SIST ETS 300 976 E3:2003

SLOVENSKI STANDARD
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHPID]D±6SORãQH]DKWHYH]D
PHGVHERMQRGHORYDQMHMDYQHJDNRSHQVNHJDPRELOQHJDRPUHåMD3/01LQ
GLJLWDOQHJDRPUHåMD]LQWHJULUDQLPLVWRULWYDPL,6'1DOLMDYQHJDNRPXWLUDQHJD
WHOHIRQVNHJDRPUHåMD3671*60UD]OLþLFD
Digital cellular telecommunications system (Phase 2+) (GSM); General requirements on
interworking between the Public Land Mobile Network (PLMN) and the Integrated
Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN) (GSM
09.07 version 5.4.1)
Ta slovenski standard je istoveten z: ETS 300 976 Edition 3
ICS:
33.040.35 Telefonska omrežja Telephone networks
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 976
TELECOMMUNICATION January 1998
STANDARD Third Edition
Source: SMG Reference: RE/SMG-040907QR4
ICS: 33.020
Key words: Digital cellular telecommunications system, Global System for Mobile communications (GSM)
R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS
Digital cellular telecommunications system (Phase 2+);
General requirements on interworking between the Public Land
Mobile Network (PLMN) and the Integrated Services Digital
Network (ISDN) or Public Switched Telephone Network (PSTN)
(GSM 09.07 version 5.4.1)
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
X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: secretariat@etsi.fr
Tel.: +33 4 92 94 42 00 - Fax: +33 4 93 65 47 16
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 1998. All rights reserved.

Page 2
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
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 Editing and Committee Support Dept." at the address shown on the title page.

Page 3
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
Contents
Foreword .7
1 Scope .9
2 Normative references.9
3 Definitions and abbreviations .11
4 Introduction.12
5 Not used.13
6 Network Characteristics .13
6.1 Key Characteristics of Networks Concerned .13
6.1.1 Characteristics of PLMNs.14
6.1.2 Characteristics of PSTNs .14
6.1.3 Characteristics of ISDN.14
7 Interworking classifications .14
7.1 Service interworking.14
7.2 Network interworking .15
7.3 Signalling interworking .17
7.4 Numbering .17
7.5 Supplementary service interworking.17
8 Compatibility and subscription checking .17
9 Interworking to PSTN .18
9.1 Speech Calls.18
9.1.1 Interworking indications to PLMN terminal.18
9.1.2 Transmission aspects .18
9.1.3 Generation of In-band Tones and Announcements (PLMN-PSTN).18
9.2 Data Calls .18
9.2.1 Network interworking mobile originated .19
9.2.1.1 Selection of interworking function.19
9.2.1.2 Modem Selection.19
9.2.1.3 DTE/Modem interface (Filtering) .20
9.2.1.4 Mapping of BC-IE from GSM 04.08 to ISUP (or other).21
9.2.2 Network Interworking Mobile terminated PSTN Originated.21
9.2.3 Transparent service support .25
9.2.3.1 Not used .25
9.2.3.2 Rate adaptation process in MSC/IWF .25
9.2.3.3 Mapping of signalling MS/MSC/IWF to modem interface
requirements.25
9.2.3.4 Establishment of end-to-end terminal synchronizations .26
9.2.3.5 Network Independent Clocking (NIC).27
9.2.4 Non-transparent service support.27
9.2.4.1 MSC-IWF Rate adaptation scheme.28
9.2.4.2 Protocol layer structure in the MSC/IWF .28
9.2.4.3 Re-constitution of user data.28
9.2.4.4 Layer 2 relay functionality .28
9.2.4.5 In band signalling mapping flow control.28
9.2.4.5.1 Conditions requiring flow control
towards the fixed network .28
9.2.4.5.2 Conditions requiring flow control
towards the MS.29

Page 4
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
9.2.4.6 Data buffers . 29
9.2.4.6.1 Transmit buffers (towards MS). 29
9.2.4.6.2 Receive buffers (from MS) . 29
9.2.4.7 Transportation of the Break condition. 29
9.2.4.8 In band signalling mapping modem status information. 29
9.2.4.9 Support of out-band flow control . 30
