18.2.1 Structure

Chapter 3 describes the tiered structure adopted by CCS systems in telecommunications networks. The IP signalling systems are also defined within a layered structure, which is illustrated in Fig. 18.1.

Figure 18.1: IP Signalling Architecture

IP uses a four-tier structure, the tiers being called 'layers'. The Application Layer provides the interface to the users. It performs functions that are application-specific and provides data in a suitable format to be applied by the users.

A 'Host' is a node or computer that originates or terminates IP traffic. This is in contrast to nodes that forward IP traffic between hosts, which are known as Routers. A host, for example, allows users to communicate with other computers on a network. The IP Host-to-Host Layer provides a communication function between host computers. It is the role of this layer to facilitate the transfer of Application Layer data either by setting up end-to-end connections or by connectionless message transfer.

The Internet Layer is responsible for routing data across networks from one end-user to another.

The Link Layer hides the details of the network implementation from the higher layers by defining the physical and link-related characteristics of the network. The attributes of the physical wiring, data rates and methods of access are defined.

18.2.2 Relationship with the OSI Model

Readers familiar with the OSI Model explained in Chapter 3 will recognise strong similarities with the 4-Layer IP architecture. Further work is needed to ensure that a comprehensive alignment is achieved,...