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[kitz]

IMHO Hake actually has a point that cant be disregarded for the future.
Contention works well on large pipes, its always going to be the where the least amount of bandwidth is where contention will likely kick in first.

Its getting late, Im grumpy and tired so dont have patience atm to type out long technical explanation other than to say congestion between the cab and the exchange is a possible place where congestion may kick in. iirc BToR use GigE links, so how many FTTC customers will that serve?

Cant compare to ISP centrals, since 21CN (no ISP will connect FTTC customers via centrals) the MSILs work very differently. Monitoring is better and EPs mean an ISP can go over bandwidth for unexpected events.. and no more waiting months for a new central to go in.
I cant speak for ISPs who use dedicated WBC and a 3rd party supplier (such as enta) or their own backhaul (GEA).

Also consider GEA FTTC where the ISP is presented with a 1GbE port in the exchange.   How many customers will this support?  In this respect GEA FTTC is reminiscent of Datastream. Knowing the type of user this exchange is renown for (luckily not my cab!) just say Id rather be with a WBMC ISP than GEA.

>> I have never heard of congestion between cabinet and exchange.

Not yet!  I do have a vague feeling of deja vu of 2002/2003 when it was said exchange contention couldnt occur. It was impossible they said, but happen it did in 2003.
Guess who predicted massive contention when 2Mbps speeds were announced in 2004 and was laughed off ADSLguide.
Guess what happened a few short months later Nationwide 

This time Im not saying it will happen, just that it is a possibility that cant be ruled out.  Depends what your neighbours are like on your cab and cant be discounted.

Theres several points where contention could occur.

1. cab <-> exchange.  (All isps)
2. exchange OLT  (GEA isps eg sky, TT)
3. MSILs   (Dedicated WMBC & WBC isps eg Plusnet, Zen)
4. own or 3rd party backhaul (WBC ISPs eg Enta)
5. Exchange backhaul (LLU/GEA eg sky, TT)
6. Host links (Shared WBMC eg smaller isps such as IDnet)

Whilst I agree the MSILs/OLTs will likely hit first, it cant be considered out of hand if youre unlucky enough to be  a full cab neighboured to a few 80/20 leech city lines.


Cant compare to B4RN - totally different topology with 1 backlink for all customers.  Yep I see contention/congestion kicking in for them too as they start filling up with customers, they dont have many actually connected atm.

/edit..  I typed more than I meant to..  another full day tomorrow so off to bed... too tired to check for typos 

[burakkucat]

... too tired to check for typos 

A tactful cat fails to notice them -- by reading with his 'blind eye'. 

[Chrysalis]

kitz if cabinets were to ever get congestion due to very extreme usage levels then the isp's themselves would be congested at very extreme levels.  The contention is almost non existant.

its approx 2-4:1 on the downstream and under 1:1 on the upstream.  Thats also assuming openreach dont enable unlit fiber's as each cabinet has spare capacity going to it.

compare that to much higher contention levels on the backhauls.  The cabinet feed to the exchange is no concern.

I think for a cabinet to get congested the average monthly usage for each customer on it would likely need to exceed 6.4tb.  As openreach guarantuee 20mbit of capacity per end user.  The capacity per end user provisioned isp side is much lower.

To put into perspective a typical openreach cabinet has 60x more capacity then BE sometimes gave to an entire exchange.

[kitz]

>> kitz if cabinets were to ever get congestion due to very extreme usage levels then the isp's themselves would be congested at very extreme levels.

Yes sorry youre right.  I did say it was late and I was tired.

My line of thought was that it would be a mix of ISPs, so some could be fine and others not which may shake things up a bit. 
At a local level the OLT is going to be the main point of weakness for GEA FTTC.

>> To put into perspective a typical openreach cabinet has 60x more capacity then BE sometimes gave to an entire exchange.

That cant be right surely or I would have maxed out way more than exchange capacity on my line alone?
My understanding was that BT used gigE links back to the exchange from the cab?  The GEA OLTs presented to the SP are 1Gb.  Or am I having another blonde moment?

[Chrysalis]

some certian exchanges BE only had a 100mbit backhaul, whilst cabinets have multiple fiber connected.  Each fiber having 2.5gbit capacity.

If we take the openreach 20mbit guarantuee (vs 300kbit on BT retail eg.) apply it to a 288 user cabinet then thats a min of 5.6gbit lit capacity.  Openreach future proofed their rollout they dont want to spend money pulling more fiber through the same ducts in 10 years time, they over provisioned.

I dont know if openreach rate limited these fiber links to 1gbit/sec butI cant think why they would do that and it is the sin's that each user is allocated at least 20mbit/sec of bandwidth.  Since isp's dont allocate anywhere near that amount on backhauls, we wont see congestion on the cabinet's, isp congestion would appear first.

[kitz]

>> Each fiber having 2.5gbit capacity.

Cheers..  what I saw referenced 1gb, hence the confusion.

[Chrysalis]

I just edited reference the 1gbit.

Also if you thinking of the size of the GEA links, those are in the exchange so are different links.

[kitz]

>> if you thinking of the size of the GEA links, those are in the exchange so are different links.
Yes the OLTs (handover to the SP) are 1Gb.  These are for mutliple cabs.

>> fiber having 2.5gbit capacity
Id not seen that figure before. Admittedly Ive not looked hard & BT are adept at keeping things hidden,  but do you know if there's a linky anywhere.

>> some certian exchanges BE only had a 100mbit backhaul,

Not that it makes any difference now, cause my info would now be old.  But I was told by Brett/Oli White that new satellite exchanges were installed with 300Mb.  Dunno what happened when o2 came on board cause be saw quite a bit of congestion during that time and backhauls had to be upgraded.  There were quite a lot of unhappy be users at that time :/

[Chrysalis]

I dont think there is a link from openreach stating the sizes, my info is probably 3rd hand that I got 2nd hand of various forum posts.  I will try to find my source if possible tho.

