Network Interface Layer TCP/IP

Introduction

• This layer is the lowest layer in the TCP/IP model.

Features

• This layer contains the protocols that the computer uses to deliver data to the other computers and devices that are attached to the network via a cable or other media.

Functions

• The protocols of this layer perform three distinct functions : –
  • They define how to use the network to transmit a frame, which is the data unit passed across the physical connection.
  • They exchange data between the computer and the physical medium of network.
  • They deliver data between two devices on the same network using the physical address.

Protocols

• The network access layer includes a large number of  LAN ( such as Ethernet, Token Ring, Token bus etc.) and WAN standards (some populars are Point-to-Point Protocol (PPP) and Frame Relay) protocols. 
• Token Passing :
  • The LAN protocols mostly uses the concept of Token Passing for message transfer during its transmission i.e. the network continuously circulates a special bit pattern known as a Token among all the nodes in the network. A token is a special bit pattern or a small packet, usually several bits in length, which circulate from node to node.
  • Token passing scheme is an access protocol that permits a terminal to transmit only on receipt of a special circulating bit sequence.
  • Each token in a token passing scheme contains network information, comprising of a header, a data field and a trailer.
  • Any node willing to send a data frame has to grab a token first. After a node has captured a token it transmits its frame. The frame is relayed by all intermediate nodes till it reaches destination, when it is copied.
  • Token passing is an example of distributed control.
  • In token passing scheme, all stations are logically connected in the form of a ring and control of the access to the medium is performed using a token.
  • Token passing mechanism is of two types – Token Bus and Token Ring i.e. token passing can be used with both broadcast (using Token bus) and sequentially connected (using Token ring) type of networks with some variation.
• The list of some important Network Interface layer’s protocols are – Ethernet, Token Ring, Frame Relay, ATM etc.