SMS: Remote Chat May Not Work on Slow Link

When you attempt a remote chat session on a slow link (such as a 9,600 bits per second link) by using only TCP/IP, the Chat window may behave as if the viewer timed out immediately. Immediately after the viewer closes its window, the client's Chat window also closes.

The TCP/IP Nagle algorithm that helps reduce small packets on a slow network is the root cause. Although the Nagle algorithm can be disabled in Microsoft Windows NT for troubleshooting or remote helpdesk issues, disabling the Nagle algorithm may be detrimental. If it is not re-enabled, performance could be degraded.

The Nagle algorithm was developed to help with a couple of problems on the Internet/ARPANET. Programs such as Telnet sometimes transmit each character at a time. 1 byte of data and 40 bytes of header information in an environment that can carry up to 1,500 byte packets is very inefficient. When a packet is sent, it is sent with a Time to Live value (TTL); if the TTL expires, the sending node retransmits the packet with a greater TTL, up to a point. In the meantime, as more and more packets hit a router, the router becomes congested, up to the point where it starts to drop packets. The Nagle algorithm holds a small packet 200 to 500 milliseconds. If there is more data to be sent to the same destination, the packet is held. This decreases the overall number of packets, thereby decrease the router congestion. On a slow link (9600 bits per second), the wait is long enough that the Chat session does not work. One of the inherent problems in the Nagle algorithm is finding a delay that works for everything.

For additional information about the Nagle algorithm and how to disable it, click the article number below to view the article in the Microsoft Knowledge Base: Be aware that this change could degrade performance in other areas.