Network Interface Guide

Connectionless Mode

Connectionless mode is message oriented. Data are transferred in self-contained units with no relationship between the units. This service requires only an established association between the peer users that determines the characteristics of the data. All information required to deliver a message (such as the destination address) is presented to the transport provider, with the data to be transmitted, in one service request. Each message is entirely self-contained. Use connectionless mode service for applications that:

Connectionless transports can be unreliable. They need not necessarily maintain message sequence, and messages are sometimes lost.

Connectionless Mode Routines

Connectionless-mode transport service has two phases: local management and data transfer. The local management phase defines the same local operations as for the connection mode service.

The data transfer phase lets a user transfer data units (usually called datagrams) to the specified peer user. Each data unit must be accompanied by the transport address of the destination user. t_sndudata(3NSL) sends and t_rcvvudata(3NSL) receives messages. Table 3-1 summarizes all routines for connectionless mode data transfer.

Table 3-1 Routines for Connectionless-Mode Data Transfer




Sends a message to another user of the transport 


Receives a message sent by another user of the transport 


Retrieves error information associated with a previously sent message