Seeing as I was bored and we lost my other post, Ive made a nice little picture to show you all about how a speed fault is investigated on an ADSL Max broadband provider. This isnt the only way, there are certainly other tests that can be run and that show other information, or the same information in other ways. This is just the way that I do it, for your information. Some of the information is specific to Plusnet, but would have an equivalent at other providers.
Test resultsThe test results comprise a DSL status check, a PTTR test, exchange contention check and three other tests.
1. This is
me, and the time when I appended the ticket. The timestamp is important if tests had to be run at a specific time such as during the evening, bad weather, or when equipment had been moved to an alternate socket
2. This is the
ticket pool that where the fault ticket is.
3.
Diagnosis. Low throughput is self explanatory, NFF stands for No Fault Found.
4.
Loop Loss is a measure of the length and quality of your line. The scale runs from about 5 (very close to the exchange) to 62-65 which is the limit at which ADSL Max will run, with speed tailing off as the loop loss increases.
5.
SNR margin is probably the most mis-understood statistic surrounding your broadband. The SNR margin is a measure of the gap between the average level of the noise and the broadband signal - think of it as headroom for the noise to vary in. A low SNR (3-6dB) will allow the signal the most room (bandwidth) but spiking noise may cut into the signal and cause a loss of synchronisation. A high SNR (12-15dB) will prevent these spikes from reaching the noise, but will cause a lower sync speed. A 3dB
decrease in SNR margin will allow around 800kbps
increase in sync speed.
6.
Sync speed, based on an 8128kbps maximum, mainly limited to by the loop loss. Higher loop loss = lower sync speed.
7.
Line rate - the local exchange needs a line rate to be applied to the line for two main reasons. The first reason is because the equipment in the exchange has a very small buffer. If there was any lag in your connection and there was no line rate, a backlog of data would form in the exchange and cause problems with the equipment there (freezes, re-syncs, etc.). The second reason is to limit the speed of data transfer on the line if there are multiple disconnections that are always determined to be a fault if they occur regularly.
8. The
Fault Threshold Rate is set during the first 10 days of your broadband connection. Its a statistic that allows us to identify whether or not the line is syncing lower than previously - if the sync is lower than the FTR, BT would accept it as a fault.
9. This is the
throughput from a speedtest run from the BT speedtester website. It is timestamped so that we can check the line profile at the time the test was run. A normal result would be about 85% of the line rate to take into account packet transmission overheads.
10.
Virtual Path capacity is a measure of contention. If the VPs are red, your exchanged is contended.
11. WP stands for
Workplace, which is our internal accounting and management system. We hold a profile which is regularly updated from the local exchange. As with the line rate in #7, this is to ensure that there is no buffer overflow.
12. The
B-RAS is another piece of kit on the service providers network and this holds a profile which should automatically match the DSLAM.
13.
Ellacoya systems allow us to inspect data in real time and enforce rate limiting across different protocols (peer-to-peer, VoIP, etc.). Each of our products have specific profiles in Ellacoya - normally one for when a customer is within their usage limit and one when they have exceeded their usage.
So heres my problem, what can be done about it?4. High loop loss will lower the sync speed. Sorry, you live too far from the exchange. Perhaps check before your next move?
5. High SNR margin will also lower your sync speed. There might be spiking noise on the line (usually obvious because it causes disconnections) or it might be stuck high if noise used to be present, but is no longer. We can request that BT lower this for you.
6. Low sync speed is usually caused by either #4 or #5, but can occasionally be brought low due to spiking noise, with a low SNR margin due to large variance in the noise itself.
7. Line rate can be pushed low due to frequent disconnections. The local exchange will need to see a stable 72 hour connection at or above the threshold rate for a higher profile in order for it to be increased.
9. Unidentified low throughput can be caused by a variety of factors which are too numerous to discuss here.
10. If your exchange is contended, BT will automatically consider an upgrade.
11. If the WP profile does not match the DSLAM, we need to manually set it.
12. If the B-RAS profile does not match the DSLAM, we need to ask BT to manually set it.
13. If Ellacoya thinks that youve exceeded your usage allowance, you probably have. Occasionally it gets out of sync and we manually set it.
Any questions?
