BT

Can anyone explain why last evening, whilst watching Amazon Prime, my broadband stopped working and I lost the connection. I immediately did a speed test and after a few seconds, the dial was showing a download speed in excess of 180Mbs against my normal 77. Then Amazon reconnected and it settled down with no further problems. Can such a high speed be possible with FTTC and I assume that on reconnecting, it took a short time to attenuate the signal in line with my contract.

No it can't.

It would have been an issue with the speedtester.

But what caused the drop out?

There are know cases of specific on demand players including ITV player and BBCs iPlayer causing certain routers or hubs to occasionally fall over!

My old 2wire router does not like ITV and will stream for a short while and then reboot ... I have come across cases where BBC iPlayer can be running and then suddenly it will stop and again the Hub has rebooted.


Your speed test is almost certainly due to measurement/reading error somewhere the network limits the max data throughput on your line to 80Mbps - maximum.

In reply to a post by MHC:

Your speed test is almost certainly due to measurement/reading error somewhere the network limits the max data throughput on your line to 80Mbps - maximum.

Just curious, while the max throughput is limited to 80, what can get 'Max Attainable' get up to? Mine is currently around 99Mbps.

Edited by deleted (Mon 12-Dec-16 22:03:38)

I believe that for Profile 17a, as implemented by BT, the max sync rate possible is 100 down and 50 up, however BT caps those at 80/20, with a potential max attainable of 120 and 55 Your figures suggest you are within, maybe, 200m of the cabinet.

With Profile 30 there is the possibility of getting up to 200Mbps down however the standard, from memory, is 100Mbps bi-directional (sync).

In reply to a post by MHC:

I believe that for Profile 17a, as implemented by BT, the max sync rate possible is 100 down and 50 up, however BT caps those at 80/20, with a potential max attainable of 120 and 55 Your figures suggest you are within, maybe, 200m of the cabinet.

With Profile 30 there is the possibility of getting up to 200Mbps down however the standard, from memory, is 100Mbps bi-directional (sync).

Thanks for the info.

I'm very lucky as the cabinet is 100m from here in a straight line ( slightly more line length due to buildings in the way ).

The fact that the line goes via a cabinet is also surprising as the straight line distance from here to the exchange is only 300m.

I asked the question as I was wondering if it was possible for BT to tweak the Infinity 2 speed the same way that they did for Infinity 1.

Surprising? More like good luck? If you were straight into the exchange then you would not get anything! VDSL has to be provided fro a cabinet and at present it is NOT available on EO lines.

In reply to a post by MHC:

I believe that for Profile 17a, as implemented by BT, the max sync rate possible is 100 down and 50 up,

I think those numbers reflect the minimum capability expected of router hardware to be able to call it compatible with profile 17a, rather than the maximum capability of the profile itself.

The theoretical maximum for 17a itself is about 170Mbps. I think they can achieve numbers relatively close to this in the labs.

Over in Ireland, where they are using profile 17a and vectoring, they sell a top package of 100Mbps, but the actual sync speed those people get is about 102Mbps.

In Denmark, the top single-line package is 105/32 for vectored VDSL2, and they get those as sync speeds. They do 150/50 packages too, but I think that is for a bonded+vectored VDSL2.

Obviously, though, you can't see these speeds unless the modem has gigabit ports...

Have a read of: www.zhone.com/solutions/docs/VDSL2_Primer.pdf has figures similar to mine.


I also believe that in Denmark they are using Profile 35b to deliver the higher throughput capability.

Edited by MHC (Tue 13-Dec-16 12:54:16)

In reply to a post by MHC:

Have a read of: www.zhone.com/solutions/docs/VDSL2_Primer.pdf has figures similar to mine.

Not exactly what I'd claim as definitive. Its a bit more like a sales brochure. It is even self-inconsistent, with graphs showing data rates of 120Mbps!

It is pretty standard for the kind of text we saw back in 2011 though ... including the fact that it makes scant reference to vectoring. Back then, vague reference to 100/50 was the common "target" for 17a, that matched the limited capability of "cheap" CPE at the time, complete with fast ethernet connectors.

Since then, a little more attention has been paid to the top-end speeds - particularly with the focus on vectoring in 2010-13. I vaguely recall that the first trials of vectoring were also limited to top-end speeds of 100Mbps because the CPE there wasn't up to the job, but getting well beyond that in subsequent years:
https://insight.nokia.com/vdsl2-vectoring-delivers-i...

In reply to a post by MHC:

I also believe that in Denmark they are using Profile 35b to deliver the higher throughput capability.

Not yet. They only announced the intention to use Vplus/35b 2 weeks ago.

The 17a vectoring rollout has been going on for almost 2 years now. As of November, they had done about 700 cabinets of the 3,300 they have, then they aim to reach another 850 next year, and the same again in the year after; I assume the rollout may well start to deploy 35b hardware soon...

But the speeds they've been using so far are a consequence of plain 17a vectoring, and can be seen in this outcome from trials in 2014, with those actual 105/32 speeds in evidence in graphs. There's an interesting bit describing the reasoning for their chosen package limits:

In reference to erhvervsstyrelsen.dk/sites/default/files/punkt1.pdf:

Aktuelle kapacitetsgr�nser:
�NVLT-P linjekortet har en systembegr�nsning p� ca. 140 Mb/s, nedstr�m + opstr�m
�NGLT-G linjekortet (Vectoring) har en gr�nse p� ca. 160 Mb/s, nedstr�m + opstr�m
�Nuv�rende CPE Broadcom chips�t (som f.eks. benyttet i HGW4) har en systemgr�nse p� ca. 150 Mb/s p� enkeltlinje og ca. 200 Mb/s ved Pair Bonding, nedstr�m + opstr�m

Disse kapacitetsgr�nser er grunden til at vi i dag maksimalt kan tilbyde 105/35 Mb/s (ned/op) p� enkeltlinje og 150/50 Mb/s p� Pair Bonding

which translates to:

Current capacity limits:
� NVLT-P line card has a system-limit of about 140 Mb/s downstream + upstream
� NGLT-G line card (Vectoring) has a limit of about 160 Mb/s downstream + upstream
� Current CPE Broadcom chipset (such as. Used in HGW4) system has a limit of about 150 Mb/s in single line and about 200 Mb/s at Pair Bonding, downstream + upstream

These capacity limits are the reason that today we maximum offers 105/35 Mb/s (up / down) on the single line and 150/50 Mb/s on Pair Bonding

It seems like the hardware over the last couple of years simply hasn't been up to the job of shifting enough bits for Vplus-type speeds, either in the line cards or in the CPE.

Edited by deleted (Tue 13-Dec-16 21:32:18)