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SCO Unix Serial Communications and UUCP

This article is from a FAQ concerning SCO operating systems. While some of the information may be applicable to any OS, or any Unix or Linux OS, it may be specific to SCO Xenix, Open There is lots of Linux, Mac OS X and general Unix info elsewhere on this site: Search this site is the best way to find anything.

How do I get better UUCP throughput on SCO Unix?

You may or may not be able to. Here are some rules of thumb which may or may apply to your situation:

If you and the remote site both use Telebit modems, enable UUCP spoofing. This enables the modems to maintain the UUCP protocol between them, and means that your CPU's response time to individual UUCP packets is not as critical. Some sites can achieve higher throughput with a Telebit link than with a direct connection at the same baud rate.

If you and the remote site are both running versions of UUCP which allow you to specify different protocols (SCO Unix 3.2v4.0 and above, for example), look through your release notes to find the highest-performing protocol that's applicable to your situation. For example, the standard g protocol has its own error detection and correction logic. If you are running over a guaranteed error-free link, this is unnecessary overhead, and eliminating it by selecting a protocol that relies on an error-free link can speed up transfers. Be careful that you don't specify such a protocol for a non-error-free link, or else your transmissions will occasionally be corrupted. Note that just because you are using error-correcting modems does not guarantee that your data will be error-free; there is a possibility of lost characters and flow control problems in the serial ports at both ends of the connection. While the link between the modems may well be error-free, the end-to-end link from one uucico to another may not. You should usually use g or G for modem links, and reserve t, e, f, etc. for network connections.

If you are running over a link that uses MNP, V.42 or V.42bis, set your window size as high as possible to ensure that the modems have as much data to work with as possible.

If the site with which you are communicating sometimes drops packets, try adjusting your packet delay to a lower number. If you are operating over a link with high latency (i.e. it takes a long time for a packet to get from one site to the other - an example would be a satellite link), you may need to increase your packet delay.

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