Indicators for the assessment of congestion in TCP over ATM-UBR

In this paper we analyse congestion in TCP over ATM-UBR, in particular the association between the congestion measures at the ATM physical and TCP transport layers. Two new indicators, protocol level congestion association factor (PLCAF) and CLR-PRR correlation coefficient are used. ATM cell loss ratio (CLR) and TCP packet retransmission ratio (PRR) are good measures of congestion at their respective layers, but do not address the relation between cell loss and its effect on TCP congestion control schemes. Both PLCAF and CLR-PRR correlation coefficient are derived to better capture the association between congestion measures at ATM and TCP levels. It is shown through simulation of multiple TCP connections over a ATM-UBR service under selected number of different operating conditions that the two new indicators can be successfully used for the analysis of congestion in TCP over ATM-UBR.