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Lesson 4 The network layer
Objective Responsibilities of the Network Layer in the TCP/IP Protocol

Responsibilities of the Network Layer in the TCP/IP Protocol

Question : What are the responsibilities of the network layer in the TCP/IP protocol?
Under TCP/IP, the network layer is called the IP layer. The network layer is responsible for moving data between machines across the boundaries of physical networks. For example, the IP layer is responsible for moving data off the office ethernet, across the company network backbone , and out onto the Internet.
The key capability added by the network layer is routing. Routing is the process that directs information among a choice of paths based on the intended destination. In the case of TCP/IP, routing is based on IP addresses.
The network layer ensures that data intended for a machine with a specified IP address arrives at its destination.
The routing problem is extremely important, and is usually handled by computers specially designed to make routing decisions.
These special-purpose computers are called routers.


  1. Router: A device used to connect networks of different types, such as those using different architectures and protocols. Routers work at the Network layer of the OSI model. This means they can switch and route packets across multiple networks. They do this by exchanging protocol-specific information between separate networks. Routers determine the best path for sending data and filter broadcast traffic to the local segment.
  2. Backbone: The top level in a hierarchical network. Stub networks and transit networks which connect to the same backbone are guaranteed to be interconnected.