Fibre 80/20 speed expectations

[#1]

Hi @ncd I discussed this type of behaviour at length with a BT faults adviser in the past and there wasn’t anything they could do or advise to shed any light onto why this happens.

I’m happy to take this to the BT complex faults team however if they’re unable to come up with anything then I’d be fresh out of ideas. 

To answer your question about L2TP I seem to have missed earlier, everyone is on WBMC Dedicated ‘new’ network because the ‘old’ network doesn’t exist anymore, however if you’ve got a static IP no matter if you’re on ADSL or VDSL you’ll have additional equipment in your route coming in via L2TP where your session terminates. There’s no benefits or drawbacks for this, it’s just how we allocate static IP’s.

I’ll get back to you on Monday. 

[#2]

Hi @Gandalf as always thanks for the detailed reply.

If we believe the restriction could lie somewhere in the BT WBMC network then I'd appreciate you making contact. I'm very happy to do whatever I can on my side to facilitate any kind of debug required.

I'm glad to hear that I'm not on an old non-existent network Also good to hear that the kit providing the L2TP link should not be limiting things in anyway too.

Thanks again,

N

[#3]

No problem @ncd To be clear though I don’t believe this is a network issue, that’s not really what I said. I just mentioned that to help explain your questions about static IP routing.

[#4]

I've discussed this with a BT quality assurance/complex faults adviser and they're puzzled too. If there are multiple examples of this behaviour (Which it looks like there is) I can raise this for further investigation.

Could you first post up your router stats showing the sync speed etc and also fill out the below template?

Sync speed: 

IP profile: 

Throughput: 

What you'd expect to see: 

[#5]

Ok, here is mine....

[Edit]  Router stats

DSL uptime:

11 Hours 53 Minutes 31 Seconds

Data rate:

20.00 Mbps / 80.00 Mbps

Maximum data rate:

30956 / 84676

Noise margin:

12.4 dB / 3.1 dB

Line attenuation:

0 dB / 14.2 dB

Signal attenuation:

0 dB / 14.2 dB

Sync speed: 

Home Hub 6 Max data rate 84,676Mb, Data Rate 80Mb

IP profile:

From Plusnet page Current Line speed 73.8Mb

Throughput:

Think broadband 71.3Mb, Ookla Multi 68.4Mb BT Wholesale 68.29Mb

What you'd expect to see: 

With the Max data rate (which I assume is the actual sync speed to cabinet) well above the cap of 80Mb I would expect to get 96.7% i.e. 77.36Mb as a current line speed, and a throughput a little lower than this, say about 76.5Mb.

[#6]

Thanks Kevin, once I've got 2 more I'll pass this along to BT for further investigation.

[#7]

Thanks @Gandalf .

Just noticed that I put "Home" Hub 6, it's not it is a Business Hub 6, but I can't edit my post now.

Don't think it will have any bearing though.

[#8]

No problem, that's cool.

[#9]

If @Kevin is on a "Retransmission High" profile, then there doesn't appear to be anything unusual about their IP profile being about 92% of their 80Mb data rate.

[#10]

Hi @Gandalf ,

Here's mine:

Router Stats:

xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    0
Last initialization procedure status:   0
Max:    Upstream rate = 25807 Kbps, Downstream rate = 102707 Kbps
Bearer: 0, Upstream rate = 20000 Kbps, Downstream rate = 79999 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State:       L0
Mode:                   VDSL2 Annex B
VDSL2 Profile:          Profile 17a
TPS-TC:                 PTM Mode(0x0)
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        11.4            10.5
Attn(dB):        7.4             0.0
Pwr(dBm):        13.1           -12.8

Sync Speed	20000 Kbps / 79999 Kbps
IP Profile	From Plusnet page: Current Line Speed (Download): 78Mbps
Throughput	Think Broadband: 71.4Mbps Ookla Multi: 71.4Mbps BT Wholesale: 70.41Mbps

In terms of expectation I was under a similar impression to @Kevin that expectation should be ~96.8% of sync speed (I've seen this quoted a few places including kitz here) giving 77.4Mbps so somewhere closer to 77 than to 70.

