Internet Core Protocols: The Definitive Guide

Slow Throughput on High-Speed Networks

The author has seen poorly written network drivers cause significant throughput problems on TCP/IP networks, particularly with regards to buffer management on the receive queue. In those instances, the sending and receiving systems are never able to get beyond the slow start ramp-up activity, as the recipient is unable to acknowledge more than a couple of segments at a time, due to poor buffer management within the device driver itself.

In this scenario, the sender transmits four segments as part of the slow start algorithm, but the recipient only returns an acknowledgment for the first two segments (or more accurately, fails to acknowledge the third and fourth segments). The sender will interpret this behavior as network congestion and reduce the size of its congestion window to one segment. This process will complete ad infinitum, with the sender never getting beyond a couple of segments. Unfortunately, the only way to resolve this problem is to either replace the recipient’s network driver, or to replace the network card entirely.

Another set of problems for this are discussed earlier in Section 7.4.3.