Abstract
The performance of the Transmission Control Protocol (TCP) over the Unspecified Bit Rate (UBR) and the Available Bit Rate (ABR) ATM service classes was investigated by simulation. These service classes are both for data communication but have different characteristics. It is therefore important to reveal the performance of TCP over UBR and ABR.
Since UBR service does not guarantee the cell loss ratio, huge buffers are needed in the ATM switches to prevent cell loss, which degrade the performance seriously in the TCP layer. If many connections are multiplexed, it is difficult to have large enough buffers in the ATM switches. Furthermore, huge buffers are undesirable for delay-sensitive TCP applications. Therefore, cell loss may be inevitable with UBR connections. Simulation showed that when there is cell loss, TCP performs better when the timer granularity is set finer because finer granularity means faster detection of data loss.
When the ABR service class is used, feedback rate flow control is used to minimize cell loss. Simulation showed that switches with Explicit Forward Congestion Indication mode, which have simple architecture, have good performance in small networks but the performance is degraded when many connections are multiplexed or when the round trip time becomes long. We recommend to set low Peak Cell Rate in such cases. Otherwise, switches with Explicit Rate mode are effective even in the networks with many connections and long round-trip times.
Whichever switch architecture is used, simulation showed that huge buffers cause a large variance in the Round-Trip-Time (RTT). As a result, TCP cannot estimate Retransmission-Time-Out correctly and retransmits TCP segments spuriously.
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© 1997 IFIP Published by Chapman & Hall
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Ishizuka, M., Kitazume, H., Koike, A. (1997). Simulated performance of TCP over UBR and ABR networks. In: Kouvatsos, D. (eds) ATM Networks. ATM 1996. IFIP Advances in Information and Communication Technology. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-35185-8_18
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DOI: https://doi.org/10.1007/978-0-387-35185-8_18
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