t r a n s m i s s i o n c a n be e s t a b l i s h e d , d a t a t r a n s m i s s i o n p e n a l i z e d by a p p r o p r i a t e c h o i c e o f w e i g h i n g f a c t o r . e . F a i r n e s s o f c h a n n e l u s a g e : - E q u a l s h a r e o f b a n d w i d t h among u s e r s o f t h e same c l a s s ( n a m e l y v o i c e o r d a t a u s e r s ) . 4.4 Summary of Re su l t s T h i s s e c t i o n c o n s i s t s o f t h r e e s u b - s e c t i o n s , n a m e l y t h e V D 1 , V D 2 , and VD3 s e c t i o n s . T h e i r p u r p o s e i s t o d e s c r i b e t h e p e r f o r m a n c e s o f t h e p r o t o c o l s p r o p o s e d i n t h e e a r l i e r p a r t s o f S e c t i o n 4 . 4 . 4 . 1 A n a l y s i s o f Resu l t s for VDl F o r a f i x e d i n t e r a r r i v a l t i m e ( F i g u r e 4 . 2 ) , t h e c h a n n e l u t i l i z a t i o n i s f o u n d t o i n c r e a s e w i t h i n c r e a s i n g number o f s t a t i o n s c o n n e c t e d t o t h e E x p r e s s n e t b r o a d c a s t b u s . The mean queue l e n g t h i s a g a i n one l e s s t h a n t h e t o t a l number o f p a c k e t s i n t h e s y s t e m . ( F i g u r e 4 . 3 ) The mean w a i t i n g t i m e o f d a t a and v o i c e p a c k e t s a r e a l m o s t i d e n t i c a l . ( F i g u r e 4 . 4 ) H o w e v e r , t h e v a r i a n c e o f t h e d e l a y e n c o u n t e r e d i n d a t a t r a n s m i s s i o n r e s e m b l e s t h a t o f v o i c e t r a f f i c o n l y up t o a u t i l i z a t i o n f a c t o r o f 0 . 8 7 , b e y o n d w h i c h p o i n t t h e v a r i a n c e o f d a t a d e l a y i s s i g n i f i c a n t l y l a r g e r . ( F i g u r e 4 . 5 ) The mean t r a i n s i z e ( F i g u r e 4 . 6 ) i n c r e a s e s as t h e u t i l i z a t i o n i n c r e a s e s and t h e v a r i a n c e o f t h e t r a i n s i z e ( F i g u r e 4 . 7 ) d r o p s r a p i d l y f r o m i t s c l i m a x a t U t l = 0 . 7 6 . The p e r c e n t a g e o f v o i c e p a c k e t s ( PDLP ) d e l a y e d more t h a n 20 ms i s v e r y s m a l l f o r U t l l e s s t h a n 0 . 8 , c o r r e s p o n d i n g t o a s y s t e m s i z e o f a p p r o x i m a t e l y 26 s t a t i o n s . ( F i g u r e 4 . 8 , F i g u r e 4 . 9 ) F o r a f i x e d number o f s t a t i o n s ( i n t h i s c a s e s e t to be 1 4 ) , t h e c h a n n e l u t i l i z a t i o n d e c r e a s e s as t h e i n t e r r a r i v a l t i m e s i n c r e a s e s . ( F i g u r e 4 . 1 0 ) F o r an i n t e r a r r i v a l t i m e o f a b o u t 12 s l o t s , t h e mean queue l e n g t h i s a p p r o x i m a t e l y 3 . ( F i g u r e 4 . 1 1 ) The mean w a i t i n g t i m e i s f o u n d t o d r o p as t h e Number of Stations (N) Figure 4.2 U t l vs N v ' O CM E C6 m CO CO cd o o 1 1 I 1 V D | 1 A T = 12 W — w v / — I I 1 1 0.5 0.7 0.9 Channel Utilization Figure 4.4 Mean wait time vs U t l (Utl) CO E CO 1^ • CO CO ~ * CO > o o 1 1 V D | 1 1 " I A T = 1 2 % ? 1 " — / V 1 1 I I 0.5 0.7 0.9 IE* I H CM CD cd cC CO © d 0.4 0.64 0.88 Channel Util ization (Utl) Figure 4.6 Mean t r a i n s i z e vs U t l 00 CM ' N CM CM CM N CO CD N 00 • 5 CM C6 J u ccj 0.4 Channel 0.64 0.88 Utilization (Utl) F igu re 4.7 Var t r a i n s i z e vs U t l 0.4 0.64 0.88 Channel Utilization (Utl) F i g u r e 4.8 PDLP v s U t l 0.0 20.0 40.0 Number of Stations (N) Figure 4.9 PDLP vs N co c O CO m N d co CM QJ c c co u o o 0.0 8.0 Interarr iva l Figure 4.10 U t l vs IAT 16.0 Time (IAT) o d 2 o CO S o o 0.0 8.0 16.0 Interarr iva l T ime (IAT) Figure 4.11 Mean queue length vs IAT i n t e r a r r i v a l t i m e o f t h e d a t a p a c k e t i n c r e a s e s . ( F i g u r e 4 . 1 2 ) A s i m i l a r t r e n d c a n be o b s e r v e d w i t h t h e v a r i a n c e o f t h e w a i t i n g t i m e ( F i g u r e 4 . 1 3 ) , t h e m e a n , and t h e v a r i a n c e o f t h e t r a i n s i z e . ( F i g u r e 4 . 1 4 and F i g u r e 4 . 1 5 r e s p e c t i v e l y ) 4 . 4 . 2 A n a l y s i s o f Re su l t s for VD2 F o r a f i x e d I A T , R ^ a t a * a n d ^ t h e c h a n n e l u t i l i z a t i o n i n c r e a s e s r a p i d l y w i t h an i n c r e a s e i n t h e t o t a l number o f s t a t i o n s i n t h e s y s t e m . H o w e v e r , t h e i n c r e a s e l e v e l s o f f a t N = 2 4 . ( F i g u r e 4 . 1 6 ) The mean queue l e n g t h ( F i g u r e 4 . 1 7 ) , mean w a i t i n g t i m e ( F i g u r e 4 . 1 8 ) , and t h e v a r i a n c e o f t h e w a i t i n g t i m e ( F i g u r e 4 . 1 9 ) a r e f o u n d t o i n c r e a s e i n s t e p w i t h t h e c h a n n e l u t i l i z a t i o n u n t i l U t l e q u a l s 0 . 