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The OSI Network Layer Service Primitives
The network layer service is defined by a Set of Primitives. These primitives tells the service to perform some action. - These primitives seem very like programming language procedures. Because the network layer must provides 2 types of service, namely connection-oriented and connectionless, there are two sets of primitives.
Primitives for the Connection-Oriented service
With this service the primitives can be divided into 4 groups, depending on their function:
- Making the connection - connection establishment
- Sending information (i.e. using the connection) - DATA, DATA-ACKNOWLEDGE, EXPEDITED-DATA.
- Closing the connection - DISCONNECT
- Resetting the connection - RESET.
You make a connection and close a connection by using the CONNECT and DISCONNECT calls. Data is sent using DATA, DATA-ACKNOWLEDGE, and EXPEDITED-DATA (for those special expedited data transmissions). If something goes wrong, then the connection can be reset, using the RESET call.
Primitives for the Connectionless service
These primitives are divided into two groups:
- Send a packet of data - UNITDATA
- Enquire into the performance of the network - FACILITY, REPORT.
Packets sent using UNITDATA. FACILITY can let you inquire to the network about things like average delivery statistics and the like. REPORT is used by the network to tell the host if there is a problem with the network, for example, if a machine has gone down.