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do ISP's have their own ports at exchange?


do ISP's have their own ports at exchange?


I am trying to beome a adsl customer with plusnet. However, my order has been severely delayed, due to "no capacity at exchange". Plusnet, after some prodding, says that there is nothing they can do, and that I have to wait until someone else cancels his contract or moves away, or maybe wait until BT upgrade the exchange.

Now I wonder whether this "no capacity at exchange" means that there is no connection free at the exchange at all, or whether I could just switch ISP and get connected right away!

I read somewhere else on this forum something about IPStream vs DataStream, and from that I gather that I should be able to change ISP... is this correct?


Benjamin :
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

do ISP's have their own ports at exchange?

Every ADSL connection has to pass through a peice of equipement that takes the signal from your line and connects it to the Data highway. this is known as a dslam card.
I think that every card in the exchange has 4 circuits through it and the no capacity will mean that all the cards provided at your exchange are in use.

PlusNet use IPstream for the method of connecting but some providers use Datastream which is a slightly different system.
I dont know though if they both require the same type of card in the exchange.

do ISP's have their own ports at exchange?

They normaly do, however I beleive DataStream cards are seperate to the IPStream ones.

A little more on your problem though. BT have two main ADSL products. DataStream & IPStream as you know.

IPStream is the process of a BT doing most of the work for the ISP on the ISP and data carrying side, at a wholesale price.

DataStream is where a ISP rents the port, and has to carry the data themselves.

To make sure that BT can pln far enough ahead, both BT and the DataStream ISPs have to reserve blocks of cards at the exchange.

Where BT run out of cards, this means that all IPStream ISPs will be unable to order supply at that exchange.

However, if a DataStream supplier has leftover reserved cards, you can order from them (once reserved, neither BT or other DataStream ISPs can used the spare ports within the reservation). This will vary from DataStream ISP to DataStream ISP, if they can supply you with your service.

As such, there are three things that can happen here

1: You wait until a port becomes free.
Provided the order is in the queue at PlusNet, then it should just go through, but this may depend on a order backlog (normaly small).

2: You wait until BT upgrade the exchange with more capacity.
The same as above will happen regarding fulfilling the order.

However, this can taker longer, if BT have no space at all for the cards, and need to bring a new DSLAM online.

Method 1 & 2 will be on a whichever one takes place first basis

Option 3 is to move to a DataStream supplier.
Without any bias what so ever, I strongly advise against it. By all means move to another IPStream supplier, however, DataStream is known to causes all sorts of issues with regards to speeds, especialy on smaller exchanges.

do ISP's have their own ports at exchange?

Thank you for your quick reaction. If I understand you correctly, there is no point in changing ISP, as long as they use IPStream (other than misguided personal gratification for ``punishing'' plusnet for something they can't do anything about) .

Is there a list somewhere where I can see which ISP's offer DataStream products?

With respect to your comment concerning unreliablity (on small exchanges), do you have some more info on that?


do ISP's have their own ports at exchange?

Regarding DataStream unreliability.

Fort ISPs to make money, they must keep costs down. For DataStream suppliers, this means supplying service at the bare minimum of speed capacity, in order to fulfill the order and make a profit.

Example. If they provide a 512Kb 30:1 contended product, that means they supply 30 people (connections) with service, for every 512Kb of data transport from the exchange.

Say a exchange has a 1Mb backhaul, this means they can accomodate 60 customers/connections at 30:1.

It only takes 2 of those 60 customers to maximise the usage of that 1Mb transport. So imagine only 10 people wanting to do some downloading (even light downloads).

It creates an issue where the DataStream supplier needs to upgrade the 1Mb pipe, for reliability reasons. This costs them, both in terms of the upgrade and also for the cost of maintaining it.

In some cases, costs will mean it simply isn't worth the upgrade.

As such, it is possible to easily have reliability issues.