8 , b e y o n d w h i c h p o i n t t h e i n c r e a s e becomes much more s i g n i f i c a n t . The mean ( f i g u r e 4 . 2 0 ) and v a r i a n c e ( F i g u r e 4 . 2 1 ) o f t h e t r a i n s i z e show s i m i l a r c h a r a c t e r i s t i c s as i n t h e V D l c a s e . The d a t a p a c k e t d i s c a r d p e r c e n t a g e i s o b s e r v e d t o be h i g h e r t h a n t h e v o i c e p a c k e t d i s c a r d r a t e by a f a i r a m o u n t . ( F i g u r e 4 . 2 2 ) The p e r c e n t a g e o f v o i c e p a c k e t s d e l a y e d ( F i g u r e 4 . 2 3 ) i s q u i t e l o w f o r a u t i l i z a t i o n up t o 0 . 7 8 . F o r f i x e d N , I A T , and K ( j a t a > t h e c h a n n e l u t i l i z a t i o n , t h e mean queue l e n g t h , t h e mean w a i t i n g t i m e , t h e v a r i a n c e o f t h e w a i t i n g t i m e , and t h e mean t r a i n s i z e i n c r e a s e as^p becomes b i g g e r . ( F i g u r e s 4 . 2 4 - 3 0 ) H i g h e r K d a t a i n c r e a s e s t h e a b o v e q u a n t i t i e s as w e l l . The mean and v a r i a n c e o f w a i t i n g t i m e o f t o to g H © tiX) ^ c CO c CO 0) 2 o o 1 1 1 V D , I — " N = 14 I I I I 0.0 B.O 16.0 Interarr iva l T ime (IAT) F i g u r e 4 . 12 Mean w a i t t i m e v s IAT CO 0) CM 05 CO C\J CO co 2 ^ CO $-1 CO > o © 0.0 8.0 16.0 Interarr iva l T ime (IAT) F i g u r e 4 . 1 3 V a r w a i t t i m e v s IAT 0.0 8.0 16.0 Interarr ival T ime (IAT) Figure 4.14 Mean t r a i n s i z e vs IAT 1 [ J I I I 0.0 8.0 16.0 Interarr iva l T ime (IAT) Figure 4.15 Var t r a i n s i z e vs IAT 3S Q 1 I I | L 0.4 0.64 0.88 O 0.4 0.64 0.88 Channel Uti l ization (Utl) Figure 4.18 Mean wait time vs U t l © 0.4 0.64 0.88 0.5 0.7 0.9 Channel Uti l ization (Utl) Fiqure 4.20 Mean t r a i n s i z e vs U t l CM • O CM CL) £ CO N GO c h cC to U CO > o o 0.5 0.7 0.9 Channel Uti l ization (Utl) Figure 4.21 Var t r a i n s i z e vs U t l T3 CD q T J CM o 5 en OH > o co o 0* O o 0.83 0.9 0.96 Channel Uti l ization (Utl) Figure 4.22 % D, V pks d i scarded vs U t l f? ^ PH ^ CD X CM 'a! Q 0) o CU 6 0.4 0.64 0.88 Channel Uti l ization (Utl) Figure 4.23 % delayed V pks vs U t l I o 0.7 0.98 1.26 Overall Scale Factor F i g u r e 4.26 Mean wa i t t ime vs^P CM 0.7 0.98 1.26 Overall Scale Factor Figure 4.29 Var wait time vs ^ d a t a p a c k e t s a r e l a r g e r f o r h i g h e r K c j a t a . ( F i g u r e 4 . 2 8 and 4 . 2 9 ) I n F i g u r e 4 . 3 1 , one o b s e r v e s t h a t an i n c r e a s e i n K d a t a h e l p s b r i n g down t h e v a r i a n c e o f t h e t r a i n s i z e . The p e r c e n t a g e o f d a t a p a c k e t s d i s c a r d e d c a n be r e d u c e d by i n c r e a s i n g K , j a t a o r by i n c r e a s i n g ^ , w i t h a l l o t h e r q u a n t i t i e s h e l d c o n s t a n t . ( F i g u r e 4 . 3 2 ) As i l l u s t r a t e d i n F i g u r e 4 . 3 3 , h i g h e r K , j a t . a g i v e s r i s e t o h i g h e r p e r c e n t a g e o f v o i c e p a c k e t s d i s c a r d e d . T h i s i s b e c a u s e t h e r e a r e more d a t a p a c k e t s i n t h e p r e v i o u s t r a i n i n g e n e r a l t h a n when K ^ a t a i s s m a l l . F o r l o w K ^ ^ a v a l u e s , p e r c e n t a g e o f d a t a p a c k e t s d i s c a r d e d i s h i g h e r t h a n t h e v o i c e c o u n t e r p a r t . ( F i g u r e 4 . 3 4 ) The r e v e r s e i s t r u e f o r h i g h e r K ^ a t a * F i g u r e 4 . 3 5 d e m o n s t r a t e s t h a t more v o i c e p a c k e t s a r e d e l a y e d a t K c j a t a = 5 t h a n when K ( j a t a = u » 0 1 » An i n c r e a s e i n w i l l a l s o b r i n g a b o u t a n i n c r e a s e i n PDLP s i n c e t h e s y s t e m w i l l be b u s i e r t h a n b e f o r e . More d a t a p a c k e t s c o m p a r e d t o v o i c e p a c k e t s i s t r a n s m i t t e d f o r an i n c r e a s e i n K ^ a t a w h i l e t h e r e v e r s e i s t r u e f o r t h e v o i c e d o m a i n . ( F i g u r e 4 . 3 6 and F i g u r e 4 . 3 7 ) 4 . 4 . 3 A n a l y s i s o f Resu l t s for VD3 S i n c e s t a t i o n s a r e now a s s u m e d t o have i n f i n i t e b u f f e r s i z e , t h e a r r i v a l r a t e o f t h e d a t a t r a f f i c has t o be r e d u c e d i n o r d e r t o a v o i d e x c e s s i v e number o f o u t s t a n d i n g p a c k e t s i n t h e s y s t e m . H e n c e , IAT i s s e t t o be 28 i n s t e a d o f 1 2 . The c h a n n e l 0.7 0.98 1.26 0.7 0.98 1.26 0.7 0.98 1.26 Overall Scale Factor F i g u r e 4.31 % D Pks D i s vs C^> 0.7 0.98 1.26 ded 4.57 1 1 l I V D 2 CO o rr\ Pks Dii 9.71 \ D A T A D, V 4.85 KQATA-O.OI NyoicE I* 0) CU o • N = 3 0 IAT I l = 12 \ 0.7 0.98 1.26 Overall Scale Factor F i g u r e 4.34 % D, V Pks D i s v s CM CL. CM CO ^ 00 CO > -CD <* Q CD o 0* cri V D 2 I A T - 1 2 KDATA5 5 2 5 I- KDATA =2 w / r / / K D A T A = 0 . 