What would cause high latency anytime there is traffic on WAN

congestionlatencywan

I have a network that has been experiencing slow internet speeds. After a great deal of troubleshooting, I have determined that any streaming content/downloads will cause the latency of WAN traffic to explode.

For example, under no load, I ping 8.8.8.8 at about 30ms. If I start streaming YouTube on the same computer, latency jumps up to around 500ms, with a variance of around 400ms. If I turn off the video, the latency returns to 30ms. But, if I have a user on the same LAN start streaming pandora, the problem returns.

My network is ran off a single 10/100 switch. The switch is connected directly to the DSL router. I typically have a 6Mb connection.

In troubleshooting, I have completed the following:

  • Scanned with wireshark from several workstations looking for erroneous packets. (I would include but scans have confidential info). Nothing even remotely out of the ordinary.
  • Replaced router with an upgraded model, then upgraded firmware.
  • Had ISP increase speed which measured correctly on speedtest.net (10 down, 1.5 up). Problem was exactly the same.
  • Had the ISP swap out cards on their end, just in case they had bad hardware/port.
  • Tested at another office with exact same ISP/package. Had multiple computers streaming YouTube @ 1080p and pandora without impacting latency.
  • Shut down every computer but one and ran at night when no users where there.
  • Monitored LAN traffic, which never experiences a latency problem.

I am aware that, if I am reaching a bandwith limit or the speed is bottlenecking at some hardware, it will cause this problem. However, it doesn't seem that way at all. Almost any traffic over the WAN will shoot up latency. The problem was the same even when I almost doubled connection speed. When I get two users on pandora and a couple surfing, internet goes to nothing (dropped packets, pages won't load). I have half the connection at home and our simultaneous netflix/youtube/pandora streaming doesn't even touch my 5 Mb.

Question: What would cause high latency anytime traffic is going over the WAN?

Best Answer

This sounds like some form of "bufferbloat", probably on the part of the DSLAM/LNS that's performing the 6Mb rate limiting.

It might be your CPE box, but that's a little less likely.

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