Computer Networks, Fifth Edition By Andrew S. Tanenbaum
• Network software: • 1 Protocol Hierarchies • To reduce their design complexity, most networks are organized as a stack of layers or levels, each one built upon the one below it. • The number of layers, the name of each layer, the contents of each layer, and the function of each layer differ from network to network. • The purpose of each layer is to offer certain services to the higher layers,
• Layer n on one machine carries on a conversation with layer n on another machine. • The rules and conventions used in this conversation are collectively known as the layer n protocol. • Basically, a protocol is an agreement between the communicating parties on how communication is to proceed. • A five-layer network is illustrated in Fig. 1-13. The entities comprising the corresponding layers on different machines are called peers.