Connection Mode Routines

Each user must establish an identity with the transport provider. A transport address is associated with each transport endpoint. One user process can manage several transport endpoints. In connection mode service, one user requests a connection to another user by specifying the other's address. The structure of a transport address is defined by the transport provider. An address can be as simple as an unstructured character string (for example, file_server), or as complex as an encoded bit pattern that specifies all information needed to route data through a network. Each transport provider defines its own mechanism for identifying users. Addresses can be assigned to the endpoint of a transport by t_bind(3NSL).

In addition to t_open(3NSL) and t_bind(3NSL), several routines support local operations. Table 3-2 summarizes all local management routines of XTI/TLI.

Table 3-2 Routines of XTI/TLI for Operating on the Endpoint

Command	Description
t_alloc	Allocates XTI/TLI data structures
t_bind	Binds a transport address to a transport endpoint
t_close	Closes a transport endpoint
t_error	Prints an XTI/TLI error message
t_free	Frees structures allocated using t_alloc(3NSL)
t_getinfo	Returns a set of parameters associated with a particular transport provider
t_getprotaddr	Returns the local and/or remote address associated with endpoint (XTI only)
t_getstate	Returns the state of a transport endpoint
t_look	Returns the current event on a transport endpoint
t_open	Establishes a transport endpoint connected to a chosen transport provider
t_optmgmt	Negotiates protocol-specific options with the transport provider
t_sync	Synchronizes a transport endpoint with the transport provider
t_unbind	Unbinds a transport address from a transport endpoint

The connection phase lets two users create a connection, or virtual circuit, between them, as shown in Figure 3-3.

Figure 3-3 Transport Connection

For example, the connection phase occurs when a server advertises its service to a group of clients, then blocks on t_listen(3NSL) to wait for a request. A client tries to connect to the server at the advertised address by a call to t_connect(3NSL). The connection request causes t_listen(3NSL) to return to the server, which can call t_accept(3NSL) to complete the connection.

Table 3-3 summarizes all routines available for establishing a transport connection. Refer to man pages for the specifications on these routines.

Table 3-3 Routines for Establishing a Transport Connection

Command	Description
t_accept	Accepts a request for a transport connection
t_connect	Establishes a connection with the transport user at a specified destination
t_listen	Listens for connect request from another transport user
t_rcvconnect	Completes connection establishment if t_connect(3NSL) was called in asynchronous mode (see "Advanced Topics")

The data transfer phase lets users transfer data in both directions through the connection. t_snd(3NSL) sends and t_rcv(3NSL) receives data through the connection. It is assumed that all data sent by one user is guaranteed to be delivered to the other user in the order in which it was sent. Table 3-4 summarizes the connection mode data-transfer routines.

Table 3-4 Connection Mode Data Transfer Routines

Command	Description
t_rcv(3NSL)	Receives data that has arrived over a transport connection
t_snd(3NSL)	Sends data over an established transport connection

XTI/TLI has two types of connection release. The abortive release directs the transport provider to release the connection immediately. Any previously sent data that has not yet been transmitted to the other user can be discarded by the transport provider. t_snddis(3NSL) initiates the abortive disconnect. t_rcvdis(3NSL) receives the abortive disconnect. Transport providers usually support some form of abortive release procedure.

Some transport providers also support an orderly release that terminates communication without discarding data. t_sndrel(3NSL) and t_rcvrel(3NSL) perform this function. Table 3-5 summarizes the connection release routines. Refer to man pages for the specifications on these routines.

Table 3-5 Connection Release Routines

Command	Description
t_rcvdis(3NSL)	Returns a reason code for a disconnection and any remaining user data
t_rcvrel(3NSL)	Acknowledges receipt of an orderly release of a connection request
t_snddis(3NSL)	Aborts a connection or rejects a connect request
t_sndrel(3NSL)	Requests the orderly release of a connection