Network Layer :

This layer is in charge to deliver the DATA of the system of origin to the system of destination. The administrator creates the diagrams of addressing of such kind that each computer present on the system is identified by a single address. Once the units placed in logical groups, part of the address indicates the network and another part indicates the individual unit in this network. As these addresses reside in the memory of the computer, one could object that the network layer is charged to transmit information of a processor has the other. This level the DATA are assembled out of packages with information of control contained in the heading. This information of control can include the address of the equivalent level on the distant system, the process of or the DATA was received and that for which it are intended. The package is then placed in the screen of connection and transmitted the unit has concerned.

With the condition of belonging has different networks, the units can have same the addresses host. The footbridge can examine the network part of the address and thus convey the packages without identifying the individual unit. This function is entrusted has a router. That Ci must know the functionality of the three sub-bases of the model, but the routing itself proceeds on the level of the network layer. Consequently each unit has two addresses: an address connection and an address network. So that each unit is clearly identified, of the specific protocols in the network layer are only used to connect the two sets.

The examples according to are protocols LAN standard present in this field:

• IPX (Internetwork Packet eXchange) of Novell.
• IP (Internet Protocol), very much used on the UNIX networks has one time and maintaining on the other networks.
• X25, X25, a protocol WAN established well functioning on this level.

This layer is not responsible to forward the DATA to a particular application, nor to guarantee its delivery in full safety.

Easy : This layer manages connections through the network and isolates the protocols FROM the roadbases of the subjacent details of the network. The protocol IP, which isolated the roadbases FROM the network and which manages the addresses as well as the DATA transmission is generally described as the layer network TCP/IP.