ADSL in the UK

[Spanners]

(Apologies if teaching to sucking eggs, but I'll explain my research so far for thread validity)

I am trying to discover a complete description of the link between "a user's computer" and "the Internet" over copper ADSL in the UK. So far I've worked for BT for 2 months (in the wrong dept unfortunately) and suckered salesmen to the point ofpayment to start my own "BT-enabled" ISP. BT's ADSL kit has still evaded me.

Brief history for the Unbritish; BT have had a stronghold in the UK over telecoms for a very long time, and ADSL is no different. They carry a huge percentage of consumers straight to a data center in the UK for distribution to sub-ISPs who simply shuttle traffic, bill the consumer and pay BT rather large sums of money. There are still alternatives, don't panic.

But over BT's network, working from PC to anywhere-else I've got the following:

* Modem: USB or LAN mod/demod through analog multiplexer to copper pair, to master BT socket in the property connected to...
* PCP: Pairs from properties amalgamated into larger copper networks destined for the...
* Exchange: And this is where I draw a blank (explained below), magically transforming into...
* Data: Fiber'd to London Telehouse over BT's own network and...
* Switched: To BT's own ISP service, or to a third party ISP for...
* Authentication: With a dedicated Radius server against a local DB of ADSL customers and...
* Routed: To internationally-connected IXPs or internal (and cheaper) country networks

It's the exchange I can't figure out. A background in property-to-exchange has helped, and faking an ISP setup has told a lot too. Old analog cards I perfectly understand, but now I believe the techs "move your pair to another rack" and magically route it to Telehouse. Has anyone got any experience of this?

Research with Google is incredibly frustrating. I've discovered almost all ADSL suppliers are shit, and consumers are scrabbling with very little knowledge to discover answers when customer services (inevitably) fail them. They prattle on about modems and lines and "the port" at "the exchange", but any further and I hit a brick wall.

What exactly does "that rack" do? Inputs/Outputs? Manufacturers? Any snippets of factual information greatly appreciated.

Spanners


PS Drunken sub-question (un-researched); if ADSL was given the full bandwidth of a copper line, wouldn't it be a bit faster? Wouldn't this equate to a form of digital dial-up? Wouldn't this break the laws of physics?

Edit: Formatting

[skroo]

Sorry if I'm missing the question here, but you're asking how BT routes from the exchange to the Interweb, correct?

* Modem: USB or LAN mod/demod through analog multiplexer to
copper pair, to master BT socket in the property connected to...
* PCP: Pairs from properties amalgamated into larger copper networks destined for the...
* Exchange: And this is where I draw a blank (explained below), magically transforming into...

At this point, the subscriber line should drop to the DSLAM, which in turn sends that traffic out to:

* Data: Fiber'd to London Telehouse over BT's own network and...

Telehouse essentially acting as a massive switching node to get the traffic where it wants to go. I think you may have just answered your own question, but I'm not sure.

It's the exchange I can't figure out. A background in property-to-exchange has helped, and faking an ISP setup has told a lot too. Old analog cards I perfectly understand, but now I believe the techs "move your pair to another rack" and magically route it to Telehouse. Has anyone got any experience of this?

Oh, it sounds like what they're doing is moving the pair from the analogue frame to the DSLAM frame - basically, one function of the DSLAM is to split communication into voice and data, routing voice back to the analogue system and data out over fibre. This is normal.

What exactly does "that rack" do? Inputs/Outputs? Manufacturers? Any snippets of factual information greatly appreciated.

Pretty much what I described above - data and voice in and out. I haven't gone through any of these links, but this may help.

PS Drunken sub-question (un-researched); if ADSL was given the full bandwidth of a copper line, wouldn't it be a bit faster? Wouldn't this equate to a form of digital dial-up? Wouldn't this break the laws of physics?

Not really - bear in mind that ADSL basically modulates a digital signal over copper, and there's only so far you can go with that. Eventually you'll hit physical restrictions that keep you from attaining multi-megabit speeds (which is one reason why most xDSL services cap at 6Mbit - it's as much as the copper between the exchange and TNI can handle).

Edit: Formatting[/QUOTE]

[Spanners]

Thanks Skroo, DSLAM is the puppy I was after

[Twigman]

This is more for people that dont know rather than the original poster:
You can get up to 8mbps on ADSL at the moment in the UK (subject to line quality). I believe this is the limit of ADSL1.
When ADSL2+ is released that will increase to 24mbps. These are both download speeds though and the upload will be much less (typically less than 1mbps for ADSL1).

I heard once that BT used Cisco equipment in their exchanges. How true that is I don't know. Im pretty sure Marconi (used to) make equipment as well, but BT turned them down.

[Spanners]

You can get up to 8mbps on ADSL at the moment in the UK (subject to line quality). I believe this is the limit of ADSL1.

I found a good comparison of ADSL1/ADSL2/ADSL2+, but "The speeds indicated on this graph show the theoretical maximum speed on good copper lines having no bad joints, faulty insulation, or high speed interferers" such as rain, kittens, global warming and man's best friend.

When ADSL2+ is released that will increase to 24mbps.

According to that source, such speeds are only attainable within 1100m of the exchange. I'm sure this will improve over time. My current hobby is rewiring my friends line to support more than 1MB (see above "high speed interferers") as neither BT or his ISP will accept responsibility for a clear maintenance requirement.

I heard once that BT used Cisco equipment in their exchanges. How true that is I don't know.

In 2003 BT were using Fujitsu and Alcatel (tech specs for Fujitsu Hub 1000 and a range of fun looking Alcatel kit) and more recently Huawei with various bits of Cisco and Siemens kit along the line. This may have changed since, but a good guide is here.

Im pretty sure Marconi (used to) make equipment as well, but BT turned them down.

They did and still do from what I can tell (PDF, HTML) and their kit is used by C&W amongst others.
But yes, BT's rejection dropped Marconi's share price 44% on the morning of the announcement!

Edited for links