1 Closed User Group (CUG)

24.0853GPPClosed User Group (CUG) supplementary serviceRelease 17Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

1.1 Normal operation

1.1.1 Mobile originated CUG calls

1.1.1.1 Successful operation

CUG calls may be invoked Implicitly or Explicitly by the calling user.

In the case of Implicit invocation, no CUG information is provided by the user in the call set-up request and a default attribute of CUG is invoked. Normal call establishment procedures are followed over the radio interface and no CUG signalling is required.

In the case of Explicit CUG invocation, CUG information is provided by the user and is included in the SETUP message using the ForwardCUG-Info operation (see figure 1.1). User provided CUG information may consist of any combination of the following parameters:

‑ CUG Index;

‑ Suppress Preferential CUG indicator;

‑ Suppress OA indicator.

NOTE: No more than one of each parameter may be included per call attempt.

MS Network

SETUP

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Facility (Invoke = ForwardCUG-Info (CUG-Index, SuppressPrefCUG, SuppressOA))

Figure 1.1: Transfer of CUG information during CUG call set-up

If the network received a non-zero SS Screening indicator from the calling user’s mobile station, the network may optionally indicate to the MS that a CUG has been invoked for a call (see figure 1.2). When a CUG Index is received from the VLR the MSC shall send it immediately to the MS in a FACILITY or CALL PROCEEDING message. If the network did not receive a non-zero SS Screening indicator from the calling user’s mobile station, it shall not send this notification.

MS Network

FACILITY/CALL PROCEEDING

<————————————————————————————————————————

Facility (Invoke = NotifySS (CUG-Index))

Figure 1.2: Indication of CUG invocation to the calling subscriber by the network

1.1.1.2 Unsuccessful operation

When an attempted CUG call is rejected for CUG related reasons, the mobile station is provided with an indication of the reason for failure.

The indication is passed to the calling MS in the first clearing message. The indication may be given in one of two ways:

‑ Diagnostics information in cause value #29 "Facility Rejected";

‑ A standard call control cause value.

Diagnostics are used when the rejection is generated locally (the serving VLR has rejected the call), or if they are provided in a cause value from a remote network node (see figure 1.3). Table 1.1 gives the diagnostics information for each potential local rejection case.

A CUG rejection from a remote network node is generally indicated using a standard (CUG related) call control cause value contained in an ISUP clearing message. These cause values are passed to the mobile station in the appropriate radio interface clearing message (see figure 1.4). Table 1.2 gives the cause values in each potential remote rejection case.

All CUG related call rejection cases are defined in 3GPP TS 23.085. Cause values are defined in 3GPP TS 24.008 and diagnostics in 3GPP TS 24.080.

NOTE: Annex A specifies the mapping of cause values between MAP, ISUP and 3GPP TS 24.008 for remotely generated CUG rejections.

MS Network

DISCONNECT/RELEASE/RELEASE COMPLETE

<————————————————————————————————————————

…..Cause #29 (Facility Rejected (diagnostics))…..

Figure 1.3: Indication of local CUG call rejection

MS Network

DISCONNECT/RELEASE/RELEASE COMPLETE

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Cause Information Element (Cause Value)

Figure 1.4: Indication of remote CUG call rejection

Table 1.1: Use of diagnostic values for local CUG call failure indications

Reason for rejection See 3GPP TS 23.085	Facility Rejected #29 Diagnostic Field (Diagnostics)
Outgoing calls barred within the CUG	Outgoing calls barred within the CUG
Inconsistent access info – No CUG Selected	No CUG Selected
Unknown CUG Index	Unknown CUG Index
Inconsistent access info – Index incompatible with requested basic service	Index incompatible with requested basic service

