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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 −
| Primitive | Explanation |
|---|---|
| Indication | Information given by an node of an event Example − The receiver just received a connection request. |
| Request | Service is requested by the node. Example − Requesting for a connection to a remote computer. |
| Response | Node is responding to an event. Example − the receiver sending the permission to connect. |
| Confirm | A 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)
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