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On Monday 12 November 2007, Grant wrote: |
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> I just switched from DSL to cable and I'm noticing a significant delay |
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> when using Skype, even when nothing else is happening on my network. |
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> Has anyone else noticed this and had success "fixing" it? I'm using a |
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> Gentoo router so I can try just about anything. |
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If this is a MTU problem (it may very well not be, see below) I would go about |
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it as follows. |
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Do you know what is the recommended MTU of your ISP? What MTU your modem is |
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set at? If not and they won't tell you you could try to find out by |
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yourself: |
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|
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Set the MTU of *all* nodes between your PC & your ISP's modem to 1500 (PC, |
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router, etc). Then run something like this: |
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$ ping -c 3 -v -M do -s 1452 www.yahoo.com (better if you use the IP address |
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of yahoo.com, of even better if you use one of your ISP's gateways, DNS |
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servers, etc. to avoid problems with network congestion upstream - in that |
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sense ebay on a Sunday afternoon may not be a good choice ;). |
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|
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Work your way up to greater packet values until you cannot ping anymore |
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because packet fragmentation occurs. Once you find the value at which it |
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switches over then add 28 (for the packet headers) to the maximum value at |
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which ping works. This should be the value at which your modem is set. |
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Set all other network components to the same MTU (inc. all PCs in your |
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network) and you should be good - BUT only if the modem's MTU was correct in |
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the first place. |
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If your modem has the wrong MTU for the ISPs network assuming they don't tell |
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you what that is, then try altering it from 1500 downwards to 1492, 1480, |
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1458, 1430, 1400, while you test for maximum line speed. Set all your |
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network components to the same MTU and check with a broadband speed tester |
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(e.g. www.speetest.net) to see when you get maximum speed. Alternatively, |
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try downloading some iso image from a main mirror near you (warning - not |
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all mirrors are born equal in terms of bandwidth, so some experimentation is |
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required). |
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Eventually, you'll find some max MTU value at which you get the best |
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comparative performance. For the tests to be meaningful they should be |
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better performed during quiet times (see contention below). BTW, from the |
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little I know about cable the MTU is usually set at 1500, but others could |
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advise better. |
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If all that doesn't fix it, then it may have nothing to do with MTU and it |
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could be related to faulty components in your network (cables, switches, |
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modem, etc.); ISP throttling (is poor performance occurring only some |
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times/days or is it universal); busy Skype servers(?), or good old high level |
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pipe contention, because the world and his wife are on the Internet these |
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days and the infrastructure has not grown enough for it. |
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|
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HTH. |
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-- |
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Regards, |
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Mick |
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