Table 1.2: Use of cause values for remote CUG call failure indications

Reason for rejection See 3GPP TS 23.085	Cause Information Element (cause value)
Called party supplementary service interaction violation	Facility Rejected #29 Diagnostic = CUG call failure, unspecified
Incompatible Destination (see note)	Facility Rejected #29 Diagnostic = CUG call failure, unspecified
Incoming calls barred within the CUG	Incoming calls barred within the CUG #55
Interlock mismatch	User not a member of CUG #87
Requested basic service violates CUG constraints	Facility Rejected #29
NOTE: In cases of interworking failures ETSI ISUP V2 clears the call with cause value #29 "Facility Rejected", Diagnostic = "Interlock Code". This is mapped to Facility Rejected with general diagnostic value "CUG call failure, unspecified" since the interlock code has no meaning for a mobile user.

1.1.2 Mobile terminated calls

If the network received a non-zero SS Screening indicator from the called user’s mobile station, when a CUG call is terminated by a CUG subscriber the Index associated with the invoked CUG may be passed to the mobile station (see figure 1.5). If the network did not receive a non-zero SS Screening indicator from the called user’s mobile station, it shall not send this notification.

MS Network

SETUP

<————————————————————————————————————————

Facility (Invoke = NotifySS (CUG-Index))

Figure 1.5: Presentation of the CUG Index to a CUG subscriber during reception of a CUG call

1.2 Activation, deactivation, interrogation, registration and erasure

Activation, deactivation, interrogation, registration and erasure of the supplementary service closed user group are not applicable.

Annex A (normative):
CUG rejection cause value mapping

Table A.1 indicates how MAP, ISUP and 3GPP TS 24.008 cause values are mapped to enable a rejection indication to be passed from the remote rejecting node to the calling user.

Table A.1: Protocol mapping for CUG call rejection cause values

GSM MAP CUG reject cause value	CCITT ISUP cause value	3GPP TS 24.008 cause value
calledPartySupplementary-ServiceInteractionViolation	#29 Facility Rejected Diagnostic = IC (see note 1)	#29 Facility Rejected Diagnostic = CUG call failure, unspecified
incomingCallsBarredWithinCUG	#55 I/C calls barred within CUG	#55 I/C calls barred within CUG
subscriberNotMemberOfCUG	#87 User not member of CUG	#87 User not member of CUG
requestedBasicService-ViolatesCUGConstraints	#29 Facility Rejected (see note 2)	#29Facility Rejected (no diagnostic)
NOTE 1: There is no specific cause value in ISUP for this rejection case. Therefore it is proposed that Cause Value #29 "Facility Rejected" is used with the diagnostic equal to the interlock of the call. This approach has been used in ISUP for interworking problems. NOTE 2: There is no specific cause value in ISUP for this rejection case. It is therefore proposed to use cause value #29 "Facility Rejected" to indicate a general supplementary service failure.

Annex B (informative):
Change history

Change history
Date	Meeting	TDoc	CR	Rev	Cat	Subject/Comment	New version
Apr 1999						Transferred to 3GPP CN1
CN#03						Approved at CN#03	3.0.0
CN#11						Release 4 after CN#11	4.0.0
CN#16						References updated	4.0.1
CN#16						Rel-5 created after CN#16	5.0.0
CN#26						Rel-6 created after CN#26	6.0.0
CT#36						Upgraded unchanged from Rel-6	7.0.0
CT#42						Upgraded unchanged from Rel-7	8.0.0
2009-12						Update to Rel-9 version (MCC)	9.0.0
2011-03						Update to Rel-10 version (MCC)	10.0.0
2012-09						Update to Rel-11 version (MCC)	11.0.0
2014-09						Update to Rel-12 version (MCC)	12.0.0
2015-12						Update to Rel-13 version (MCC)	13.0.0
2017-03						Update to Rel-14 version (MCC)	14.0.0
2018-06						Update to Rel-15 version (MCC)	15.0.0
2020-07						Update to Rel-16 version (MCC)	16.0.0
2022-03	–	–	–	–	–	Update to Rel-17 version (MCC)	17.0.0