Connections to these cabinets & maximum bandwidth per cab?

Does anyone know what the maximum number of connections are possible to these cabinets?

http://beusergroup.co.uk/technotes/index.php?title=F...

http://beusergroup.co.uk/technotes/index.php?title=F...

If a cabinet supports 100 connections can the back haul to the cabinet support all the 100 connections running at the same time at 80/20?

If the maximum is not supported what is the overall up/down bandwidth of a cabinet?

Thanks

Edited by think26872 (Fri 27-Jun-14 18:36:10)

First cabinet takes 96 connection, second 288.

The cabs may or may not have enough capacity for everyone to run at 80/20 however everyone is guaranteed at least 30Mb, so for all intents and purposes the cabinet backhaul isn't a bottleneck.

In reply to a post by Ignitionnet:

The cabs may or may not have enough capacity for everyone to run at 80/20 however everyone is guaranteed at least 30Mb, so for all intents and purposes the cabinet backhaul isn't a bottleneck.

That's interesting.
Could you please provide a reference for that guarantee as this is all I get by the time it reaches my home:-

Max: Upstream rate = 3847 Kbps, Downstream rate = 21276 Kbps
Bearer: 0, Upstream rate = 3850 Kbps, Downstream rate = 18729 Kbps

http://www.sinet.bt.com/sinet/sins/pdf/498v5p1.pdf
Check the wording for correct understanding
"A downstream prioritisation rate of 15 Mbit/s or 30 Mbit/s (depening on the product variant purchased) or line rate, whichever is the lower,"

In reply to a post by Bald_Eagle1:

In reply to a post by Ignitionnet:

The cabs may or may not have enough capacity for everyone to run at 80/20 however everyone is guaranteed at least 30Mb, so for all intents and purposes the cabinet backhaul isn't a bottleneck.

That's interesting.
Could you please provide a reference for that guarantee as this is all I get by the time it reaches my home:-

Max: Upstream rate = 3847 Kbps, Downstream rate = 21276 Kbps
Bearer: 0, Upstream rate = 3850 Kbps, Downstream rate = 18729 Kbps

The poster specifically asked about backhaul, your VDSL sync rate is a quite different matter.

The guarantee is on the link between the cabinet and the exchange.

There are no guarantees on the speed of the VDSL2 segment, since this is impacted by the length of copper to the cabinet and other factors like RF Noise, crosstalk and what VDSL2 modem you are using on the line, plus state of wiring in the home etc.

With ~18 Meg sync once presumes you are 1km or more from the cabinet, or if closer may be unlucky and the telephone line takes a longer route, e.g. goes away from cabinet then crosses road and heads back to the cabinet.

a contention ratio that low is extremely unlikely to ever be congested. ISP's themselves contend way way higher.

I'm pretty sure I read once that each cabinet has a 10Gbit link to the headend but I'm not sure where I read it unfortunately.

Backhaul is usually 1Gbps but can be multiples of this

In reply to a post by Icaras:

I'm pretty sure I read once that each cabinet has a 10Gbit link to the headend but I'm not sure where I read it unfortunately.

Me either. It's GPON or 1000BASE-BX on the Huawei here.

In reply to a post by MrSaffron:

Backhaul is usually 1Gbps but can be multiples of this

Is that from exchange to fibre cabinet using 1Gbps speed down & up but capped at 80Mbps / 20Mbps or 40Mbps / 10Mbps whichever the customers choose product?

No. That is like saying your PC has a 1Gb link to your router but capped to 100Mb by the Open reach modem and 80Mb by the VDSL line.

There is no capping. The speed of your VDSL link and the speed of the cabinet backhaul are nothing to do with each other they are completely separate links so no capping of one to the other.

Actually 1Gbps doesn't sound enough to me for anything but a lightly-loaded cabinet. A fully-connected one would need a lot more than that.

Bearing in mind (for those who don't know) that if the user modem is on then the number of bps passing is as per the connection speed independent of how much data that user is consuming at any given time.

Edit - final paragraph struck out as per Ignitionnet's points. I was thinking ADSLx not FTTC . 1Gbps still doesn't sound enough for a well-used cabinet.

Edited by RobertoS (Sun 29-Jun-14 20:30:59)

If you look at the specs for the ECI M41 MSAN it supports link speeds up to 2Gbit per card so I guess it is possible to have a link up to that speed.

And the DSLAM in the cabinet will not be passing on the handshakes etc, only the useful data from the PPPoE tunnel

NOTE: Multiple Gig fibre links is possible and as many FTTH advocates keep pointing out once you have a fibre link in place you can run what ever speed you like across it.

