ETSI ETS 300 945 ed.7 (1999-03)

Digital cellular telecommunications system (Phase 2+) (GSM); Rate adaption on the Mobile Station - Base Station System (MS - BSS) interface (GSM 04.21 version 5.6.1 Release 1996)

RE/SMG-040421QR5

Digitalni celični telekomunikacijski sistem (faza 2+) – Prilagoditev hitrosti na vmesniku sistema mobilna postaja-bazna postaja (MS-BSS) (GSM 04.21, različica 5.6.1, izdaja 1996)

General Information

• Status: Published
• Publication Date: 16-Mar-1999
• Technical Committee: SMG 4 - Data Services
• Current Stage: 12 - Completion
• Due Date: 19-Mar-1999
• Completion Date: 17-Mar-1999
• Ref Project: SIST ETS 300 945 E7:2003 - Digital cellular telecommunications system (Phase 2+) (GSM); Rate adaption on the Mobile Station - Base Station System (MS - BSS) interface (GSM 04.21 version 5.6.1 Release 1996)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 945 E7:2003
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHPID]D±3ULODJRGLWHYKLWURVWLQD
YPHVQLNXVLVWHPDPRELOQDSRVWDMDED]QDSRVWDMD06%66*60UD]OLþLFD
L]GDMD
Digital cellular telecommunications system (Phase 2+) (GSM); Rate adaption on the
Mobile Station - Base Station System (MS - BSS) interface (GSM 04.21 version 5.6.1
Release 1996)
Ta slovenski standard je istoveten z: ETS 300 945 Edition 7
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
SIST ETS 300 945 E7:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 945 E7:2003

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SIST ETS 300 945 E7:2003
EUROPEAN ETS 300 945
TELECOMMUNICATION March 1999
STANDARD Seventh Edition
Source: SMG Reference: RE/SMG-040421QR5
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+);
Rate adaption on the Mobile Station - Base Station System
(MS - BSS) Interface
(GSM 04.21 version 5.6.1 Release 1996)
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.

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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.

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Contents
Intellectual Property Rights.5
Foreword .5
1 Scope .7
2 Normative references.7
2.1 Abbreviations and definitions.7
3 General approach.8
3.1 Overview of the multislot data rates.8
4 The RA0 Function .10
4.1 Asynchronous-to-Synchronous Conversion (RA0) .10
4.2 Break signal .11
4.3 Overspeed/Underspeed.11
4.4 Parity Bits.11
4.5 Flow Control.11
5 The RA1 Function .11
5.1 Adaptation of synchronous data rates up to 38,4 kbit/s.12
5.1.1 Network Independent Clocking .13
5.1.1.1 Multiframe Structure .13
5.1.1.2 Encoding and compensation .13
6 The RA1’’ function.14
6.1 Rate adaptation of 48 kbit/s user rates with DTE/DCE status to 64 kbit/s.14
6.2 Rate adaptation of 56 kbit/s user rate to 64 kbit/s .14
7 The RA2 Function .14
8 The RA1/RA1' Function.15
8.1 Single slot rates .15
8.1.1 Radio interface rate of 14,5 kbit/s .15
8.1.1.1 Multiframe structure over the radio-interface.16
8.1.1.2 Radio-interface data block for TCH/F14.4 channel coding.17
8.1.2 Radio Interface rate of 12 kbit/s .18
8.1.4 Radio Interface rate of 6 kbit/s .18
8.1.5 Radio Interface rate of 3,6 kbit/s (transparent services only).19
8.1.6 Synchronisation.20
8.1.7 Idle frames.20
8.2 Multislot rates.20
8.2.1 TCH/F14.4 multislot operation.20
8.2.2 AIURs up to 38,4 kbit/s using TCH/F9.6 and TCH/F4.8 channel codings.20
8.2.3 AIURs up to 38,4 kbit/s using TCH/F14.4 channel coding .21
8.2.4 AIUR of 48 kbit/s; Intermediate rate of 64 kbit/s; Radio interface rate of 5·
12 kbit/s.21
8.2.5 AIUR of 48 kbit/s; Intermediate rate of 64 kbit/s; Radio interface rate of 4·
14,5 kbit/s.21
8.2.6 AIUR of 56 kbit/s; Intermediate rate of 64 kbit/s;.22
8.2.7 AIUR of 56 kbit/s; Intermediate rate of 64 kbit/s; Radio interface rate of
4 · 14,5 kbit/s.22
8.2.8 AIUR of 64 kbit/s; Radio interface rate of 6 · 12 kbit/s .22
8.2.9 AIUR of 64 kbit/s; Radio interface rate of 5 · 14,5 kbit/s .23
9 The RA1' Function.23