0 L N = 3 0 0.7 0.98 1.26 Overall Scale Factor F i g u r e 4.35 PDLP vs ^ CO CO CM CD X H in co <° CO CD <o a. q co <0 CD CD CJ o > CD 0.7 0.98 1.26 Overal l Scale Factor Figure 4.36 % data txd vs ^ co co co co CO © CO CO 0.7 0.98 1.26 Overal l Scale Factor Figure 4.37 % voice txd vs u t i l i z a t i o n , mean queue l e n g t h , mean w a i t i n g t i m e , and v a r i a n c e o f t h e w a i t i n g t i m e i n c r e a s e w i t h i n c r e a s i n g s i z e o f t h e s y s t e m . ( F i g u r e s 4 . 3 8 - 4 . 4 1 ) The e f f e c t i s more r e m a r k a b l e on t h e l a t t e r two q u a n t i t i e s , s i n c e d a t a p a c k e t s w h i c h a r e not t r a n s m i t t e d a r e now " s t o r e d " i n b u f f e r f o r l a t e r d e l i v e r y . T h i s i m p l i e s an i n c r e a s e i n t h e number o f p a c k e t s i n t h e s y s t e m . W h i l e t h e mean and v a r i a n c e o f t h e d a t a d e l a y s a r e l a r g e f o r N g r e a t e r t h a n 3 0 , t h e mean and v a r i a n c e o f t h e v o i c e d e l a y s a r e w e l l w i t h i n r e a s o n a b l e b o u n d s . ( F i g u r e s 4 . 4 2 - 4 . 4 3 ) The mean and v a r i a n c e o f t h e t r a i n s i z e a r e a l s o q u i t e a c c e p t a b l e . ( F i g u r e s 4 . 4 4 - 4 . 4 5 ) I n f a c t , t h e two v a r i a n c e s show d e c l i n e s f o r N g r e a t e r t h a n 3 0 . D a t a t r a f f i c o c c u p i e s a b o u t t w o - t h i r d s o f t h e t o t a l b a n d w i d t h a t N = 3 0 . ( F i g u r e 4 . 4 6 ) The p e r c e n t a g e o f v o i c e p a c k e t s d i s c a r d e d i s a b o u t 1 when N i s 3 0 . ( F i g u r e 4 . 4 7 ) The p r o b a b i l i t y o f d a t a p a c k e t s d e l a y e d i n c r e a s e s r a p i d l y when t h e t o t a l number o f s t a t i o n s i n t h e s y s t e m e x c e e d s 3 0 . ( F i g u r e s 4 . 4 8 - 4 . 4 9 ) 0.0 16.0 32.0 of Stations Figure 4.39 Mean queue length vs N Number (N) 0.0 Number 16.0 32.0 of Stations (N) F i g u r e 4 . 4 0 ' M e a n w a i t t i m e v s N Number of Stations (N) F i g u r e 4 . 4 1 V a r w a i t t i m e v s N 0.0 16.0 32.0 Number of Stations (N) F igu re 4.42 Mean wait time of v pks vs N 0.0 16.0 32.0 Number of Stations (N) Figure 4.43 Var wait time of vo i ce pks vs N 0.0 16.0 32.0 Number of Stations (N) Figure 4.44 Mean t r a i n s i z e vs N 0.0 16.0 32.0 Number of Stations (N) Figure 4.45 Var t r a i n s i z e vs N 16.0 32.0 of Stations Fianre 4.46 % D, V Tx vs N 0.0 Number (N) Q CD co o Q CO ^ CM 0.0 16.0 32.0 Number of Stations (N) Figure 4.47 % v pk d i sca rded vs N > » OS CO © Q CO co CM CO d CO o O o 0.4 0.64 0.88 Channel Util ization (Utl) Figure 4.48 Prob data tx/delayed vs N "So >> CO 2 h CO CO O O $M CO o o o © 0.0 16.0 32.0 Number of Station: Figure 4.49 Prob data delayed vs N 5. COMPARISON OF THE DIFFERENT PROTOCOLS The r e s u l t s f o r t h e d i f f e r e n t p r o t o c o l s a r e now p l o t t e d o n t h e same g r a p h s f o r e a s y c o m p a r i s o n . C o m p a r i n g t h e s e w i t h t h e c a s e s whe r e p u r e v o i c e o r p u r e d a t a p a c k e t s a r e t r a n s m i t t e d , t h e i n t e g r a t e d p r o t o c o l s y i e l d much h i g h e r c h a n n e l u t i l i z a t i o n f a c t o r . ( F i g u r e 5 .1 ) T h i s i s due t o t h e f a c t t h a t more p a c k e t s a r e r e a d y f o r t r a n s m i s s i o n , w h i c h i n t u r n l e a d s t o more " f u l l - s i z e " t r a i n s . The a r g u m e n t a l s o e x p l a i n s t h e c o r r e s p o n d i n g i n c r e a s e i n mean queue l e n g t h ( F i g u r e 5 . 2 ) , mean w a i t i n g t i m e ( F i g u r e s 5 . 3 , 5 . 5 ) , and v a r i a n c e o f t h e w a i t i n g t i m e ( F i g u r e s 5 . 4 , 5 . 6 ) . H o w e v e r , as N i n c r e a s e s t o v a l u e s l a r g e r t h a n 3 3 , t h e VD2 w i l l d i s c a r d many o f t h e p a c k e t s , r e n d e r i n g t h e s y s t e m a l o w e r u t i l i z a t i o n . S i m i l a r t r e n d i s o b s e r v e d w i t h t h e mean and v a r i a n c e o f v o i c e and d a t a d e l a y s . The mean t r a i n s i z e s o f a V/D E x p r e s s n e t e m p l o y i n g t h e V D 1 a n d VD2 p r o t o c o l s a r e much g r e a t e r t h a n t h o s e i n t h e V I , V2 c a s e s . ( F i g u r e 5 .7 ) The v a r i a n c e o f t h e t r a i n s i z e ( F i g u r e 5 .8 ) w i l l i n c r e a s e as t h e number o f s t a t i o n s i n c r e a s e , b u t w i l l d r o p a b r u p t l y b e c a u s e a t h i g h u t i l i z a t i o n , t h e E x p r e s s n e t b e h a v e s l i k e a TDM s y s t e m . F o r a s y s t e m s i z e o f a b o u t 30 s t a t i o n s (15 d a t a s t a t i o n s and 15 v o i c e s t a t i o n s ) , t h e p a c k e t d i s c a r d r a t e f o r VD 2 i s a b o u t 1%, w h i l e t h e amount o f " l a t e " p a c k e t s i s a b o u t 20%. ( F i g u r e s 5 . 