At some time, you'll likely find yourself noticing that your network seems sluggish. It's not down, but things web pages seem to be taking significantly longer than usual to appear in the browser, downloading files is slow or maybe the ping times to your favorite gaming server seem to have increased for no reason. This section of troubleshooting is to show some tools for use in diagnosing these sorts of problems.
The first thing to test is to see if there really is a slowdown or not. It could just be that the particular web site or game server to which you are connecting is congested; your Internet connectivity is fine if that is the case, and there may be nothing you can do. On the other hand, there may be something on your machine or your LAN that's causing your slowdown. A quick way to check this is by using one of network speed test tools like the ones found at Speedtest.net or Speakeasy Speed Test. With both tools, you (usually) choose the server that is closest to your geographic location. For Speedtest.net, I choose the Ashburn, VA server by clicking on it on the map. The tool then downloads a mock test file as fast as possible from the test server and then reverses and uploads a mock file back to the server. The results for that Speedtest.net test are shown below.
I have upload and download speeds of 20 Mbps and 5 Mbps, respectively. This test shows that I'm getting pretty much what I'm paying for. I know from past testing, that I never seem to quite reach the 5 Mbps upload speed even with a test server as close as mine is. If I was having trouble connecting to some web site or game server and got this result, I would have to conclude that my connection is fine, but there is a problem somewhere between my ISP and that server. One thing I might try in this case is to pick a test server that is geographically nearer to the site I'm trying to reach (assuming I knew that information) and run the test again. If that test shows reasonable speeds, it's probably a problem with the site itself. Don't be surprised, however, if the speed test results when going across the country are significantly lower than those going 20 miles from your home. That's not unusual nor is there anything wrong (most likely).
What if the tests indicate you aren't getting the speeds you expect? (That is, what if you're not getting the speeds you paid for?) Assuming you have picked the nearest server to your location and maybe a few others in the same general area, if none of the sites return test speeds in the vicinity of what you should be getting, the next question is, "Is it them or me?" Is the problem inside your LAN, your portion of your ISP's network or somewhere else? Time to do some more testing.
If network speed tests indicate you aren't getting the speeds you expect, the next step is to see if the problem is in your LAN or in the Internet. If your connection is shared among several devices used by others besides yourself, now is the time to ask around if anyone is downloading or uploading anything (large). It's also possible that one of the devices is doing an automatic update that you are unaware of. A cursory check can often find out who/what the culprit is. If not, it's time to do some snooping .. literally.
Tools that monitor network traffic can be helpful with this step to some degree. Windows doesn't come with any such tools. There are few free tools available, but they can be difficult to set up and the results can also be difficult to interpret. One of the best I have found is Paessler's PRTG Traffic Grapher. It comes in both freeware and commercial editions. The freeware edition is limited to 10 "sensors," where a sensor is a network traffic metric. For checking LAN usage, we only need one sensor - one that monitors all network data as seen by the LAN adapter on which the software is running. This tool can be used for many other things than just checking your LAN usage.
If you think you might be interested in such a tool, go to Paessler's web site and download the the freeware edition of the PRTG Traffic Grapher. (The version at the time this example was created was 6.2.1.962.) You should also download the PDF version of the manual found on the same page. There is also an HTML version of the manual. Both contain installation and operational instructions.
Unfortunately, running this tool on one of the machines on the LAN gives you an incomplete picture. You may recall that in the discussion on hubs and switches, once the switch has learned where the devices on the network are attached, it only sends data to the ports that absolutely require it. That means you will see all the data coming to and from the particular machine upon which the monitoring tool is running, but none of the traffic from the other devices on the network unless the monitoring machine is the source or target of the traffic. There are enterprise-level (i.e., more costly) switches that allow a monitoring port to be enabled such that all traffic is sent to it, but those found in typical home and small offices do not.
Monitoring tools are still useful to verify that the ISP's connection is up, but given that a typical home user can't rely on such tools to get a picture of the whole network, we have to resort to more rudimentary methods - seeing the lights. In Test 3: Check the Link Lights, we checked that the lights we expected to be are were indeed lit. In nearly all routers/switches, there is one light per port. If the port is connected to a device, the light is lit. The light remains steady when there is no traffic coming from or going to that port. On the other hand, the light will flicker or blink to indicate traffic on that port.
Start by checking the link/activity lights on the router (or switch) closest to your ISP Internet connection. If you have a port on your router that is flashing wildly, you have your first clue. If this is a stand alone switch and two of the ports are flashing wildly and more or less in concert, you again are narrowing the search. Typically, one of ports connects to another switch or directly to the router that leads to the Internet. Whatever device is connected to the other port is probably the cause of the slowdown. It doesn't necessarily have to be another computer/Xbox/etc. hogging the Internet connection. If you have one computer transferring a lot of large files to another computer over the LAN such as when doing a full backup, that may well generate sufficient traffic to slow down the LAN to the point the Internet connection is also affected.
Once you know which device (or devices) are involved, it's time to investigate them more closely. If this is little Billy's gaming PC, he may be updating a game on "patch Tuesday." Sometimes these patches are several hundred megabytes in size. With the increased use of online game (purchasing) services like Steam, downloading several gigabytes of data isn't unusual. It may well be your network is slow for just such a reason. Time to ask Billy what's up and also time to remind him of the family downloading etiquette. It may also be a good time to explain to little Billy that while downloading games for free from BitTorrent sounds neat, one letter from the RIAA to your ISP about alleged copyright infringement may well end your family's Internet fun for good (at least with that ISP). Other possibilities include such things as the Xbox getting an Xbox Live update or even your DVR getting a new firmware update.
What do you do if, on the other hand, you look at your link lights and none of them are blinking madly? The occasional blink is seen maybe a couple times a second, but by and large, nothing really seems to be going on on your LAN. In this case, it may be time to give your ISP's technical support line a call. One thing you should do (or be prepared to do) is to disconnect all devices from the LAN except the one doing the speed testing. Physically disconnect the cables from the router/switch. This also includes shutting down any wireless connections from laptops/netbooks/Nintendo DSi's and the like. (We often forget those are even on the network.) Run the speed test again to check that the result is the same. If it is, leave your network connected like that and call your ISP's technical support line. They may ask how many computers are sharing the connection, so it's good to be able to say credibly that you only have one device at the moment - the one reporting the sub par speeds. I have even gone so far as to hook up a laptop directly to the connection from my ISP - bypassing the router/firewall/switch completely - in order to test the connection. That configuration pretty much rules out any possibility that the problem is in your router or elsewhere on your LAN.
ISP's can generally run their own speed tests to your neighborhood or even your specific connection. Don't be surprised to call and find out they are already aware of and working on the problem. If you are a cable modem subscriber, don't be surprised if this problem tends to crop up every weekday around the time kids are getting home from school. The first thing they often do is check their email, their MySpace/Facebook account (or whatever social networking site is currently popular) and then play a game or two. Some portion of most cable networks are shared among several customers or whole neighborhoods. During the peak times of the day, the shared portion becomes saturated with traffic. In this case, you may need to complain to your cable provider about the problem - possibly on a daily basis. They can do things to balance the network up to and including running more cable.