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9.1 Synchronous user rates up to 9,6 kbit/s. 23
9.2 Synchronous user rates from 9,6 kbit/s onward; TCH/F9.6/4.8 channel codings. 24
9.3 Synchronous user rates from 9,6 kbit/s onward; TCH/F14.4 channel coding. 24
10 The Split/Combine and Padding-functions .24
10.1 Data frame distribution into the substreams/channels by the Split/Combine function . 24
10.1.1 Data frame distribution into the substreams/channels by the
Split/Combine function (TCH/F9.6 and TCH/F4.8 channel codings). 24
10.1.2 Data block distribution into the substreams by the Split/Combine function
(TCH/F14.4 channel coding). 25
10.2 Substream numbering in transparent operation. 25
10.2.1 Substream numbering for TCH/F14.4 channel coding . 26
10.3 Initial Substream Synchronisation for TCH/F9.6 and TCH/F4.8 channel codings . 26
10.3.1 Initial Substream Synchronisation for TCH/F14.4 channel coding . 26
10.4 Action on loss of synchronisation. 26
10.4.1 Non-transparent services (TCH/F9.6 and TCH/F4.8 channel codings). 26
10.4.2 Transparent services (TCH/F9.6 and TCH/F4.8 channel codings) . 27
10.4.3 Non-transparent services (TCH/F14.4 channel coding) . 27
10.4.4 Transparent services (TCH/F14.4 channel coding). 27
10.5 Network independent clocking . 27
10.5.1 Network Independent Clocking for TCH/F14.4 channel coding (both
single- and multilinks) . 27
10.5.1.1 Negative compensation . 28
10.5.1.2 Positive compensation . 28
10.6 Padding TCH/F frames when the AIUR is not a multiple of 9,6 or 4,8 kbit/s . 28
10.6.1 Padding for TCH/F14.4 channel coding. 29
11 Support of Non-Transparent Bearer Services . 29
11.1 Support of non-transparent operation for TCH/F9.6 and TCH/F4.8 channel codings. 29
11.2 Support of non-transparent operation for TCH/F14.4 channel coding . 30
12 Figures on Frame structures . 31
Annex A (informative): Stacks of rate adaptation . 36
A.1 Stacks of rate adaptation for 9,6/4,8 kbit/s single slot operation . 36
A.2 Stacks of rate adaptation for 14,4 kbit/s single slot operation . 37
A.3 Stacks of rate adaptation for 9,6/4,8 kbit/s multi slot operation. 38
A.4 Stacks of rate adaptation for 14,4 kbit/s multi slot operation. 39
Annex B (informative): An example of mapping Network Independent Clocking information for
TCH/F14.4 when the S-interface is deployed: . 40
Annex C (informative): Change history. 41
History. 42

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Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The
information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-
members, and can be found in SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially
Essential, IPRs notified to ETSI in respect of ETSI standards", which is available free of charge from the
ETSI Secretariat. Latest updates are available on the ETSI Web server (http://www.etsi.org/ipr).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI.
No guarantee can be given as to the existence of other IPRs not referenced in SR 000 314 (or the
updates on the ETSI Web server) which are, or may be, or may become, essential to the present
document.
Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) of the European Telecommunications Standards Institute (ETSI).
This ETS defines the rate adaptation functions to be used in Mobile Stations (MS) for adapting terminal
interface data rates to the Mobile Station - Base Station System (MS - BSS) interface data rates within the
digital cellular telecommunications system.
The contents of this ETS is subject to continuing work within SMG and may change following formal SMG
approval. Should SMG modify the contents of this ETS, it will 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:
5 indicates GSM Phase 2+ Release 1996;
x the second digit is incremented for all changes of substance, i.e. technical enhancements,
corrections, updates, etc.
y the third digit is incremented when editorial only changes have been incorporated in the
specification.
Transposition dates
Date of adoption of this ETS: 19 March 1999
Date of latest announcement of this ETS (doa): 30 June 1999
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 December 1999
Date of withdrawal of any conflicting National Standard (dow): 31 December 1999

