Basic ADSL Troubleshooting Guide

This is a basic ADSL troubleshooting guide. Before proceeding, you should try and eliminate the problem being a problem with your own network. Please see our Basic Connectivity Troubleshooting guide for more information on this.

My ADSL connection is down

If your ADSL connection is hard down, the first thing is obviously to try and reboot the kit. It does sound like a cliché but in a lot of cases it can help bring the connection back to life. Switching the router off for a few seconds and back on again should do the trick, but it is always advised to leave it off for at least a minute or so before retrying it. Another thing that is always worth a go is switching out the micro filter at the phone socket. Micro filters are often made of very cheap components, and can and will go wrong. For the sake of a couple of pounds, it is always a good idea to have a few spares in the office so you can try alternatives if the line goes down. A lot of ISPs incorporate this in their troubleshooting process and will ask that you switch it out as a mandatory step before sanctioning an engineer visit. Also try and ensure that the cables going to your router are not hindered or obstructed, have kinks in the cable or anything resting on top of them.

If a reboot has not worked, and you have eliminated the possibility of it being a problem on your network or kit, then there is little else you can do other than speak to your ISP to log a fault. However there are a few very useful pieces of information that you can record and pass onto your ISP that will speed up the process dramatically for both yourself and them:

  • Make sure you tell them that you have done a full power cycle on the router and you have switched out the micro filter.
  • Refer to your routers manual or user guide to determine the status of the line. All routers will have a synchronisation light and a PPP session light. The sync light determines whether the router is in sync with the exchange while the PPP session light tells you whether the ADSL username and password has authenticated on your ISP’s authentication server. Both are crucial to an ADSL connecting successfully. Check the manual to see which lights indicate these and what the light’s status is telling you in your situation. It is isn’t an exact science, but generally if your router doesn’t have sync on the line, there is most likely some sort of line fault, where as if your router does have sync but cannot negotiate a PPP session, the problem is more likely to be server issue or a problem with your username or password. When you log a fault with ISP, pass on the information of the status of the lights and it will help them determine what the issue may be.
  • If at all possible, try plugging an analogue phone handset into the line and listen for any static, interference, dial tone, weak or interrupted dial tone, essentially anything that doesn’t appear normal. An ADSL connection requires a clean dial tone to work effectively and you may find that your fault is being caused by a faulty phone line. If you detect anything abnormal then speak to your phone provider and get them to run some remote tests on there. If you don’t find anything suspicious then make sure to tell your ISP support desk that you have done this test and found nothing. 

My ADSL connection is intermittent

Probably the hardest thing to troubleshoot and pinpoint exactly about an ADSL line is if your line is running intermittently and drops out at random times of the day. There is no exact science to it. Ultimately you should be speaking to your ISP about it. They can run various tests and adjust numerous settings remotely to try and help improve the situation, but there are some things you can try independently of them to try and solve the problem. If you have been through this list and made an effort, always tell your ISP what you have tried already.

Much of troubleshooting an intermittent connection is already covered in our Basic Connectivity Troubleshooting and Basic Router Troubleshooting guides.

  • Always try giving your ADSL router a good power cycle. ADSL routers are piece of electrical equipment that are usually left on 24 hours a day, 365 days a year. They can get old and clunky, components can fail or get burnt out. Some routers are left on for months or years at a time. It is probably not a very viable long term solution to any problems you are having, but it is certainly a good first thing to try.
  • ADSL can be very sensitive to environmental interference. Always make sure there is nothing close to the router that could cause electrical or radio interference. In extreme cases, devices such as cordless kettles, Christmas tree lights or fish tanks have been known to cause problems, but generally things to look out for are devices like scanning machines, alarm systems, anything that emits or receives any sort of radio or wireless signal. Sometimes this is easy to determine because there will be a direct correlation between when the intermittency occurs and when the problematic device activates or deactivates, so look out for that. Where at all possible, you should be ensuring that your ADSL router is reasonably isolated.
  • Test an analogue phone on the line and see if there is any interference or crackling on the line, or whether the dial tone is a weak or not. Possibly also speak to your phone provider about running some remote tests on there to rule out any problems.
  • Another thing to watch out for in the physical environment is the cables going into the router. A lot of offices neglect to keep the wires free from obstruction and wires can end up with serious kinks or twists in them, or might end up with desks or chairs wheeled over them. The cables are very important and can be damaged very easily. The longer the cable, the more sensitive it is likely to be to intermittency problems. Always keep an eye on them and make sure they are protected and free from any hazards.
  • If you’ve tried everything and anything you can think of that might be causing any of the above problems, then chances are you will have to speak to your ISP about it. Always ensure to tell them what you have tried and haven’t tried to help the troubleshooting process along. Be honest with them too – it’s no good telling them you have done something when you haven’t, it will just slow the process down.

It may help to understand DSL statistics, such as attenuation and SNR margin, which is explained in this video.

My ADSL connection is slow

Another very common complaint of ADSL, or any form of connectivity for that matter, is that the line is under performing in the speed department. Again you will probably end up having to speak to your ISP about the problems you are seeing, but it is always best to try and solve the problem yourself first, or at the very least run some comprehensive tests for analysis.

A lot of the common causes for a slow connection can also be caused by those of an intermittent connection, so please see the previous section on good things to try. An additional problem that might come up when using wireless ADSL is that another party might be using your connection without your knowledge. Please see our Basic Router Troubleshooting guide for tips on how to eliminate this as a possibility.

Also ensure that the bandwidth you are feeding into your office is enough for the requirements of your user base. It is very easy to underestimate what the bandwidth requirements of your network is, especially when using a low end product like ADSL. A good way to check this is have your ISP monitor the connection, or implement some monitoring tools yourself. If you find that your usage graphs are often maxing out then chances are your speed is just not high enough for the amount of bandwidth you require, and you will see slow speed issues. Speak to your ISP about upgrading the product you are using.

If you have eliminated all of the above and there is clearly still a problem with your speed then you will need to log a fault with your ISP. They should be able to shed light on the situation and adjust certain profiling values on the line that will help improve the situation. In some cases an engineer visit might be necessary. Before going to your ISP, always try running some speed tests on the line at different times of the day so you have as much helpful data as possible for them. A good website to use for this www.speedtest.net and if possible you should always try and run the tests with a laptop or PC plugged directly into the back of the router.