Sunday, 24 October 2010

Planning for a five-year plan

Martha Lane Fox, the UK's digital champion, attended the industry day on 15th July at which Jeremy Hunt abandoned the 2 Mb/s target for 2013. She said it was essential that Britain achieved universal broadband coverage at 2Mbps as soon as possible. "I know fibre rollout is important, but I personally think we can do a lot by hitting the universal service commitment," she said.
In Scotland, our analysis shows that even to deliver 2 Mb/s will require the rollout of more fibre infrastructure. In fact, our analysis suggests that to deliver any significant improvement on the status quo, for communities outwith the major conurbations, will require a coordinated national strategy. To deliver 16 Mb/s internet access to Scotland’s population will require concerted and coordinated infrastructure planning, and sustained commitment.
Here we only presume to identify the key infrastructure that must be developed, and to outline the kind of planning that is required.
At a local level, the population densities at which most of Scotland’s population live are comparable with those in England. Indeed, for 90% of the population they are higher. We conclude from this that Scotland can exploit the same “last mile” technologies as the remainder of the UK. The un-forested scottish countryside may facilitate more use of wireless for backhaul and access distribution.

Backhaul is the issue

A prerequisite for local provision of an access network is the availability of a “backhaul” internet connection. Wireless and copper connections can only provide limited bandwidth. For our calculations, we use an optimistic figure of 512 Mb/s for the maximum backhaul that can be delivered by copper and wireless technologies. The total bandwidth required to serve a community is the product of the subscriber bandwidth and the number of subscribers, divided by the contention ratio. So a simple calculation allows us to quantify the subscriber bandwidth delivered by a given backhaul capacity.
Backhaul for current consumer connections is typically provisioned at a contention ratio of 50:1. As households include more connected devices, and as the use of streaming media and distributed interactive applications (such as cloud-based services, multi-player games, and video chat) increases, we believe that assuming 50:1 contention will be unrealistic. We use a figure of 25:1 to estimate the backhaul required to connect a community to the internet.
For these estimates we do not add a separate allowance for business connections. The main distinguishing feature of business connections is currently that they require more symmetric connections. This will affect the design of local access networks, but is not relevant to the issue of fibre backhaul provision. For our purposes, we assume that the population will make similar demands on backhaul whether working at work, working from home, or just using the internet for everyday life.
We assume an average household size of 2.5 people. A 512 Mb/s connection can support a 512 Mb/s service for 25 subscribers, or a 256 Mb/s service to 50 subscribers (population 125) at a 25:1 contention ratio. Working backwards from a required subscriber bandwidth, we can compute the maximum population that can be served by a wireless or copper backhaul connection. Larger populations require multiple connections; wherever these are aggregated, there must be access to fibre.

How much backhaul do we need?

Population served by a 512 Mb/s backhaul @ 25:1
speed (Mb/s)population
If we want to get beyond the 2 Mb/s barrier we have to bring a fibre point of presence to every 16,000 people, and to get to next-generation speeds beyond 16 Mb/s will require a fibre connection to every population of 2,000. To do less would be short-sighted.
The accompanying map (2.4 MB pdf) shows the minimum spanning tree of Scotland's census output areas coloured to show, in green roughly where there is documented existing fibre, in red the new rural fibre that would be needed to bring fibre to each community of 2,000, and in blue the distal parts of the network, the local access networks that will use a mixture of wireless, existing copper, and fibre to the home.


  1. Can someone confirm the backhaul calculations, looks like back of an envelope sums.

  2. Which aspect of the calculations are you querying? there is more detail in the final report
    If you have further questions I'm happy to try to answer them.