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1 Scope
This European Telecommunication Standard (ETS) defines the rate adaptation functions to be used in
GSM PLMN Mobile Stations (MS)s for adapting terminal interface data rates to the Mobile Station - Base
Station System (MS-BSS) interface data rates in accordance with GSM 03.10 [3].
The provision of these functions will depend on the services a particular station is designed to support.
NOTE: This ETS should be considered together with GSM 08.20 [9] (Rate Adaptation on the
BSS-MSC Interface) to give a complete description of PLMN rate adaptation.
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] GSM 01.04 (ETR 350): "Digital cellular telecommunication system (Phase 2+);
Abbreviations and acronyms".
[2] GSM 02.34: "Digital cellular telecommunications system (Phase 2+); High
Speed Circuit Switched Data (HSCSD) -Stage 1".
[3] GSM 03.10: "Digital cellular telecommunication system (Phase 2+); GSM Public
Land Mobile Network (PLMN) connection types".
[4] GSM 03.34 (TS 101 038): “Digital cellular telecommunications system
(Phase 2+); High Speed Circuit Switched Data (HSCSD) - Stage 2 Service
Description”.
[5] GSM 05.03 (ETS 300 909): "Digital cellular telecommunications system
(Phase 2+); Channel coding".
[6] GSM 07.01 (ETS 300 913): "Digital cellular telecommunication system
(Phase 2+); General on Terminal Adaptation Functions (TAF) for Mobile
Stations (MS)".
[7] GSM 07.02 (ETS 300 914): "Digital cellular telecommunications system
(Phase 2+); Terminal Adaptation Functions (TAF) for services using
asynchronous bearer capabilities".
[8] GSM 07.03 (ETS 300 915): "Digital cellular telecommunications system
(Phase 2+); Terminal Adaptation Functions (TAF) for services using
synchronous bearer capabilities".
[9] GSM 08.20: "Digital cellular telecommunication system (Phase 2+); Rate
adaption on the Base Station System - Mobile-services Switching Centre (BSS -
MSC) interface".
[10] CCITT Recommendation V.110: "Support of data terminal equipments (DTEs)
with V-Series interfaces by an integrated services digital network".
[11] CCITT Recommendation X.30: "Support of X.21,X.21 bis and X.20 bis based
terminal equipments (DTEs) by integrated services digital network (ISDN)".
2.1 Abbreviations and definitions
Abbreviations used in this ETS are listed in GSM 01.04.

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Overall data stream: The data stream in those parts of the network where the data flow is not split into
multiple channels.
Substream: Stream of data with explicit or implicit numbering between splitter and combiner functions.
Channel: A physical full rate channel on the radio interface (TCH/F) independent of the contents
Multislot intermediate rate: Intermediate rate per substream in those parts of the network where the
overall data stream is split into substreams.
Intermediate rate: Intermediate rate in the overall data stream.
Substream rate: The user rate including padding, if applicable, on one individual substream
3 General approach
GSM 03.10 defines the PLMN connection types necessary to support the GSM PLMN data and telematic
services.
Within the MS there are several different data rate adaptation functions - and a Split/Combine-function in
case of a multislot data configuration - which are combined as shown in GSM 03.10 as part of the
connection type.
The rate adaptation functions are RA0, RA1, RA2, RA1', RA1’’ and RA1/RA1'. The RA0, RA1 and RA2 are
equivalent to those functions described in CCITT recommendation V.110 [11].
The RA1' function is similar to RA1 but has a reduced bit rate output compatible with the coding scheme
proposed for data services on the radio interface.
The RA1’’ function is used for converting between synchronous user rates of 48 and 56 kbit/s and the rate
64 kbit/s.
The RA1/RA1' is a relay function, used as indicated in GSM 03.10.
In multislot data-configurations the overall data stream is split into parallel substreams between the
Split/Combine-functions.
3.1 Overview of the multislot data rates
For TCH/F9.6 and TCH/F4.8 channel codings, the multislot intermediate rates are 16 and 8 kbit/s per
TCH/F, respectively.
For TCH/F14.4 channel coding, the multislot intermediate rate is 16 kbit/s per TCH/F.
Between the TE and the Split/Combine-function at the MS, where the overall data stream is not split,
intermediate rates of 8, 16, 32 and 64 kbit/s are applicable

