Chapter 1

Network Operation

1.1. Basic concepts

The purpose of the network is to convey data between the terminal stations, or hosts. The network is comprised of nodes that are interconnected with one another by links. The network nodes perform two elemental functions:

– transmission: this function allows for the adaptation of the data to be transmitted on the transmission medium (copper pair, optical fiber, free space);

– connectivity: this function allows for the transfer of the data between an input and an output of the network node.

The network includes two entities:

– the local area network (LAN): this is a private network, deployed inside a company, and provides a connection between hosts (client stations, servers, telephone terminals);

– the wide area network (WAN): this is a public network, deployed by operators or service providers, and provides interconnection between LANs. The WAN is comprised of access networks, aggregation networks, and a core network.

1.1.1. Layered structure

The transmitted data are structured in layers (Figure 1.1). Each layer implements an encapsulation that corresponds to a PCI (protocol control information) header including fields whose interpretation is defined by a protocol. The Internet or Transmission Control Protocol (TCP)/Internet Protocol (IP) model is composed of three layers:

– the application layer (layer 7), which enables communication between distant software applications. The obtained data structure constitutes the message;

– the ...

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