- BT 21CN
The 21st Century Network (21CN) programme is the network transformation project of the UK telecommunications company
BT Group plc . It will see the UK incumbent's telephone network move from the present AXE/System XPublic Switched Telephone Network (PSTN) to anInternet Protocol (IP) system. As well as switching over the PSTN, BT has revealed plans to deliver many additional services over their new network, such as on-demand interactive TV services.BT has stated that it will accrue annual savings of £1 billion when the transition to the new network is complete, with over 50% of its customers transferred by 2008. Capital expenditure is put at £10 billion over the next five years, this being 75% of BT's total capital spending plans in that period.
21CN architecture
The new network is based on an architectural model of 5 network nodes. These are:
* Premises
* Access (MSAN)
* Metro
* Core
* iNodePremises
The premises node 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
ADSL or otherDSL technologies) or over fibre, as either PON or direct fibre in the case of large enterprises. The sole exception to this presumption is for legacy PSTN, where provision will continue to be made for analogue voice.Access Node
21CN introduced the concept of the Multi-Service Access Node (
MSAN ). This logical node takes the various access technologies (mentioned above) and, where possible, aggregates these onto a single backhaul network technology. This includes converting analogue voice into Voice over IP (VoIP ) using the MSAN as aMedia Gateway (MGW). The aim is to implement a few hundred access nodesFact|date=June 2008. Note that these will not have any IP routing capability, but will essentially be Layer 2Ethernet devices.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 inMPLS terminology, encapsulating the IP traffic in MPLS tunnels for transmission over the core. The aim is to implement around 100 metro nodes Fact|date=June 2008.Core Node
The core nodes are MPLS switches, with the MPLS traffic carried over optical (
DWDM ) transport. They are completely unaware of customer IP traffic, and only switch based on MPLS tags (all customer IP traffic is encapsulated with an MPLS header by the Metro node PEs). Native IP is only used by the Core nodes for protocols such as MP-BGP, an IGP, LDP, and RSVP to exchange routing and label information between all Core and Metro nodes. The aim is to have approximately 10 core nodes Fact|date=June 2008.iNode
The iNode is the name for the logical node that provides the control for the services implemented using the other 4 nodes. 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 BYB501 AXE10 TSS (Telephony Softswitch Server) and is currently using the grade 50 HP based processor (APZ 212 50) as well as the IS-Blade in the APZ logic. After extensive field testing and countless iNode soft revisions 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.
uppliers
In April 2005, BT announced that it had selected 8 suppliers for its 21CN roll out. These were:
*Fujitsu (MSAN)
*Huawei (MSAN and core optical)
*Alcatel (Metro)
*Cisco (metro and core MPLS)
*Siemens (metro, using Juniper components)
*Lucent (core MPLS, using Juniper components)
*Ciena (core optical)
*Ericsson (iNode)The fact that Marconi received no major 21CN contract was a surprise to commentators and sent the company's shares tumbling. An example of analysis before BT announced the winners of contracts is
Dresdner Kleinwort Wasserstein 's: " [Marconi is] so advanced with its products and so entrenched with BT Group PLC that its selection looks certain." [cite news
last =Le Maistre
first =Ray
coauthors =
title =Analyst: Marconi in Line for 21CN
work =
pages =
language =
publisher =Light Reading
date =27 April 2005
url =http://www.lightreading.com/document.asp?doc_id=72867
accessdate =2006-11-28 ]Implementation
BT has announced that its initial roll-out of the network will take place in the South Wales area, around Cardiff, beginning in November 2006. This will initially involve the migration of 350,000 customers from the old PSTN to the new network. It has announced that it expects 50% of its customer base to have been migrated by 2008, and the migration to be "substantially complete" by the end of the decade.
BT will be transferring customers on its
IPstream product in the West Midlands area (circa 650 exchanges) to the 21CN equivalent IPstream product between October and December 2007 before transferring them over to ADSL2+ products in early 2008.In October 2006, the first call was made on a migrated test line between 21CN and today's networks.
On
28 November 2006 the first 100 voice customers in Wick were switched onto 21CN.cite news | title=BT's 21CN has 100 users | work=The Register | date =2006-11-28 | url=http://www.theregister.co.uk/2006/11/28/21cn_online/ | accessdate=2007-12-04]On
14 September 2007 BT announced thatEntanet ,BT Wholesale andBT Retail were chosen for the first service trial in the West Midlands [cite news | title=Entanet selected for first 21CN broadband trial | publisher=thinkbroadband | date=2007-09-14 | url=http://www.thinkbroadband.com/news/3195-.html | accessdate=2007-12-04]BT also plans to launch
ADSL2+ services from early 2008.Criticism
The plan has come under some criticism, mainly due to BT's plans for
broadband internet access services. BT's main plan for providing internet access is to upgrade theirdslam s to ADSL2 in the exchange. This has been controversial because ADSL2+ is already an old technology and is limited to 24Mbit/s downstream, and will be even more dated by the time 21CN is completed (Around 2011), leading to criticisms that BT is notfuture proof ing their network. Critics argue thatfibre to the home would be more appropriate, which would mean replacing the current copper wire which supplies individual homes (the "last mile").UK security agency CESG has privately voiced concerns over the decision to use
Huawei to provide some of the equipment, citing security concerns, as much UK government, intelligence and military traffic will run on 21CN infrastructure. [ [http://wilde-world.co.uk/?p=43 Wilde World] Huawei and snooping]Potential issues
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 does simplify 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 documentation to obtain.By moving the
MSAN s 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. In addition changes inwire gauge (thickness) are often common and introducesignal reflection due to changes in impedance.The current 21CN roll out does 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 very 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 extremely hard to achieve.
Openreach is looking at the possibility of integrating MSANs into the access network, although this will probably not happen because there are only 5600 exchange buildings and over 85 000 Primary Connection Points (the place of possible siting of the MSANs, which would push the costs up unnecessarily.
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