Endpoint Initiation

Transport users must initialize XTI/TLI endpoints before transferring data. They must choose the appropriate connectionless service provider using t_open() and establish its identity using t_bind().

Use t_optmgmt() to negotiate protocol options. Like connection mode service, each transport provider specifies the options, if any, it supports. Option negotiation is a protocol-specific activity. In Example 3-1, the server waits for incoming queries, and processes and responds to each query. The example also shows the definitions and initiation sequence of the server.

Example 3-1 CLTS Server

#include <stdio.h>
#include <fcntl.h>
#include <xti.h>	/* TLI applications use <tiuser.h>  */
#define SRV_ADDR 2	/* server's well known address */

main()
{
   int fd;
   int flags;
   struct t_bind *bind;
   struct t_unitdata *ud;
   struct t_uderr *uderr;
   extern int t_errno;

	if ((fd = t_open("/dev/exmp", O_RDWR, (struct t_info *) NULL))
	        == -1) {
      t_error("unable to open /dev/exmp");
      exit(1);
   }
 	if ((bind = (struct t_bind *)t_alloc(fd, T_BIND, T_ADDR))
         == (struct t_bind *) NULL) {
      t_error("t_alloc of t_bind structure failed");
      exit(2);
   }
   bind->addr.len = sizeof(int);
   *(int *)bind->addr.buf = SRV_ADDR;
   bind->qlen = 0;
   if (t_bind(fd, bind, bind) == -1) {
      t_error("t_bind failed");
      exit(3);
   }
   /*
    * TLI interface applications need the following code which
    * is no longer needed for XTI interface applications.
    * -------------------------------------
    * Verify if the bound address correct?
    *
    * if (bind -> addr.len != sizeof(int) ||
    *      *(int *)bind->addr.buf != SRV_ADDR) {
    *	fprintf(stderr, "t_bind bound wrong address\n");
    *	exit(4);
    * }
    * ---------------------------------------
    */

The server establishes a transport endpoint with the desired transport provider using t_open(). Each provider has an associated service type, so the user can choose a particular service by opening the appropriate transport provider file. This connectionless mode server ignores the characteristics of the provider returned by t_open() by setting the third argument to NULL. The transaction server assumes the transport provider has the following characteristics:

• The transport address is an integer value that uniquely identifies each user.

• The transport provider supports the T_CLTS service type (connectionless transport service, or datagram).

• The transport provider does not require any protocol-specific options.

The connectionless server binds a transport address to the endpoint so that potential clients can access the server. A t_bind structure is allocated using t_alloc() and the buf and len fields of the address are set accordingly.

One difference between a connection mode server and a connectionless mode server is that the qlen field of the t_bind structure is 0 for connectionless mode service. There are no connection requests to queue.

XTI/TLI interfaces define an inherent client-server relationship between two users while establishing a transport connection in the connection mode service. No such relationship exists in connectionless mode service.

TLI requires that the server check the bound address returned by t_bind() to ensure that it is the same as the one supplied. t_bind() can also bind the endpoint to a separate, free address if the one requested is busy.