- From: The Natural Philosopher <a@xxx>
- Date: Wed, 15 Oct 2008 13:16:48 +0100
Howard Neil wrote:
21cn seems to be more a plan than any particular technology.
Peter Crosland wrote:Thank you. Unfortunately, that is the site that I found slightly ambiguous as it talks of the 21CN network being end to end.Surely, that would also mean that the local loop would be able to carry ADSL?Thanks for that link. Yes, copper does still figure. However DSL is carried over copper today. While it would be nice to have end to end fibre, I am more concerned about my neighbours being able to get broadband.As I understand it, the primary difference in the local loop will be the use of IP all the way to the customer rather than IP over ATM for the final miles - as it is at the moment.
As helpful as that web site is, it still seems slightly ambiguous. For instance, there is the statement: "As an end-to-end Internet Protocol (IP)-based network, 21CN will consolidate BT’s 17 separate network platforms into one." To me, an end to end IP network is one that goes all the way to the customer; not one that stops at the switch. Have I misread this, please? Am I perhaps grasping at straws?
Voice would remain as baseband delivery over copper from the exchange to the customer, but all inter-exchange traffic would be IP - including voice. There are indeed many and varied internal legacy networks, but these are transparent to the end customer.
At least, that's what I think is intended .....
This might clarify things
Well it seems to me that for anyone except fibre to the premises thefinal stage will be exactly as it is at present i.e. over copper.
Yes but, in your opinion (and I do respect your opinion), will the 21CN signal standard be continued over those copper wires, in the same way that ADSL is carried over them?
In essence - and I am willing to be corrected - it is simply te inevitable flip from 'IP over voice' to 'voice over IP'
That is, the IP transport layer will dive deeper into the system, and whatever core technology is carrying the signals, will have IP as the layer above it.
It matters little what the actual technology and basic layer is: I wouldn't expect copper to be used for anything but Ethernet sub 100 meters, and DSL above it, though Ethernet can be used at higher speeds over slightly more distance than that.
I don't think 21CN per se will net better customer bandwidth: its more a stremlini9ng of BT'S core infrastructure to simplify it. Somewhat akin to the 50 years ago transition to system X and digital 64 k channels..
What it MIGHT do however, is enable BT to replace a lot of (quite valuable) copper with fibre in the street. In short a step that reduced the current 'local exchange' with about a 10km diameter reach and full of DSL and analogue to digital voice equipment, with a simple fibre switch, plus street cabinets doing analoague to iP fr voice (or indeed simply IP only concentration (with IP based phones with ADSL on the other end perhaps)
I.e. fiber essentially goes as far as the pole, or the street cabinet. Its only a step from there to take it to the house a well, but that is a heavy investment.
It looks like the first step would be to lay in IP equipment at the exchanges (currently its ATM frame relay and digital switch gear) and terminate ADSL and voice onto that, and do IP conversion actually in the exchange and push that out down the line to where it has to go. i.e a replacement of BT's BACKHAUL with whatever this new crap is.
Pushing IP in the raw out further will be another issue entirely, and even the above means that the terminating DSLAMS will need new customer kit, or have to terminate a now unneeded ATM circuit themselves.
The best I think one could hope for would be that the new Dslams might be simple enough and rugged enough to go into street boxes or underground ducts: That would solve - or at least improve - the bandwidth to utilise much shorter less interference prone copper runs. That can't be done right now, as to terminate the copper in street boxes would require full blown exchange gear there as well to cope with the analogue voice traffic..
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