Minimum Guaranteed Line Access Speed - ADSL+2

[#1]

I currently receive ADSL+2 service from TalkTalk and the modem syncs at 18.4Mb/s giving me a download speed of around 15.5Mb/s. (Although I used to get nearer 17Mb/s.) The exchange is only 650m away.

I am fed up with TalkTalk's dismal customer service and a recent price hike of £9 a month has prompted me to look elsewhere. I would like to sign up with Plusnet, but the Minimum Guaranteed Access Line Speed I have been quoted is a pathetic 1.5Mb/s. My concern is that should a fault develop on the line and the speed is reduced to, say, 3Mb/s (which has happened in the past), will PN wash their hands and say the speed is above the MGLAS and the problem won't be investigated?

[#2]

If you can PM me your address I can look into this for you.

[#3]

PM sent 16 days ago - no response.

PM sent 13 days ago - not even read yet.

I guess PN are not interested in a potential customer.

[#4]

Sorry to hear that Matthew didn't get back to you.

He's on annual leave at the moment, mind PMing me instead?

Thanks,

Anoush.

[#5]

Perhaps I was a little harsh above, I hadn't considered annual leave.

I've sent a PM.

[#6]

No worries, thanks for your PM.

Checking your speeds against just your postcode, the estimates are pretty good at between 10-19mbps. Adding your house name into the equation does dramatically reduce that to 2-6mbps.

MGALs is always a tad below the lowest of the estimate, so 1.5mbps sounds about right.

If you sync at 20mbps with TalkTalk, it's possible your line is just overperforming which is good and to be honest I wouldn't expect a significant drop in speed if you transfer to Plusnet. Here's the but, though, if the sync speeds did drop significantly we wouldn't be able to send an engineer until it dropped below the estimates.

Leave this with me though, I'll investigate a little further if I can and get back to you tomorrow.

[#7]

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@Gandalf wrote:

Here's the but, though, if the sync speeds did drop significantly we wouldn't be able to send an engineer until it dropped below the estimates.

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Which is exactly my point.

[#8]

Although on ADSL2+ connections we can report a fault if the speed drops below the FTR (Fault Threshold Rate), this is determined during the initial 10 day training period of the line.

The FTR is set based on the MSR (Maximum Stable Rate), the MSR is set to the lowest rate your line connects at during the 10 day training period and the FTR is around 70% of this speed.

FTTC doesn't use FTR and is purely based on the estimates/MGALS for the connection.

[#9]

These estimates seem quite odd.  Is there a possibility that the BT data for this address is flawed?

I could understand a marked difference if this is an exchange where a LLU provider (such as Talk Talk) offer an ADSL2+ service  but BTw have failed to invest in CN21 technology and therefore there is no WBC ADSL2+ service available to ISPs such as PlusNet.

But even then, if the ADSL (1) estimate is as low as 1.5Mbps, ADSL2+ ain't going to be that much faster.

@McT - what's the line attenuation reported by your router please?

[#10]

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@Townman wrote:

These estimates seem quite odd.  Is there a possibility that the BT data for this address is flawed?

Yes. When the line was installed and the first two times an OR engineer visited to correct a fault, the routing data stated cabinet 7 whereas the line actually goes through cabinet 1. However, the third and final time an OR engineer came he said that the routing data was now correct.

[#11]

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Townman wrote:

@McT - what's the line attenuation reported by your router please?

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Upstream line rate (kbit/s)            1099
Downstream line rate (kbit/s)        18431
Line standard                                ADSL2+
Channel type                                 Interleaved
Upstream SNR (dB)                      6.7
Downstream SNR (dB)                  3.3
Upstream line attenuation (dB)      12
Downstream line attenuation (dB)  23
Upstream output power (dBmV)     11.5
Downstream output power (dBmV) 0
Upstream CRC                                9514
Downstream CRC                            0
Upstream FEC                                 47796
Downstream FEC                            0

I think there is still a problem with the line. The above stats suggest there is and although the router is syncing at 18.5Mb/s, the actual throughput as measured by a speed test is 15.5Mb/s. Allowing for IP overheads I would expect a download speed of 16.5-17MB/s, which is what I used to get.

Whilst diagnosing the most recent problem, I tried another router. This one also also showed the interleave depth, which was an outrageous 320!

[#12]

Something is quite odd here.  The attenuation suggests a circuit length of about 1.5 km which at a 6dB SNRM should deliver higher speeds than you are seeing at 3dB.

The speed predictions seem rather silly.  Are they based on address / postcode or phone number?

Please use the following links to check the services available and their estimated speeds. From the first link, please record and report back the distance from the exchange. The second link advises of which fibre services (if any) are available on your line and their anticipated speed.

• Kitz line check
• Kitz BT checker

 How long had the synch been up when you took thise stats?  The error rate could be impacting the data speed.  To be honest the lower SNRM though delivering a higher raw synch rate could result in a lower data throughput due to a higher error rate.

[#13]

@Townman - Thank you for taking an interest.

The Kitz line check, which was based on post code only (my TT number was not recognised), suggests the following:

Direct - 762m   By Road: 1km

The true figures are:

Direct - 650m    By Road - 950m

The line speed estimation for ADSL 2+ is 17Mb/s.

The BT broadband availability checker fails because it doesn't recognise the phone number and if I use my address it incorrectly states that it is served by cabinet 7 with a downstream line rate of 'Up to 3.5' and a range of 2-6. However, if i plug in my next door neighbour's address, it correctly states cabinet 1 with a line rate of 'Up to 17' and a range of 10-19.5. There is no possibility that we are on the boundary between cabinets - I can see both drop wires connected to the same DP.

So despite the OR engineer telling me that the routing records had been corrected - it is still wrong in at least one database.

[#14]

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@McT wrote:

I think there is still a problem with the line. The above stats suggest there is and although the router is syncing at 18.5Mb/s, the actual throughput as measured by a speed test is 15.5Mb/s. Allowing for IP overheads I would expect a download speed of 16.5-17MB/s, which is what I used to get.

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If you allow for the ATM layer overheads (48 bytes of data with a 5 byte cell header), that gives 16.2Mb/s, which is not that far off 15.5, the IP overheads (maximum 1460 bytes of data with 40 bytes of headers) are negligible.

The interleave depth itself is largely irrelevant, the important figures are the interleaving delay, and the INP value.

I'd also guess that the upstream and downstream error counts are the wrong way round.

[#15]

It does rather look like somewhere there is incorrect BTOR data for your line routing.  I suspect that this would not be an issue if you migrated as ADSL, however a migration to fibre might be fraught given the incorrect cabinet data.

An on the ground engineer check might be required as per another user required around here recently.  The poor quality of BTOR infrastructure data records seems to be a significant contributor to service migration issues.  I hope your migration is not blighted by such trials and tribulations.