The broadband system in the UK is ADSL based or Asymmetric Digital Subscriber Line, this is an asynchronous system which means that the data rate allowed is not equal in both directions. Therefore most ADSL lines have a far higher inbound or download speed than outbound or upload speed. The basic broadband offering in the UK is a 512k (kilobits) download and a 256k upload speed, although many ISP's are now providing 2mbits (2000k) download however the upload remains fixed at 256k.

The ADSL system is based upon the UK telephone infrastructure which put simply is a twisted pair of cabled between you and your local telephone exchange. While the telephone exchange has undergone a complete refit replacing old analogue switching systems from much smaller and faster digital ones, no one has been back and replaced the bit of old cable that links your house to the exchange. Even new homes are regularly cabled with twisted pair and not fibre which would seem the obvious choice for improved last mile connectivity. if you live very close to the exchange you will find that your indicated speed may well be 2mbits however the further away from the exchange you go the more the speed drops off with users who are 3 miles away being unable to get the 2mbit service, this is why ISP's say "up to 2mbits".

The exchange is then connected to the internet backbone via large switches, these are still fairly old units and are due to be replaced by BT's 21st century network in the next few years. The 21CN installs IP routers instead of Telco infrastructure making the Telephone network look more like an IP network and your normal telephone service becomes VOIP (voice over internet protocol).

Most ISP's or Internet Service Providers buy the "last mile" connection from BT as BT own that cable but under regulation they have to offer that access at the same price as they pay for it within their own ISP service sold though the brand BT Yahoo. The company set-up to sell these services is called BT Wholesale and they also sell they key part of the Broadband service, the IP connection between the exchange and the internet backbone.

Not all ISP's take this service and some have chosen to use another result of government regulation LLU or Local Loop Unbundling. This gives access to ISP's to host their own IP router inside a BT exchange at a fair rate allowing them to connect this to your phone line and offer you services directly without having to buy them through BT wholesale. This is how some of the new phone providers started and lately how some provider have been offering 8mb broadband services.

There is a dirty secret within every Broadband service and it's one that is not often spoken about and just quietly hidden in the T&C's of ISP's. Contention is the phrase to look for, this means that your service is contended with other users. Contention means that ISP's will sell 10 people in your street a 512k ADSL service but may only provision 512k between the exchange and the backbone for all of you to share. The thinking is that you are not all online at once and even in peak hours (6pm - 10pm weekdays) we are not all downloading at the same time. The dirty secret is the ratios used, BT's own services from BT Yahoo use 50:1 meaning that your ISP has only allowed 10k of connectivity per subscriber between the exchange and the internet.

Then there is the Cap, most Broadband users were tempted away from dial up by the lack of restrictions and increased speeds. However the all you can eat Broadband is having to be slowly withdrawn as ISP's realise that many users are trying to use their connections all day long downloading many gigabytes of data perhaps using peer to peer (P2P) sharing services. So in comes a usage cap commonly somewhere between 30gb - 50gb per month after which you may be in breech of the fair use policy!

ISP's are moving to this cap model in droves and trying to mimic the mobile providers who have started with this kind of service model, however this seems flawed as to date mobile data has failed to grow as users see it as expensive. What the providers are having to fight is that they have set the expectation that the public pay for a 2mb connection and that is what we get, we can use it as much as we like and download as much as we like for free. What ISP's are faced with is a growing bill for the bandwidth between exchanges and the backbone that they have no way of charging for!

So what next for Broadband? ADSL2 and ADSL2+ are already a reality and a small group of users already have up to 24mbit ADSL2+ in parts of London. ADSL2+ is on the edge of what is possible via a twisted pair and a move to fibre has to happen at some point or else wireless service providers may be able to enter the home market with technologies like WiMAX.

What forces us to need this extra bandwidth? well apart from the growing use of the web one activity is breaking the very infrastructure the web was founded upon, Video. Watching streamed video is a double whammy for the ISP's as it is both a very large file transfer ( a broadcast quality feed is 2 - 3mbits) and also we tend to use it for much longer watching hours at a time, this is very different to picking up a couple of emails.

At last weeks Streaming Media Europe conference in London Richard Griffiths director of technology for the forthcoming BT Vision service explained that the internet backbone in the UK is just not designed to carry video. One user watching a 1.5mbit feed for a few hours during peak time would consume the entire contention ratio for another 50 subscribers.

BT Vision the Video On Demand product being launched by the Telco goliath will instead provision new connectivity to one of 10 staging (cache) servers around the UK just for video delivery supposedly ensuring that BT Vision users are able to maintain multiple 1.5mbit Video streams. But even this service is contended and although Mr Griffiths did not elude to what the ratios are it seems that even BT are not fully providing for media delivery over IP.

The answer lies in allowing one protocol to work across the backbone, that protocol is multicasting. At present all traffic is unicast a one on one relationship with the streaming server and the user, Multicast as its name suggested is like a broadcast to multiple users. Imagine BBC 1 being sent over the web, unicast would mean that every exchange may have many unicast streams of exactly the same content hitting the IP connection to the backbone. In a multicast scenario a single multicast protocol stream would be sent to the exchange where it is in effect broadcast to each user (the same stream) thus not duplicating bandwidth.

But for now BT says it will not enable its backbone routers to be multicast and therefore the BT wholesale product will continue to favour BT Yahoo / BT Vision when it comes to delivery of Video. Of course Griffiths was quick to point out that access to the underlying technology behind BT Vision would be made available through BT wholesale to keep Ofcom happy, but real service provision by other ISP's really needs multicasting in order to be viable.

The next few years of Broadband promise to be as turbulent and fast changing as the last, ADSL2+ will become the norm and yet ISP's will continue with insane contention ratios and caps despite us having a supposed 24mbit connection. The backbone will eventually have to be multicast enabled as it is in other European countries and perhaps then we can really enjoy video over IP and get the real value out of broadband. If you want to see this happen sooner rather than later then stream a little video between 6 and 10pm each weekday evening, that should put a little heat under BT and the other ISP's.

Published - 15/10/2006

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