9.2.4.10 Establishment of end-to-end terminal synchronizations . 30
9.2.4.11 Data compression. 30
9.3 Interworking Alternate Speech / Data Calls. 31
9.3.1 Alternate Speech/Data Interworking. 31
9.3.1.1 General . 31
9.3.1.2 Mobile originated PSTN terminated calls. 31
9.3.1.3 PSTN originated mobile terminated calls. 31
9.3.2 Speech followed by data interworking . 32
9.3.2.1 General . 32
10 Interworking to the ISDN. 32
10.1 Speech Calls . 32
10.2 Data Calls. 33
10.2.1 Network interworking mobile originated. 33
10.2.1.1 Circuit switched calls. 33
10.2.1.2 Packet calls. 33
10.2.2 Network interworking mobile terminated . 33
10.2.2.1 Circuit switched calls. 51
10.2.2.2 Packet calls. 51
10.2.3 Transparent service support (see GSM 03.10) . 51
10.2.3.1 MSC - IWF rate adaptation scheme . 51
10.2.3.2 Rate adaptation process in MSC/IWF . 51
10.2.3.3 Mapping of signalling MS/MSC/IWF to modem interface
requirements . 52
10.2.3.4 Establishment of end-to-end terminal synchronizations . 52
10.2.3.5 Network independent Clocking (NIC). 53
10.2.4 Non-transparent service support (See GSM 03.10) . 53
10.2.4.1 MSC - IWF Rate adaptation scheme. 53
10.2.4.2 Protocol layer structure in the MSC/IWF. 53
10.2.4.3 Re-constitution of user data . 54
10.2.4.4 Layer 2 relay functionality. 54
10.2.4.5 In band signalling mapping flow control . 54
10.2.4.5.1 Conditions requiring flow control - if
flow control is provided -towards the
fixed network . 55
10.2.4.5.2 Conditions requiring flow control
towards the MS . 55
10.2.4.6 Data buffers . 55
10.2.4.6.1 Transmit buffers (towards MS). 55
10.2.4.6.2 Receive buffers (from MS) . 55
10.2.4.7 BREAK Indication. 55
10.2.4.8 Signalling mapping modem status information or in band
rate adapted frame information. 56
10.2.4.9 Support of out-band flow control . 56
10.2.4.10 Synchronizations. 56
10.2.4.10.1 V110 Frame synchronizations. 56
10.2.4.10.2 RLP Frame start indication. 56
10.2.4.10.3 L2R Frame synchronizations. 56
10.2.4.10.4 Establishment of end-to-end terminal
synchronizations. 56
10.2.4.11 Data compression. 57
10.2.4.12 V.120 Interworking . 57
10.2.4.13 Interworking with restricted 64 kbps networks . 57
10.2.5 DTE/Modem interface (Filtering) . 57
10.3 Interworking Alternate speech data calls . 58
10.3.1 Alternate speech data bearer interworking. 59
10.3.1.1 General . 59

Page 5
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
10.3.1.2 Mobile originated ISDN terminated.59
10.3.1.3 ISDN originated mobile terminated.59
10.3.2 Speech followed by data interworking.60
10.3.2.1 General.60
11 Frame Synchronization .60
11.1 Initial frame synchronization .60
11.2 Action on loss of frame synchronization for non transparent services.60
11.3 Action on loss of frame synchronization for transparent services.60
Annex A (Informative): SDLs.62
History.64

Page 6
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
Blank page
Page 7
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) of the European Telecommunications Standards Institute (ETSI).
This ETS identifies the Mobile-services Switching Centre/Interworking functions (MSC/IWFs) and
requirements to support interworking between:
i) PLMN and PSTN
ii) PLMN and ISDN
within the digital cellular telecommunications system.
The contents of this ETS are subject to continuing work within SMG and may change following formal
SMG approval. Should SMG modify the contents of this ETS it will then be resubmitted for OAP by ETSI
with an identifying change of release date and an increase in version number as follows:
Version 5.x.y
where:
y the third digit is incremented when editorial only changes have been incorporated in the
specification;
x the second digit is incremented for all other types of changes, i.e. technical enhancements,
corrections, updates, etc.
