Q My Open Transport TCP application exchanges a number of
small packets of information, which may or may not generate a
response from the other side. In some cases, I find that the
application delays sending packets, and performance is terrible. How
can I solve this problem?
A One possible reason for this behavior is
explained by the TCP_NODELAY option. As per the XTI
specification, under most circumstances TCP sends data as soon as it
is presented to TCP. However, when outstanding data has not yet been
acknowledged, TCP delays sending small amounts of data, gathering it
into a single packet which is sent when an acknowledgment is
received. This technique, known as the Nagle Algorithm, is designed to prevent "send-side silly window
syndrome." If an application generates data one byte at a time, this
algorithm prevents it from filling the network with lots of one-byte
payload TCP packets.
For some applications, this packetization may cause significant
delays. Setting the TCP_NODELAY option defeats this
algorithm. The following snippet shows how to set this option.
err = SetFourByteOption(ep, INET_TCP, TCP_NODELAY, 1);
This snippet relies on the the SetFourByteOption,
shown in
Listing
7-5 of
Inside
Macintosh: Networking with Open Transport.
In general, disabling the Nagle Algorithm is a bad idea because it decreases the efficiency with which you use the network. A better solution is for you to structure your application so that it sends all logically associated data in one chunk. You may find OT's ability to send non-contiguous data helpful in this case.
-- Rich Kubota
-- Revised by Quinn "The Eskimo!"
Worldwide Developer Technical Support
Technical Q&As
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