9 - 5 . 1 0 ) The i d e a b e h i n d t h e s e f i g u r e s i s t h a t w i t h 15 v o i c e s t a t i o n s a l o n e , no p a c k e t d i s c a r d i n g i s r e q u i r e d t o g u a r a n t e e t h a t p a c k e t s a r r i v e w i t h i n 20 ms . H o w e v e r , a d d i t i o n a l d a t a s t a t i o n s a p p e n d e d t o t h e s y s t e m m i g h t v i o l a t e t h i s c o n s t r a i n t . Now w i t h a s u i t a b l e p r o t o c o l V D 2 , t h e E x p r e s s n e t c a n a c commoda t e a l m o s t d o u b l e t h e o r i g i n a l number o f s t a t i o n s w i t h o u t i n c u r r i n g e x c e s s i v e amount o f l o s s p a c k e t s , a n d y e t manage t o t r a n s m i t most o f t h e p a c k e t s on t i m e t o t h e d e s t i n a t i o n . 10.0 24.0 38.0 Number of Stations (N) Figure 5.1 U t l ys N 10.0 24.0 38.0 Number of Stations (N) Figure 5.2 Mean queue length vs N z 10.0 24.0 38.0 Number of Stations (N) Figure 5.5 Mean wait time of v pks vs N 10.0 24.0 38.0 Number of Stations (N) Figure 5.6 Var of wait time of v pks vs N 10.0 24.0 38.0 Number of Station Figure 5.7 Mean t r a i n s i z e vs N CO CM CM • N CM CM —« 6 1 1 1 1 V D | — // V, IAT = 12 1 — 1 — / K d a t a = 5 <f =1.3 1 1 1 V F 1 » CJ g m a CO CM u ^ CO > o o 10.0 24.0 38.0 Number of Stations (N) Figure 5.8 Var of t r a i n s i z e vs N 10.0 24.0 38.0 Number of Stations (N) Figure 5.9 % vo ice pks d iscarded vs N 10.0 24.0 38.0 Number of Stations (N) Figure 5.10 % delayed v pks vs N 6 . CONCLUSIONS The a i m o f t h i s t h e s i s i s t o s t u d y v o i c e and d a t a t r a n s -m i s s i o n s i n E x p r e s s n e t — a h i g h - s p e e d l o c a l a r e a c o m m u n i c a t i o n n e t w o r k w i t h b r o a d c a s t c a p a b i l i t y . The m a j o r d i f f e r e n c e i n p e r f o r m a n c e r e q u i r e m e n t b e t w e e n t h e two c l a s s e s o f t r a f f i c i s t h a t w h i l e i n t e r a c t i v e d a t a t e r m i n a l s r e q u i r e h i g h l e v e l o f a c c u r a c y , v o i c e t r a n s m i s s i o n c a n t o l e r a t e a h i g h e r e r r o r r a t e i n e x c h a n g e f o r a r e d u c t i o n i n t h e n e t w o r k t r a n s i t d e l a y . T h i s i s p o s s i b l e b e c a u s e o f t h e l a r g e amount o f r e d u n d a n c y i n human s p e e c h . The d a t a p r o t o c o l f o r a 1 - b u f f e r c a s e has b e e n v e r i f i e d by t h e o r e t i c a l f i g u r e s . The i n f i n i t e b u f f e r c a s e was a l s o e x a m i n e d . F o r v o i c e t r a n s m i s s i o n s , t h e e n d - t o - e n d a v e r a g e n e t w o r k d e l i v e r y t i m e w o u l d have t o be s m a l l and r e l a t i v e l y i n v a r i a n t i n o r d e r t o a v o i d gaps t h a t w o u l d r e d u c e s p e e c h i n t e l l i g i b i l i t y . To m a i n t a i n good s p e e c h q u a l i t y , i t i s n e c e s s a r y t o keep t h e p a c k e t d i s c a r d r a t e b e l o w 1%. I n f a c t , t h e p a c k e t d i s c a r d r a t e i n t h e s e c o n d p r o t o c o l p r o p o s e d (V2) i s g i v e n by a n e x p r e s s i o n s i m i l a r t o t h e T ime A s s i g n m e n t S p e e c h I n t e r p o l a t i o n ( T A S I ) s p e e c h l o s s e q u a t i o n . T h i s s e c o n d v o i c e p r o t o c o l was s u b j e c t e d t o a maximum t o l e r a b l e d e l a y c r i t e r i o n , w h i l e t h e f i r s t p r o t o c o l ( V I ) has no s u c h c o n s t r a i n t . The a f f i l i a t e d s e c t i o n on c a l l e s t i m a t i o n has i n v e s t i g a t e d t h e r e l a t i o n s h i p b e t w e e n p a c k e t d i s c a r d i n g r a t e and c a l l b l o c k i n g p r o b a b i l i t y , t r a d e o f f b e t w e e n t h e two was o b s e r v e d . The e f f e c t i v e n e s s o f t h e e s t i m a t o r was a l s o l o o k e d i n t o , t h r o u g h a c o m p a r i s o n o f t h e e s t i m a t e d v e r s u s t h e a c t u a l number o f a c t i v e v o i c e c a l l s . The e s t i m a t o r s were f o u n d to be good o n e s . F o r i n t e g r a t e d v o i c e and d a t a t r a n s m i s s i o n , t h r e e p r o t o c o l s have b e e n p r o p o s e d , i n v e s t i g a t e d , and c o m p a r e d t o t h e p u r e d a t a , p u r e v o i c e t r a n s m i s s i o n c a s e s . T h e s e i n c l u d e t r