Friday, 16 December 2016

OFCOM Broadband USO

Arrrrg! This is a knee jerk reaction - I'll do a proper response to them shortly.

OFCOM published guidance to Government on technical specification for the Universal Service Obligation for broadband. Here (PDF).

In it they have three scenarios:-
  1. a standard broadband service, characterised only by a 10Mbit/s download speed; 
  2. a more highly specified standard broadband service, adding upload speed (1Mbit/s), latency (medium response time), maximum sharing between customers (a ‘contention ratio’ of 50:1), and a defined data cap based on current usage profiles (100GB per month); and 
  3. a superfast broadband service, with download speeds of 30Mbit/s, upload of 6Mbit/s, fast response times, a ‘committed information rate’ of 10Mbit/s (i.e. guaranteed 10Mbit/s at all times) and an unlimited usage cap.
Now, I am pleased there is mention of latency, but no mention of the latency being when idle (i.e. not when a queue on the customers own router adds latency), and no mention of packet loss when idle. They also don't define where latency is measured.

But again, they talk of "speed" and "contention" and even "committed" rates.


Speed (of what?, and to where?)

So, let's start with speed. In the industry and since the days of modems, this has always been the modem link speed (or radio link, etc). It is the raw speed of the link (and usually before overheads like ATM, but that is just a matter of percentage adjustments). It is the speed from the modem at the customer premises to or from the modem at the other end of a wire or radio link.

This speed is important as it was usually the key factor in the user experience - but times have changed. These days users may find that they have an 80Mb/s VDSL sync, but cannot download some film or game at more than a few Mb/s. This could be down to congestion from cabinet to exchange, from exchange to BRAS, from BRAS to ISP, from ISP to internet, within the internet backhaul, or at the serving end. Only some of these factors are within the ISPs control, and some are within the back-haul carriers control. Often you find you cannot fill your 80Mb/s because of other factors. So are OFCOM actually only talking of sync speed still?

They do mention speed as between ISP access network and premises. But this is not a lot of help, as one could have the "ISP access network" in the exchange and/or contention within the ISP. If they are talking of Openreach here, it would be to the exchange only. They ignore congestion in the Internet back-haul or at the serving end of communications. They also talk of it varying depending on contention in the network when actually the issue is congestion. They also talk of it varying depending on home wiring - but that is not between the ISP and consumer premises - but within the premises and not ISPs job!

Committed speed?

This is special. The back-haul providers may offer committed speeds in parts of their network, and will charge a lot for it. In practice it is simply not needed as both BT and TT back-haul are generally not congested. But you, once again, have to ask where this 10Mb/s is committed too?

On the modem to modem link, if the sync is over 10Mb/s then you have a committed speed of that sync all the way to the other end of the wire where the other modem is, simple. Does that meet the requirements, or does this commitment have to go further?

What of to the ISP? Well, as an ISP we have lots of people on what we would call "super fast" links. But we do not buy 10Mb/s times the number of such lines. We buy capacity to avoid being the bottle neck (and we are better than many ISPs in that respect). Where the average download of customers at peak time is around 0.5Mb/s then obviously the capacity we buy is of the order of 0.5Mb/s * number of lines and a bit of headroom. Buying 20 times that will not make anybody's downloads any faster, it just means we charge 20 times as much to cover extra costs (well, not quite, but a lot of the price is the back-haul bandwidth). It makes no financial sense for an ISP to dedicate 10Mb/s on a service where the usage is way less, even if a back-haul provider would offer that as a service. And the back-haul providers have the same model - to get a dedicated 10Mb/s would be stupidly expensive. I may price it up on BT in my reply to OFCOM. But it is silly - why have a service offering that needless costs 20 times what is needed to offer no extra performance and just the nice feeling of links at only 5% utilisation?!

But what then - this dedicated 10Mb/s gets to the ISP. Maybe the ISP even buys transit and peering links to accommodate that, what then. That adds again to the expense - meaning even a small ISP like us would need many 10Gb/s external links - around 20 times what we need for customer traffic.

Well, then there is the Internet. Let's say there is a web site on the Internet. Let's say that server has a 1Gb/s link to the Internet. Let's say we look at UK only, and there are what, 4 million people in UK that can get super fast broadband? If they all have 10Mb/s dedicated, that one web site needs a 40Tb/s link to the Internet to ensure all of the UK super fast users have a dedicated 10Mb/s to that one server...

But that is crazy, clearly. This is not a USO on web sites is it? Well if not, then what is the metric for? Where does that 10Mb/s have to go. End users are buying internet access, so anything short of 10Mb/s dedicated to their favourite website is not actually 10Mb/s dedicated, is it? Is 10Mb/s dedicated to their street cabinet acceptable? This is going to cause customer confusion.


Contention is no longer a sensible measure, and even when it was, it only make sense if you specific the two points where the contention is measured.

Specifying 50:1 makes no sense. For a start, it is massively different if you have 50:1 or 5000:100. If you have 10Mb/s and there are 49 others sharing a 10Mb/s link, then two people downloading at once get 5Mb/s each and see "slow" Internet. If there are 5000 people sharing a Gb/s link, then you need 100 other people downloading at 10Mb/s to slow your link 1%, so access seems much faster.

In practice, what matters is a capacity for each end user that reflects normal end user access rates at peak times, e.g. 500kb/s (as it seems now). That means you normally have uncontested links. That measure needs to change over time. You need links at least a number of times the size of the end user min size, so if 10Mb/s is min, then links that are 1Gb/s. Specifying contention is not the way to do it.

But also, where is that contention measured. Once again, modem to modem is 1:1 and not shared. Cabinet to exchange will have some contention, but if not congested the contention does not matter. Contention in backhaul and back to ISP is another factor.

Also, with line speeds going up so much - contention is more problematic. If a line is 80Mb/s at 50:1 then that means an average capacity per user of 1.6Mb/s per user, when in fact all you need us around 0.5Mb/s. But if users are 10Mb/s you only need 0.2Mb/s per user, which is poor these days in the netflix generation.

We still come back to this being an Internet service and so that web server with 1G/s link, and accessible by a billion people around the world, what is that contention ratio?

They also talk of contention "at a node" but do not say at what node, or why they have picked that node rather than any of the other points elsewhere between some Facebook server and the end users laptop. Again, user confusion.


It does look like they are talking just access network broadband and maybe back-haul here, but I do not think the document makes that at all clear. I assume they hope if good access networks exists then Internet access will simply follow and not be an issue. That may be true in some aspects, but ISP models depend on the pricing of the back-haul, and that is expensive, so some ISP models involve congestion at the ISP. That model is not helped by this USO at all.

I am not sure they are addressing user confusion on this at all - even someone paying (at lot) for 10Mb/s committed rate cannot expect to download 10Mb/s from their favourite web site, but they probably will expect that from the ISP somehow if that is what they are paying for.

Bear in mind, one of the providers here is Openreach, and they only operate from master socket to the exchange. So do they meet a USO if the speed to/from the exchange meets this spec? What of BTW/TT back-haul? To be fair, that is usually fine, but won't meet defined contention or committed speeds without stupidly big links from them to the ISP being mandated somehow.

It needs work!


  1. What are they counting as being a "Universal service"? e.g. in Scotland the SNP promised that broadband would be a universal service before the last election, and then after the election they "clarified" that "Universal" meant "reaching 98% of households".

  2. Let's not forget that all the adsl and adsl max infrastructure still in use doesn't reach any of those scenarios!