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Speed Fault Diagnosis


Speed Fault Diagnosis

In order to try and help diagnose and help with speed issues that some customers may see from time to time we have put this simple step by step guide together.

A number of issues can create speed problems for ADSL customers and these include:

• Equipment failure/fault at your premises (router, modem, filter, internal wiring, secondary phone sockets, extension leads etc.)
• Third-party software using the upstream and/or downstream capacity of your ADSL connection (includes p2p, viruses or Internet applications) leading to the connection becoming congested
• BT Exchange contention this can be checked here
• Contention on the BT Central pipes which connect you to the PlusNet Network
• Account management when usage thresholds have been passed details of which can be seen here

BT has provided the following speed thresholds for accounts when reporting speed issues (note that account management across the PlusNet network will not affect BT speed tester results):

Home 250: 50-250kbit/s
Home 500: 100-500kbit/s
Home 1000: 200-1000kbit/s
Home 2000: 400-2000kbit/s
Office 500: 200-500kbit/s
Office 1000: 400-1000kbit/s
Office 2000: 800-2000kbit/s

How to diagnose speed problems:

Step 1:
If you believe you are experiencing problems with your ADSL speed the first step is to confirm the speed you are experiencing. To do this you should close all open programs and switch off any other computers on your network. Once done use a speedtester from either our site which can be found here or one such as the ADSLGuide which will give you an indication as to your account speed. Remember however any account management which may be on your account will affect this result.

Follow the instructions and note the results – including the time of day and date. If your performance falls within the performance thresholds then BT would not accept a fault raised against your line, however there may be steps you can take to determine whether the cause is contention across BT’s network or something else.

Step 2:
Once you have your results recorded, restart your computer. If you use an ADSL router/modem restart this as well. This should ensure that any temporary problems with your equipment are eliminated (though there could be other problems of a more permanent nature). Once again, shut down any open applications and other computers on your network then try a speed tester again and record the results.

Step 3:
If you are using a Wireless router ensure you have enabled encryption and Access Control lists. This will prevent anybody nearby “piggy-backing” on your connection – and therefore prevent them using your bandwidth. This can also be checked from the DHCP table of your device which will tell you how many machines are connected to your router and obtaining an IP address.

Step 4:
Account management can cause your speed to vary at peak and off peak times and across different protocols so please check to see if you have received any emails to inform you of this and also check your VMBU usage to see if you have breeched any of the management levels outlined here if this is not the case or if you have hit management levels but feel you are still having other unrelated speed issues then please progress to step 5.

Step 5:
To determine if your speed problem is caused by BT Exchange contention you should perform a test using BT’s Speed Tester. Instructions for using this can be found here:

Record the results of this test. If the speeds on this appear normal you can skip Step 6 and got to Step 7.

If the speeds are below the thresholds published above, then follow Step 5. If this does not resolve the issue contact Technical Support to report a fault.

Step 6:
Speed issues could be caused by a problem with your internal wiring setup. To eliminate this as a cause you should ensure your DSL filters are set up correctly. A brief overview of setting up Broadband hardware, filters and general installation can be found here:
Alternatively you can test from the master socket and unplug all other telephony equipment (including Sky digital boxes, telephones, fax machines etc.). This would be a required step if a fault were to be raised with us to BT. Once you are sure everything is set up correctly repeat the speed test process, and record the results.

Step 7:
Viruses or other malware such as spywear may be responsible for your poor speeds as they use your connection to propagate. If you are not already running Anti-virus and Firewall software install some, and then perform a full system scan for viruses. You should also check for Adware/Spyware.

Step 7:
If problems still persist, and no viruses or malware are present on your system, perform a traceroute to (one of our DNS servers) and record the results.

Step 9:
If the speed problems are still present, and you have eliminated BT as the cause, you should perform speed tests at various points in the day (3 times one in the morning, one on the afternoon and one in the evening if possible). Once done contact Technical Support with your results and the result of your traceroute using the Broadband Faults Checker as these results are too complex to take over the phone and we may need to pass them directly to BT.

Step 10:
Please ensure that once you have raised a speed issue you leave you connection and your hardware on and powered up to allow testing to be carried out.