Thanks again!

N

[#11]

Thanks @ncd looking at your BRAS profile this is currently at 75.9mbps (We've incorrectly reported that at 78mbps) and while I believe it should be 77.36mbps, I suspect that may be caused by retransmission being enabled on your line.

Based on the BRAS of 75.9mbps a throughput of 71mbps is about right and isn't far off the mark to be honest.

@Kevin going back to your connection, our tests aren't showing any BRAS profile for your line which is odd and what's even more odd is that the test is reporting your sync speed is 76.6mbps which is giving you a BRAS profile of 73.8mbps.

We receive what's known as delta reports to tell us what your BRAS profile is, the last one we got was on the 12th December and it's advising it's at 73.8mbps (This is what the Current Line Speed you can see in your account online is based on)

While a sync speed of 76.6mbps should give you a BRAS of 74.07mbps, you've got high transmission enabled on your line, which likely explains this slight reduction.

Having said that if your sync speed was showing correctly at 79.9mbps you may see a few more meg in speed. Before I pass this on to our suppliers, I've first raised this across to a colleague to review.

[#12]

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@Gandalf wrote:

@Kevin going back to your connection, our tests aren't showing any BRAS profile for your line which is odd and what's even more odd is that the test is reporting your sync speed is 76.6mbps which is giving you a BRAS profile of 73.8mbps.

That's not unusual either. It always shows that on Retransmission High. You'll note that the IP profile will be about 96.8% of the 76.6. Everything about @Kevin's stats and speeds are what is generally seen for someone on Retransmission High. It's like you're only just noticing something that's been like that for quite a long time.

[#13]

@ejs thanks for the input.

92% of the sync speed at 80mbps is about 73mbps which is Kevin’s BRAS profile. It seems that our testing is just looking at this a different way and coming to same conclusion. 

@Kevin and @ncd Not sure there’s an issue here actually, it looks like this is just normal behaviour.

[#14]

@ejs 

I agree that @Kevin's throughput speed looks about right on a retransmission high profile. The max attainable is not relevant it is just a theoretical figure if there was no cap at 80Mbps.

@ncd  Your speeds look similar to Kevin's and correct for retransmission high which gives an  BT IP profile of about 92% of sync speed. The PlusNet line speed seems to be set manually to the maximum so is not having any effect.. It is the BT Wholesale IP profile that controls the throughput speed.

@Gandalf 

Here are my figures which are from a few weeks ago when I had full sync (79999Mbps actually) on a Dynamic IP service

Sync Speeds 79.999 Mbps down 20Mbps up

BT IP profile 70.61 Mbps which just over 88% of sync speed, I am on retransmission high but this is lower than expected

Throughput speed on TBB test around 65Mbps 

In this thread https://community.plus.net/t5/Everything-else/Monitoring-Throughput/m-p/1694371#M22933

you suggested that my sync speed was 76.6 Mbps on a GEA test, it was not, I had been syncing at full speed for several weeks. this reduced value for the sync seems to be the main reason why my IP profile is so low.

I have seen other posts where users have an IP profile of 70.61 Mbps with full sync speed such as this one by @fwdlink which looks very similar to my situation.

https://community.plus.net/t5/Fibre-Broadband/Profile-speed-dropped/td-p/1677063/page/2 

Hope this gives you some useful info.😊 

[#15]

Thanks @RealAleMadrid Assuming our testing is still showing your sync speed at 76.6mbps, it does look like the BRAS profile of about 70mbps is based on 92% of this with retransmission high. 

Similar to Kevin’s but different in the way that it just doesn’t seem to add up.

You may be in the same boat as @fwdlink I’ll retest both your lines when I’m back in the office tomorrow.