Transposition dates
Date of adoption of this ETS: 2 January 1998
Date of latest announcement of this ETS (doa): 30 April 1998
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 October 1998
Date of withdrawal of any conflicting National Standard (dow): 31 October 1998

Page 8
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
Blank page
Page 9
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
1 Scope
This European Telecommunication Standard (ETS) identifies the Mobile-services Switching
Centre/Interworking Functions (MSC/IWFs) and requirements to support interworking between:
a) PLMN and PSTN
b) PLMN and ISDN
It is not possible to treat ISDN and PSTN as one type of network, even when both ISDN and PSTN
subscribers are served by the same exchange because of the limitations of the PSTN subscribers access
i.e. analogue connection without D-channel signalling.
Within this ETS, the requirements for voice and non-voice (data) calls are considered separately.
2 Normative references
This ETS incorporates by dated and undated reference, provisions from other publications. These
normative 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] CCITT Recommendation G.711: "Pulse code modulation (PCM) of voice
frequencies".
[2] CCITT Recommendation I.460: "Multiplexing, rate adaption and support of
existing interfaces".
[3] CCITT Recommendation V.25: "Automatic answering equipment and/or parallel
automatic calling equipment on the general switched telephone network
including procedures for disabling of echo control devices for both manually and
automatically established calls".
[4] CCITT Recommendation V.42bis: "Data Compression for Data Circuit
Terminating Equipment (DCE) using Error Correction Procedures"
[5] CCITT Recommendation V.110: "Support of data terminal equipments (DTEs)
with V-Series interfaces by an integrated services digital network".
[6] ETS 300 102-1 Edition 1 (1990): "Integrated Services Digital Network (ISDN);
User-network interface layer 3 Specifications for basic call control".
[7] ETS 300 121: "Integrated Services Digital Network (ISDN); Application of the
ISDN User Part (ISUP) of CCITT Signalling System No.7 for international ISDN
interconnections (ISUP version 1)".
[8] GSM 01.04 (ETR 350): "Digital cellular telecommunication system (Phase 2+);
Abbreviations and acronyms".
[9] GSM 02.01: "Digital cellular telecommunication system (Phase 2+); Principles of
telecommunication services supported by a GSM Public Land Mobile Network
(PLMN)".
[10] GSM 02.02 (ETS 300 904): "Digital cellular telecommunications system
(Phase 2+); Bearer Services (BS) supported by a GSM Public Land Mobile
Network (PLMN)".
[11] GSM 02.03 (ETS 300 905): "Digital cellular telecommunications system
(Phase 2+); Teleservices supported by a GSM Public Land Mobile Network
(PLMN)".
Page 10
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
[12] GSM 02.04 (ETS 300 918): "Digital cellular telecommunications system
(Phase 2+); General on supplementary services".
[13] GSM 02.81: "Digital cellular telecommunication system; Line identification
supplementary services - Stage 1".
[14] GSM 02.82: "Digital cellular telecommunication system; Call Forwarding (CF)
supplementary services - Stage 1".
[15] GSM 02.83: "Digital cellular telecommunication system; Call Waiting (CW) and
Call Hold (HOLD) supplementary services - Stage 1".
[16] GSM 02.84: "Digital cellular telecommunication system; MultiParty (MPTY)
supplementary services - Stage 1".
[17] GSM 02.85: "Digital cellular telecommunication system; Closed User Group
(CUG) supplementary services - Stage 1".
[18] GSM 02.86: "Digital cellular telecommunication system; Advice of charge (AoC)
supplementary services - Stage 1".
[19] GSM 02.88: "Digital cellular telecommunication system; Call Barring (CB)
supplementary services - Stage 1".
[20] GSM 03.03 (ETS 300 927): "Digital cellular telecommunications system
(Phase 2+); Numbering, addressing and identification".
[21] GSM 03.08: "Digital cellular telecommunication system (Phase 2+);
Organization of subscriber data".
[22] GSM 03.11 (ETS 300 928): "Digital cellular telecommunications system;
Technical realization of supplementary services".
[23] GSM 03.45 (ETS 300 931): "Digital cellular telecommunications system;
Technical realization of facsimile group 3 transparent".
[24] GSM 03.46: "Digital cellular telecommunication system; Technical realization of
facsimile group 3 non-transparent".
[25] GSM 03.50 (ETS 300 903): "Digital cellular telecommunications system
(Phase 2+); Transmission planning aspects of the speech service in the GSM
Public Land Mobile Network (PLMN) system".
[26] GSM 04.08 (ETS 300 940): "Digital cellular telecommunications system
(Phase 2+); Mobile radio interface layer 3 specification".
