ultrix man page for intro

intro(3xti)															       intro(3xti)

Name
       intro - introduction to the X/Open Transport Interface (XTI)

Description
       The X/Open Transport Interface defines a transport service interface that is independent of any specific transport provider.  The interface
       is provided by way of a set of library functions for the C programming language.

Transport Providers
       The transport layer can comprise one or more transport providers at the same time. The transport provider identifier  parameter	passed	to
       the function determines the required transport provider.

Transport Endpoints
       A  transport  endpoint  specifies a communication path between a transport user and a specific transport provider, which is identified by a
       local file descriptor (fd).  When a user opens a transport provider identifier, a local file descriptor fd is returned that identifies  the
       transport endpoint.

Synchronizing Endpoints
       One  process can simultaneously open several fds. In synchronous mode, however the process must manage the different actions of the associ-
       ated transport connections sequentially. Conversely, several processes can share the same fd (by or operations) but they have  to  synchro-
       nize themselves so as not to issue a function that is unsuitable to the current state of the transport endpoint.

Modes Of Service
       The  transport service interface supports two modes of service: connection mode and connectionless mode. A single transport endpoint cannot
       support both modes of service simultaneously.

       The connection-mode transport service is circuit-oriented and enables data to be transferred over an established connection in a  reliable,
       sequential  manner. In contrast, the connectionless-mode transport service is message-oriented and supports data transfer in self-contained
       units with no logical relationship required among multiple units.

Error Handling
       Two levels of error are defined for the transport interface.  The first is the library error level. Each library function has one  or  more
       error  returns.	 A  return of -1 indicates a failure. An external integer, t_errno, which is defined in the header file <xti.h>, holds the
       specific error number when such a failure occurs. This value is set when errors occur but is not cleared on successful library calls, so it
       should be tested only after an error has been indicated. If implemented, a diagnostic function, t_error, prints out information on the cur-
       rent transport error. The state of the transport provider may change if a transport error occurs.

       The second level of error is the operating system service routine level. A special library level error number has been defined called [TSY-
       SERR],  which  is  generated  by each library function when the operating system service routine fails or some general error occurs. When a
       function sets t_errno to [TSYSERR], the specific system error can be accessed through the external variable errno.

Key For Parameter Arrays
       Each XTI function description, includes an array that summarizes the content of the input and output parameter. The key is as follows:

       -------------------------------------------------------------
       Key   Description
       -------------------------------------------------------------
       x     The parameter value  is  meaningful  (input  parameter
	     must  be set before the call and output parameter must
	     be read after the call).
       (x)   The content of the object pointed by the x pointer  is
	     meaningful.
       ?     The  parameter  value is meaningful, but the parameter
	     is optional.
       (?)   The content of the object pointed by the ? pointer  is
	     optional.
       /     The parameter value is meaningless.
       =     After  the call, the parameter keeps the same value as
	     before the call.
       -------------------------------------------------------------

																       intro(3xti)