12.3.1 Calling Side -- Outgoing Call Setup

The calling side initiates a virtual circuit connection by calling connect, supplying the called (remote) DTE address (including subaddress, if any) and a user data field as arguments. After connect completes successfully, the socket may be used for data transfer.

int   s /* socket */, error;
 CONN_DB   addr;
 error = connect(s, &addr, sizeof(addr)); 

Solstice X.25 supports multiple physical interfaces (or links). A single link maps to a serial port device, such as zsh0.

A link is automatically selected for the outgoing call. Among multiple links, Solstice X.25 routes outgoing calls based on the called address. Calls are routed according to the full or partial addresses (X.121, or NSAP or non-NSAP extended addresses) you specify in a routes file, the syntax for which is described in Solstice X.25 9.2 Administration Guide. The lowest-numbered link is the default.

If the interface supports 1984 X.25, the user may also specify a Called Address Extension Facility (AEF). In this case, Solstice X.25 will use the Called AEF to route the call over a particular link, provided the user has not specified an X.121 address. If the user wants the call to be routed based on the Called AEF, the hostlen field should be set to zero:

addr.hostlen = 0;

Where AEFs are used for routing, Solstice X.25 will select the interface to use and will also supply the X.121 address (if any) for the Call Request packet. In addition, if it is a LAN interface, Solstice X.25 will supply the necessary LSAP address.

Called and Calling AEFs are described in the section "12.7.1 Facility Specification and Negotiation".

error is used in most examples to indicate the return code. A value of zero indicates a successful operation. A non-zero value indicates an unsuccessful operation. The cause of the error is stored in a global variable errno which is used throughout this manual. Values of errno are enumerated in <errno.h>. These values are listed in intro(2) in the SunOS Reference Manual. Programmers may access errno by inserting the following line in their programs: extern int errno; Note that errno indicates the cause of the very last system call failure and is therefore invalid for operations returning an error value of zero. To get more information on the meaning of the error string printed, use the perror function.