[27] GSM 04.21 (ETS 300 945): "Digital cellular telecommunications system; Rate
adaption on the Mobile Station - Base Station System (MS - BSS) interface".
[28] GSM 04.22 (ETS 300 946): "Digital cellular telecommunications system
(Phase 2+); Radio Link Protocol (RLP) for data and telematic services on the
Mobile Station - Base Station System (MS - BSS) interface and the Base Station
System - Mobile-services Switching Centre (BSS - MSC) interface".
[29] GSM 07.01 (ETS 300 913): "Digital cellular telecommunications system
(Phase 2+); General on Terminal Adaptation Functions (TAF) for Mobile
Stations (MS)".
[30] GSM 07.02 (ETS 300 914): "Digital cellular telecommunications system
(Phase 2+); Terminal Adaptation Functions (TAF) for services using
asynchronous bearer capabilities".

Page 11
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
[31] GSM 07.03 (ETS 300 915): "Digital cellular telecommunications system
(Phase 2+); Terminal Adaptation Functions (TAF) for services using
synchronous bearer capabilities".
[32] GSM 07.05: "Digital cellular telecommunication system (Phase 2+); Use of Data
Terminal Equipment - Data Circuit terminating Equipment (DTE - DCE) interface
for Short Message Service (SMS) and Cell Broadcast Service (CBS)".
[35] GSM 08.20: "Digital cellular telecommunication system; Rate adaption on the
Base Station System - Mobile-services Switching Centre (BSS - MSC)
interface".
[36] GSM 08.60 (ETS 300 737): "Digital cellular telecommunications system
(Phase 2+); Inband control of remote transcoders and rate adaptors for
Enhanced Full Rate (EFR) and full rate traffic channels".
[37] GSM 09.02 (ETS 300 974): "Digital cellular telecommunications system
(Phase 2+); Mobile Application Part (MAP) specification".
[38] GSM 09.03: "Digital cellular telecommunication system; Signalling requirements
on interworking between the Integrated Services Digital Network (ISDN) or
Public Switched Telephone Network (PSTN) and the Public Land Mobile
Network (PLMN)".
[39] GSM 09.05: "Digital cellular telecommunication system; Interworking between
the Public Land Mobile Network (PLMN) and the Packet Switched Public Data
Network (PSPDN) for Packet Assembly/Disassembly facility (PAD) access".
[40] GSM 09.06 (ETS 300 975): "Digital cellular telecommunications system
(Phase 2+); Interworking between a Public Land Mobile Network (PLMN) and a
Packet Switched Public Data Network/Integrated Services Digital Network
(PSPDN/ISDN) for the support of packet switched data transmission services".
[41] CCITT Recommendation V.120: "Support by an ISDN of data terminal
equipment with V-Series type interfaces with provision for statistical
multiplexing".
[42] ETR 018: "Integrated Services Digital Network (ISDN); Application of the Bearer
Capability (BC), High Layer Compatibility (HLC) and Low Layer Compatibility
(LLC) information elements by terminals supporting ISDN services".
NOTE: As regards ETS 300 102-1 [6], the first edition of this ETS from 1990 shall be used,
with one exception: the encoding of the field modem type in the ISDN BC-IE shall be
handled as specified in table 6A and 6B of GSM 09.07.
3 Definitions and abbreviations
Use is made of the following terms within this ETS. These terms refer to information requirements
necessary to support interworking functions, some of these terms will be identifiable with their use in other
GSM specifications.
bearer capability information: Specific information defining the lower layer characteristics required
within the network.
low layer compatibility information: Information defining the lower layer characteristics of the terminal.
high layer compatibility information: Information defining the higher layer characteristics of the
terminal.
compatibility information: This term subsumes the entirety of Bearer Capability, Low Layer
Compatibility, High Layer Compatibility, Progress Indicator and Address Information conveyed out-of-band

Page 12
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
prior to call establishment for the support of compatibility checking and terminal/function/service selection
at the ISDN-type user-network interface.
protocol identifier: Information defining the specific protocols utilized for the support of data transfer by a
terminal.
progress indicator: Information supplied to indicate to the terminal that network interworking has taken
place.
out-of-band parameter exchange: Information exchanged via an associated or non-associated
signalling link e.g. SS No 7.
