We've been investigating a possible problem with TalkTalk VDSL circuits not able to reach the full speed potential when doing downloads. This is more prevalent on circuits which have near 80M sync speed. The throughput of these circuits seem to be unable to download at IP rates faster than 69Mb/s. We are investigating this with TalkTalk, and have also been testing both TalkTalk and BT based circuits with the help of other customers.
We will update this post as things develop.
This Kitz Forum thread is also relevant to this: https://forum.kitz.co.uk/index.php/topic,21750.0.html
Regular readers may remember that we migrated our TalkTalk lines on to a brand new TalkTalk network in April of this year. Many lines saw a drop in latency, which has been well received by customers.
With the help of TalkTalk, this evening we tested a circuit via the old network. Although the latency increased (from 6.4ms to 11.8ms) the throughput as measured by using the iperf3 tool showed an increase from 67.4Mb/s to 71.9M/s. (This is a line with a 75.6M sync rate)
We are still testing things further so as to rule out other factors that could be involved.
We have passed this on to TalkTalk and they are investigating further too.
Some good news. TalkTalk have been doing some tests and changes on a single line as part of their investigations.
This is what we're looking for when looking at our CQM graphs of traffic:
A constant download of lots of http and torrents at 75.2M (sync is a bit below 76M), filling the link (red line at bottom)
iperf alone gives 71.9 when before it was getting 67.4 yesterday.
The change TT have made has only been applied to this one line, we'll update this post when the change has been made across the board.
It looks like this has been fixed, we'd appreciate any feedback
TalkTalk have rolled out a change to the "overhead accounting mode in use for VDSL customers." Customers can now try reconnecting (restart PPP or reboot the router), and try speed tests and downloads.