Congestion Control Algorithm

Summing the relative delay measurements over a period of data flow gives us an indication of the level of queueing at the bottleneck. If the sum of relative delays over an interval was 0, we would know that no additional congestion or queueing was present in the network at the end of the interval with respect to the beginning. Likewise, if we were to sum from the beginning of a session, and at any point if the summation was equal to zero, we would know that all of the data was contained in the links and not in the network queues. The congestion control algorithm of TCP-Santa Cruz operates by summing the relative delays from the beginning of a session, and then updating the measurements at intervals equal to the amount of time to transmit a windowful of data and receive the corresponding ACKs. The relative delay sum is then translated into the equivalent number of packets (queued at the bottleneck) represented by the sum of relative delays. In other words, the algorithm attempts to maintain the following condition:

$$N_{t_{i}} = n \eqno{2}$$

where

$$N_{t_{i}} = N_{t_{i-1}} + M_{W_{i-1}} \eqno{3}$$

and N_ti is the total number of packets queued at the bottleneck from the beginning of the connection until t_i; n is the desired number of packets, per session, to be queued at the bottleneck; M_Wi-1 is the additional amount of queuing introduced over the previous window W_i-1; and N_t1 = M_W0.