PSTN: Subscriber to network interface supports only analogue terminals.
ISDN: Subscriber to network interface supports digital or analogue terminals, plus a standardized user to
network associated signalling system and a standardized internetwork signalling system.
autobauding type 1: This information element value may be contained in the setup or call confirm
messages from the MS in association with a non transparent data service. This implies that the MSC/IWF
may select any speed and modem type according to what it can negotiate with the remote modem on the
PSTN/ISDN. The maximum speed to be used by the MSC/IWF is the user speed indicated in the
setup/call confirm message.
multi self selecting speed modem: This term applies to V series modems capable of handling one or
more lower speeds as a fall back position. When such a modem is requested in the call setup or call
confirm message from the MS in association with a non transparent service, the MSC/IWF may select any
of the speeds supported according to the negotiation with the remote modem on the PSTN/ISDN. In this
instance the maximum starting negotiation speed to be used by the MSC/IWF is the one indicated by the
user speed in the setup/call confirm message.
In addition to the following, abbreviations used in this ETS are listed in GSM 01.04 [8].
ADPCM Adaptive Differential Pulse Coded Modulation
DP Dial Pulse
ITC Information Transfer Capability
LE Local Exchange
NT Network Termination
PABX Private Automatic Branch Exchange
SPC Stored Program Control
SS No.7 Signalling System No.7
TE Terminal Equipment
TA Terminal Adaptor
TUP Telephone User Part (of Signalling System No.7)
DSS1 Digital Subscriber Signalling 1
UNI User Network Interface
4 Introduction
General Network Interworking Scenarios are described in GSM 09.01. Since the numbering plan for the
ISDN era (E.164) includes the numbering plan for the telephone network (E.163), it is not possible to
distinguish by the number whether a given subscriber is a PSTN or ISDN subscriber. Further, in some
countries both PSTN and ISDN subscribers will be connected to the same exchange, so the only
difference for this type of combined network will be in the nature of the customer access. In this document
a PSTN is considered to support only an analogue interface towards the subscriber. An ISDN shall be
considered to support digital interface towards the subscriber. In addition, the ISDN is considered to
support a standardized outband signalling protocol both between the subscriber and the network and
within the network, i.e DSS1 and ISUP, thus enabling the generation and transport of Compatibility
Information for compatibility checking and terminal/function/service selection at the user-network interface
as well as for MSC/IWF selection.
There now exist networks which do not fall into either of these categories in that they provide for digital
connectivity from subscriber to subscriber through the network. The subscribers have access to a wide

Page 13
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
range of services by a limited set of standard multi-purpose user network interfaces. However, these
networks do not support the standardized inter-exchange signalling protocol throughout, in that they are
e.g. using TUP or National User Part (NUP). These types of network support 64 kbit/s connections, so in
service support are comparable to ISDN, however, the signalling system provided may not support
transport of all Compatibility Information allowed for in the standardized ISDN signalling. This document
will therefore identify interworking to PSTN and ISDN on the principle of the network characteristics as
identified in the previous paragraph. The aforementioned existing networks then constitute one particular
case in the ISDN interworking scenarios. These cases will be itemized when the implication of the various
degrees of exhaustiveness of the Compatibility Information - delivered via the ISDN - used for deducting a
GSM Basic Service needs to be set forth.
When two dissimilar networks are required to interwork in order to support a communication between two
subscribers, one on each network, a number of Interworking Functions (MSC/IWFs) are required to
support the communication. Some of these are related to the differences in signalling and are dealt with in
GSM 09.03.
Examples of other aspects of interworking are:
a) the need or otherwise of echo control devices;
b) the need or otherwise of modem pools and network-based rate adaptation.
For the purposes of determining the required MSC/IWFs, it is necessary, however, to consider separately
each type of interworking (i.e. PLMN-ISDN and PLMN-PSTN) since, in the worst case, "PSTN" could refer
to an essentially analogue network with electromechanical switching not controlled by software and
without common-channel signalling.
Some facilities associated with alternate speech and data may not be available with version 1 of the MAP
(GSM 09.02). Version 1 of the Mobile Application Part (MAP) does not support transfer between the HLR
and VLR, and VLR and VMSC of multiple bearer capabilities. In addition, version 1 of the MAP does not
support in-call modification and channel mode modification following an inter-MSC handover.