Taking the extreme figure, a 1Gb connection on a 288 user cabinet would provide on average 3.47Mbps per user. So 10Gbps would be necessary.

Edit - typo of 3.74.

Edited by RobertoS (Sun 29-Jun-14 19:43:32)

In reply to a post by RobertoS:

Bearing in mind (for those who don't know) that if the user modem is on then the number of bps passing is as per the connection speed independent of how much data that user is consuming at any given time.

Yes the cabinet is sending up to 80Mb of 0s to the end user if the line is entirely idle. Relevance to the backhaul question though Bob?

The relevance is probably related to the lines being in use.

In reply to a post by RobertoS:

Taking the extreme figure, a 1Gb connection on a 288 user cabinet would provide on average 3.47Mbps per user. So 10Gbps would be necessary.

Edit - typo of 3.74.

Taking the extreme. However with the average uptake and the use of 40Mb products by some I can easily imagine most cabinets being okay with a single backhaul or at most 2.

There are at least 5 hanging off here. Hmm. That 5 would've been ample to backhaul 320 premises via GPON. They could even have used the minimally 40mm ducting network specified for copper or CATV that's already in the ground serving each and every house.

You just reminded me of something actually Bob, thank you!

Isn't it sending empty packets, as does ADSLx?

Anyway, we are talking about the link from the cabinet to the exchange, not to the end user.

Thinks ....

How is the PPP session between the user and ISP get maintained if there is no traffic? The norm appears to be to keep FTTC routers switched on as well as the modem. Plus BT and Sky at least are now both supplying modem/routers.

In reply to a post by BatBoy:

The relevance is probably related to the lines being in use.

Pass, just seemed odd to remind everyone that each and every line passes its full sync rate regardless of what the user is doing in context of backhaul. If the lines only switched on when a customer pulled data and passed nothing otherwise the contention ratio on the backhaul is still the same.

If the cabinet and modem are exchanging data to maintain the connection, would that involve the E-side?

In reply to a post by RobertoS:

Isn't it sending empty packets, as does ADSLx?

Anyway, we are talking about the link from the cabinet to the exchange, not to the end user.

Thinks ....

How is the PPP session between the user and ISP get maintained if there is no traffic? The norm appears to be to keep FTTC routers switched on as well as the modem. Plus BT and Sky at least are now both supplying modem/routers.

Yeah this was exactly my confusion, the only things that go past the cabinet to the exchange and onwards are user data and overheads.

PPP is maintained via LCP mostly. LCP echo requests and echo responses. Just as link failures are detected at a lower level rather than by IP or TCP same bag here. LCP / Link Control Protocol handles such things via periodic echos and responses. Pings basically. 5 go without an answer the link is assumed to be down.

I'm sure there are others but that's the most intuitive one.

EDIT: I should mention these keepalives are to the LAC not the cabinet. The cabinet pretty rapidly sees when the CPE is offline - it stops receiving superframes and/or receives a dying gasp then nothing else.

Edited by deleted (Sun 29-Jun-14 20:00:13)

'Tis OK. You are right of course. It was my post stipulating the modem that was wrong. My brain goes dodgy when I'm hungry.

Assuming both the modem and router are up, (which I believe to be the norm), I am right in thinking that there is sync-speed traffic constantly between the cabinet and the user modem. What I gather is the case, and fairly obviously now I have brain in gear, is that if there is no user activity then there is little traffic between the cab and exchange/ISP. Merely enough to maintain the PPP link. (I have no idea how much usage that involves). Without the router up, possibly zilch.

Which is fine until we have the Olympics/Commonwealth Games/Andy Murray in the finals again/etc.

Leaving open the question of the capacity needed to support 288 connections of a typical mix of usage.

Edited by RobertoS (Sun 29-Jun-14 20:31:25)

See my reply to Ignitionnet .

A single GigE would be fine for 288 modems right now to be honest. ISPs provision a few hundred kbps per customer still.

I said it was a guarantee Openreach have but that is a simplification. There is no guarantee there at all beyond that an 80Mb line's first 30Mb runs at a higher priority than the rest. No CIR is given.

Ummm.

I see your point, but not entirely happy.

In reply to a post by simon194:

If you look at the specs for the ECI M41 MSAN it supports link speeds up to 2Gbit per card so I guess it is possible to have a link up to that speed.

The ECI uses a dedicated network interface card to backhaul subscribers. Be surprised if it could only manage 2 x 1Gb.

There is no 2Gb link speed - closest to that would be 2.4Gb GPON.

Edited by deleted (Sun 29-Jun-14 22:13:44)

Waiting for checks but have one new final 5% provider who may be using 25Mbps sat to feed a village WiFi network