ETSI ETS 300 392-10-13 ed.2 (1999-09)

Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 10: Supplementary services stage 1; Sub-part 13: Call completion to busy subscriber

RE/TETRA-03001-10-13

Prizemni snopovni radio (TETRA) – Govor in podatki (V+D) – 10. del: Dopolnilne storitve stopnje 1 – 13. poglavje: Dokončanje klicanja zasedenega naročnika

General Information

• Status: Published
• Publication Date: 13-Sep-1999
• Technical Committee: TCCE 3 - TCCE Air Interface and Network Protocols
• Current Stage: 12 - Completion
• Due Date: 10-Sep-1999
• Completion Date: 14-Sep-1999
• Mandate: T-172-1A
• Ref Project: SIST ETS 300 392-10-13 E2:2003 - Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 10: Supplementary services stage 1; Sub-part 13: Call completion to busy subscriber

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 392-10-13 E2:2003
01-december-2003
3UL]HPQLVQRSRYQLUDGLR7(75$±*RYRULQSRGDWNL9'±GHO'RSROQLOQH
VWRULWYHVWRSQMH±SRJODYMH'RNRQþDQMHNOLFDQMD]DVHGHQHJDQDURþQLND
Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 10: Supplementary
services stage 1; Sub-part 13: Call completion to busy subscriber
Ta slovenski standard je istoveten z: ETS 300 392-10-13 Edition 2
ICS:
33.070.10 Prizemni snopovni radio Terrestrial Trunked Radio
(TETRA) (TETRA)
SIST ETS 300 392-10-13 E2:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST ETS 300 392-10-13 E2:2003

---------------------- Page: 2 ----------------------

SIST ETS 300 392-10-13 E2:2003
EUROPEAN ETS 300 392-10-13
TELECOMMUNICATION September 1999
STANDARD Second Edition
Source: TETRA Reference: RE/TETRA-03001-10-13
ICS: 33.020
Key words: CCBS, data, radio, speech, stage 1, supplementary service, TETRA
Terrestrial Trunked Radio (TETRA);
Voice plus Data (V+D);
Part 10: Supplementary services stage 1;
Sub-part 13: Call completion to busy subscriber
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Internet: [e-mail] - http://www.etsi.org
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1999. All rights reserved.

---------------------- Page: 3 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 2
ETS 300 392-10-13: September 1999
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Standards Making Support Dept." at the address shown on the title page.

---------------------- Page: 4 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 3
ETS 300 392-10-13: September 1999
Contents
Foreword . 5
1 Scope. 7
2 References. 7
3 Definitions, symbols and abbreviations. 8
3.1 Definitions. 8
3.2 Symbols. 10
3.3 Abbreviations. 10
3.3.1 General abbreviations. 10
3.3.2 Supplementary service abbreviations . 10
4 SS-CCBS Stage 1 Specification . 11
4.1 Description. 11
4.1.1 General description. 11
4.1.2 Qualifications on applicability to telecommunication services. 11
4.2 Procedures . 11
4.2.1 Provision/Withdrawal . 11
4.2.2 Normal procedures . 12
4.2.2.1 Activation/deactivation/registration/Interrogation. 12
4.2.2.2 Invocation and operation. 12
4.2.2.3 Cancellation. 13
4.2.2.4 Group call considerations. 13
4.2.2.5 Timers . 13
4.2.3 Exceptional Procedures. 13
4.2.3.1 Activation/deactivation/registration/interrogation. 13
4.2.3.2 Invocation and Operation . 14
4.2.3.2.1 Rejection of SS-CCBS Service
request. 14
4.2.3.2.2 User A is busy on SS-CCBS recall. 14
4.2.3.2.3 Network congestion. 14
4.2.3.2.4 User B becomes busy after SS-CCBS
recall. 15
4.2.3.2.5 Duplicate SS-CCBS requests. 15
4.2.3.2.6 Other situations . 15
4.2.3.2.7 Other failure situations . 15
4.2.3.3 Cancellation. 15
4.3 Interactions with other supplementary services and ANFs . 15
4.3.1 Calling Line Identification Presentation (SS-CLIP) . 16
4.3.2 Connected Line Identification Presentation (SS-COLP) . 16
4.3.3 Calling/Connected Line Identification Restriction (SS-CLIR). 16
4.3.4 Completion of Calls on No Reply (SS-CCNR) . 16
4.3.5 Call Forwarding Unconditional (SS-CFU) . 16
4.3.5.1 SS-CFU activated by user B before user A requests SS-
CCBS . 16
4.3.5.2 SS-CFU activated by user B after user A requests SS-
CCBS . 16
4.3.5.3 SS-CFU activation by user A. 16
4.3.6 Call Forwarding Busy (SS-CFB) . 16
4.3.6.1 SS-CFB activated by user B before user A requests SS-
CCBS . 16
4.3.6.2 SS-CFB activated by user B after user A requests SS-
CCBS . 16
4.3.6.3 SS-CFB activation by user A. 16
4.3.7 Call Forwarding on No Reply (SS-CFNR). 17
4.3.8 Call Report (SS-CR) . 17

