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Originally Posted by Chrysalis
erol well the datastream packages do state contention levels, I believe bulldog is 40:1, but the problem is datastream is going down a small virtual pipe and not shared between isp's like ipstream so eg. Bulldog might have 2 2mbit customers on a exchange so they get a 2 mbit virtual pipe (they wouldnt get a 4mbit virtual pipe they already losing money on the 2mbit pipe), now if both of these users use the connection the contention is going to be very noticeable speeds will be halved but the contention is only 2:1, on ipstream users on the same exchange but different isp's are bundled together on a virtual pipe that bt maintains, this normally means a bigger pipe, usually a 10mbit pipe in this case it would take 21 512kbit users downloading to start contention of and then it would be less noticeable then the above case it would need 40 for half speed, in short ipstream means contention is much less noticeable and in most cases you wont suffer from it, but datastream is littered with contention problems, isp's such as bulldog,tiscali, and netcentral use datastream and hence the low prices, Pipex,nildram and plusnet use the ipstream so are better quality isp's but of course cost a bit more.
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I understand what you are saying and generally you are right that the more people that are contended on a larger pipe (at same contention ratio) the less such contention tneds to affect users. You are also right that with IP Stream all ISPs with users on that exchange are contended by BT onto a 'big pipe'. However it does not necesarily mean that a datastream or LLU will naturaly have greater contention or the same contention as IP stream on a smaller pipe. If you take easynet for example, they (generally) have their own physical network built out to exchanges they have DSLAMS in. As it costs them pretty much the same to put a small pipe into an exchange as a massive one, the chances are they have ample capacity, both in terms of actual contention and in terms of the size of the pipe for a given contention.
You are right that bulldogs quoted contention of 40:1 may have more impact on a users as an IP stream product at 50:1 contention (because of the effect of size of pipe and also because in general BT does not actually run anywhere near its maximums. As ever the subject of 'contention' is a complicated one (even contentious you could say). Personally I would not discount an ISP just because they use Datastream (or LLU) rather than IP Stream. A good ISP using Datastream will ensure that they have sufficent capacity from an exchange to their pop. It' s true however that for an ISP that wants to load users beyond the BT 50:1 contetion in the IP stream products would look at datastream as a means of achieveing this, as well as the general idea that their connection from echange to themselves will tend to be less users on a smaller pipe than IP stream services on that exchange.