10.30.3. Subaddressing (SUB)> 
Subaddressing enables users to extend the addressing capacity beyond
the ISDN number. The subaddress can be used, for example, for:
- the additional selection of terminals
- the activation of special processes in the called terminal.
The subaddress (if outdialed by the A subscriber) is transmitted transparently
to the called party. The maximum length of a subaddress is 23 octets.
This length can be changed to any value between 0 and 23 (default=23)
on the terminal side by means of AMO ZAND (see below). At the NW interface
this value is permanently assigned to a protocol variant.
Classes of service SUBCAL, SUBDB and SUBMSN
There are 3 alternative authorizations per service for EURO-ISDN terminals.
By means of these authorizations, the provision of the ISDN subaddress
is controlled for those cases in which the B subscriber definitely expects
an ISDN subaddress but this address is not supplied by the A subscriber.
- SUBCAL: B is provided with the A number as the subaddress
- SUBMSN: B is provided with the MSN (Multiple Subscriber Number) as the subaddress (either the number dialed by A or a call forwarding number)
- SUBDB : B is provided with the default B number (main subscriber number) as the subaddress
One of these authorizations must be set in the COS assigned to the EURO-ISDN
terminal on a service-specific basis:
CHA-COSSU:TYPE=COS,COS=<number>,AVCE=SUBCAL, AFAX=SUBCAL,ATTX=SUBCAL,AVTX=SUBCAL,ADTE=SUBCAL;
IMPORTANT:
Since the SUB authorizations are mutually
exclusive, only one of these values may be set per COS and service. If
several are specified, the first authorization set in the order indicated
above is authomatically given precedence.