Internet Core Protocols: The Definitive Guide

Buffer size considerations

Part of determining the most efficient segment size is derived from the size of the send and receive buffers in use on the two systems. If the send buffer is very small, then the sender cannot build a very large segment. Similarly, if the receive buffer is small, then the sender cannot transmit a large segment (even if it could build one), as that would cause overruns at the destination system, which would eventually require the data to be retransmitted.

Every system has a different default buffer size, depending upon its configuration. Most PC-based client systems have eight kilobyte send and receive buffers, while many server-class systems have buffers of 16 kilobytes or more. It is not uncommon for high-end servers to have 32 or 48 kilobyte send and receive buffers. However, most systems will let you specify the default size for the receive buffers on your system, and they will also let the application developer configure specific settings for their particular application.

Sometimes the size of the local system’s send buffer is the bottleneck. If the send buffer is very small, then the sending device just won’t be able to generate large segments, regardless of the amount of data being written, the size of the receive buffer, or the MTU/MRU sizes in use on the two networks. Typically, this is not the case, although it can be in some situations, particularly with small hand-held computers that have very limited system resources.

Similarly, sometimes ...