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When is a 2Mbps ADSL line not a 2Mbps line?
Friday 15 August 2003 17:59:00 by Andrew Ferguson

Bulldog Communications appear to have generated a ground swelling of dissatisfaction among its rapidly growing user-base of Datastream 2Mps users.

From the various speed tests that forum users are running it has become apparent that the maximum speed of a Primetime 2000 ADSL line is around 1.7Mbps. This is not the average but the peak speed that many people are seeing. From the few posts of people who have successfully contacted Bulldog and had the problem resolved it would appear that the Bulldog has actually only provisioned a 2Mbps ATM back-haul for the first user at each exchange.

At first glance, a 2Mbps back-haul for a 2Mbps ADSL line sounds fine, but actually there is more to it than that. There are overheads due to the use of the ATM protocol in the back-haul and transporting TCP/IP data across this. This overhead is normally of the order of 13%, which means a 2Mbps ATM pipe will only carry around 1.7Mbps (around 210-220 KiloBytes/second) of TCP/IP data. The relatively simple solution is to provision the basic back-haul at a size that will allow for the overhead, i.e. so for a single 2Mbps user, the back-haul should be 3Mbps. In a few cases it appears Bulldog have re-sized the back-haul connections and connections have improved.

The real question now is how long will Bulldog take to re-allocate all the virtual paths that form the back-haul on their Datastream enabled exchanges. There is also the pertinent question of what will Bulldog be doing when more users connect to the exchange? As the service is a contended one, they could be nasty and just connect 50 users to the single 2Mbps of back-haul, which means if any one user is downloading something the pipe is likely to be full. The more traditional way of doing the contention is to install a pipe large enough to cope with a couple of heavy users, and populate it at a ratio of 50:1. This means for 2-100 users a back-haul of 4 to 5Mbps would be used, this means that even if there is a single heavy user that there is still spare bandwidth for the other users who are just web browsing or doing other intermittent tasks. As a general rule the larger the pipe the less noticeable the effects of contention will be, even if it has the full number of users.

[Update 15/08/2003 22:20]: We have received a statement from Bulldog in relation to the previous news article. They would like to point out that the person whom ADSLguide tried to contact was on holiday and as such were not aware of this until the article appearing on the site. Bulldog's response with regard to these problems is set out below:

"We believe the concerns you raise deserve to be put into perspective. The issue is not new, nor do we believe it is highly significant.

Bulldog delivers performance and service that exceed customer expectations and market standards, delivering superior value for money. ADSLGuide's own service provider comparator metrics show that Bulldog has consistently been among the highest rated SPs for service, speed and customer satisfaction for each of the last six months. You rightfully comment that some of our users are failing to get a full 2Mbps, with some receiving 13% below the peak. With this performance, we compare very favourably with the best service providers on the 512kbps speed test results hosted on your own website. The best performer of any SP in July scored 11% below its peak rate of 512kbps with the 10th best SP 16% below the user's expected peak [Eclipse scored 457kbps on the 512kbps speed test, with Demon at 433kbps].

Readers should realise Bulldog also has the broadest portfolio of DSL services in the UK, offering them via three platforms: Local Loop Unbundling (LLU), IPStream and DataStream. All users of our LLU and IPStream services are provisioned to be capable of receiving a 'full' 2Mbps service (with some receiving even higher). Our initial user-base for DataStream services has been provisioned with leased line-like performance with sustainable high data throughput for a fraction of the price of the service they receive. Some may not hit their peaks during the first initial weeks of operation, but they will receive superior throughput - likely far superior to our LLU or IPStream customers receiving a higher peak bandwidth. Indeed, the value of service received by early DataStream users exceeds that of our competitors' business grade services.

Bulldog has and will continue to invest heavily in upgrading and upsizing network infrastructure. This is normal for a rapidly growing service provider.

1. In July we upgraded our Broadband Access Server to significantly increase capacity to support our rapid growth in subscribers

2. This month we have already added DataStream capacity via new In Span Handover connections to BT's core ATM network. Further capacity is coming online in the next few weeks, giving us the ability to enlarge our service footprint and/or upgrade VPs.

3. Next month we will experience a huge increase in capacity in our own infrastructure with new Gigabit Ethernet links coming on line Bulldog intends to remain a disruptive force in the UK broadband industry, giving customers what they have been wanting for years: the performance and service they deserve."

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