---------------------- Page: 5 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 4
ETS 300 392-10-13: September 1999
4.3.9 Talking Party Identification (SS-TPI) .17
4.3.10 Call Forwarding on Not Reachable (SS-CFNR ) .17
c
4.3.11 List Search Call (SS-LSC).17
4.3.12 Call Authorized by Dispatcher (SS-CAD) .17
4.3.13 Short Number Addressing (SS-SNA) .17
4.3.14 Area Selection (SS-AS).17
4.3.15 Access Priority (SS-AP) .18
4.3.16 Priority Call (SS-PC).18
4.3.17 Call Waiting (SS-CW) .18
4.3.18 Call Hold (SS-HOLD) .18
4.3.19 Late Entry (SS-LE) .18
4.3.20 Transfer of Control (SS-TC).18
4.3.21 Pre-emptive Priority Call (SS-PPC).18
4.3.22 Include Call (SS-IC).18
4.3.23 Advice of Charge (SS-AoC) .18
4.3.24 Barring of Outgoing Calls (SS-BOC).18
4.3.25 Barring of Incoming Calls (SS-BIC).18
4.3.26 Discreet Listening (SS-DL).19
4.3.27 Ambiance Listening (SS-AL) .19
4.3.28 Dynamic Group Number Assignment (SS-DGNA).19
4.3.29 Call Retention (SS-CRT).19
4.3.30 Interaction with ANFs .19
4.3.30.1 Mobility.19
4.3.30.1.1 Migration of user B while SS-CCBS is
active for a given call .19
4.3.30.1.2 Migration of user A while SS-CCBS is
active.19
4.3.30.1.3 Migration of either user A or user B to
a SwMI not supporting SS-CCBS .19
4.3.31 Inter-working considerations .19
4.4 SS-CCBS overall SDL .20
Annex A (informative): Bibliography.23
History.24

---------------------- Page: 6 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 5
ETS 300 392-10-13: September 1999
Foreword
This European Telecommunication Standard (ETS) has been produced by the Terrestrial Trunked Radio
(TETRA) Project of the European Telecommunications Standards Institute (ETSI).
This ETS is a multi-part standard and will consist of the following parts:
Part 1: "General network design";
Part 2: "Air Interface (AI)";
Part 3: "Interworking at the Inter-System Interface (ISI)";
Part 4: "Gateways basic operation";
Part 5: "Peripheral Equipment Interface (PEI)";
Part 6: "Line connected Station (LS)";
Part 7: "Security";
Part 9: "General requirements for supplementary services";
Part 10: "Supplementary services stage 1";
Part 11: "Supplementary services stage 2";
Part 12: "Supplementary services stage 3";
Part 13: "SDL model of the Air Interface (AI)";
Part 14: "Protocol Implementation Conformance Statement (PICS) proforma specification".
Transposition dates
Date of adoption of this ETS: 3 September 1999
Date of latest announcement of this ETS (doa): 31 December 1999
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 30 June 2000
Date of withdrawal of any conflicting National Standard (dow): 30 June 2000