a n s m i s s i o n w i t h o u t d i s c a r d i n g o f p a c k e t s , d i s c a r d v o i c e p a c k e t s / d i s c a r d d a t a p a c k e t s , and d i s c a r d v o i c e p a c k e t s / d e l a y d a t a p a c k e t s s c h e m e s . W i t h t h e l a t t e r t w o , s chemes were d e v i s e d t o a s s i g n t e m p o r a l p r i o r i t y o n t h e t r a n s m i s s i o n o f v o i c e p a c k e t s , a t t h e e x p e n s e o f d e l a y e d o r d i s c a r d e d d a t a p a c k e t s . I t was f o u n d t h a t a c c e p t a b l e l e v e l o f p e r f o r m a n c e c a n be a c h i e v e d f o r a f a i r l y l a r g e number o f s t a t i o n s . F u t u r e r e s e a r c h w i t h r e g a r d t o t r a n s m i s s i o n i n t h e E x p r e s s n e t c o u l d be c a r r i e d o u t i n t h e f o l l o w i n g a r e a s : 1. I m p l e m e n t a t i o n o f v o i c e c a l l e s t i m a t i o n scheme i n i n t e g r a t e d V/D p r o t o c o l s . The c a l l e s t i m a t i o n scheme d e v i s e d i n S e c t i o n 3 . 4 c a n be a p p l i e d t o t h e i n t e g r a -t i o n o f v o i c e and d a t a s e c t i o n i n S e c t i o n 4 t h r o u g h t h e f o l l o w i n g p r o c e d u r e . F i r s t o f a l l , t he oC c a n be s e t , s a y , t o 0 . 1 . T h i s i m p l i e s t h a t t h e i n c o m i n g c a l l s may be b l o c k e d a c c o r d i n g t o t h e v a r i o u s p a r a m e t e r s c a l c u l a t e d f r o m p r e v i o u s e s t i m a t e s . I n c a s e a c a l l i s a c c e p t e d , t h e n t h e i n d i v i d u a l v o i c e packet is t r a n s m i t t e d or d i s c a r d e d a cco rd ing to the p r o b a b i l i t y p j . R e l a t i o n s h i p s between packet d i s c a r d r a t e s and c a l l b l o c k i n g p r o b a b i l i t y can be det e rmined . 2. I n v e s t i g a t i o n in to e f f e c t s of preambles on the o v e r a l l t r a n s m i s s i o n e f f i c i e n c y , mean, and v a r i a n c e of wa i t ing t ime , t r a i n s i z e , e t c . 3. Study of behav iour of p r o t o c o l s i n which more than one packet may be t r a n s m i t t e d by heavy t r a f f i c u s e r s . 4. Performance study of the system under d i f f e r e n t channe l c a p a c i t i e s . 5. I n v e s t i g a t i o n of p r o t o c o l s which r e a l i z e t r a n s m i s s i o n of v o i c e and data v i a d i f f e r e n t t r a i n t y p e s . 6. P roposa l of o ther p r o b a b i l i t y d e t e r m i n a t i o n schemes. 7 . P roposa l of other t r a n s m i s s i o n a l g o r i t h m s . The t o p i c of i n t e g r a t i o n of v o i c e and data i n communicat ion networks (ISDN) is of cu r r en t i n t e r e s t and possesses enormous p o t e n t i a l towards the de s i gn of b e t t e r communications systems i n the f u t u r e . In order to reap the f u l l p o t e n t i a l of the i n t e g r a t e d t r a n s m i s s i o n p l a n t s , work has to be done on va r i ous networking a s p e c t s . The f o l l ow ing are h i g h l i g h t s of the p o s s i b l e r e s e a r ch d i r e c t i o n s : - Des ign of s m a l l , f l e x i b l e , and economica l vo i ce t e r m i n a l s wi th c a p a b i l i t y to accommodate a v a r i e t y of v o i c e d i g i t i z a t i o n a l g o r i t h m s , t r a n s m i s s i o n r a t e s , c o n f e r e n c i n g t e c h n i q u e s , and s e c u r i t y measures . - I n v e s t i g a t i o n o f p e r f o r m a n c e c r i t e r i a and r e l i a b i l i t y o f i n t e g r a t e d p a c k e t v o i c e and d a t a s y s t e m s . - E x a m i n a t i o n and c o m p a r i s o n o f l o c a l d i s t r i b u t i o n s t r a t e g i e s and n e t w o r k c o n f i g u r a t i o n s f o r p a c k e t -s w i t c h e d n e t w o r k s . - T h e r e i s much room f o r r e s e a r c h i n t h e a r e a o f i n t e r -a c t i o n b e t w e e n v o i c e and d a t a f l o w c o n t r o l s i n i n t e g r a t e d s y s t e m s . Problems t h a t can be f o r e s e e n i n c l u d e : - The v o i c e s e c t i o n s o f t h e t h e s i s as w e l l as a l o t o f t h e w o r k done so f a r were b a s e d on a 2 - s t a t e m o d e l o f a l t e r n a t i v e t a l k s p u r t and s i l e n c e i n t e r v a l s . O t h e r s i t u a t i o n s ( e . g . d o u b l e t a l k ) w e r e no t e x t e n s i v e l y e x p l o r e d . H o w e v e r , t h e d e g r e e o f c o m p l e x i t y i n s i m u l a t i o n and a n a l y s i s i n c r e a s e d r a s t i c a l l y w i t h m u l t i - s t a t e m o d e l s . - S t r i n g e n t p a c k e t d i s c a r d i n g r a t e s and c a l l b l o c k i n g p e r f o r m a n