INTERNATIONAL  TELECOMMUNICATION  UNION

		     ITU-T RECOMMENDATION SUMMARY
 

Rec. No. : Q.955.1

Title :	Stage 3 description for community of interest supplementary  
	services using DSS 1

Study Group : XI - Switching and Signalling

Version : New

Date of adoption : 1992

Notes :	


			CLOSED USER GROUP (CUG)

The supplementary service Closed User Group (CUG) enables users to 
form groups, to and from which access is restricted. A specific user 
may be a member of one or more CUGs. Members of a specific CUG can 
communicate among themselves but not, in general, with users outside 
the group. Specific CUG members can have additional capabilities that 
allow them to originate calls outside the group, and/or to receive 
calls from outside the group. Specific CUG members can have additional 
restrictions that prevent them from originating calls to other members 
of the CUG, or from receiving calls from other members of the CUG.

Essentially normal call establishment procedures apply, but 
additionally, to provide CUG service, the network analyses the call 
request from the calling user in conjunction with the CUG attributes 
associated with both the calling and called users (as identified by 
their ISDN numbers). As a result of this analysis the call either 
fails for CUG reasons or is allowed to proceed.

The network provider may define the maximum number of CUGs of which a 
user can be a member.

Since the fundamental purpose of the CUG service is to prevent certain 
connections, it is necessary to strictly control interactions with 
some other supplementary services to protect CUG integrity.



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