5 Not used
6 Network Characteristics
6.1 Key Characteristics of Networks Concerned
Table 1/09.07: Key Characteristics of Networks Concerned
Characteristic GSM PLMN ISDN PSTN
Subscriber Interface Digital Digital Analogue
User-network signalling GSM 04.08 DSS1, other UNIs loop-disconnect and DTMF
User-terminal equipment MT0, MT1 or MT2 Digital TE Analogue TE (e.g. dial pulse
supported functions (see (ISDN NT, TE1 or telephones PABXs modem
GSM 04.02) TE2+TA) equipped DTEs)
see e.g. I.411
Inter-exchange signalling SS No.7 ISUP TUP+, SS No.7 ISUP Channel associated
MAP TUP+, TUP, NUP (e.g. R2, No.4, No.5) or
common channel (e.g.
No.6)
Transmission facilities Digital Digital Analogue
Exchange types Digital Digital Analogue/digital
Information transfer mode Circuit Circuit/Packet Circuit
Information transfer capability Speech, digital Speech, digital 3,1 kHz audio
unrestricted, alternate unrestricted, (voice/voice- band data)
speech/ group 3 fax etc. 3,1 kHz audio,
video etc.
Page 14
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
6.1.1 Characteristics of PLMNs
The GSM PLMN is fully defined in the GSM Technical Specifications.
6.1.2 Characteristics of PSTNs
Because of the efforts at an early stage to standardize ISDNs in different countries, the differences
between any two ISDNs will be small compared with the differences between PSTNs, which have evolved
in different ways in different countries. In some cases the evolution has occurred over many decades, and
therefore each PSTN is distinct, and for a recommendation on interworking, it is necessary to make
certain assumptions about a generalized PSTN.
Whilst the key characteristics of PSTNs are given in table 1/09.07 above, the specific MSC/IWFs needed
to allow interworking between a PLMN and a PSTN will depend on the nature of the PSTN concerned.
Table 2/09.07 below gives a number of categories that can be used to classify PSTNs and a number of
possibilities within each category.
Table 2/09.07: Characteristics of PSTNs
Category Possibilities within Category
Type of subscriber a) PSTN with loop disconnect subscriber signalling (10 pps)
signalling b) PSTN with DTMF subscriber signalling
Type of interexchange a) PSTN with channel-associated signalling
signalling b) PSTN with common-channel signalling
Type of interexchange a) Analogue
transmission b) Digital
Type of exchange a) PSTN with electro-mechanical switching
switching b) PSTN with electronic (non-digital) switching
c) PSTN with electronic digital switching
Type of exchange a) Non-SPC
control b) SPC
NOTE: Under each category, it is possible that a PSTN will have a combination of the
possibilities rather than only one.
6.1.3 Characteristics of ISDN
For the "standardized ISDN" in principle taken into account here, these are defined in the ETS-series.
7 Interworking classifications
7.1 Service interworking
Service interworking is required when the Teleservices at the calling and called terminals are different. No
service interworking, except for facsimile group 3 (GSM Teleservice 61 or 62 interworking with standard
facsimile group 3 service), has been identified as a requirement of the GSM system for PSTN/ISDN
network based services.
Page 15
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
7.2 Network interworking
Network interworking is required whenever a PLMN and a non-PLMN together are involved to provide an
end to end connection and may be required in instances of PLMN to PLMN connections.
The concept of Bearer Services was developed for the ISDN and has been extended to the PLMN. A
bearer service is defined (in GSM 02.01) as:
A type of telecommunication service that provides the capability for the transmission of signals between
user-network interfaces.
Bearer services are described by a number of attributes, where an attribute is defined as a specified
characteristic of an object or element whose values distinguish that object or element from others.
For the purpose of this TS, a PSTN is assumed to provide a bearer service which equates to an ISDN
3,1 kHz audio bearer service.
Refer to GSM 02.02 for complete list of bearer services. Refer to GSM 04.08 for coding of Bearer
Capabilities.
