Network Layer

Introduction of OSI Network Layer

• The network layer is the 3rd layer of the OSI model from the bottom side(Physical Layer).
• This layer lies in between the Data link layer and the Transport layer.

Characteristics of OSI Network Layer

• The unit of data at the network layer is popularly called Data Packet/Packet.
• The device found at the Network layer is a Router.
• There are so many mechanisms have been proposed to solve the different types of network problems, mostly by the network layer as when a packet has to travel from one network(source) to another to reach its destination, many problems can arise such as the addressing mechanism is used by the second network may be different from the first one. The second network may not accept the packet due to variable length. The protocols may also differ, and so on. It is up to the network layer to overcome all these problems to allow heterogeneous networks to be interconnected.

Functions of OSI Network Layer

• Host to Host(Source to Destination/Machine to Machine) Data Delivery:
  • The network layer ensures that each data packet travels from its sources to its destination (located on different IP address networks) successfully and efficiently using a Logical/IP address.
• Routing:
  • The network layer establishes the dynamic route between the sending and receiving stations for each packet, to reflect the current network load. This is done by making a decision as to where to route the packet based on information and calculations from other routers, or according to static entries in the routing table, if any.
  • It provides network routing and determines flow & congestion functions across computer-network interfaces using various routing algorithms located on Routers.
• Logical/IP Addressing:
  • This layer provides different IP or logical addresses to different networks which helps in reaching data from source to destination.
• Fragmentation:
  • Breaking of large-size data packets, as compared to transmitting medium bandwidth,  into smaller-size data packets to flow data easily and efficiently is called fragmentation.
• Congestion:
  • This work is mainly performed by the Transport layer but is also performed by the network layer to some extent.