In reply to a post by yarwell:

the CIR on FTTC is 20M or sync rate, so there's a limit for a start.

I haven't a clue what that means, so I doubt if the OP has either .

Simple summary

The Openreach segment is designed to provide a certain minimum throughput (assuming you connect at a higher speed).

This helps to avoid the problems that Virgin Media has where one or two 100 Meg customers can dominate the bandwidth at a cabinet. Perhaps a news item I did recently did not express that in such clear terms.

you're only guaranteed 20M from the cab to the exchange, or the sync rate if lower. That's the CIR (Committed Information Rate). Hence 6 Gbit/s for a 288 user cab.

Goes up to 30M before too long.

So it's not "truly unlimited"

Thanks Andrew.

Thanks Phil.
(But Mbps?)

not M, G - 288 circuits at 20 Mbits/s each = 5660 Mbits/s ie 6 Gbits/s hence 6 * 1G fibre. TTC.

Perhaps a news item I did recently did not express that in such clear terms

Greater explanation would be good - there's contention in the local loop to the cabinet on cable, as well as on the backhaul from the cabinet, isn't there ?

The (single) coax just tee's off to consumers so they share the physical wire not sure how the frequencies are sliced up on DOCSIS

interesting the figures you posted do correct that misinformation as I thought it was uncontended, when in actual fact they meant just uncongested.

6gbit/sec for 288 users compared to what VM supply, is a clear indication why VM are struggling and have so much traffic management.

For VM its more like about 200mbit downstream and 40/60mbit upstream for 200-300 users.

Although I dont understand why xDSL providers need to rate limit upstream traffic as they have synchronous capacity?

In reply to a post by Chrysalis:

For VM its more like about 200mbit downstream and 40/60mbit upstream for 200-300 users.

Yes it's the low capacity local pipes that are cable's Achilles heel.

With FTTC you are 1:1 on what can be a 40Mbps pipe back to fibre where it seems the contention ratio is still very generous indeed. With cable a single 100Mbps user can take over half of the local upstream available to 200+ other unlucky punters. IMO the new VM traffic management policies won't adequately address the issue of constant seeders on VPNs chewing up far too big a share of the local upstream yet it has still attracted a lot of negative comment and threats to move on to the imagined land of milk and honey which many are expecting from Sky FTTC if and when it arrives.

the new STM they had a chance to address the very high upload limits but failed to do so, so I fully agree with you. Its clear VM's protocol management is ineffective, which leaves STM to do the job but as you say the limits are set too high to address the 24/7 seeders.

its so unbalanced that on VMs top tier the download usage limit is actually lower than the upload usage limit.

Edited by Chrysalis (Wed 04-Apr-12 12:00:28)