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UBC Theses and Dissertations

Performance evaluation of rate-based congestion control schemes for ABR service over broadband satellite networks interworking with ATM/B-ISDNs Zhang, Bin


Asynchronous Transfer Mode (ATM) is an emerging networking technique which supports quality of service (QoS) guarantees for different traffic types. The Available Bit Rate (ABR) service is proposed to provide the efficient use of limited network resources for data traffic. For ABR service, ATM Forum has suggested the rate-based congestion control schemes: Explicit Forward Congestion Indication (EFCI, a binary feedback scheme) scheme, Explicit Rate (ER) scheme, and Enhanced Proportional Rate Control Algorithm (EPRCA). In addition, the segmented closed-loop scheme was also recommended to reduce the size of the control loop. In this thesis, the effects of satellite link (long delay) on the EFCI and ER schemes are analyzed by using calculation results. Based on the analytical results, the simulations of endto- end congestion control schemes are performed. For the EFCI scheme, both the calculation and simulation results show that the long delay will worsen the network performance in terms of buffer occupancy, link utilization and cell loss ratio (CLR). Our study also finds that the buffer threshold, buffer size in ATM switch, as well as the rate increase and decrease factors, will affect the buffer occupancy, link utilization and cell loss ratio in the various ways. Procedures are suggested to minimize the buffer requirement and maximize the link utilization with the required CLR and maximum link delay. Moreover, a delay-based method (DBCI scheme) is proposed to dynamically adjust the traffic rate in order to minimize the buffer requirement. For the ER scheme, since-the product of data rate and link delay in each ABR connection plays a key role on the buffer occupancy of the ATM switch, the delaybased adaptation method (DBER scheme) to reallocate the left-over bandwidth is proposed. Simulation results show that the suggested approaches can improve the buffer occupancy efficiently when congestion happens. The generic and delay-based EPRCA schemes are investigated with different parameters in different links. Simulation results are compared and the delay-based EPRCA scheme is found to be a more efficient scheme. Furthermore, the segmented (double-loop) congestion control schemes are evaluated by simulations methods and analyzed with different combinations of EFCI and ER schemes. The results are compared with those of end-to-end (single-loop) schemes. From the comparisons, the segmented congestion control scheme is considered to be a better scheme in the long delay environment because it can respond to congestion more quickly and be able to distribute the queued cells (e.g. the long queue length occurred in the single loop scheme) into more ATM switches involved in the congestion.

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