Computer network - Service

 Service :-

Service

_______________________|___________________

|                                                                                 |

                   Connection Oriented                                                       Connectionless

                   _______|_________                            ___________________|__________

                   |                              |                         |                              |                        |

Reliable connection       Unreliable connection      Unreliable        Acknowledgement      Request-

oriented service                                                    data-gram            data-gram                   reply

      ______|__________

      |                               |

Message stream         Byte stream

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Difference between Connection oriented and Connectionless

          Connection-oriented                                                    Connectionless

1. It is similar to telephone system.                     1. This is modeled after the postal system.

2. Packets received are in same order as sent.    2. Messages arrive out of order.

3.Each service can be characterized by quality    3.Not all applications require reliable service

   of service-reliable or unreliable.                           and not all require connection oriented

                                                                              communication.

4.It has services:                                                 4.It has services: -

   i) Reliable message stream.                                  i) Unreliable data-gram

   ii) Reliable byte stream                                         ii)  Acknowledged data-gram

   iii) Unreliable connection.                                     iii) Request -reply

5. It has example:-                                               5.It has example

   i) Sequence of pages                                            i) Electronic junk mail.

   ii) Remote login.                                                   ii) Registered mail.

   iii) Digitized voice                                                 iii) Database query.

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Services primitive :-
1) Set of primitives (operations)
2)Available to user process to access service.
3)depend on service.


Service primitive for implementing a simple connection oriented service:
     Primitive                                                           Meaning
1) LISTEN                -      Block waiting for an incoming connection.
2) CONNECT          -      Establish a connection with a waiting peer
3) RECEIVE             -      Block waiting for an incoming message
4) SEND                   -      Send a message to the peer.
5) DISCONNECT    -      Terminate a connection.

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