c e c r i t e r i a e s s e n t i a l f o r v o i c e q u a l i t y c o n t r o l pose d e s i g n p r o b l e m s and l i m i t a t i o n s . - T h e r e i s a l w a y s a t r a d e o f f b e t w e e n v o i c e and d a t a t r a n s m i s s i o n s . V o i c e t r a n s m i s s i o n c a n o n l y be f a v o u r e d a t t h e e x p e n s e o f d a t a t r a n s m i s s i o n ( o r v i c e v e r s a ) , i m p l y i n g t h a t t h e r e i s a l w a y s g o i n g t o be c o n t e n t i o n o f c h a n n e l c a p a c i t y among t h e d i f f e r e n t k i n d s o f t r a f f i c s . - P a c k e t l e n g t h o p t i m i z a t i o n i n t e r m s o f i n f o r m a t i o n t h r o u g h p u t and mean t i m e d e l a y i s no t an e a s y t a s k . I n s u m m a r y , i t s r o u n d - r o b i n s t y l e o f t r a n s m i s s i o n r e n d e r s t h e E x p r e s s n e t an a d v a n t a g e o v e r t h e c o n v e n t i o n a l m u l t i a c c e s s s c h e m e s ( e . g . C S M A / C D ) . A n a l y s i s and s i m u l a t i o n s i n d i c a t e t h a t t h e r e i s an u p p e r b o u n d on t h e maximum amount o f t h e d e l a y e n c o u n t e r e d by a ( v o i c e ) p a c k e t . I t i s t h i s u n i q u e f e a t u r e o f t h e E x p r e s s n e t t h a t makes i t a t t r a c t i v e f o r i n t e g r a t e d v o i c e / d a t a t r a n s m i s s i o n a p p l i c a t i o n s i n a l o c a l a r e a o f f i c e e n v i r o n -m e n t . The s y s t e m c a n d y n a m i c a l l y a l l o c a t e c h a n n e l c a p a c i t y t o d a t a t r a f f i c d u r i n g i d l e p e r i o d s o f v o i c e t e r m i n a l s , r e s u l t i n g i n g r a c e f u l t r a n s m i s s i o n o f v o i c e as w e l l as d a t a p a c k e t s . APPENDIX A l . CLASSIFICATION 07 DATA PERFORMANCE PARAMETERS £PFM 1] PERFORMANCE CRITERION SERVICE TRANSMISSION Qua 1 i t y - User i n f o r m a t i o n l o s s probab i l i t y - User i n f o r m a t i o n m i s -d e l i v e r y p r o b a b i l i t y - User i n f o r -mat io n probab i l i t y Delay - Access de lay ( c a l l setup t ime ) - User i n f o r -mat i on t rans fer de lay Ava i l a b 11 i t y - Access d e n i a l p r o b a b i l i t y (network, b l o ck ing ) - S e r v i c e a v a i l a b l i t y - User i n f o r -mat io n t rans fer ra te ( t hro ug hput ef f i c ienc y) APPENDIX A2. CLASSIFICATION OF VOICE PERFORMANCE PARAMETERS CPFM 13 PERFORMANCE CRITERION SERVICE TRANSMISSION Qua l i t y - I n c o r r e c t treatment - Ec ho - Q u a n t i z a t i o n No i s e - I n t e r r u p t i o n s - E r r o r s Delay - D i a l tone de lay - Abso lu te f i x e d de lay - V a r i a b l e s peechburst de l ay Ava i l a b i l i t y - C a l l b l o c k i n g - Long i n t e r r u p t ions - C a l l cu to f f APPENDIX B. TRANSMISSION MECHANISM OF EXPRESSNET In the Expressnet access p r o t o c o l , the mechanism used i n de te rmin ing the access r i g h t s to users i n a g i ven round is made independent o f the p ropaga t i on d e l a y t , in c o n t r a s t to other m u l t i p l e access schemes. A g l o b a l t i m i n g diagram and the f lowchart of the procedure as c a r r i e d out by an i n d i v i d u a l s t a t i o n are i l l u s t r a t e d in F igures B l and B2 r e s p e c t i v e l y . In the Expressnet access p r o t o c o l ( F i gu r e B2) the time r e f e r ence used i s the e n d - o f - c a r r i e r on the outbound channel (EOC(OUT) ) . The event EOC(OUT) is s a i d to occur when c ( t , 0UT ) undertakes a t r a n s i t i o n from 1 to 0. c ( t ,0UT ) is a Boolean f u n c t i o n denot ing the presence or absence of c a r r i e r with a de l ay of t j s econds . Here r ep re sen t s the time r e q u i r e d for the d e t e c t i o n o p e r a t i o n . Thus the gap between c o n s e c u t i v e t r a n s m i s s i o n s are reduced to va lues on the same order of magnitude as the time r e q u i r e d to detect c a r r i e r . A t r a n s m i s s i o n un i t (TU) c o n s i s t s of a preamble ( for s y n c h r o n i z a t i o n purposes at the r e c e i v e r ) f o l l owed by the i n f o r m a t i o n packet i t s e l f . An ACTIVE u s e r , who has a message to t r a n s m i t , i s s a i d to be back logged (or READY). Otherwise i t i s s a i d to be i d l e (NOT-READY). The s t a t e of an ACTIVE s t a t i o n can be determined by examining whether i t s t r ansmi t bu f f e r i s empty or not . To that e f f e c t , a f u n c t i o n TB(t ) i s de f ined for each s t a t i o n : ( 1 i f i t s t r ansmi t buf fer i s nonempty 0 ot herwis e . An i d l e user does not contend for the c h a n n e l . A backlogged user (a user w ish ing