TCP compression over T-1

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Nov 12th, 2008
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If you have full T-1 and an application that is sending accross TCP packets of 1514 bytes(with don't fragment set) will there be a benefit to using TCP payload compression on the link?


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Richard Burts Wed, 11/12/2008 - 11:39
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It may depend a bit on who/what does the compression. But my experience of traditional compression is that as you get to speeds like full T1 the overhead of compress/decompress washes out the benefit gained from compression. If you are looking at some acceleration technology like WAAS then it is a different situation and may well be worth it.



mbroberson1 Wed, 11/12/2008 - 11:50
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As always thank you for your post response. On thing I forgot to mention is that we are also running voice over this link (which we are prioritizing with MQC). From my understanding it can take sometime to serialize large packets over the serial interface. Could something such as LFI be helpful so the delay sensitive packets don't have to wait on the larger packets through the exiting output queue?


Joseph W. Doherty Wed, 11/12/2008 - 12:39
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Normally, LFI isn't necessary for VoIP if the link provides more than 768 Kbps.

My experience with software router compression has been it often doesn't seem to provide a very high compression ratio (I've often seen under 2x), and CPU impact (at least on older equipment) was quite noticable. Compression varies much based on your traffic, smaller packets and/or encryped and/or already compressed data usually benefits little. I also recall, payload compression, isn't recommended when passing VoIP because of the additional delay it might create.

I haven't tried router payload compression on the newer ISRs, which might do much better at T1 speeds. However, if the equipment is that new, you might also want to look an the various add-on equipment, for instance, the NCE AIMs, for WAN compression.

Giuseppe Larosa Wed, 11/12/2008 - 11:44
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Hello Brandon,

be aware that usually when TCP and compression are put together we think of TCP header compression.

you can use payload compression at Layer2 on the link with the benefit to be able to handle these packets.

TCP header compression on big packets is usually not good: a lot of work for a little gain.

Again, if this can be a way to have these packets travel the link it can be tried.


Hope to help



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