A key to enabling BT to build the unified 21CN network is Internet Protocol (IP). It has the potential to act as an end-to-end transport protocol for all types of communication and applications - both now and in the future.
So what is IP and how does it work? In data networks when a large string of data - and this could be an e-mail, a web-page audio or video content including a voice call - is to be transmitted between terminations the string is divided into many standard packets at the origin and reassembled at the destination. Each packet contains the information to be carried and a 'header' that tells the network where it is going, the packet size and its position in the sequence of packets making up a complete string. This ensures each packet finds its way to its destination where they are reassembled in the right order. This is a bit like sending the chapters of a large book in separate parcels to be reassembled by the recipient. IP specifies the format of the packets or 'datagrams' and the routing and handling of these packets as they traverse the network
On the internet the IP packets which make up a string of data are sent freely onto the network, making their own way to their destination. Because packets take different routes and may arrive at slightly different times, and sometimes have to contend for network capacity with other data strings, quality can be an issue. Most internet data traffic can tolerate this impact on quality, for example it does not matter if part of an email or music download arrives a few milliseconds later than the rest but conversational speech, or video telephony packets need to arrive in 'real-time'.