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21CN: the 21st century nightmare?

Posted on 16 Jun 2008 at 16:56

Assured Rate This is a guaranteed bandwidth of 2Mb/sec that can be activated "on request" for specific, short periods of time. Aimed at businesses that want to guarantee bandwidth for specific applications during busy periods or consumers wanting to use video on-demand services. BT offers Assured Rate to its BT Vision customers to ensure they can achieve decent video streaming.

Best Effort Or, perhaps more accurately, "the leftovers". This is the best possible speed remaining after the two premium services. However, even this will be divided into two packages: Elevated Best Effort and Standard Best Effort. "For every three [data] packets of Elevated that get through, you get two packets of Standard," explained Entanet's Blessing. "You'll pay 50% more and get a 50% better service."

Real Time and Assured Rate packages won't be available until later this year, but ISPs are excited at the prospect of offering these "enhanced" packages to business and consumers. "The advantage of buying Quality of Service is that it's constant," said Blessing. "Gamers, for example, want permanent performance enhancement."

The QoS options also give the ISPs - and consequently BT Wholesale - a chance to earn additional revenue, by providing enhanced bandwidth to customers when the "best effort" isn't good enough. But should customers have to pay more simply to receive adequate bandwidth for popular applications? Some argue that having spent billions on a new network, the least it should provide is sufficient bandwidth for today's intensive applications, let alone tomorrow's.

There's also doubt over how many of these "premium" sessions will be available to customers, with Ferguson speculating it could be as few as 20 or 30 on each exchange. "It's first come, first served," he said. "BT Wholesale hasn't said how big the capacity coming back is."

Dependable connections

Aside from speed boosts for the lucky minority who live close to their exchange, does 21CN offer any other genuine advantages for broadband customers? "What they will get is a line that's more stable," said Blessing, a view shared by BT Wholesale and the other experts we spoke to.

ADSL Max lines are bad at providing consistent data rates, with connection speeds fluctuating and routers often needing to resynch at lower speeds to maintain a connection. While that won't be eliminated on ADSL2+, the results from the trials suggest it will certainly be less of an issue. That's a big plus - not only for consumers and businesses, but for the ISPs themselves, who anticipate significantly reduced support costs.

ADSL2+ also introduces a technology called Seamless Rate Adaption, which "can change the connection speed without throwing the connection away," to quote Ferguson. And the wild fluctuations in speed when you're first connected to an ADSL line should also be greatly reduced, according to Blessing. "There will be shorter periods of line training - BT is aiming for less than five days," he said. "The training data will be carried across [from ADSL Max], so it should have a good guess at the likely speed of the line."

Also coming later down the line is a service called Annex M that will allow broadband customers to sacrifice some of their download speed for improved upload bandwidth.

Avoiding the rush

Will ISPs rush headlong into offering customers services based on 21CN, as they did with the introduction of ADSL Max? Initially, they'll be constricted by BT's limited rollout, with only 80 exchanges upgraded to 21CN - almost exclusively in the West Midlands - at the recent launch, with 540 expected by the end of the year. (You can find out when you're scheduled to be upgraded to 21CN using the Exchange search on www.samknows.com/broadband).