---------------------- Page: 7 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 6
ETS 300 392-10-13: September 1999
Blank page

---------------------- Page: 8 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 7
ETS 300 392-10-13: September 1999
1 Scope
This ETS specifies the Call Completion on Busy Subscriber (SS-CCBS) supplementary service which is
applicable to various basic services supported by TETRA Switching and Management Infrastructures
(SwMIs). TETRA basic services are specified in ETS 300 392-2 [8].
SS-CCBS allows completion of a call to a subscriber that was unsuccessful because of a busy condition
without making a new call attempt.
Supplementary service specifications are produced in three stages, according to the method described in
ITU-T Recommendation I.210 [4]. This ETS contains the stage 1 specifications of SS-CCBS. The stage 1
descriptions specify the supplementary services as seen by users of SwMIs.
This ETS is applicable to circuit mode TETRA tele-services and bearer services only. This ETS does not
address the case where the MS/LS is not reachable. SS-CCBS assumes MS/LS is reachable.
Man Machine Interfaces and charging principles are outside the scope of this ETS.
This first edition of this ETS was presented as a delta document to the first edition of ECMA-185 [2]. This
version has been redrafted based on the latest published text of ECMA-185 [2] as a self-contained
document so as to be more readable. Additions to ECMA-185 [2] have been made to take into account
particular TETRA specifics (e.g. group call) and to include user requirements and situations not addressed
in ECMA-185 [2].
NOTE: Contrary to PISN SS-CCBS and SS-CCNR which are both specified in ECMA-185 [2],
TETRA SS-CCBS and TETRA SS-CCNR are specified in two separate ETSs.
2 References
This ETS incorporates by dated and undated reference, provisions from other publications. These
references are cited at the appropriate places in the text and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this ETS
only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies.
[1] Void.
[2] Standard ECMA-185 (1997): "Private Integrated Services Network (PISN);
Specification, Functional Model and Information Flows; Call Completion
Supplementary Services (CCSD)".
[3] ITU-T Recommendation I.112 (1993): "Vocabulary of terms for ISDNs".
[4] ITU-T Recommendation I.210 (1993): "Principles of telecommunication services
supported by an ISDN and the means to describe them".
[5] ITU-T Recommendation I.221 (1993): "Common specific characteristics of
services".
[6] ITU-T Recommendation Z.100 (1993): "CCITT specification and description
language (SDL)".
[7] Void.
[8] ETS 300 392-2 (1996): "Terrestrial Trunked Radio (TETRA); Voice plus Data
(V+D); Part 2: Air Interface (AI)".
[9] ETS 300 392-9 (1997): "Terrestrial Trunked Radio (TETRA); Voice plus Data
(V+D); Part 9: General requirements for supplementary services".
[10] CCITT Recommandation Q.9 (1988): "Vocabulary of switching and signalling
terms".

