08/01/1997 09:00 AM
Computer Engineering
We study the performance of TCP in an internetwork consisting of both rate-controlled and non-rate-controlled segments. A common example of such an environment occurs when the end systems are part of IP datagram networks interconnected by a rate- controlled segment, such as an ATM network using the ABR service. In the absence of congestive losses in either segment, TCP keeps increasing its window to its maximum size. Mismatch between the TCP window and the bandwidth-delay product of the network will result in accumulation of large queues and possibly buffer overflows in the devices at the edges of the rate-controlled segment, causing degraded throughput and unfairness. We develop an explicit feedback scheme, called Explicit Window Adaptation based on modifying the receiver\'s advertised window in TCP acknowledgments returning to the source. The window size indicated to TCP is a function of the free buffer in the edge device. Results from simulations with a wide range of traffic scenarios show that this explicit window adaptation scheme can control the buffer occupancy efficiently at the edge device, and results in significant improvements in packet loss rate, fairness, and throughput over a packet discard policy such as Drop-from-Front or Random Early Detection.
