XTI and TLI

XTI is derived from TLI, which was first introduced with System V Release 3.0 of UNIX in 1986. Both XTI and TLI are Application Program Interfaces (APIs) that allow user processes to access transport providers in a (mostly) transport-independent fashion.

From the standpoint of syntax and semantics, the two libraries are nearly identical. The name of the header file used for TLI is tiuser.h. The syntax of the include preprocessor directive to use is

   #include <sys/tiuser.h>

The name of the library to be searched when compiling and linking a program that uses TLI is nsl (Network Services Library). The syntax of the cc command to use is

cc option file -lnsl

Applications written to use TLI can be ported relatively easily to XTI. You should note the points listed below when porting your application.

• The T_ERROR event is not defined in XTI.
  Consequently, t_look never returns this event as its result value.

• XTI defines the events T_GODATA
  
  and T_GOEXDATA to assist in managing flow control. TLI does not define these events, so a process written to use TLI must continue to try sending data until it is successful. When porting your application to XTI, you can redesign it to either call t_look or be event-driven.
  

• More of the XTI functions can return the
  TOUTSTATE error than in TLI.

• The flags O_RDONLY and O_WRONLY
  
  
  are not defined in XTI. You must change them to O_RDWR.