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Table 1: AIUR/Multislot intermediate rates
Air interface user DTE/DCE RA0 RA1/RA1’ RA1’
rate statuses
Padding
Multislot intermediate Frame type Radio
rate interface rate
X X 8 kbit/s 80 bit frames 3,6 kbit/s£ 600 bit/s
1200 bit/s X X 8 kbit/s 80 bit frames 3,6 kbit/s
2,4 kbit/s X X 8 kbit/s 80 bit frames 3,6 kbit/s
4,8 kbit/s X X 8 kbit/s 80 bit frames 6 kbit/s
9,6 kbit/s X X 80 bit frames 12 kbit/s or
16 kbit/s or 2·8 kbit/s
2·6 kbit/s
14,4 kbit/s X X 2·16 kbit/s or 3·8 kbit/s 80 bit frames 2·12 kbit/s or P
(note 1)
3·6 kbit/s
16 kbit/s 14,5 kbit/s
Note 7
19,2 kbit/s X X 80 bit frames
2·16 kbit/s or 4·8 kbit/s 2·12 kbit/s or
4·6 kbit/s
28,8 kbit/s X X 80 bit frames
3·16 kbit/s 3·12 kbit/s
2 x 16 kbit/s
2·14,5 kbit/s
Note 7
38,4 kbit/s X X 80 bit frames P
4·16 kbit/s 4·12 kbit/s
(note 6)
3 x 16 kbit/s 3·14,5 kbit/s
Note7
48 kbit/s X Note 2 Note 2 P
5·12 kbit/s
(note 6)
4 x 16 kbit/s 4·14,5 kbit/s
Note7
56 kbit/s Note 2 Note 2 P
5·12 kbit/s
(note 3) (note 6)
4x16 kbit/s
4·14,5 kbit/s
Note7
64 kbit/s Note 2 Note 2 P
6·12 kbit/s
(note 1)
(note 3)
(note 6)
5·14,5 kbit/s
P=Padding used