---------------------- Page: 9 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 8
ETS 300 392-10-13: September 1999
[11] TS 101 282: "Digital cellular telecommunications system (Phase 2+);
Completion of Calls to Busy Subscriber (CCBS); Service description, Stage 1
(GSM 02.93 version 6.0.1 Release 1997)".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of this ETS, the following definitions apply:
Additional Network Feature: Capability, over and above that of a basic service, provided by a SwMI, but
not directly to a user.
basic (…) service: Any stand alone bearer service or tele-service (derived from ITU-T
Recommendation I.210 [4]).
bearer service: type of telecommunication service that provides the capability for the transmission of
signals between user-network interfaces (as defined in ITU-T Recommendation I.112 [3]).
busy: Property of a user for whom either a "network determined user busy" or "user determined user
busy" condition (see subclause 3.1 of ITU-T Recommendation I.221 [5]) exists.
call, basic call: Instance of the use of a basic service.
call completion: Successful presentation of a previously unsuccessful Call to a destination user (user B)
which occurs when the call has entered an alerting phase or has been answered.
NOTE 1: CCBS call completion could result in a CCNR condition in which case user A would
invoke SS-CCNR and not SS-CCBS anymore.
CCBS busy: Any one of the following conditions will cause user A to be considered as CCBS busy:
- maximum number of calls queued at user A;
- CCBS recall pending on user A;
- no resource available at user A.
NOTE 2: It is assumed that SS-CCNR busy is independent from SS-CCBS busy; one could
consider merging the two conditions in an SS-CC busy which would combine the total
numbers of CCBS and CCNR requests.
compatible MS/LS: MS/LS presenting the same basic TETRA class of service as the TETRA class of
service requested by the calling user MS/LS. By analogy to ISDN "compatible terminal".
free: Property of a user who can accept any attempt by the SwMI to present a call to that user (i.e. allow
the call to reach the alerting or answered state).
group busy: group is busy when group controlling SwMI determines that group is busy; group busy shall
generally be equivalent to NDUB.
NOTE 3: How the SwMi determines group busy condition is implementation dependent and is
outside the scope of this draft ETS.
idle guard time: Time the network will wait after user B has become free before initiating a “CCBS recall”
to user A (definition from TS 101 282 [11]).
Line Station (LS): Physical grouping that contains all the fixed equipment that is used to obtain TETRA
services through a line.
Mobile Station (MS): Physical grouping that contains all of the mobile equipment that is used to obtain
TETRA services. By definition, a mobile station contains at least one Mobile Radio Stack (MRS).

---------------------- Page: 10 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 9
ETS 300 392-10-13: September 1999
Network Determined User Busy: Analogy to ISDN, when all available interface resources are busy, the
busy shall be network determined user busy.
path reservation: Reservation of resources just prior to SS-CCBS Recall in order that a connection path
through the network is available when user A accepts the SS-CCBS Recall.
NOTE 4: Path Reservation would not guarantee that user B will be free when user A accepts the
SS-CCBS Recall.
NOTE 5: Path Reservation is not the preferred mode of operation in the TERA environment due
to mobility considerations.
recall timer: Timer specifies the length of time the network shall wait for a response from user A to a
CC Recall.
retention timer: Timer specifies the period of time the network retains the originating call information after
a valid call attempt is released.
SS-CCBS busy: See CCBS busy.
SS-CCBS call: Call generated by the network from user A to user B resulting from user A's acceptance of
a SS-CCBS recall.
SS-CCBS recall: Indication informing user A that user B is no longer busy (in the case of SS-CCBS).
Acceptance of this indication by user A will cause the call to be completed by the SwMI.
SS-CCBS request: Instance of an activation of SS-CCBS held in a queue pending the correct conditions
for the SS-CCBS to be completed.
SS-CCBS service duration timer: Timer specifies the length of time that the service shall be active
within the network.
supplementary service: Any service provided by a network in addition to its basic service or services
(defined in CCITT Recommendation Q.9 [10]). A supplementary service modifies or supplements a basic
telecommunication service. Consequently, it cannot be offered to a customer as a stand alone service. It
must be offered together with or in association with a basic telecommunication service (except from
ITU-T Recommendation I.210 [4]).
suspended CCBS request: CCBS request that cannot be served even if destination B is not busy,
because user A is busy or CCBS busy.
Switching and Management Infrastructure (SwMI): All of the TETRA equipment for a Voice plus Data
(V+D) network except for subscriber terminals. The SwMI enables subscriber terminals to communicate
with each other via the SwMI.
tele-service: Type of telecommunications service that provides the complete capability, including terminal
equipment functions, for communication between users according to agreed protocols.
User A: Specific user that originated the call and requested the supplementary service.
User B: User that was initially addressed in the original individual call set up. In the case of a group call,
Group (B) will be used in place of user B.
user B idle guard timer: See idle guard timer definition.
User Determined User Busy: Analogy to ISDN, busy shall be user determined user busy when
subscriber resources (either the terminal itself or the user) do not respond positively to an incoming call
request.
NOTE 6: In the case where the MS/LS has a single resource and is involved in an individual call,
UDUB and NDUB will be confounded. In other words, NDUB could result of a single
call occurrence.

