What are the Service Primitives in Computer Network?

A service is a set of primitives or we call it as operations where a user can invoke to access the service.

The selective primitives tell the service to perform an action taken by peer nodes.

  • The initiating node wants to establish a connection send CONNECT.

    • Request − A node wants to do some work or a packet is being sent.

  • The receiver accepts the request and CONNECT.

    • Indication − A node is saying that it wants to set up a connection to it.

  • The CONNECT. The node issuing the initial CONNECT. request finds out what happened via a CONNECT. Confirm primitive.

    Response is primitive to tell whether it wants to accept or reject the proposed connection.

Types of Service Primitives

Generally service primitives are divided into four classes −

  • Request − A service node wants some service from its adjacent layer to pass the parameters to mention the requested service.

  • Indication − Another Service node or receiver node gets an indication that a procedure has been invoked by the adjacent service node.

  • Response − A receiver service node acknowledges or completes some procedure.

  • Confirm − service nodes acknowledge the permission to get connected or not.

The different types of service primitives are explained below −

IndicationInformation given by an node of an event
Example − The receiver just received a connection request.
RequestService is requested by the node.
Example − Requesting for a connection to a remote computer.
ResponseNode is responding to an event.
Example − the receiver sending the permission to connect.
ConfirmA node acknowledges the response to its request.
Example − receiver acknowledge after receiving the data from sender

Parameters of Service Primitives

The parameters of primitives are: CONNECT, DATA, DISCONNECT which are used to establish a connection, to send data, and Disconnect a connection.

Generally services can be either confirmed or unconfirmed.

  • Confirmed service − the connection oriented services are called confirmed services.

  • Unconfirmed service − the connectionless services are called unconfirmed services.

Connection Oriented Service

The service primitives for the connection oriented services are as follows −

  • CONNECT. request: Request a connection to be established.

  • CONNECT. indication: Signal the called party (phone ringing).

  • CONNECT. response: Accept / reject calls.

  • CONNECT. confirm: Tell the caller whether the call was accepted.

  • DATA. request: Request that data be sent.

  • DATA. indication: Signal the arrival of data.

  • DISCONNECT. request: Request that a connection be released.

  • DISCONNECT. indication: Signal the peer about the request.

  • Example: Modern Telephone and Internet Services

Connection less Service

The service primitives for the connection less services are as follows −

  • SENDING. data − Sender just sending data (traditional postal service).

  • REPORT. confirm − availability of reports the data reached at destination (registered post)

Updated on: 17-Mar-2022

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