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Table 2: AIUR / Intermediate rates
Air interface DTE/DCE RA0 RA1 RA1’
user rate statuses
Padding
Intermediate Frame type Radio interface
rate rate
X X 8 kbit/s 80 bit frames 3,6 kbit/s£ 600 bit/s
1200 bit/s X X 8 kbit/s 80 bit frames 3,6 kbit/s
2,4 kbit/s X X 8 kbit/s 80 bit frames 3,6 kbit/s
4,8 kbit/s X X 8 kbit/s 80 bit frames 6 kbit/s
9,6 kbit/s X X 16 kbit/s 80 bit frames 12 kbit/s or
2·6 kbit/s
14,4 kbit/s X X 32 kbit/s 80 bit frames 2·12 kbit/s or P
(note 1)
3·6 kbit/s
1x14,5 kbit/s
19,2 kbit/s X X 32 kbit/s 80 bit frames
2·12 kbit/s or
4·6 kbit/s
28,8 kbit/s X X 64 kbit/s 80 bit frames
3·12 kbit/s
2·14,5 kbit/s
38,4 kbit/s X X 64 kbit/s 80 bit frames 4·12 kbit/s P
(note 6)
3·14,5 kbit/s
48 kbit/s X Note 4 Note 4 5·12 kbit/s P
(note 6)
4·14,5 kbit/s
56 kbit/s Note 4 Note 4 5·12 kbit/s P
(note 6)
(note 3)
4·14,5 kbit/s
64 kbit/s Note 5 Note 5 P
6·12 kbit/s
(note 1)
(note 3)
(note 6)
5·14,5 kbit/s
P=Padding used
NOTE 1: For information on the padding procedure, please refer to clause 10 of this document.
NOTE 2: No multislot intermediate rate; substreams combined at the BSS when TCH/F9.6/4.8
channel coding is used.
NOTE 3: AIUR 11,2 kbit/s per channel
NOTE 4: For this rateGSM-specific rate adaptation function RA1’’ rather than RA1is applied.
NOTE 5: For this rate RA1- and RA2- adaptations are not applied.
NOTE 6: Padding used as specified for TCH/F14.4 channel codings
NOTE 7: At the network side, RA1’/RA1 not applied; instead a TCH/F14,4-specific adaptation
RA1’/RAA’ used (GSM 08.20)
4 The RA0 Function
4.1 Asynchronous-to-Synchronous Conversion (RA0)
The RA0 Function is only used with asynchronous interfaces. Incoming asynchronous data is padded by
the addition of stop elements to fit the nearest higher rate defined by 2 to the power n ( where n£ 6) times
600 bit/s or, if applicable, to either 14,4 or 28,8 kbit/s. Thus both 75 bit/s and 300 bit/s user data signalling
rates shall be adapted to a synchronous 600 bit/s stream. The resultant synchronous stream is fed to RA1
or RA1'.

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Asynchronous user rate Synchronous user rate
0.6 kbit/s£ 0.6 kbit/s
1,2 kbit/s 1,2 kbit/s
2,4 kbit/s 2,4 kbit/s
4,8 kbit/s 4,8 kbit/s
9,6 kbit/s 9,6 kbit/s
14,4 kbit/s 14,4 kbit/s
19,2 kbit/s 19,2 kbit/s
28,8 kbit/s 28,8 kbit/s
38,4 kbit/s 38,4 kbit/s
4.2 Break signal
The RA0 shall detect and transmit the break signal in the following fashion:
If the converter detects 2M to 2M+3 bits, all of start polarity, where M is the number of bits per character in
the selected format including start and stops bits, the converter shall transmit 2M+3 bits of start polarity.
If the converter detects more than 2M+3 bits all of start polarity, the converter shall transmit all these bits
as start polarity.
The 2M+3 or more bits of start polarity received from the transmitting sides shall be output to the receiving
terminal.
The terminal must transmit on circuit 103 at least 2M bits stop polarity after the start polarity break signal
before sending further data character. The converter shall then regain character synchronism from the
following stop to start transition.
4.3 Overspeed/Underspeed
A RA0 shall insert additional stop elements when its associated terminal is transmitting with a lower than
nominal character rate. If the terminal is transmitting characters with an overspeed of up to 1 %, the
asynchronous-to-synchronous converter may delete stop elements as often as is necessary to a
maximum of one for every eight characters at 1 % overspeed. The converter on the receiving side shall
detect the deleted stop elements and reinsert them in the received data stream (circuit 104).
The realization of overspeed handling, as described above, at the interface to the associated terminal is
implementation dependent. Possible implementations are e.g. the reduction of the length of the stop
elements according to V.110 [9] or increased data rates between the TA and terminal.
4.4 Parity Bits
Possible parity bits included in the user data are considered as data bits by the RA0 function (and RA1
function).
4.5 Flow Control
Where applicable, this function is as specified in the relevant terminal adaptation function Specification
(see GSM 07 series).
5 The RA1 Function
This function is used to adapt between the synchronous user rates, or the output of the RA0 function and
the intermediate rate of 8, 16, 32 or 64 kbit/s.

