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q955_1s.txt
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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.
To order the complete text of this Recommendation, please use the
Order Form for ITU-T Recommendations. An electronic version of this
form is available on ITUDOC (Winword 2.0: UPI=ITU-5265; ASCII: UPI=ITU-2488).