21CN Overview

More details about BT Wholesale 21CN

What is "21CN"?

21CN (21st Century Network) is a Next Generation Network (NGN) being deployed by British Telecom over the next 5 years. The core aim of the project is to bring the UK's telecoms network in to the digital age, whilst at the same time allowing BT to save up to £1billion per year in costs [0]. The total cost of the project is estimated at £10billion [1].

The following are some of the key changes that 21CN will bring:

  • The national PSTN phone network will be moved on to a digital IP network
  • The retirement of 16 existing legacy networks and the introduction of a single "multi-service" network [2]
  • The national roll-out of ADSL2+, offering services at up to 24Mbps. ADSL2+ Annex M will also be deployed, offering upstream rates of up to 2.5Mbps
  • A complete overhaul of the broadband services offered. A range of new configurable QoS (Quality of Service) products will be made available. DataStream products are being removed completely. See the broadband page for more.

In recent years BT has seen its traditional revenue sources (i.e. phone calls) decline considerably, and its "new wave" products (such as broadband) explode in popularity. Ultimately, 21CN should help BT to surf this new wave of demand and reduce their dependence on traditional revenue streams.

How 21CN will affect your existing phone and internet services

Put simply, 21CN will have no immediate effect on any end users. 21CN focuses on the core of BT's network - it makes no changes to your phone line, nor does it require you to change any equipment in your home (e.g. phone, ADSL modem/router, wireless equipment).

The services that are being migrated on to the 21CN network (such as the phone system, IPStream broadband connections, and ISDN connections) will experience a few minutes downtime on the night of the migration. Beyond that, service should be indistinguishable from present.

Services that are not being migrated on to the 21CN network (i.e. LLU, SDSL, DataStream broadband services) will be completely unaffected.

21CN and VoIP (Voice over IP)

People often refer to 21CN as BT simply moving everyone over to VoIP. Firstly, 21CN will achieve a lot more than this (see the bullet points at the top of this page). Secondly, the 21CN is not a VoIP network in the traditional sense of the term.

The term VoIP is commonly associated with Skype and other providers such as Tesco. Such VoIP solutions require you to either use your computer, have a VoIP phone, or have a VoIP adaptor which your regular phone connects to. A common complaint with existing VoIP services is that call quality can degrade if the broadband line is being used heavily at the same time.

21CN will not be afflicted by any such problems. You will not need a new phone or adaptor. You will not have to plug your phone into a router - it stays plugged in to the phone line. Whilst it is true that the 21CN PSTN migration will see phone calls run over an IP network (which is the definition of VoIP), there will be dedicated bandwidth for such calls to ensure that quality will not degrade.

It is important to note that although the phone calls will travel over an IP network, they will not use your broadband providers network - they will use a dedicated IP network for this task. Therefore the calls will not go out via the Internet - a big security concern for many people.

21CN roll-out summary

The trial stages of 21CN have been well publicised in the press. In case you've missed out on it all, a brief recap of the trials that are ongoing in South Wales is shown below.

WBC roll-out plan January 2008 [3]

  1. Wick was the first exchange to be migrated to the 21CN network. It appears that the Wick migration was staggered in to two stages - a first round o f 275 customers were changed over in April, followed by the remaining ones in May (our estimates have Wick at circa 500 phone lines).
  2. The Bedlinog exchange was next, followed shortly after by Nelson and Ynysybwl.
  3. Between July and September 2007 another 10 exchanges made the change. In total 75 exchanges in South Wales will have been involved in testing so far, covering some 350,000 phone lines.

Following the successful trials of the voice component of 21CN in South Wales, the original plan was to initiate a two-stage migration process for IPSteam users to 21CN. The first step was to move users to the 21CN variant of IPStream via a process they dubbed "Transfer Engineering".

However, problems with the testing of this migration has led BT to cancel the automatic migration of IPStream connections. This sudden change of plans surprised and angered some ISPs. BT's stance is that this means that ISPs can migrate users directly to WBC-based products in a single step. This certainly simplifies the process and reduces the chance of error.

The new WBC product is scheduled to launch at 84 exchanges at the beginning of May 2008. This will be followed by a further 667 "sprint" exchanges (dates unknown), with the rest of the exchange base to follow between now and 2012. At launch the WBC product will support ADSL2+ (up to 24Mbps), but the Annex M variant will not be available (this will be trialed and made available later in the year). The other WBC products - WBMC and WBCC - will be trialed following the successful launch of WBC and launch themselves later in 2008.

Please note that the information for this item was derived from [4] and [5]

High level 21CN network structure

21CN involves the construction of an entirely new hierarchical network. Note that the network runs over Ethernet, rather than ATM (as in the current Colossus network). We'll start from the bottom level (the 5600 exchanges) and work our way up to the core of the new BT network.

21CN sees BT do away with the traditional concentrators, switching equipment and DSLAMs that you'd find at BT exchanges. In their place MSANs (Multi Service Access Nodes) will be installed, which will terminate phone connections and DSL connections. Again, note that the physical copper pair between your home/business and the telephone exchange will remain unchanged, as will your internal wiring. 21CN changes nothing in that respect.

