Infinity upgrade fail

Following on from my thread in the general forum HERE I spoke to a couple of guys on the BT community forum today HERE who have basically stated that it doesnt matter what the IP profile is on the upstream, you will only get what the BT wholesale checker states. Somebody convince me this isnt true??

You posted in the first link

3. My upload profile is 10Mbps but speedtests have never been above 6Mbps, is this normal?
...
Good news! We predict your download speed will now be 27Mb/s and your upload speed will now be 5Mb/s

So it wasn't true for you on 12 April.

To be fair, that post is not entirely accurate. The prediction was 5.7 up, which is almost exactly what I get.
Still doesnt explain the part about the profiling though.

Can anybody confirm this? It would certainly go some way to explaining my speed issues

In reply to a post by steadyeddie:

Can anybody confirm this? It would certainly go some way to explaining my speed issues

I would suggest this is not the case.

The availability checker says this for my line:

Our test also indicates that your line currently supports a fibre technology with an estimated WBC FTTC Broadband where consumers have received downstream line speed of 55.1Mbps and upstream line speed of 13.2Mbps.

This is what I actually get:

http://www.speedtest.net/result/1928298579.png

Although I do find that the upstream benchmarks much lower than this from certain speedtest sites. I suggest you try via the "London > Virtual Internet" server.

BTW these speeds are corroberated by what I can upload at via uTorrent, I hit just shy of 2MByte / Sec. Obviously I'm capping the hell out of that down to about 128KByte/sec but if I don't, that's what I get

http://www.speedtest.net/result/1928534079.png
The upload is scarily predictable!!

Edited by steadyeddie (Wed 02-May-12 21:04:07)

I don't actually know the answer, but I think I may understand what they are on about.

My thoughts:
the backhaul back to their core network from the mini-DSLAM in the street via the exchange is all symmetric (i.e. same maximum speed up and down). However the VDSL service on customer lines is asymmetric.

The profiling is used to prevent an overwhelming amount of traffic hitting a given route.

e.g. you choose to download a massive file from a server on the internet somewhere that can happily serve that file at say 300Mbps+. All well and good - 300Mbps flies across the internet, over BT's core, down the backhaul to the DSLAM in your cabinet - at which point it hits a bottleneck as your downstream rate is a lot lower. The net result being buffering and/or discard of data by the DSLAM, in turn resulting in the dropped packets needing to be retransmitted again all the way from the server somewhere on the internet.

Not a very sensible thing to do as that would throw a stack of useless traffic over the backhaul to the cabinet which could unnecessarily lead to congestion as well as incurring the additional back scatter of upstream retransmit requests coming from you.

So the downstream data rate is limited so as not to bottleneck when it hits the VDSL segment. I presume this is applied at the BRAS so it relieves the unnecessary data from their on out i.e. the fibre feeding the exchanges and the fibre to the cabs.

Now think about the upstream - as far as BT are concerned - what need do they have to profile the data rate on that? You can only generate as much traffic as the VDSL segment can handle in the upstream direction which poses no risk to the onward upstream fibre capacity into the core.

To BRAS profile on the upstream would be plain stupid as by the time the data arrives there to be throttled it has already traversed the "narrowest" part of the network i.e. the fibre from cabinet to exchange. Upstream needs to be managed on the CPE (your router) which would be achieved by capping the VDSL synch rate in that direction or using capping on the VLAN (presuming the CPE is intelligent enough).

Basically what I believe they are saying is that they have no concerns about upstream congestion becoming an issue so they don't bother profiling it. Understandable really as downstream congestion is going to occur sooner on the symmetric backhaul, which will require the backhaul to be increased in size - adding more available upstream... and so on.

And yes - before anyone jumps in - I'm deliberately ignoring the ability (or otherwise depending on implementation) for the TCP stack to back off the transmit speed in either direction if required. It's a somewhat unreliable mechanism over the t'interweb.

GeeTee, I feel incredibly guilty, the time and effort that went into that post was totally wasted on me!!
I do think I understand the basics of what you are saying though, and thanks for taking the time to post it.
It will be interesting to hear what the BT technical bods have to say when (if) they ring me back.

Apologies - I got a bit carried away

Basically if my theory is correct then your upload data rate is only limited by the connection speed between your router and the street cabinet. Unfortunately you can't see what that is without somehow unlocking the Openreach modem.

I should probably go and read your other threads so I know what the actual issue is