12.3.4 Address Binding

When an Incoming Call packet is received by Solstice X.25, the called address and user data field are matched against all listening sockets. In addition, if the interface supports 1984 X.25, and if the listener has specified a value for the Called AEF, the Called AEF field in the Incoming Call (if any) will be matched with the Called AEF specified by the listener. If a match is found, the call is accepted and the user process associated with that socket will be notified when the user process does an accept. This permits incoming calls to be bound to the correct user process. X.25 supports binding by either address or by both address and protocol identifier. The method used is determined by the fields of the CONN_DB structure passed to bind.

The address a socket is bound to is specified in the host field of the CONN_DB parameter passed to the bind call. The address is specified in packed BCD format, and the hostlen field contains the length of the address in BCD digits.

You can specify the bound address in a number of ways, depending on whether you want to accept all calls (from any link, for any subaddress), or all calls for a specific subaddress (from any link, for a particular subaddress), or calls from a specific link for any subaddress, or calls for a specific address (from a specific link, for a specific subaddress).

If you want to accept all calls (from any link, for any subaddress), set the bits ANY_LINK (0x80) and ANY_SUBADDRESS (0x40) in the hostlen field and do not specify any address:

bind_addr.hostlen = ANY_LINK | ANY_SUBADDRESS;

If you want to accept calls from any link, but only for a specific subaddress, specify only the subaddress, and set the ANY_LINK bit in the hostlen field:

bind_addr.hostlen |= ANY_LINK;

If you want to accept calls from a specific link, but for any subaddress, specify the link address (without the subaddress) and set the ANY_SUBADDRESS bit in the hostlen field:

bind_addr.hostlen |= ANY_SUBADDRESS;

If you want to accept calls for a specific address (including subaddress) specify the exact address in the CONN_DB structure passed to bind. In this case, the address you specify must exactly match the called address field of the received Incoming Call packet. The address of a link may be obtained with an X25_RD_LINKADR ioctl call (see the section "12.7.6 Accessing the Link (X.25) Address " of this chapter for details).

The sample programs provided with Solstice X.25 illustrate the above features.