Re: [gentoo-user] {OT} Cable latency Skype
On Monday 12 November 2007, Grant wrote: I just switched from DSL to cable and I'm noticing a significant delay when using Skype, even when nothing else is happening on my network. Has anyone else noticed this and had success fixing it? I'm using a Gentoo router so I can try just about anything. If this is a MTU problem (it may very well not be, see below) I would go about it as follows. Do you know what is the recommended MTU of your ISP? What MTU your modem is set at? If not and they won't tell you you could try to find out by yourself: Set the MTU of *all* nodes between your PC your ISP's modem to 1500 (PC, router, etc). Then run something like this: $ ping -c 3 -v -M do -s 1452 www.yahoo.com (better if you use the IP address of yahoo.com, of even better if you use one of your ISP's gateways, DNS servers, etc. to avoid problems with network congestion upstream - in that sense ebay on a Sunday afternoon may not be a good choice ;). Work your way up to greater packet values until you cannot ping anymore because packet fragmentation occurs. Once you find the value at which it switches over then add 28 (for the packet headers) to the maximum value at which ping works. This should be the value at which your modem is set. Set all other network components to the same MTU (inc. all PCs in your network) and you should be good - BUT only if the modem's MTU was correct in the first place. If your modem has the wrong MTU for the ISPs network assuming they don't tell you what that is, then try altering it from 1500 downwards to 1492, 1480, 1458, 1430, 1400, while you test for maximum line speed. Set all your network components to the same MTU and check with a broadband speed tester (e.g. www.speetest.net) to see when you get maximum speed. Alternatively, try downloading some iso image from a main mirror near you (warning - not all mirrors are born equal in terms of bandwidth, so some experimentation is required). Eventually, you'll find some max MTU value at which you get the best comparative performance. For the tests to be meaningful they should be better performed during quiet times (see contention below). BTW, from the little I know about cable the MTU is usually set at 1500, but others could advise better. If all that doesn't fix it, then it may have nothing to do with MTU and it could be related to faulty components in your network (cables, switches, modem, etc.); ISP throttling (is poor performance occurring only some times/days or is it universal); busy Skype servers(?), or good old high level pipe contention, because the world and his wife are on the Internet these days and the infrastructure has not grown enough for it. HTH. -- Regards, Mick signature.asc Description: This is a digitally signed message part.
Re: [gentoo-user] {OT} Cable latency Skype
