BT originally stated that it would accrue annual savings of £1 billion when the transition to the new network was completed, and hoped to have over 50% of its customers transferred by 2008 (see External links below for current progress on the roll-out of optical fibre by Openreach).
The sole exception to this presumption is for legacy PSTN, where provision will continue to be made for analogue voice.
Common capabilities include session management, authentication, profile, address book, presence and location.
By moving the MSANs deeper into the network, i.e. to street side cabinets, length issues are more likely to be reduced; however, line transmission characteristics are still highly variable since lines may be bridged with materials other than copper (such as aluminium) which have a degrading effect on conductivity and hence signal strength.
Without detailed information on the critical local routings, it is difficult to ascertain what capacity remains in the duct network and which connections run through it.
Openreach considered integrating MSANs into the access network, although this was originally deemed unlikely to happen because there are only 5,600 exchange buildings and over 85,000 'primary connection points', usually in the form of street cabinets.
Subsequently, Openreach began a rollout of VDSL2 FTTC technology over 21CN, deploying DSLAMs in thousands of new street-side cabinets.
[5] The FTTC deployment essentially installs a small (96-288 line) DSLAM into thousands of street cabinets, each backhauled using direct fibre to a larger exchange or metro node, removing much of the local-loop length limitations and allowing end-user speeds exceeding 100 Mbit/s following future upgrades.
The fact that Britain's Marconi received no major 21CN contract was a surprise to commentators and sent the company's shares tumbling.
This led to criticisms that BT was not future proofing their network, since fibre, while more expensive to lay, is a lot more future-proof.
These systems are much fussier than the human ear, and as such the conversion chain from analogue (between premises and local exchange) to 64 kbps digital, to VoIP and back again combined with IP routes of varying quality reduces the signal quality enough such that the devices at either end cannot communicate effectively.
As such, there is talk of a 'network of last resort' being retained using TDM technology (64 kbps digital all the way through) to provide service for m2m calls until such a point as devices are replaced.