OSI Model – Network Layer (Layer 3)

Here, after Transport Layer has made multiple segments of the data stream, and labeled them, the segments are handed to the next layer, which is the Network Layer.

Network Layer, well the name suggests that this layer is concerned about the network.

The data segments that is handed to this layer is like “A Ship Without A Radar”, it doesn’t know where to go, it doesn’t have any address, network layers work is to give them their identification, i.e. to add Source IP Address and Destination IP Address to each of the segments, and now they are called Data Packets. Now our packets know its Source, from where it originated and also the Destination, where to go. And then the Data Packets are handed down to next layer. which is the Data Link Layer.

Routers work on Layer 3 Address, routers makes routing decision based on Layer 3 Logical Address.

This layer manages device addressing, tracks the location of the devices in the network, and determines the best way to move data between devices that aren’t locally attached.

Two types of packets are used at this layer:

1.       Data Packets

2.       Route Update Packets

Data Packets:

Data packets are used to transport user data through the internetwork. Protocols used to support data traffic are called Routed Protocols, e.g. IP, IPv6, AppleTalk, etc. Protocols that are getting routed are called Routed Protocols.

Route Update Packets:

These packets are used to update the routers about the neighbor routers that are connected within the internetwork. Protocols that send Route Update Packets are called Routing Protocols. E.g. RIP, RIPv2, IGRP, EIGRP and OSPF. Protocols that are routing, routed protocols are called Routing Protocols.

Route Update Packets helps to build and maintain routing tables in a Router.

 

User	Service
Application Layer	Web Browser, Email Clients
Presentation Layer	Formats data, compression, encryption, etc
Session Layer	Maintains dialog control, creating session and controlling session and ending session.
Transport Layer	End-to-end communication
Network Layer	Layer 3 logical addressing and routing

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