Network Sales and Services Handbook (Cisco Press Networking Technology)
Large internetworks often are organized as hierarchies, providing advantages such as ease of management, flexibility, and a reduction in unnecessary traffic. It is for these reasons the ISO developed a hierarchical network model. Although this model is not as strictly adhered to in the internetworking community as the OSI Reference Model, the ISO Hierarchical model serves to define internetwork boundaries between users and user communities. Figure 1-6 illustrates this ISO Hierarchical Network model.
Figure 1-6. ISO Hierarchical Network
The ISO Hierarchical Network model defines some terminology conventions for addressing network entities. These terms are as follows:
End System (ES) Network device that does not perform any routing or traffic forwarding functions. Some examples of end system hardware are terminals, personal computers, and printers.
Intermediate System (IS) Network device that performs routing or other traffic-forwarding functions. Some examples of intermediate system hardware are routers, switches, and bridges. Two types of IS networks exist: intradomain IS and interdomain IS.
- Intradomain ISs communicate within a single autonomous system (AS)
- Interdomain ISs communicate within and between autonomous systems
Autonomous System (AS) Collection of networks under a common administration sharing a routing strategy. Autonomous systems are subdivided into areas, and an AS is sometimes called a domain.
NOTE
An area is a logical group of network segments and their attached devices; areas are subdivisions of autonomous systems. |