Network Layer

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The Network Layer is Layer 3 of the seven-layer OSI model of computer networking.

The Network Layer is responsible for routing packets delivery including routing through intermediate routers, whereas the Data Link Layer is responsible for Media Access Control, Flow Control and Error Checking.

The Network Layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination host via one or more networks while maintaining the quality of service functions.

Functions of the Network Layer include:

  • Host addressing
  • Message forwarding

Within the service layering semantics of the OSI network architecture the Network Layer responds to service requests from the Transport Layer and issues service requests to the Data Link Layer.

Contents

Protocols

Relation to TCP/IP model

The TCP/IP model describes the protocol suite of the Internet (RFC 1122). This model has a layer called the Internet Layer, located above the Link Layer. In many text books and other secondary references the Internet Layer is often equated with OSI's Network Layer. However, this is misleading as the allowed characteristics of protocols (e.g., whether they are connection-oriented or connection-less) placed into these layer are different in the two models. The Internet Layer of TCP/IP is in fact only a subset of functionality of the Network Layer. It only describes one type of network architecture, the Internet.

In general, direct or strict comparisons between these models should be avoided, since the layering in TCP/IP is not a principal design criterion and the Internet Engineering Task Force (IETF) considers it to be "harmful" (RFC 3439).

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