BT 21CN
Encyclopedia
The 21st Century Network (21CN) programme is the network transformation project of the UK telecommunications company BT Group plc for data and voice. It had been intended to move BT's telephone network from the present AXE
/System X
Public Switched Telephone Network
(PSTN) to an Internet Protocol
(IP) system. As well as switching over the PSTN, BT planned to deliver many additional services over their new data network, such as on-demand interactive TV services.
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.) Capital expenditure was put at £10 billion over five years, this being 75% of BT's total capital spending plans in that period.
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.
). 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 a Media Gateway
(MGW). The aim is to implement a few hundred access nodes . Note that these will not have any IP
routing capability, but will essentially be Layer 2
Ethernet
devices.
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 .
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 using HP Alpha processors (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.
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."
services. BT's main plan for providing internet access is to upgrade their DSLAMs 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). This has led to criticisms that BT is not future proof
ing their network, since fibre, while more expensive to lay, is a lot more future proof. Critics argue that fibre to the home would be more appropriate, which would mean replacing the current copper wire which supplies individual homes (the "last mile").
– 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 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 in wire gauge
(thickness) are common and introduce signal 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 difficult. 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, which usually come in the form of street cabinets.
In July 2007, Sir Christopher Bland, the chairman of BT said that BT was considering fibre to the kerb and that VDSL2 was a 'likely development going forward' but that no final decisions had yet been taken.
In October 2007, Ofcom
launched a consultation into Next Generation Access Networks in the UK after pressure from the government. BT will be attending the meetings due to take place soon, although it is expected that they will not be the sole funder of upgrading the access network because they would have to give equal access to other service providers, so they will probably end up footing some of the bill.
In late 2009, British ISP Andrews & Arnold
is still reporting severe issues with 21CN, citing multi-hour outages due to single points of failure, and opining that 21CN is still not "fit for purpose" due to this and numerous other problems.
AXE telephone exchange
The AXE telephone exchange is a product line of circuit switched digital telephone exchanges manufactured by Ericsson, a Swedish telecom company. It was developed in 1974 by Ellemtel, a research and development subsidiary of Ericsson and Televerket.. The first system was deployed in 1976...
/System X
System X (telephony)
System X was the name of the UK's first national digital telephone exchange system.-Development:System X was developed by the UK Post Office , GEC, Plessey, and Standard Telephones and Cables and first shown in public in 1979 at the Telecom 79 exhibition in Geneva Switzerland...
Public Switched Telephone Network
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
(PSTN) to an Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) system. As well as switching over the PSTN, BT planned to deliver many additional services over their new data network, such as on-demand interactive TV services.
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.) Capital expenditure was put at £10 billion over 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 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 ADSL or other DSL technologies) or over fibre, as either PONPassive optical network
A passive optical network is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 16-128. A PON consists of an optical line terminal at the service provider's central...
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 (MSANMSAN
A Multi-service access Node also known as a Multi-service access gateway is a device typically installed in a telephone exchange which connects customers' telephone lines to the core network, to provide telephone, ISDN, and broadband such as DSL all from a single platform.Prior to the deployment...
). This logical node takes the various access technologies (mentioned above) and, where possible, aggregates these onto a single backhaul
Backhaul (telecommunications)
In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between the core network, or backbone, of the network and the small subnetworks at the "edge" of the entire hierarchical network...
network technology. This includes converting analogue voice into Voice over IP (VoIP) using the MSAN as a Media Gateway
Media gateway
A Media gateway is a translation device or service that converts digital media streams between disparate telecommunications networks such as PSTN, SS7, Next Generation Networks or PBX...
(MGW). The aim is to implement a few hundred access nodes . Note that these will not have any IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
routing capability, but will essentially be Layer 2
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
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 softswitchSoftswitch
A softswitch is a central device in a telecommunications network which connects telephone calls from one phone line to another, typically via the internet, entirely by means of software running on a general-purpose computer system...
or an IMS CSCF
IP Multimedia Subsystem
The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem is an architectural framework for delivering Internet Protocol multimedia services. It was originally designed by the wireless standards body 3rd Generation Partnership Project , as a part of the vision for evolving mobile...
) 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
Multiprotocol Label Switching
Multiprotocol Label Switching is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links between...
terminology, encapsulating the IP traffic in MPLS tunnels for transmission over the core. The aim is to implement around 100 metro nodes .
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.iNode
iNodes are the logical nodes that provide the control for the services implemented using the other 4 nodes. BT has announced that it intends to create an IMSIP Multimedia Subsystem
The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem is an architectural framework for delivering Internet Protocol multimedia services. It was originally designed by the wireless standards body 3rd Generation Partnership Project , as a part of the vision for evolving mobile...
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
AXE telephone exchange
The AXE telephone exchange is a product line of circuit switched digital telephone exchanges manufactured by Ericsson, a Swedish telecom company. It was developed in 1974 by Ellemtel, a research and development subsidiary of Ericsson and Televerket.. The first system was deployed in 1976...
TSS (Telephony Softswitch Server) and is currently using HP Alpha processors (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.
Suppliers
In April 2005, BT announced that it had selected 8 suppliers for its 21CN roll out. These were:- FujitsuFujitsuis a Japanese multinational information technology equipment and services company headquartered in Tokyo, Japan. It is the world's third-largest IT services provider measured by revenues....