to t r an smi t ) waits u n t i l i t d e t e c t s EOC(OUT) on the outbound channel and then immediate ly s t a r t s t r a n s m i t t i n g i t s own packet (TU) . S i m u l t a n e o u s l y , the user senses, the outbound channel for a c t i v i t y on the upstream s i d e . If a c t i v i t y i s d e t e c t e d , the user aborts i t s c u r r e n t t r a n s m i s s i o n . Otherw ise , i t completes i t . The s u c c e s s i o n of t r a n s m i s s i o n u n i t s t r a n s m i t t e d in the same round is de f ined as a " t r a i n . " A t r a i n is generated on the outbound channe l and i s e n t i r e l y seen on the inbound channe l by a l l u s e r s . However, i t can on ly be seen by a s t a t i o n on the outbound channe l as long as the TU ' s in i t are be ing t r a n s m i t t e d by s t a t i o n s with lower i ndexes , i . e . , s t a t i o n s on the upstream s i d e of i t s t r a n s m i t t e r . The maximum number of packets i n the t r a i n is the maximum number of s t a t i o n s connected to the network. Acco rd ing to the c o n f i g u r a t i o n and the t r a n s m i s s i o n p r o t o c o l , the re is a s i n g l e u se r , the one with the lowest index among those ready s t a t i o n s . The user is ab le to detect EOC(OUT). It does not have to abort i t s t r a n s m i s s i o n and hence t r a n s m i t s s u c c e s s f u l l y . Moreover , a user who has completed the t r a n s m i s s i o n of a packet in a g i v en round does not encounter the event EOC(OUT) aga in in that round . This guarantees that no user can t ransmi t more than once in a g i v en r ound . The d e t e c t i o n of the presence of a t r a i n on the inbound channe l is ach ieved by d e f i n i n g TRAIN(t , IN) [= c ( t - t d , I N ) + c ( t , I N ) ] whose va lue i s 1 as long as the t r a i n is in p r o g r e s s . The t r a n s i t i o n TRAIN ( t . IN ) : ( l ->0 ) de f ines the end of t r a i n EOT(IN) and the t r a n s i t i o n TRAIN ( t . IN ) : C 0 l ) d e f i n e s the beg inn ing of a t r a i n BOT(IN) . The main f e a tu r e of the topo logy r e s t s on the fact that when the inbound channel is made e x a c t l y p a r a l l e l to the o u t -bound c h a n n e l , the event EOT(IN) v i s i t s each user i n the same order as they are pe rmi t ted to t r a n s m i t . T h e r e f o r e , to s t a r t a new round , EOT(IN) i s used as the s y n c h r o n i z i n g even t . The mechanism a l lows the ready s t a t i o n s with the lowest index to be the f i r s t to complete t r a n s m i s s i o n of i t s TU . Then the new t r a i n takes i t s normal c o u r s e . When the ALIVE s t a t i o n becomes ready , i t does not have to wait for an EOT(IN) to s t a r t t r a n s m i s s i o n . If an outbound t r a i n is ob se rved , the s t a t i o n synch ron i ze s t r a n s m i s s i o n s w i th EOC(OUT). I f , however, at the t ime i t becomes ready , no t r a i n i s observed on the outbound c h a n n e l , then EOT(IN) becomes the s y n c h r o n i z i n g even t . To a v o i d l o s i n g the s y n c h r o n i z i n g event EOT(IN) i f the t r a i n were to be empty, i n the Expressnet a new round is always s t a r t e d by having a l l users t r ansmi t a shor t burs t of unmodulated c a r r i e r , termed " l o c o m o t i v e , " of d u r a t i o n t<j be fore a t tempt ing to t r ansmi t a packe t . If the t r a i n i s empty, then the l ocomot ive c o n s t i t u t e s the end of t r a i n , and EOT(IN) s u r e l y takes p l a c e . From the above d e s c r i p t i o n , one can see that the Expressnet ach ieves a " c o n v e n t i o n a l " round r o b i n d i s c i p l i n e where users are s e r v i c e d in a p r e s c r i b e d order determined by t h e i r p h y s i c a l l o c a t i o n on the network. If a user has not message i n bu f f e r when i t s t u r n comes up, i t d e c l i n e s to t r ansmi t so i t must wait for the next round be fore g e t t i n g another t u r n . Th i s type of d i s c i p l i n e is r e f e r r e d to as the non-gated s e q u e n t i a l s e r v i c e d i s c i p l i n e (NGSS). 