---------------------- Page: 11 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 10
ETS 300 392-10-13: September 1999
NOTE 7: It appears, after further investigation, that UDUB will never happen in a TETRA Mobile
Station; however, the definition of UDUB is left to clarify the distinction with NDUB and
for the case of inter-working.
3.2 Symbols
For the purposes of this ETS, there are no special symbols besides the symbol used in SDL diagram and
defined in ITU-T Recommendation Z.100 [6].
3.3 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
3.3.1 General abbreviations
AI Air Interface
ANF Additional Network Feature
CC Call Control (functional entity)
CC Call Completion (generic term for both CCBS and CCNR)
CCBS Completion of Calls to Busy Subscribers
CCNR Completion of Calls on No Reply
GTSI Group TETRA Subscriber Identity
ISDN Integrated Services Digital Network
ISI Interworking at the Inter-System Interface
LS Line Station
MS Mobile Station
NDUB Network Determined User Busy
PICS Protocol Implementation Conformance Statement
PISN Private Integrated Services Network
SDL Specification and Description Language
SS Supplementary Service
NOTE: The abbreviation SS is only used when referring to a specific supplementary service.
SwMI Switching and Management Infrastructure
TETRA TErrestrial Trunked RAdio
TE Terminal Equipment
UDUB User Determined User Busy
V+D Voice Plus Data
3.3.2 Supplementary service abbreviations
AL Ambiance Listening
AoC Advice of Charge
AP Access Priority
AS Area Selection
BIC Barring of Incoming Calls
BOC Barring of Outgoing Calls
CAD Call Authorized by Dispatcher
CCBS Call Completion to Busy Subscriber
CCNR Call Completion on No Reply
CFB Call Forwarding on Busy
CFNRy Call Forwarding on No Reply
CFNRc Call Forwarding on Not Reachable
CFU Call Forwarding Unconditional
CLIP Calling Line Identification Presentation
CLIR Calling/Connected Line Identification Restriction
COLP COnnected Line Identification Presentation
CR Call Report
CRT Call Retention
CW Call Waiting
DGNA Dynamic Group Number Assignment
DL Discreet Listening

---------------------- Page: 12 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 11
ETS 300 392-10-13: September 1999
HOLD Call Hold
IC Include Call
LE Late Entry
LSC List Search Call
MRS Mobile Radio Stack
PC Priority Call
PEI Peripheral Equipment Interface
PPC Pre-emptive Priority Call
SNA Short Number Addressing
TC Transfer of Control
TPI Talking Party Identification
4 SS-CCBS Stage 1 Specification
4.1 Description
4.1.1 General description
SS-CCBS is offered to a calling user (user A). On encountering a busy condition at the called user
(user B), SS-CCBS may be offered to the calling user (user A). If user A invokes SS-CCBS, the SwMI B
shall monitor user B. If user B becomes not busy and stays free during the ‘idle guard time’ (user B does
not place an outgoing call and does not receive an incoming call with higher priority than the pending
CCBS call), user A is notified that user B is not busy. On positive response by user A to that notification,
the SwMI shall attempt to complete the call to user B.
4.1.2 Qualifications on applicability to telecommunication services
This supplementary service is applicable to all basic circuit mode TETRA V+D services.
4.2 Procedures
4.2.1 Provision/Withdrawal
SS-CCBS may be provided after pre-arrangement with the service provider (to selected users), or may be
generally available to all users. SS-CCBS may be withdrawn on request of the user or for administrative
reasons.
No subscription options shall be offered by the SwMI.
NOTE 1: Contrary to ECMA-185 which offers two subscription options for recall mode,
SS-CCBS Recall shall be offered only to the terminal which has invoked SS-CCBS.
NOTE 2: As a guidance to stage 3 ETS, the following main options in relation to ECMA 185 are
selected for TETRA SS-CCBS:
- Path reservation is not provided;
NOTE 3: In the TETRA network environment, path reservation is deemed not to be necessary
due to mobility considerations; a path reserved between two SwMIs could become not
available when one of the user migrates.
- Signaling connection is retained for the duration of the SS-CCBS request;
- Retention of the SS-CCBS service until expiration of the service duration timer (if user A and/or
user B is found busy after the recall).

