Upstream connection speed

I pay for an 40/10 FTTC broadband service. My router tells me that the max connection speed is 47,456 Kbps and the downstream rate is 40,000 Kbps, limited because that is what I pay for. But why is my upstream rate only 7501 Kbps?

What determines which tones are used for upstream and which are used for downstream?

I am thinking that in my case there may be under utilized downstream tones that could be better used to give me the full 10,000Kbps upstream speed that I pay for.

You cannot swap around the upstream and downstream tones, if you did this you would have to do the same for every VDSL2 line on a cabinet and other bundles from other cabinets that may pass close enough to experience cross talk

As for why? Maybe downstream is running at a 3dB target margin

You pay for up to 40/10, Sir, with an estimated range or at least a minimum provided on the downstream. You definitely don't pay for those sync speeds to be guaranteed. Sorry.

OpenReach use VDSL2 Annex-B Profile 17a.
This has set upstream/downstream tones.
These tones can't be changed for individual lines.

The upstream varies not just by distance to the cabinet, but also the cabinets distance to the exchange.

Take the example of 2 cabinets.
Cabinet 1 is only 300m from the exchange.
Cabinet 2 is 4.3km from the exchange.

250m from cabinet 1 you may get 65/20
250m from cabinet 2 you may get 65/10

The guy on cabinet 2 is wondering why his upload is so poor compared to others he sees with similar downstream syncs. It's his cabinets distance from the exchange. This is all to prevent the vdsl2 signal killing existing adsl lines.

If you think your upstream is low compared to others with similar downstream, it's probably because your cabinet is some distance from your exchange.

edit: typo

Edited by j0hn83 (Wed 22-Aug-18 10:48:24)

Pardon me if I'm wrong, but since when did cabinet distance to the exchange matter with VDSL2 sync?

The reason the upload could be low may be down to crosstalk, poor wiring or something else between the property and cabinet.

The cabinet can be 10000miles from the exchange and it won't affect the sync as it's the DSLAM and router distance that matters?

Poster is referring to the three different power masks used to avoid undue crosstalk with ADSL/ADSL2+ services

NOTE: While these exist I don't subscribe to the illustration that on one cabinet it is 65/20 dropping to 65/10

The differences are a lot less than that in general

In reply to a post by j0hn83:

OpenReach use VDSL2 Annex-B Profile 17a.
This has set upstream/downstream tones.
These tones can't be changed for individual lines.

The upstream varies not just by distance to the cabinet, but also the cabinets distance to the exchange.

Take the example of 2 cabinets.
Cabinet 1 is only 300m from the exchange.
Cabinet 2 is 4.3km from the exchange.

250m from cabinet 1 you may get 65/20
250m from cabinet 2 you may get 65/10

The guy on cabinet 2 is wondering why his upload is so poor compared to others he sees with similar downstream syncs. It's his cabinets distance from the exchange. This is all to prevent the vdsl2 signal killing existing adsl lines.

If you think your upstream is low compared to others with similar downstream, it's probably because your cabinet is some distance from your exchange.

edit: typo

I agree with jOhn83 because there is always latency involved due to distance.
Therefore cabinet 2 being further from the exchange would matter.?
But as the OP is paying for 10mbps then with at least 2mbps deducted then the 7mbps upstream seems ok.?

Edited by deleted (Wed 22-Aug-18 12:24:33)

In reply to a post by ironman12345:

I agree with jOhn83 because there is always latency involved due to distance.

Latency is nothing to do with sync speed.

No what I said is correct.

I may have exaggerated the impact of it but upstream is absolutely lower for lines further from the exchange.

it is not related to latency but power levels to prevent ADSL interference.
The ADSL power levels are much lower further from the exchange and so the VDSL2 power must also be.

edit: changed wording slightly

Edited by j0hn83 (Wed 22-Aug-18 12:41:20)

In reply to a post by candlerb:

In reply to a post by ironman12345:

I agree with jOhn83 because there is always latency involved due to distance.

Latency is nothing to do with sync speed.

But that is saying that no time is taken for the signal to travel to the exchange,?
Surely if the cab is further from the exchange it must effect the speed.?
Ok latency is the wrong word but as everything takes time, then due to power drops at further distances the speed would still be lower.?

Edited by deleted (Wed 22-Aug-18 12:42:24)

No. Latency is how long a packet takes to travel.
The latency can be higher if distance to exchange is longer but on a bit of fibre latency will be negligible over a couple miles.

Latency on the link between cabinet and exchange has NO impact on the VDSL2 link speed, since it is not VDSL2 between the exchange and cabinet.

If someone can find the distances between exchange and cabinet that the ANFP uses to specific mask for a cabinet can do some analysis on speed test results to see how different or not the upload figures are.

In reply to a post by ironman12345:

But that is saying that no time is taken for the signal to travel to the exchange,?

No, it's not.

The sync speed is the number of bits per second transferred between the VDSL DSLAM in the cabinet, and the VDSL modem at the end user side. It's an attribute of this copper point-to-point link only.

Even if the fibre from the cabinet was cut, it would not affect the sync speed - it's just that data wouldn't be able to travel any further than the cabinet.

In reply to a post by ironman12345:

Surely if the cab is further from the exchange it must effect the speed.?

It does not affect the speed of the link between the cabinet and the user's VDSL modem, which is what we're talking about here.

For end-to-end data transfers over the Internet, there *is* a relationship between latency, maximum achievable throughput, TCP window size and packet loss. You can achieve any throughput you like, for a given latency, as long as the TCP window size is large enough and the packet loss is low enough.

In reply to a post by ironman12345:

Ok latency is the wrong word but as everything takes time, then due to power drops at further distances the speed would still be lower.?

There is no VDSL "power" sent along the fibre link between exchange and cabinet. The cabinet has its own mains connection, and the VDSL electrical signal originates at the cabinet.

So for VDSL sync speed, the distance between cabinet and end user matters (i.e. the length of the copper link); the fibre between exchange and cabinet does not.

My cabinet is at least 4.5km from the exchange and I have never had less than full 20Mbps upstream sync. This is the first time I have heard it suggested that distance from the exchange affects VDSL.

In reply to a post by candlerb:

So for VDSL sync speed, the distance between cabinet and end user matters (i.e. the length of the copper link); the fibre between exchange and cabinet does not.

But of course, I agree with what was said before: cabinets which are further from the exchange may be configured to use lower VDSL power in order not to interfere with ADSL, which in turn means for a given length of copper you'll get a lower sync speed.

I don't recall the question ever being asked before, Kevin . But the upstream power masking on the local loop theory makes sense to me.

Thank you for all the replies. Did BT Openreach decide the tone assignments and have they published anything to justify the decision that they made? Is it at issue that Ofcom gets involved with?

You can enjoy reading the ANFP NICC documents if you want