tcp_sendspace

Description

This parameter controls the default size of the send buffer on TCP/IP sockets. There is a pair of buffers associated with each socket in use. There is a buffer on the receiving side of the socket, and on the sending side. The size of these buffers represent the maximum amount of data that can be queued.

Value

Default: 60Kbytes

Range: 0-512Kbytes

When to Change

The tcp_sendspace parameter may require tuning for slow throughput links, and for compatibility with TCP implementations based on 4.2BSD. For slow throughput links (such as lower speed PPP or SLIP connections), lower the value of this and the tcp_recvspace parameters until the best performance level is found. Very slow links such as PPP or SLIP over modems usually find a 3 Kbyte or 4 Kbyte buffer size to be the most efficient.

The tcp_sendspace parameter may require tuning for slow throughput links, and for compatibility with TCP implementations based on 4.2BSD. For slow throughput links (such as a Wide Area Net with a lower speed PPP or SLIP component), lower the value of this and the tcp_recvspace parameters on systems where the connection goes from fast (ethernet, or FDDI, etc) to slow (PPP or SLIP) until the best performance level is found. Very slow links such as PPP or SLIP over modems usually find a 3 Kbyte or 4 Kbyte buffer size to be the most efficient.

Conversely, high speed connections may profit from increasing the buffer size incrementally from 60 KBytes until maximum performance is achieved.

See the setsockopt(2) reference page for more information on setting specific socket options.