Table 3/09.07: Bearer Service Interworking
Bearer service category in Bearer Service in GSM Bearer service in Service in
GSM PLMN ISDN PSTN
Circuit mode unstructured with Asynchronous Data 300 bit/s
unrestricted digital capability
Asynchronous Data 1.2 kbit/s
Transparent and Asynchronous Data Not
Non transparent 1 200/75 bit/s Applicable
Asynchronous Data 2.4 kbit/s Cct mode
structured 64 kbit/s
unrestricted
Asynchronous Data 4.8 kbit/s
Asynchronous Data 9.6 kbit/s
Asynchronous Data general
Circuit mode unstructured with Synchronous Data 1.2 kbit/s
unrestricted digital capability
Transparent
Synchronous Data 2.4 kbit/s
Synchronous Data 4.8 kbit/s
Synchronous Data 9.6 kbit/s
Synchronous Data general
Circuit mode unstructured with Packet Services Packet Services
unrestricted digital capability. see GSM 09.06 see GSM 09.06
Non-transparent
(continued)
Page 16
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
Table 3/09.07 (concluded): Bearer Service Interworking
Bearer service category in Bearer Service in GSM Bearer service in Service in
GSM PLMN ISDN PSTN
3,1 kHz Audio Ex PLMN Asynchronous Data 300 bit/s
Transparent and
Non-transparent
Asynchronous Data 1.2 kbit/s Cct Mode
3,1 kHz
Audio
Asynchronous Data Cct Mode
1 200/75 bit/s
Asynchronous Data 2.4 kbit/s 3,1 kHz Audio
Asynchronous Data 4.8 kbit/s
Asynchronous Data 9,6 kbit/s
Asynchronous Data general
3,1 kHz Audio Ex PLMN Synchronous Data 1.2 kbit/s
Transparent Synchronous Data 2.4 kbit/s
Synchronous Data 4.8 kbit/s
Synchronous Data 9.6 kbit/s
Synchronous Data general
3,1 kHz Audio Ex PLMN See GSM 09.06 See GSM 09.06
Non Transparent
Alternate speech /data circuit
alternate speech/
mode unstructured with 3,1 kHz
asynchronous
audio ex PLMN (with user rates 300 to
28800 bit/s as above)
Transparent
alternate speech/
synchronous
(with user rates 1200 to
28800 bit/s as above)
Alternate speech/data circuit Cct mode Cct mode
alternate speech/
mode unstructured with 3,1 kHz 3,1 kHz Audio 3,1 kHz
asynchronous
(with user rates 300 to
audio ex PLMN Audio
28800 bit/s as above)
non transparent
Circuit mode with speech Cct mode
Cct mode speech followed by
followed 3,1 kHz audio
data
by data 300 to 28800 bit/s
asynchronous as above
Transparent and Non
transparent
Page 17
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
Table 4/09.07: Network interworking of GSM Teleservices
Teleservice in Lower layer capabilities Bearer service Service
GSM PLMN addressed in the GSM Bearer in ISDN in PSTN
Capabilities IE
Telephony Unstructured with speech capability Speech or Cct mode Cct Mode
Emergency calls Unstructured with speech capability 3,1 kHz audio 3,1 kHz audio
Alternate speech/ Data Cct duplex synchronous Cct mode 3,1 kHz Cct mode 3,1 kHz
facsimile group 3 access audio audio
alternate speech
group 3 fax
Automatic Data Cct duplex synchronous Cct mode 3,1 kHz
Facsimile group 3 access audio
group 3 fax
This table does not identify any relationship between Teleservices in the GSM PLMN with those in the
ISDN/PSTN, it is merely to identify the interworking of the lower network layers of that teleservice with the
network layers i.e. bearer service in the ISDN/PSTN.
7.3 Signalling interworking
See GSM 09.03.
7.4 Numbering
See GSM 03.03.
7.5 Supplementary service interworking
For general aspects of supplementary services refer to GSM 03.11, GSM 03.8x and 03.9x series.
Not every supplementary service may be used in combination with each basic service. The applicability of
each supplementary service for a basic service is defined in GSM 02.8x and 02.9x-series. Certain
application rules are also set out in GSM 02.03, 09.05 and 09.06.
This subclause only deals with data service specific aspects of supplementary services, i.e. MSC/IWF
functions concerned in combination with supplementary services. This interworking is described in
GSM 02.04, GSM 02.8x, and 02.9x-series, GSM 03.11, GSM 03.8x and GSM 03.9x-series, if applicable.
8 Compatibility and subscription checking
Compatibility checking is carried out on the following items:
a) Low layer compatibility - utilizing low layer compatibility and bearer capability information elements.
b) High layer compatibility - utilizing high layer compatibility information element.