---------------------- Page: 13 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 12
ETS 300 392-10-13: September 1999
4.2.2 Normal procedures
4.2.2.1 Activation/deactivation/registration/Interrogation
SS-CCBS shall be permanently activated upon provision and permanently deactivated upon withdrawal.
User B needs not to have subscribed to SS-CCBS for calling user A invocation of SS-CCBS to operate
properly.
Restriction of SS-CCBS for called user B is outside the scope of this ETS.
NOTE: A mechanism provided to user B which causes rejects of CCBS requests is outside
the scope of this ETS.
Interrogation will not be used to interrogate activation/deactivation status; a process similar to interrogation
may be implemented; see invocation clause below.
4.2.2.2 Invocation and operation
When a call from user A fails because the destination user, user B, is busy, the network shall retain the
call information provided by user A, for a period governed by the SS-CCBS Retention Timer. User A
shall be able to request SS-CCBS during that period. On receipt of a request for SS-CCBS during that
period, the network shall check whether it is possible to initiate the service, and if so shall send a
positive acknowledgment to user A, start monitoring user B and start the SS-CCBS service duration
timer. The acknowledgment means that user A can expect to receive a SS-CCBS Recall if user B
becomes not busy within the period of the SS-CCBS service duration timer.
NOTE 1: The fact that user B is already being monitored, as a result of a call completion request
from another user, needs not cause rejection of the request from user A. The handling
of multiple requests against the same user B is an implementation matter, typically
involving some sort of queue arranged in chronological and/or priority order.
NOTE 2: The fact that user A has already invoked call completion against another user needs
not cause rejection of any further requests for call completion from user A. The
handling of multiple requests by the same user A is an implementation matter.
NOTE 3: Only users for which SS-CCBS has been activated by subscription are allowed to
invoke SS-CCBS for a particular busy subscriber; users for which SS-CCBS has not
been activated and invoking SS-CCBS will receive a negative response to their
request.
After the SS-CCBS request has been acknowledged, user A shall be able to receive and initiate other
calls.
A network may provide user A with the ability to request a list of outstanding SS-CCBS requests that user
A has invoked. Only details of requests made by the user from that terminal should be provided. The list
will be empty if there are no outstanding SS-CCBS requests.
When the monitoring of user B indicates that user B has become free, and if user A is also free, the
network shall provide user B with an optional time guard during which user B can place outgoing call but
can only receive incoming calls which have a higher priority level than the original CCBS call priority level.
If user B is still free after the idle guard time, the network shall then provide an SS-CCBS Recall to user A,
and start the SS-CCBS Recall timer. The priority of the recall signaling process shall be equal to the
priority of the original call.
If user A accepts the SS-CCBS Recall, the network shall attempt to complete the call between user A and
user B. User A shall not be able to modify the call parameters in the CCBS Call; this holds true for the
basic call setup (such as basic service, priority and area selection) as well as for the supplementary
services invoked for the initial call. If the call is successfully presented to user B and enters an alerting
phase or is answered, SS-CCBS shall be regarded as complete.

---------------------- Page: 14 ----------------------

SIST ETS 300 392-10-13 E2:2003
Page 13
ETS 300 392-10-13: September 1999
In the case where several invocations of SS-CCBS are in the queue, the calls shall be handled in the
order they occurred unless their priority lev
...