Beyond the exchange/MSAN level we find 106 Metro nodes, which are dotted around the country - typically in major cities or near POPs. It is at the Metro nodes where the IP packets are routed and switched. It is worth noting that the MSANs will be tiered; Tier 1 MSANs will connect directly to Metro nodes, whereas other MSANs will have to connect via a Tier 1 MSAN to a Metro node. There are about 1100 Tier 1 MSANs and 4400 Tier 2 and 3 MSANs. Tiering is not a new concept in BT's network - providers currently receive discounts on IPStream products purchased on 1016 Tier 1 exchanges.

Beyond the Metro node level we have 20 Core nodes. Core nodes handle very high speed (10Gbps) switching and routing of traffic between Metro nodes. These are further split down to 8 inner-core and 12 outer-core nodes, but for the purposes of explanation here I will always refer to there being 20 Core nodes. Each metro node will terminate at at least two Core nodes. It is also worth noting that Core nodes also have the functionality of Metro nodes, which is why you will sometimes see "106 Metro nodes" or "86 Metro nodes" quoted.

These 20 Core nodes are believed to be the same as the 20 WBC (Wholesale Broadband Connect) nodes. In order for a service provider (CP in BT's terminology) to have full WBC coverage they must install an aggregation point at each of the 20 WBC nodes. More information about WBC can be found on the 21CN Broadband page.

The 20 Core nodes reside in the locations show below [6]

Birmingham London North West

21CN Topology Diagram [7]

Bristol Manchester
Cardiff Milton Keynes
City of London Newcastle
Clyde Valley Peterborough
Derby Preston
Docklands Sheffield
Glasgow Slough
Guildford Southbank
Leeds Wolverhampton

A further three broadband interconnect nodes may be added following a request from numerous service providers. These addition sites would be Edinburgh, Nottingham and London South West.

21CN myths and legends

Since BT's announcement of 21CN three years ago, there has been a significant amount of conjecture about what it may and may not encompass. Whilst the rest of the 21CN articles on these pages attempt to describe what you can expect from 21CN, this one attempts to dispel some of the myths that surround 21CN.

  1. Broadband speeds

    One of the most common questions I receive about 21CN is this: "I have a really slow broadband connection. Will 21CN improve my speeds?". Technically 21CN alone will not. However, once the Wholesale Broadband Connect (WBC) product line becomes available at your exchange (April 2008 at the earliest, excluding trials), you can order ADSL2+. One of the inherent advantages of ADSL2+ is the speed boost attainable on longer/poorer phone lines (See [8]). Keep in mind that this is by no means a dramatic boost though.

  2. SDSL and DataStream

    As a part of the 21CN roll-out certain products are not being migrated on to the new platform. This includes ADSL DataStream products and SDSL (both IPStream and DataStream variants). But there's no reason to panic! DataStream connections will remain active until the very last exchange has been enabled for Wholesale Broadband Connect (which can be seen as the direct successor to DataStream). This story is less clear for SDSL because at present there appears to be no firm plans for a 21CN SDSL product. The Consult21 documentation strongly suggests that one is in the making though, so I would suspect that we would see this new product replace all existing SDSL connections at some point in the future.

  3. ISDN

    ISDN services will still be available after the 21CN roll-out. In fact, a national migration of ISDN services will commence from August 2008 following trials starting in March 2008.

  4. Incompatible products

    According to the WBC Operational Handbook Draft 1, the same products that are incompatible with ADSL will also be incompatible with Wholesale Broadband Connect [9]

  5. Broadband access without phone service (Naked DSL)

    According to a recent consultation on Naked DSL (BT calls this "BLA" - Broadband Line Access), which involves providing a phone line purely for broadband service, there was no demand from ISPs for such a product [10]. The consultation was closed on 16th July with the conclusion that "there is insufficient rationale to justify pursuing the BLA initiative at this time".

  6. 21CN and ATM

    ATM is largely being replaced by Ethernet in 21CN. That said, there will still be traces of it since PPPoA (PPP over ATM) will still be used for handling DSL connections between end user premises and the MSAN in the exchange.

21CN and FTTP

In November 2007 BT Wholesale consulted on its plans to launch a pilot of WBC over FTTP (Fibre to the Premises). This is being run off the back of a BT Opeanreach FTTP product BT Openreach FTTP product.

This pilot will take place during the latter half of 2008 in Ebbsfleet valley, the site of a large new housing development by Land Securities. Indeed, it is likely that only new developments will be served by the Openreach FTTP product at the moment. BT Wholesale have proposed that the Openreach GEA (Generic Ethernet Access) be included in the WBC product set as early as July 2008.

The product itself will feature 10Mbps downstream and 2Mbps upstream, but will be burstable to 30Mbps [12].

It is important to note that this product will not be succeptible to line length issues, as found on all existing DSL based products. So a 20Mbps really will deliver 20Mbps (providing the ISP has the necessary bandwidth and backhaul to support it).

Indicative pricing has been released by BT Openreach (note: Not BT Wholesale!). This places a 10Mbps/2Mbps line at £8.33 per month, and a 100Mbps line at £44 per month [13]