Service Primitives in Computer Network

Hello friends, today we are going to discuss the service primitives in computer networks. 

A service primitive is a set of operations that the user can invoke to access the service.

In the data transmission in the OSI model, when one layer requires help from its adjacent layer, i.e. the communication between the two layers is carried out through a set of operations called service primitives that are available to a user or other entity to access the service.  

These primitives tell the service to perform some action or report on an action taken by a peer entity. 

Operations:

• The initiating entity does CONNECT. Request: An entity wants to do some work Or a packet being sent.
• The receiver then gets a CONNECT. Indication: An entity is to be announcing that somewhere wants to set up a connection to it.
• The CONNECT. Response is primitive to tell whether it wants to accept or reject the proposed connection.
• The entity issuing the initial CONNECT. request finds out what happened via a CONNECT. Confirm primitive.

According to these actions service primitives have the following types.

Types of Service Primitives:

• Request: A service user wants some service from its adjacent layer to pass the parameters to specify the requested service.
• Indication: Another Service user or receiver user gets an indication that a procedure has been invoked by the adjacent service user.
• Response: A receiver service user acknowledge or complete some procedure i.e accept or reject the proposed connection.
• Confirm: service user gets acknowledge the permission to get connect or not.

Types of service Primitives 

 

Parameters of Service Primitives

Primitives can have parameters such as CONNECT, DATA, and DISCONNECT to establish a connection, send data, and Disconnect a connection through these four primitives.

Services can be either confirmed or unconfirmed. 
In a confirmed service called connection-oriented service, there is a request, an indication, a response, and a confirmation.

In an unconfirmed service called connectionless service, there is just a request and an indication. 
These parameters are as follows.

For Connection-Oriented Service

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

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

3. CONNECT.response: Accept / reject calls. 

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

5. DATA.request: Request that data be sent.

6. DATA.indication: Signal the arrival of data.

7. DISCONNECT.request: Request that a connect be released.

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

Example: Modern Telephone and Intenet Services

For Connection Less Service:

1. SENDING.data: Sender just sending data (traditional postal service).

2. REPORT.confirm: availability of reports the data reached at the destination (registered post) 

You might also like these posts:

1. The software protocol hierarchy

2. The TCP/IP reference model

3. Difference between connection-oriented and connectionless service

If you want more posts on communication networks please click here

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