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5.1 Adaptation of synchronous data rates up to 38,4 kbit/s
Synchronous user rate Intermediate
rate
£ 2,4 kbit/s 8 kbit/s
4,8 kbit/s 8 kbit/s
9,6 kbit/s 16 kbit/s
14,4 kbit/s 32 kbit/s
19,2 kbit/s 32 kbit/s
28,8 kbit/s 64 kbit/s
38,4 kbit/s 64 kbit/s
A CCITT V.110 80 bits frame is constructed using the user data bits received (from the RA0 in the
asynchronous case), the values of the S bits are deduced from the R interface.
Adaptation of 600 bit/s to 8Kbit/s is performed by 8 times consecutive duplication of each user data bit.
(Figure 9)
Adaptation of 1200 bit/s to 8 Kbit/s is performed by 4 times consecutive duplication of each user data bit.
(Figure 8)
Adaptation of 2400 bit/s to 8kbit/s is performed by 2 times consecutive duplication of each user data bit.
(Figure 7)
Adaptation of 4800 bit/s to 8 Kbit/s is performed by transmitting the bit stream with no duplication.
(Figure 3)
Adaptation of 9600 bit/s to 16 Kbit/s is performed by transmitting the bit stream with no duplication (the
emitting period is halved with respect to the 4800 bit/s case). (Figure 3)
Adaptation of 14400 bit/s to 32 Kbit/s is performed as for 3600 bit/s to 8 kbit/s (the emitting period is
divided by four with respect to the 3600 bit/s case).( Adaptation of 3600 bit/s to 8 kbit/s is performed by
transmitting the bit stream with no duplication.) (Figure 12)
Adaptation of 19200 bit/s to 32 Kbit/s is performed as for 4800 bit/s to 8 kbit/s (the emitting period is
divided by four with respect to the 4800 bit/s case). (Figure 3)
Adaptation of 28800 bit/s to 64 Kbit/s is performed as for 3600 bit/s to 8 kbit/s (the emitting period is
divided by eight with respect to the 3600 bit/s case). (Figure 12)
Adaptation of 38400 bit/s to 64 Kbit/s is performed as for 4800 bit/s 8 kbit/s (the emitting period is divided
by eight with respect to the 4800 bit/s case). (Figure 3)
The CCITT V.110 80 bit frames shown in Figures 3 and 12 are used. The D bits are used to convey the
user data and the S and X bits are used to convey channel control information according to the relevant
terminal adapter function Specification.
The E bits are used to convey the following information:
i) User Data Rate - E1, E2, E3 (for single slot operation see Figure 4, and for multislot operation
Figure 4 and subclause 10.7)
ii) Network Independent Clocking - E4, E5, E6
iii) Multiframe Synchronisation - E7
The order of transmission of the 80 bit frame is from left to right and top to bottom.

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5.1.1 Network Independent Clocking
Synchronous data signals received by the MT from the DTE at the MS or by IWF from the modem on the
PSTN may not be synchronized to the PLMN. The following method shall be used to enable transfer of
those data signals and the corresponding bit timing information via the V.110 frames. Such a situation
would exist where the signals received from the modem at the IWF require its own clock or where the
signals received from the DTE at the MS employs its own network independent clock. In any case, the
frequency tolerance of the clocks involved is 100 ppm.
5.1.1.1 Multiframe Structure
The transmitting end of the GSM PLMN connection shall establish a multiframe structure utilizing bit E7
consisting of four frames by setting E7 in every fourth frame to binary 0. This structure is identical to the
use of E7 in V.110 (and X.30) except that such a multiframe structure will exist for all user data rates. This
frame synchronization will be achieved and maintained during the entire call so that corrections for the
network independent clocking by the receiving end of the GSM PLMN connection can be easily
recognized and applied based on the code words (in c1, c2, c3, c4 and c5) positioned in bits E4, E5 and
E6 of two consecutive V.110 frames as illustrated in figure 1. Thus, the multiframe structure allows for one
5-bit code words to be transmitted every two V.110 frames for the purposes of network independent
clocking. The two code-words may be different from each other within the multiframe shown in figure 1.
Frame E4 E5 E6 E7
MF 0a c1 c2 1
...