Troubleshooting Internet Latency & Packet Loss Issues

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:

http://support.uo.com/latency.html

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.