INTERNATIONAL  TELECOMMUNICATION  UNION

	  	     ITU-T RECOMMENDATION SUMMARY


Rec. No. : Q.951.8

Title :	Stage 3 description for number identification supplementary 
	services using DSS 1

Study Group : XI - Switching and Signalling

Version : New

Date of adoption : 1992

Notes :	


			SUB-ADDRESSING (SUB)

The Sub-addressing (SUB) supplementary service allows the called 
(served) user to expand his addressing capacity beyond the one given 
by the ISDN number.

The sub-addressing possibility offers an additional addressing 
capacity independent from the ISDN number.

A called party sub-address, if presented by a calling user is delivered 
unaffected to the called user. The called party sub-address may form 
part of the compatibility checking by the called user. Only the served 
user defines the significance of the sub-address.

The functions offered by the SUB supplementary service can be used to 
identify a particular endpoint of a call beyond the ISDN access.

If a calling user wants to transfer called party sub-address 
information to the called user, the calling user shall insert the 
called party sub-address information into the SETUP message as part of 
the basic service.

The sub-address information is transferred transparently through the 
network from the originating to the destination user-network 
interface. At the called user side, the called party Sub-address shall 
be offered to the served user within the SETUP message, if the called 
user has subscribed to this supplementary service.

Note 1 - Other sub-address information elements, e.g. calling party 
sub-address or Connected party sub-address information elements are 
not the subject of the SUB supplementary service and hence are 
described in the appropriate supplementary service specifications 
(e.g., in the Calling Line Identification Presentation and Connected 
Line Identification Presentation supplementary services 
specifications).

Note 2 - The maximum size of the called party sub-address is 20 
octets. However, for a certain period of time, the size of the 
sub-address may be less than 20 octets either within certain networks 
or between networks.



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