1 2 J TRAIN (t,OUT) TX TAP c(t,OUT) c ( t , IN) TRAIN (t . IN) f— second a r r i v a l of f packet for s ta t i on 1^  f i r s t packet a r r i v a l for s t a t i on i£ t * t . * *d i i — i r f- TA H- T A h T - H i i s t a t i on J can only 1 2 sense transmission | j j from upstream users inbound channel achieves broadcasting funct ion k1 a 2 I 1 K t * t « -4 t r a i n i n progress as observed from inbound channel /-locomotive E l i n . TIME TIME TIME TIME TIME TIME TIME TIME ~S TIME BOT(IN) EOT(IN) BOT(IN) Signals and events as observed by s ta t i on J , assuming that s tat ions with indexes i ^ ^ i g - ^ J ^ ^ a r e n o n i d l * . F i g u r e B l G l o b a l t i m i n g diagram o f E x p r e s s n e t £T H l ] EOT(IN) NEW TRAIN TRANSMIT LOCOMOTIVE station with lower index want YES c(t,OUT)« 1 ? ABORT TRANSMISSION s to tx therefore can transmit COMPLETE TRANSMISSION OF TU F i g u r e B2 F l o w c h a r t f o r t h e E x p r e s s n e t a c c e s s p r o t o c o l [ T H l j increment trainnumber I CHECKSERVE CHECKAFTER I ENTER | 1 CHECKQUEUE COUNTRT 1 LISTRAVERSE TRAVERSE » BOTRAIN F l o w c h a r t f o r Main Program ( Data , V o i c e ) Q START J CLOCIUBOT « exi t t ime 1 t r a i n s i z e - 0 t r a i n s i z e _ t r a i n s i z e + 1 1 pkreaain m pkremain - 1 pktxd - pktxd • 1 delay exi t t ime -front?.entryt ime pkdelay - pkdelay • delay aqsv - sqsv • sqr(delay) SIMREKAIN m SUM REMAIN _ 1 1 e x i t t i a e m exi t t ime * Te CLOCK m CLOCK + Te busy-tine m busytine • T < discard(front) ^ front : & n i T T ~ " ~ ^ > -k TRUE [ nexttine » frontd.entrytime FALSE t r a i n t r a i n loaded empty loaded-t r a i n loaded-t r a i n • 1 CLOCK -CLOCK • Tcable* Tlocom EOT - BOT -exi t t ime - CLOCK ( END ) F lowchar t f o r BOTRAIN ( Data ) FALSE TRUE 5ervtime|_iJ - timsert IfCR - TRUE •sgRD[i]« 1 BCK-BCK • 1 INCReFALSE »SgRD[l] -0 timesert«tiiDesert+Te c Q END ^ F lowchar t f o r CHECKSERVE ( Data ) TRUE Short packet/ talkspurt finished FALSE lastarrvt-lastarrvt • tspleft futpkslze-tspleft/pgtfull have to generate new 1 tspbegin«silend tspend •tspbegin • tspdar(tapmean) tspleft -tspend -tspbegin FALSE A short packet remains lastarrvt • tspbegin • tspleft futpksize tspleft/ i silbegin » tspend silend m silbegin • sildur(siloean) s i l le f t « silend silbegin F lowchar t for. VOICEGENERATE ( V o i c e ) APPENDIX C5 ( START ) CLOCK- BOT -exittime trainsize » 0 FALSE FALSE ^ check nex^ station FALSE I delay-exlttlme-frontff. entry time] TRUE delay* pgtfull * 1 pktxd pktxd • 1 Uncreaent I check nex~f station FALSE discardpk | place delay in LFD i f delay is larger; update pkdelay.sosv ; Both exittime and CLOCK i incremented by TRANS fqindx^+t^q Busytime incremented by TRANS [qindx] ; trainsize • trainsize * 1 I pkremain • pKremain - 1 SUflREHAIN.SUHREMAIN. 1 discard(front) TZ :trainsize PC :pgtfull EOT exittime train loaded tra in empty loaded-train loaded-train • 1 empty-train empty-train • 1 CLOCK -CLOCK • Tcable* Tlocom CLOCK -CLOCK • Tlocom ["TRUE* FALSE iLClNG TRAIN i n r T » m » n t » d SUMTRAIN incremented SQTRAIN updated 3 EOT - BOT -exittime • CLOCK C END ) F l o w c h a r t f o r BOTRAIN ( V o i c e , w i t h d i s c a r d i n g o f p a c k e t s ) 1 LIST OF REFERENCES I SDN 1. R . D . R o s n e r , " D i s t r i b u t e d T e l e c o m m u n i c a t i o n s N e t w o r k s v i a S a t e l l i t e s and P a c k e t S w i t c h i n g , " L i f e t i m e L e a r n i n g P u b l i c a t i o n s , C h a p t e r 1 1 . 2 . W. S t a l l i n g s , " D a t a and C o m p u t e r C o m m u n i c a t i o n s , " M a c m i l l a n P u b l i s h i n g Company , 1 9 8 5 , C h a p t e r 1 7 . 3 . W. C h o u , " C o m p u t e r C o m m u n i c a t i o n s , " V o l . I I , P r e n t i c e H a l l , 1 9 8 5 , C h a p t e r 1 7 . MOB 1. P . S p i l l i n g , " D i g i t a l V o i c e C o m m u n i c a t i o n s i n t h e P a c k e t R a d i o N e t w o r k , " I E E E , 1 9 8 0 , p p . 2 1 . 4 . 1 - 7 . 2 . N . S h a c h a m , " S p e e c h T r a n s p o r t i n P a c k e t - R a d i o N e t w o r k s w i t h M o b i l e N o d e s , " I E E E , J o u r n a l o n S e l e c t e d A r e a s i n  C o m m u n i c a t i o n s , V o l . S A C - 1 , No . 6 , D e c . 1983 , p p . 1 0 8 4 - 9 7 . 3 . S . A . Mahmoud , " A n I n t e g r a t e d V o i c e / D a t a S y s t e m f o r VHF/UHF M o b i l e R a d i o , " I E E E , J o u r n a l o n S e l e c t e d A r e a s i n  C o m m u n i c a t i o n s , V o l . S A C - 1 , No . 6 , D e c . 1983 , p p . 1098¬1 1 1 1 . PFM 1. J . G . G r u b e r , " P e r f o r m a n c e R e q u i r e m e n t s f o r I n t e g r a t e d V o i c e / D a t a N e t w o r k s , " I E E E , J o u r n a l o n S e l e c t e d A r e a s i n  C o m m u n i c a t i o n s , V o l . S A C - 1 , N o . 6, D e c . 1 9 8 3 , p p . 9 8 1 - 1 0 0 5 . MUX 1. C . J . W e i n s t e i n , A . J . M c L a u g h i n , and T . B i a l l y , " E f f i c i e n t M u l t i p l e x i n g o f V o i c e and D a t a i n I n t e g r a t e d D i g i t a l N e t w o r k s , " i n I n t . Commun. C o n f . R e c . , V o l . 2 , S e a t t l e , WA, J u n e 1 9 8 0 , p p . 2 1 . 1 . 1 - 2 1 . 1 . 7 . TH ( T h e s i s ) 1. L . 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