Troubleshooting Internet Latency & Packet Loss Issues

January 4, 2008 at 11:19 pm 3 comments

I got an email today asking for advice troubleshooting cable Internet issues. They seem to think they were suffering from intermittent latency issues. As I was writing my reply, I thought others might benefit from this as well, regardless of if they were using Cable or DSL.

I have had issues with both Cable and DSL in the past. About the best free troubleshooting tool that I can recommend for people who aren’t overly technical is UOtrace. You can get it here:

It’s a Windows tool (sorry Mac users, I’ve not been able to find an equivalent) written specifically to troubleshoot latency issues with a game called Ultima Online, but you can put any server or website name you want in the field at the top (ignoring the ones in the drop down list). It may be best just to test to their servers, though since we know they are allowing ICMP traffic all the way through their firewalls. Here are some quick instructions (adapted from the website link above):

  1. Double-click on UOTRACE.EXE to run the program.
  2. Click on OPTIONS, then ADVANCED.
  3. Choose the server you wish to trace to from the drop-down list. (This is where you can also just enter the name of any site you want to use as a test endpoint.)
  4. Click the TRACE ROUTE button. A succession of host names will begin to appear in the main window. These are the computers your data passes through on its way to the desired server. Once the function is complete, a message that says “Traceroute successful” will appear in the lower left corner of the window. If you get a message saying “Maximum number of hops exceeded” click on OPTIONS then SETTINGS and change the max hops to a higher number and re-trace.
  5. Click the POLL button. This tells the program to send multiple packets of data through the route to the final host. As the data is being sent, look at the PKTS R/S column. Let it send about 100 packets then select STOP POLL.
  6. If you want to copy the results to send to someone else or post on a forum, click Copy in the Edit menu, then paste it where you want it to go.

Once you have stopped the polling, take a look at the results. The list displayed there shows every hop that your machine goes through to get to the destination server. Now it’s time to interpret your results…

  • When you are experiencing latency issues, you’ll probably see that your first few hops are fine, with very low round trip times, but then at some point you’ll hit a router that is responding much slower than the previous ones. You’ll probably notice that all the hops after this point have high latency. That hop, or the one just before it, is the problem. You can get this data to someone at your ISP, and if they can filter it up to their network department, they should be able to take a look into the problem.
  • If you see packet loss to every hop past a particular hop, the first hop with loss is probably the problem. (All packets to hops past the first one with loss have to pass through the one that is dropping packets.)
  • If you see packet loss pretty much from start to finish, it’s probably an issue with your cable/DSL modem, or possibly your connection itself.

Notice that I’ve started talking about packet loss. That’s because most people aren’t able to tell the difference between latency issues and packet loss issues. You see, TCP/IP handles dropped packets gracefully, and will retransmit if it doesn’t get a reply within a certain time span. Perhaps on the second transmission, your packet will get the proper reply, so it may just look like things are running slower than usual. In this case, latency isn’t the problem at all, but rather packet loss.

Note that weather can be a factor as well. If the connection works fine most of the time, but you start seeing latency issues on rainy days, or when it gets extremely cold or hot, then chances are that it isn’t really a latency issue, but a packet loss issue. I’ve seen issues where problems have cropped up after having a lot of rain, then it would clear up later after things dried up. The problem here is that you can’t get a repair man onsite when the problem is happening. In some cases, you might end up with a tech who would pretty much look at it and say “It’s working now”, and not want to really try to do anything to fix it. In other cases, you might get someone who will replace a splitter, just to be able to say they replaced something. I was lucky enough to get a tech with the right gear to diagnose the problem. I had a marginal signal from the ISP. When I had a lot of rain, the signal degraded to the point that I had severe packet loss. He was able to make changes that boosted the signal strength and that fixed my issue.

Another problem that comes to mind from my experience years ago was between my ISP and another upstream provider. This was problematic because the two sides wanted to point fingers at each other. I think they got it fixed though, eventually.

Of course, I’ve since cancelled my Cable internet service, switched to DSL, then later switched back to Cable, and now I’m back on DSL, since they started offering Naked DSL (DSL without requiring phone service) in my area.

Intermittent issues can be very frustrating to troubleshoot, especially if your ISP isn’t very responsive. Hint: That’s pretty much all of them! So, just try to remain calm.

Above all, if it gets to the point that you have a service person sent out from the ISP, be very kind to them and explain the issue in as much detail as possible. Realize that they probably deal with a few intermittent problems every week, and it can be very frustrating to them also, when they can’t see the problem.


Entry filed under: Networking.

ReadyNAS NV+ Expansion AT&T’s random DSL configuration changes begin!

3 Comments Add your own

  • 1. My frustrating cable « What are the hours?  |  March 1, 2009 at 12:29 pm

    […] This link made me feel better, only in the sense that someone else is out there….Troubleshooting Internet Latency & Packet Loss Issues […]

  • 2. jamesjohnson54  |  May 16, 2013 at 12:14 pm

    I’ve been unable to play multiplayer Need for Speed Most Wanted for more than a few minutes, sometimes up to maybe 15 but most of the time only about 6 minutes then getting dropped out of connection. Been going back and forth to highest levels of support at both EA and ISP At&t for 6 months and they all say its the other guy. Did several UO traces and polling while playing and being dropped out, sent results to EA and also to At&t and EA says its the provider. At&t still looking into it but they say they don’t have anything to do with the signal once it leaves the house, or some such thing. Opened ports on home router per EA instructions and also had At&t open TCP and UDP ports per EA instructions and no difference. Getting 3 Unknown hosts with 100% packet loss in the same place every UO Trace/Polling. Don’t know what else to do but live with it. Doesn’t seem very many are having this problem according to EA and At&t. Seems I’m kinda by myself here. Its just a game but why is this happening and not to everyone or many besides my connection?

    • 3. ptaylor  |  May 16, 2013 at 6:17 pm

      They don’t have anything to do with it once it leaves the house? Really? If you look at each hop along the path you’ll probably find that many of them are AT&T owned routers. They may have ATT in the DNS name, or possibly bellsouth, sbc, or one of the other companies that AT&T has gobbled up over the years. The tech support person might be telling you they don’t have anything to do with it after it leaves the house, but that’s hogwash. He might not know what to do next, but that is just an inditement of AT&T’s training. As long as it’s going through a router they own (really, through the CIRCUIT), they have something to do with it. The first 6-8 hops after it leaves your home are almost certainly AT&T owned devices. Once it leaves their network, AT&T couldn’t directly fix it, but they might be able to get their business partners to look into the problem. The three hops with 100% packet loss are probably part of a transit network (one that isn’t routable to the public internet), or they being blocked by a firewall/ACL. Don’t worry about those. The one you are interested in is the FIRST one that is losing any significant number of packets. Hops past the first one are probably being dropped BY that first one. After all, they have to go through each hop along the way. If you aren’t seeing any significant packet loss during a time when you’ve been dropped from the game, then perhaps your issue isn’t with packet loss at all, but something else. Is your computer wired or wireless? At work we ran into an issue with Windows Zero Config on Windows XP causing the wireless network on PCs to drop out on a pretty regular basis. To see if this is your problem (assuming you are wireless), after you are connected to your wireless network, disable the Windows Zero Config service, then try playing to see if you drop off at some point. Oh, and I don’t think you are alone in connectivity issues. I made this post a few years ago, and it’s still consistently among the top two or three pages that people hit on my entire blog.


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