(MSAN) - HuaweiHuaweiHuawei is a Chinese multinational networking and telecommunications equipment and services company headquartered in Shenzhen, Guangdong, China...
(MSAN and core optical) - AlcatelAlcatelAlcatel Mobile Phones is a brand of mobile handsets. It was established in 2004 as a joint venture between Alcatel-Lucent of France and TCL Communication of China....
(Metro) - CiscoCisco SystemsCisco Systems, Inc. is an American multinational corporation headquartered in San Jose, California, United States, that designs and sells consumer electronics, networking, voice, and communications technology and services. Cisco has more than 70,000 employees and annual revenue of US$...
(metro and core MPLS) - SiemensSiemens AGSiemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....
(metro, using Juniper components) - Lucent (core MPLS, using Juniper components)
- CienaCiena CorporationCiena Corporation is a United States-based global supplier of telecommunications networking equipment, software and services that support the delivery and transport of voice, video and data services. Its products are used in telecommunications networks operated by telecommunications service...
(core optical) - EricssonEricssonEricsson , one of Sweden's largest companies, is a provider of telecommunication and data communication systems, and related services, covering a range of technologies, including especially mobile networks...
(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."
Criticism
The plan has come under some criticism, mainly due to BT's plans for broadband internet accessBroadband Internet access
Broadband Internet access, often shortened to just "broadband", is a high data rate, low-latency connection to the Internet— typically contrasted with dial-up access using a 56 kbit/s modem or satellite Internet with inherently high latency....
services. BT's main plan for providing internet access is to upgrade their DSLAMs to ADSL2+
ITU G.992.5
ITU G.992.5 is an ITU standard, also referred to as ADSL2+ or ADSL2Plus. Commercially it is notable for its maximum theoretical download speed of 24 Mbit/s.-Technical information:...
in the exchange. This has been controversial because ADSL2+
ITU G.992.5
ITU G.992.5 is an ITU standard, also referred to as ADSL2+ or ADSL2Plus. Commercially it is notable for its maximum theoretical download speed of 24 Mbit/s.-Technical information:...
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). This has led to criticisms that BT is not future proof
Future proof
The phrase future proofing describes the exclusive process of trying to anticipate future developments, so that action can be taken to minimize possible negative consequences, and to seize opportunities. For more on the process and practitioners, see Futures studies.-Data storage:Electronically...
ing their network, since fibre, while more expensive to lay, is a lot more future proof. Critics argue that fibre to the home would be more appropriate, which would mean replacing the current copper wire which supplies individual homes (the "last mile").
Potential issues
Any chain is only as strong as its weakest link, and in the case of 21CN, its weakest link – the access networkAccess network
An access network is that part of a telecommunications network which connects subscribers to their immediate service provider. It is contrasted with the core network, which connects local providers to each other...
– 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
Local loop
In telephony, the local loop is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider's network...
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 MSAN
MSAN
A Multi-service access Node also known as a Multi-service access gateway is a device typically installed in a telephone exchange which connects customers' telephone lines to the core network, to provide telephone, ISDN, and broadband such as DSL all from a single platform.Prior to the deployment...
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 in wire gauge
Wire gauge
Wire gauge is a measurement of how large a wire is, either in diameter or cross sectional area. This determines the amount of electric current a wire can safely carry, as well as its electrical resistance and weight per unit of length...
(thickness) are common and introduce signal reflection
Signal reflection
Signal reflection occurs when a signal is transmitted along a transmission medium, such as a copper cable or an optical fiber, some of the signal power may be reflected back to its origin rather than being carried all the way along the cable to the far end. This happens because imperfections in the...
due to changes in impedance
Characteristic impedance
The characteristic impedance or surge impedance of a uniform transmission line, usually written Z_0, is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections. The SI unit of characteristic impedance is the ohm...
.
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 difficult. 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, which usually come in the form of street cabinets.
In July 2007, Sir Christopher Bland, the chairman of BT said that BT was considering fibre to the kerb and that VDSL2 was a 'likely development going forward' but that no final decisions had yet been taken.
In October 2007, Ofcom
Ofcom
Ofcom is the government-approved regulatory authority for the broadcasting and telecommunications industries in the United Kingdom. Ofcom was initially established by the Office of Communications Act 2002. It received its full authority from the Communications Act 2003...
launched a consultation into Next Generation Access Networks in the UK after pressure from the government. BT will be attending the meetings due to take place soon, although it is expected that they will not be the sole funder of upgrading the access network because they would have to give equal access to other service providers, so they will probably end up footing some of the bill.
In late 2009, British ISP Andrews & Arnold
Andrews & Arnold
Andrews & Arnold Ltd is an Internet service provider based in Bracknell in the United Kingdom founded in 1997 and launched in 1998, primarily serving businesses and "technical" home users....
is still reporting severe issues with 21CN, citing multi-hour outages due to single points of failure, and opining that 21CN is still not "fit for purpose" due to this and numerous other problems.
External links
- BT 21 CN - BT's 21st Century Network website provides key information and plans for network
- BT GS 21CN pages - Insight and commentary on BT's 21CN from its Global Services division
- Zdnet News - Key information on the major technology companies supporting the network, including additional information on the network itself
- BBC News - BT transforms phone network
- BBC News - First call on 21CN Network
- The Register - BT signs contracts with 21CN suppliers