4.1 Introduction; access and core networks
Because of the ubiquity of wireless communications, such as WiFi and cellular mobile communications, it is tempting to think that it is only a matter of time before fixed-line communications, such as broadband and optical fibre, are superseded by forms of wireless communication. This is unlikely to occur because in many countries wireless communication depends on an infrastructure of fixed-line communications. In addition, it is likely that fixed-line communications will generally (but not in all cases) out-perform wireless communication because of the greater amount of frequency spectrum available in fixed-line communications.
The major fixed-line infrastructure in countries with a long history of telecommunications (such as the UK) is a ‘legacy’ public switched telecommunications network (PSTN) initially devised for telephony. The PSTN now carries much more than telephony. Parts of it have become essential infrastructure for carrying data as well as voice. In addition, there are newer networks such as those created for mobile telephone and data services. A useful structural division of these networks is as follows.
- A core network, which is largely a fixed, high-speed, intensively used communications network. It is somewhat analogous to a network of motorways and major trunk roads. Core networks often interconnect with other core networks. For example, all the mobile operators’ core networks interconnect with the PSTN core network.
- An access network, which links end-users’ equipment to the core network via a local exchange or local radio node. The access network is analogous to the minor roads that give access to motorways and other trunk routes.
- Consumer premises equipment (CPE) consists of the devices used by subscribers for consuming data (for example, fixed-line telephones, computers and fax machines). In the mobile world, user equipment (UE) is the term used for this part of the network.
This section is concerned with three widely used access networks:
- DSL broadband, which is currently the most widely used form of fixed-line broadband;
- fourth generation (4G) mobile broadband;
Other forms of access, which this section does not look at, include:
- third generation (3G) mobile broadband;
- ‘cable’, more properly known as Hybrid Fibre-Coaxial (HFC), which delivers television, broadband and telephony;
- optical fibre, which, in the form of ‘fibre to the premises’, can be used to give access to the core network (which itself is usually based on optical fibre).