BT 21CN
The 21st Century Network (21CN) programme is the data and voice network transformation project, under way since 2004,
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). Capital expenditure was put at £10 billion over five years, this being 75% of BT's total capital spending plans in that period.
Architecture
The new network is based on an architectural model of five classes of network nodes. These are:
- Premises
- Access (MSAN)
- Metro
- Core
- iNode
Premises
Premises nodes includes residential, small-medium enterprise (SME) and enterprise. The presumption is that all these will have high speed connections to the network, delivered over copper (in the form of
Access node
21CN introduced the concept of the
Metro node
The backhaul network will terminate on the metro nodes. At this point the IP-based services will be implemented, and the metro nodes are the first location where IP traffic is routed. Call control (via a softswitch or an IMS CSCF) will be implemented here, although the softswitches and the IMS components won't be described as a part of the metro node – they are parts of the iNode. The metro nodes are also provider edge (PE) routers in MPLS terminology, encapsulating the IP traffic in MPLS tunnels for transmission over the core. The aim is to implement around 100 metro nodes.[2]
Core node
The core nodes are MPLS switches, with the MPLS traffic carried over optical (
iNode
iNodes are the logical nodes that provide the control for the services implemented using the other four types of node. BT has announced that it intends to create an IMS based iNode capability, although its initial PSTN replacement will not be an IMS implementation. The iNode will implement a set of standardized functions – common capabilities – that deliver layered services. Common capabilities include session management, authentication, profile, address book, presence and location. Combinations of these capability primitives will be used to deliver different service types and functionality.
The iNode is built upon the AXE telephone exchange TSS (Telephony Softswitch Server) and is currently[when?] using HP Alpha processors (APZ 212 50) as well as the IS-Blade in the APZ logic. After extensive field testing in the South Wales Pathfinder area, all current logical and intelligent network services now operate in conjunction with the existing PSTN and the MPLS network.
Differences
The most significant differences between the legacy 20th century network (20CN) and 21CN are:
- The use of VoIP landline telephone services served digitally, rather than the previous analogue PSTNsystem. This does not mean telephone services are provided over the Internet with 21CN. In reality this will make no difference to the end user.
- The availability of ADSL Maxwith a maximum download throughput of 8 Mbit/s whereas ADSL2+ allows a maximum theoretical download throughput of 24 Mbit/s.
- The retirement of legacy IPstreamdata services previously available with 20CN.
Evolution towards FTTC
This section is written like a personal reflection, personal essay, or argumentative essay that states a Wikipedia editor's personal feelings or presents an original argument about a topic. (December 2020) |
Any chain is only as strong as its weakest link, and in the case of 21CN, its weakest link – the access network – is also its most valuable. Although the architecture of 21CN simplifies the network plant, it does not look to solve the problem which will have the greatest effect on data rate, that is loop length i.e. the length of cable from the exchange to the customer. Unlike the active core network, the access network is a passive network and has no capability for self-discovery. Reasonable consumer expectations can be established based upon the length and characteristics of these wires. A more global model would require precise knowledge of wire material (e.g. copper or aluminium), where the wires are routed, and the direction in which traffic flows around the circuit. This information is not held at present, and would need significant effort to obtain.
By moving the
The original 21CN design did not look to drive MSANs deeper into the network; instead it locates them in each exchange. 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. This makes planning of future upgrades or fibre additions difficult. 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.
However, in July 2007, Sir Christopher Bland, chairman of BT, stated that BT was considering fibre to the kerb and that
launched a consultation into Next Generation Access Networks in the UK after pressure from the government.Subsequently, Openreach began a rollout of
Suppliers
In April 2005, BT announced that it had selected eight suppliers for its 21CN roll-out. These were:
- Fujitsu – MSAN
- Huawei – MSAN and core optical
- Alcatel – metro
- Lucent – core MPLS, using Juniper components
- Cisco– metro and core MPLS
- Siemens– metro, using Juniper components
- Ciena– core optical
- Ericsson – iNode
Alcatel and Lucent merged in December 2006 to form Alcatel-Lucent.
The fact that Britain's
Criticism
This article possibly contains
fibre to the home would be more appropriate, which would mean replacing the current copper wire which supplies individual homes (the "last mile").
In late 2009, British ISP Andrews & Arnold reported severe issues with 21CN, citing multi-hour outages due to single points of failure and said that 21CN was not "fit for purpose" due to this and numerous other problems.[8] 21CN's core technology of using VoIP has resulted in many problems with machine to machine communications - faxes, telemetry, alarm systems etc. 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. These problems are very difficult to fault find as any individual section of the call functions perfectly well; the effect only becomes apparent when all sections are joined together to make the end-to-end call. T38 fax promises to eliminate the fax issues (the fax is essentially sent as a JPEG with error correction), however the other realtime m2m comms has no solution other than to move to IP-based devices at each end, a mammoth and costly undertaking for the users. 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. See also
References
External links
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