On Nov 12, 2007 6:59 PM, Grant [EMAIL PROTECTED] wrote: I just switched from DSL to cable and I'm noticing a significant delay when using Skype, even when nothing else is happening on my network. Has anyone else noticed this and had success fixing it? I'm using a Gentoo router so I can try just about anything. - Grant -- [EMAIL PROTECTED] mailing list I work for as a cable modem technician. The first thing to check for when you're having cable internet problems is the modem. Call up tech support and ask them to check the signals on the modem (upstream power, downstream rcv, downstream SNR, upstream SNR, headend receive) and make sure they're in range. Also ask them to ping and (if available) rf ping to check for latency/packet loss. Also ask them to check the circuits/backbone. Also, can you reproduce this latency in the form of a ping/traceroute? This will go a long way with ISPs in determining where the problem is (although Comcast just blows off high latency on pings as the result of dropping them due to lower priority). -- - Mark Shields
Re: [gentoo-user] {OT} Cable latency Skype
On Tuesday 13 November 2007, Mark Shields wrote: On Nov 12, 2007 6:59 PM, Grant [EMAIL PROTECTED] wrote: I just switched from DSL to cable and I'm noticing a significant delay when using Skype, even when nothing else is happening on my network. Has anyone else noticed this and had success fixing it? I'm using a Gentoo router so I can try just about anything. - Grant -- [EMAIL PROTECTED] mailing list I work for as a cable modem technician. The first thing to check for when you're having cable internet problems is the modem. Call up tech support and ask them to check the signals on the modem (upstream power, downstream rcv, downstream SNR, upstream SNR, headend receive) and make sure they're in range. Also ask them to ping and (if available) rf ping to check for latency/packet loss. Also ask them to check the circuits/backbone. Also, can you reproduce this latency in the form of a ping/traceroute? This will go a long way with ISPs in determining where the problem is (although Comcast just blows off high latency on pings as the result of dropping them due to lower priority). Interesting to hear this. The OP will no doubt have a different traceroute to show the ISP, but does the comment on dropping pings explain the % loss shown below in certain hops, or is it just a matter of overloaded switches? == HOST: lappy Loss% Snt Last Avg Best Wrst StDev 5. 217.41.177.66 0.0%15 17.9 18.0 15.7 22.8 1.7 6. 217.41.177.1346.7%15 21.0 17.5 15.7 21.0 1.5 7. 217.41.177.54 0.0%15 17.0 16.6 15.1 20.7 1.4 8. 217.47.166.1060.0%15 16.0 16.9 15.3 18.9 1.1 9. core1-pos5-2.faraday.ukcore. 0.0%15 17.0 45.3 15.2 192.3 52.7 10. core1-pos0-15-0-10.ilford.uk 0.0%15 18.9 18.3 17.1 19.5 0.7 11. 194.74.77.222 0.0%15 18.1 17.1 15.5 19.1 1.0 12. t2c1-ge14-0-0.uk-ilf.eu.bt.n 6.7%15 17.9 17.3 15.7 19.1 0.9 13. t2c1-p4-0-0.us-nyc.eu.bt.net 0.0%15 107.3 108.1 106.1 109.7 1.1 14. 12.116.102.17 0.0%15 108.3 107.9 105.5 110.0 1.3 15. tbr1.n54ny.ip.att.net 0.0%15 133.2 133.8 131.2 135.4 1.4 16. cr2.n54ny.ip.att.net 0.0%15 135.2 133.5 131.6 135.7 1.3 17. cr2.wswdc.ip.att.net 0.0%15 132.2 132.9 131.3 134.7 1.1 18. cr1.attga.ip.att.net 0.0%15 134.2 133.6 132.1 135.7 1.2 19. tbr2.attga.ip.att.net 0.0%15 135.2 134.0 132.0 136.2 1.3 20. gar4.attga.ip.att.net 0.0%15 132.2 134.1 130.0 159.4 7.1 21. 12.124.64.62 20.0%15 140.2 138.6 137.0 140.4 1.1 22. te-9-1-ur01.south.tn.knox.co 6.7%15 141.2 140.4 138.1 141.5 1.0 23. te-8-3-ur02.west.tn.knox.com 0.0%15 141.2 140.3 139.1 141.2 0.6 24. ge-1-46-ur01.west.tn.knox.co 0.0%15 138.2 138.6 137.8 140.6 0.9 == Note some of these are being dropped in the UK, rather than by Comcast. -- Regards, Mick signature.asc Description: This is a digitally signed message part.