The use of the progress indicator for compatibility checking is outside the scope of this ETS.
Indication of compatibility requirements is carried out as described in subclause 9.2.2 under "a) Functional
operation" or "b) Mobile subscriber indicates requirement in call confirmation message" and subclause
10.2.2 "Network interworking mobile terminated".
For subscription checking, relevant for the interworking described in clauses 9 and 10 of this ETS, refer to

GSM 02.01.
Page 18
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
9 Interworking to PSTN
9.1 Speech Calls
9.1.1 Interworking indications to PLMN terminal
An indication to inform the PLMN terminal that:
i) instead of receiving out-of-band indications for certain types of failure conditions, a tone or
announcement will be received in-band from the PSTN.
ii) the available compatibility information will be not exhaustive for deducing a GSM Basic Service and
there will be a limitation on address - the terminal may be required to accept the call on the basis of
indicating its compatibility requirements.
iii) (if a DTE) in-band handshaking signals should be anticipated.
9.1.2 Transmission aspects
Includes control of Speech Processing and Echo Control Devices, see GSM 03.50.
9.1.3 Generation of In-band Tones and Announcements (PLMN-PSTN)
In-band tones and announcements shall be provided for all speech and 3,1 kHz audio bearer services
between a PLMN and a PSTN.
9.2 Data Calls
Low Layer Compatibility Checking on the received GSM bearer capability information element will be
carried out by the MSC/IWF to check if the call setup is compatible to the bearer service (3,1 kHz audio)
provided by a PSTN and to the IWFs provided by the PLMN.
In case the call setup does not conform to these requirements (e.g. an information transfer capability
value "unrestricted digital information" is requested), the call shall fail with an error cause indicating that
the network is unable to support the service requested.
As well as compatibility checking subscription checking shall be performed. If the subscription check fails
the call setup shall be rejected.
For the case where the MS offers negotiable values in the GSM bearer capability information element
(e.g. both transparent and non-transparent connection element) refer to the definitions specified in
GSM 07.01.
For interworking of data calls between a PLMN and a PSTN a modem will be utilized to provide the
interworking function.
PLMN
TE MT RA MODEM PSTN MODEM
IW F
V.series
Figure 1: PLMN PSTN interworking for circuit switched calls

Page 19
ETS 300 976 (GSM 09.07 version 5.4.1): January 1998
9.2.1 Network interworking mobile originated
9.2.1.1 Selection of interworking function
The interworking function will need to negotiate with the user to establish the appropriate modem selection
e.g. data rate, modulation scheme, etc. In addition, it will also be required to convert the signalling format,
from a combination of out of band and in band, to that suitable for controlling the modem and the
autocalling line procedure function where applicable. In the following modem selection procedures it is
assumed that the interworking function and modems will be associated with each MSC. As an alternative,
a centralized modem resource is possible as a network provider option. Signalling between the MSC and
the centralized modem resource is outside the scope of this specification.
For a data call originated by a circuit mode data terminal on the PLMN, the modem selection is done by
using the element "modem type" in the call set-up message (bearer capability).
In addition, other elements of the call setup will indicate the user rate, etc. to be used via that modem. The
use of this information however means that the network is only able to select a modem from the modem
pool which conforms to the speed which the terminal is utilizing at the DTE/DCE interface at the MS
(e.g. V.22 for 1 200 bps). The exception to this is where the user has selected the non transparent service
in which case either an autobauding or multi self selecting speed modem (e.g. V.32) may be used.
In case the GSM-BC(s) received with the set-up message indicated a multislot or 14.4kbit/s-operation
(refer to GSM 07.01) and the network does not support this service, the GSM-BC(s) sent with the call
proceeding message shall not contain the “fixed network user rate”, “other modem type” and “user
initiated modification indicator” parameters - the MSC shall discard the multislot or 14.4kbit/s-related
parameters and use the fall-back bearer service indicated by the remaining parameters of the GSM-BS(s)
on a singleslot configuration (refer to GSM 08.20 and GSM 04.21) on the MSC/IWF-BSS link.
If the MSC supports the multislot or 14.4kbit/s-operation, the GSM-BC(s) shall include the “fixed network
user rate”, “other modem type”
...