There are a number of key technological elements apparent in BT’s 21st Century Network (21CN). These include methods of transport as well as session management and authentication and are apparent, almost exclusively in the Metro Nodes.
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Internet Protocol (IP)
Perhaps the most integral component of the 21CN is its implementation of the Internet Protocol.
The 21CN digitises all traffic at the Access Nodes before forwarding the data to its desired destination; this turns the 21CN into a digital data network.
When working with any network, there arises a need to send data from one point to another. To achieve this on a computer network, the data is cut up into small chunks, called packets, which are then reassembled at the receiving end. Each packet has a ‘header’, a block of information which tells the system where it came from, where its going to, its size and what number in the sequence it should be put back. Internet Protocol is the mechanism used to control how this information is laid out in the packet and how to handle the packets as the move around the network.
By chopping large chunks of data into smaller packets with Internet Protocol, each part of the data can take a different route around the network and still be reassembled in the correct order, thus increasingly the efficiency of the network.
Unfortunately, because the packets may take a different route to one an other, time delays can occur. Most information will happily survive with this small delay, it doesn’t matter if part of an email or video arrives a couple of milliseconds after the rest. However, with speech or video conferencing this can become an issue and further technologies are required to help rectify this.
More information about IP at Wikipedia.
Internet Protocol Multi-media Subsystem (IMS)
Originally designed as part of the mobile communication industries framework, the Internet Protocol Multi-media Subsystem (IMS), is a method used to add a common session layer on top of the IP network layer to support many different applications – such as call control or multi-media streaming.
Standardised by the 3rd Generation Partners Project (3GPP) of the mobile communications industry, and recently improved for the use on wired networks by ETSI, the IMS supplies the 21CN with authentication, authorisation and accounting (AAA) and Quality of Service (QoS).
The advantages of employing IMS on a network are that you have the potential to run the system independent of platform, whether it be wired, mobile, WiFi or WiMax, this lends itself well to a society that is increasingly demanding on the move IT solutions. Another benefit of using IMS is that it supplies a common session layer, which means that a user profile only need to specified once yet accessed by any application on any device.
More information about IMS at Wikipedia.
Multi Protocol Label Switching (MPLS)
The 21st Century Network allows communications to be sent over a single high quality, secure network using Internet Protocol as the transport method. Multi Protocol Label Switching is a protocol that runs on top of IP and enables the efficient routing and switching of the IP traffic streaming through the network. With MPLS, each packet of data is assigned an extra marker, which allows it to be prioritised on the network.
Essentially, Multi Protocol Label Switching allows the prioritisation of the data on the network. For 21CN, this means that each service can be assigned its own section of the networks bandwidth between Metro Nodes. MPLS is a major factor in Next Generation Converged Networks, as it allows time critical services, such as voice calls and video conferencing precedence over less critical services such as email and instant messaging.
More information about MPLS at Wikipedia.
Synchronous Digital Hierarchy (SDH)
Synchronous Digital Hierarchy, or SDH, is another key transport protocol present in BT’s 21st Century Network. It allows the transmission of bit streams at a number of different rates across the network. Running between each of the nodes, at a typical rate of 2.5Gbit/s and 10Gbit/s (155Mbps and 622Mbps also common), are the pipes provided by SDH. Each of these pipes can be subdivided into smaller pipes of speeds 2, 34, 45, 150 and multiples of 150Mbps, which can then be switched using SDH to generate an end-to-end connection. Once set-up, the capacity of the smaller pipes will always be available, making it suitable for leasing and third party service providers.
More information about SDH at Wikipedia.
Session Initiation Protocol (SIP)
Session Initiation Protocol is known as a “signalling” standard. It is used to set-up sessions across an Internet Protocol based network – such as 21CN. SIP provides a framework for messages that can be sent between to points, preparing a session on the network before any media is sent between the two points, thus insuring that the data is being sent to the correct destination.
With the addition of the Internet Protocol Multi-media Subsystem (IMS), one end point is able to signify to another its desire to communicate, using IMS session controllers and the SIP applications, this means that the network can set-up sessions by itself. This intelligence lends itself to location based routing as discussed in our Introduction to the 21st Century Network.
More information about SIP at Wikipedia.
Virtual Local Area Network (VLAN)
A Local Area Network (LAN) in computing refers to a number of computer terminals, servers, printers and other devices all connected within a local area, such as an office complex, usually via ethernet cables. Remote terminals, far away, can be added to the network if required, resulting in a Wide Area Network (WAN).
Virtual Local Area Networks (VLAN) take this a step further by taken a common ethernet switched network and splitting the links to offering the ability to provide the capacity of several individual LANs.
For the 21CN, this means that services can share a common infrastructure whilst allowing the partitioning of the links in accordance with the needs of the service; voice, video, etc.
More information about VLAN at Wikipedia.
Wave Division Multiplexing (WDM)
WDM is a very efficient form of multiplexing – increasing the number of channels for communication. It applies to fibre optics and works by splitting the light in the fibre into a number of wavelength channels, in much the same way as a prism will separate light into red, green and blue. Each wavelength channel can then act as an independent communications conduit carrying the same amount of data as a fibre optic link that has no WDM applied to it.
Wave Division Multiplexing comes in two flavours:
Coarse Wave Division Multiplexing (CWDM) – Where the wavelengths are spaced well apart. This means substantial cost savings on optical transceiver hardware. However, fewer channels are available.
Dense Wave Division Multiplexing (DWDM) – DWDM allows for many more channels to be present, the downside is that the hardware used to send and receive data is much more expensive.
More information about WDM at Wikipedia.
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