Although I watched the openreach guy pull the fiber across the road from me, there was most defenitly more than one fiber going through.

the 20mbit/sec per customer is printed by openreach tho.

[Chrysalis]

kitz I remembered the figures wrong.

The guarantuee is 15mbit for 40mbit tier, and 30mbit for 80mbit tier.

http://www.openreach.co.uk/orpg/home/updates/briefings/super-fastfibreaccessbriefings/super-fastfibreaccessbriefingsarticles/nga00612.do

Presumably this means if provisioned capacity isnt enough to provide those speeds for everyone at the same time, then more is provisioned.  So its slightly over 2.5 contention ratio on the downstream which is circa leased line spec.  Upstream should be effectively below 1:1 contention.

[ryant704]

Nevermind, posted.

[SE]

Hi folks,
Was hoping for a bit of advice here as I seem to be going in circles with plusnet support.

I had a new line installed from plusnet when I moved to my new home. The choice of home was made in part by the location to a FTTC enabled cabinet, as I am particularly throughput hungry in my line of work. The cabinet is approx 200m (300 tops) in terms of actual line length from the home and the BT line speed estimator is 71.9mbps. Its a new estate (8 years) with all new wiring. My in laws live next door, have ADSL2+ and their attenuation is around the 7db mark direct to exchange one 600 metres away.

for the first 14 days of my line being installed, it ran at a sync of 78mbps solid. Did not change once and throughput was fine (though there was some throughput decreases during peak periods, the vdsl2 line sync rate did not change and off peak was full throughput). Ping was a steady 8ms.

About 5 days after the email from plusnet saying my line speed (after training) was 78mbps, the line speed started to go down. At first it was 76mbps, then 72, then 68, then 65, then 64 and today its down further to 62mbps. Upstream has remained solid at 20mbps sync rate with 20mbps ip profile (though throughput is only about 15mbps). Ping has shot up to mid 20's.

The attenuation stats of the line are

VDSL Band Status U0 U1 U2 U3 D1 D2 D3
Line Attenuation(dB): 2.7 12.6 19.1 N/A 7.0 14.3 22.2

Which seems very high on D1 for the wire going just around the corner. We also have people reporting its very hard to hear us on a voice call (though we hear them just fine). We have tried different handsets and the same result.

Also saw this on the HG612 last time I pulled the stats when it dropped to 64mbps sync.

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 2
Max: Upstream rate = 24713 Kbps, Downstream rate = 77612 Kbps
Path: 0, Upstream rate = 19499 Kbps, Downstream rate = 64601 Kbps

What is the difference between 'path' and 'max' ? Why would my path be lower than my 'max' ? Plusnet said that 'max' just means the capability of the cabinet, not my line (which seems odd).


Plusnet are saying that as throughput is actually at near line sync rate, there is not a problem. Even though I have demonstrated line sync rate was high but is deteriorating over time they state (via their faults checker) that my line just cannot support the throughput it originally had and there is no way they can raise a BTW fault until my throughput is 50% of the sync speed (which as the sync speed just keeps decreasing over time, seems like a catch 22). As a techie, it bugs the hell out of me that something 'did' work then deteriorates, but is actually 'operating correctly'...

There are no extensions wired in to phone socket, its straight to the NTE. Theres the FTTC faceplate on there direct to modem. Speed tests have all been carried out via BTW checker using Ethernet on my side not wireless. Quiet line test seems fine, I cant hear any buzz, crackles or hum. I have changed both the VDSL2 modem and the router itself and the problem remains, so I am pretty confident this is not a CPE side issue.

You can see from plusnets own diagnostics (taken before the recent line sync rate drop to 62mbps) that things appear OK, though I do note that the connection uptime was at this highest speed the longest.

Test Outcome   Pass
Test Outcome Code   GTC_FTTC_SERVICE_0000
Description   GEA service test completed and no fault found .
Main Fault Location   OK
Sync Status   In Sync
Downstream Speed   65.5 Mbps
Upstream Speed   20.0 Mbps
Appointment Required   N
Fault Target Fix Time   null
Fault Report Advised   N
NTE Power Status   PowerOn
Voice Line Test Result   Pass
Bridge Tap   Not Detected
Radio Frequency Ingress   Not Detected
Repetitive Electrical Impulse Noise   Not Detected
Cross Talk   Not Detected
Profile Name   37M-74M Downstream, Interleaving Low - 10M-20M Upstream, Interleaving Off
Time Stamp   2013-09-23T03:00:00
Parameters   MIN   MAX   AVG
Down Stream Line Rate   64.5 Mbps   80.0 Mbps   71.1 Mbps
Up Stream Line Rate   18.8 Mbps   20.0 Mbps   19.7 Mbps
Up Time   21577 Sec   86394 Sec   76967 Sec
Retrains   0   5   0

Ive demonstrated to plusnet via the ticket that the speeds were stable, but are now deteriorating. They are just saying this is normal and until my throughput is 50% of sync speed there is nothing that can be done, which seems stupid if the sync speed just keeps decreasing. Right now I get throughput of about 58mbps down, which means essentially I am paying them 50% more than their 40mbps product for 18mbps of gain (which im sure as the situation continues will end up being even less).

Does anyone have any advice here? I feel like im banging my head off a brick wall with their support team.

One day one my PlusNet speed was 57Mbps, with no problems, but on day 10 it went down to 47Mbps and as they guessed it would be 47 they would not help and I've had to stick with that 

Do you have Address Based Filtering set to on?