Re: [gentoo-user] {OT} Cable latency Skype
On Nov 13, 2007 9:15 AM, Mick [EMAIL PROTECTED] wrote: On Tuesday 13 November 2007, Mark Shields wrote: On Nov 12, 2007 6:59 PM, Grant [EMAIL PROTECTED] wrote: I just switched from DSL to cable and I'm noticing a significant delay when using Skype, even when nothing else is happening on my network. Has anyone else noticed this and had success fixing it? I'm using a Gentoo router so I can try just about anything. - Grant -- [EMAIL PROTECTED] mailing list I work for as a cable modem technician. The first thing to check for when you're having cable internet problems is the modem. Call up tech support and ask them to check the signals on the modem (upstream power, downstream rcv, downstream SNR, upstream SNR, headend receive) and make sure they're in range. Also ask them to ping and (if available) rf ping to check for latency/packet loss. Also ask them to check the circuits/backbone. Also, can you reproduce this latency in the form of a ping/traceroute? This will go a long way with ISPs in determining where the problem is (although Comcast just blows off high latency on pings as the result of dropping them due to lower priority). Interesting to hear this. The OP will no doubt have a different traceroute to show the ISP, but does the comment on dropping pings explain the % loss shown below in certain hops, or is it just a matter of overloaded switches? == HOST: lappy Loss% Snt Last Avg Best Wrst StDev 5. 217.41.177.66 0.0%15 17.9 18.0 15.7 22.8 1.7 6. 217.41.177.1346.7%15 21.0 17.5 15.7 21.0 1.5 7. 217.41.177.54 0.0%15 17.0 16.6 15.1 20.7 1.4 8. 217.47.166.1060.0%15 16.0 16.9 15.3 18.9 1.1 9. core1-pos5-2.faraday.ukcore. 0.0%15 17.0 45.3 15.2 192.3 52.7 10. core1-pos0-15-0-10.ilford.uk 0.0%15 18.9 18.3 17.1 19.5 0.7 11. 194.74.77.222 0.0%15 18.1 17.1 15.5 19.1 1.0 12. t2c1-ge14-0-0.uk-ilf.eu.bt.n 6.7%15 17.9 17.3 15.7 19.1 0.9 13. t2c1-p4-0-0.us-nyc.eu.bt.net 0.0%15 107.3 108.1 106.1 109.7 1.1 14. 12.116.102.17 0.0%15 108.3 107.9 105.5 110.0 1.3 15. tbr1.n54ny.ip.att.net 0.0%15 133.2 133.8 131.2 135.4 1.4 16. cr2.n54ny.ip.att.net 0.0%15 135.2 133.5 131.6 135.7 1.3 17. cr2.wswdc.ip.att.net 0.0%15 132.2 132.9 131.3 134.7 1.1 18. cr1.attga.ip.att.net 0.0%15 134.2 133.6 132.1 135.7 1.2 19. tbr2.attga.ip.att.net 0.0%15 135.2 134.0 132.0 136.2 1.3 20. gar4.attga.ip.att.net 0.0%15 132.2 134.1 130.0 159.4 7.1 21. 12.124.64.62 20.0%15 140.2 138.6 137.0 140.4 1.1 22. te-9-1-ur01.south.tn.knox.co 6.7%15 141.2 140.4 138.1 141.5 1.0 23. te-8-3-ur02.west.tn.knox.com 0.0%15 141.2 140.3 139.1 141.2 0.6 24. ge-1-46-ur01.west.tn.knox.co 0.0%15 138.2 138.6 137.8 140.6 0.9 == Note some of these are being dropped in the UK, rather than by Comcast. -- Regards, Mick I would like to mention that while I am not a cable modem field tech, I do work in an escalated dept (Tier II). That said, most of the time when you see packet loss/high latency at one hop, you'll see it at the sequential hops after that if it's a true packet loss/latency issue and not just the ICMP packets being given lower priority/dropped. The packet loss could also be that hop/ISP dropping the packet because it detected what it might consider too many pings (flood protection, I assume). I've seen Comcast drop on a 3rd hop before.In the case of ICMP packets having lower priority, it's best to just ping the host you're trying to get to then go from there - like an average of 100 sequential pings, for example. Generally speaking, if a basic ping such as this returns latency/packet loss, there's a problem somewhere along the line, and you can continue with further testing such as traceroutes, speed tests, and individually pinging possible problematic hops. Concerning Comcast, I called them once and complained about latency; they rebutted with the fact ICMP packets have a lower priority on their network. That doesn't make any sense to me, though. If they're having to drop ICMP packets, what does that say about the capacity of the network? Regardless, the best way to test for packet loss is to run a speed test. If your speeds are decently consistent and what you pay for (or close to it), then packet loss isn't an issue (I recommend speedtest.net). One last thing: this thread is way off-topic. I suggest we take this to another forum or just e-mail off this mailing list if we wish to continue. -- - Mark Shields
