In reply to a post by David_W:

If I remember correctly, the DOCSIS cable modem technology involves each modem being told when to transmit, which allows the system to optimise the upstream throughput.

Yes indeed. Periodically, usually ever 2ms, an upstream bandwidth allocation MAP is broadcast to all modems informing of when they can transmit. If a modem requires upstream bandwidth and has none in the map there is a space in the upstream MAP, a contention slot, where any modem can attempt to send a request for upstream bandwidth. A modem broadcasts a request in a contention slot, it is granted within the upstream MAP, and they then send the actual upstream burst in the dedicated time slot they are granted in the MAP.

That's the DOCSIS request-grant upstream cycle. If the upstream is congested a modem may have to wait multiple MAPs before it gets a chance to transmit, that's the cause of the DOCSIS jitter.

In reply to a post by David_W:

I'm not familiar with the precise configuration used by Virgin Media at present, but EuroDOCSIS 3.0 with 8 downstream channels and 4 upstream channels has a usable throughput of 400/108 Mbit/s across all the users of the channel group.

8 downstream, 2 upstream is standard, 400Mb down, 36Mb up. However there are moves towards 27Mb upstream channels, and up to 4 of them in a bonded group. There are also areas where even though modems are bonded to 2 upstreams there are 3 or 4 to choose from.

Moreover more than 8 downstreams can be added. A modem might only be able to acquire 8 channels at once but spreading all the modems across 12 channels will reduce load.

It is possible to balance modems across channels as they don't acquire all the channels at once, they acquire a primary channel which, via a MAC Domain Descriptor message, informs them of the information they need on the other downstream channels. By varying the information provided, say by offering 1-8, then 5-12 to modems as they come online they can be balanced across the downstreams with native DOCSIS 3 load balancing within the bonded groups taking care of the rest.

The same MDD message will also inform which upstream channels to bond, too.

In reply to a post by brandscill:

I only know of some (perhaps now most) 120mb customers having 12mb uploads.

120Mb has never had anything other than a 12Mb upstream. There are no plans to increase upstream with downstream in this wave, that will come later.

In reply to a post by Ignitionnet:

120Mb has never had anything other than a 12Mb upstream. There are no plans to increase upstream with downstream in this wave, that will come later.

The previous wave of doubling had plans and still has plans to increase the upload on all tiers so it's 10%

http://community.virginmedia.com/t5/Up-to-60Mb-Speed...

Indeed, though I did say 'with downstream'. It might go to 3Mb and 6Mb but won't go to 5Mb and 10Mb to preserve the 10:1 ratio until after all the downstream uplift has been done.

Same as with this lot really, downstream first then up.

Think slightly crossed wires, I was just bemoaning the fact they've failed to deliver on their last promise of upgrades in it's entirety and yet already they're moving on to the next marketing ploy.

It's not that I don't appreciate the increased download speeds but I'm not really maxing out the 60mbps, what I do frequently max out is the 3mbps upload. When open reach pull some fibre round here hopefully there will be some better choice.

We're still waiting for our 6MB upload that's supposed to go with our 60MB download.
We only get 3MB upload at the present.

Our local box is oversubscribed and the upgrade to that equipment won't happen till the end of December they say.
So our TV service can be sketchy at times and broadband download frequently slows to a crawl.

Sometime in 2014 is the best I can get out of Customer Service for the 6MB upload that we're supposed to be getting.

They want to be sorting out their regular service before they go boasting about doubling down speeds.

Edited by deleted (Tue 12-Nov-13 10:16:39)

http://www.thinkbroadband.com/images/news/5775-virgi...

Interesting scatter plot with upload speeds as a line

Most go and have another look and see if the 152 Mbps testing areas show up

Sorry I wasn't clear, was referring to the upcoming wave of upgrades, the last set of upstream upgrades are a work in progress still, the downstream having completed a while ago.