SIST EN 62106:2007

Specification of the radio data system (RDS) for VHF/FM sound broadcasting in the frequency range from 87,5 to 108,0 MHz

RDS is intended for applications to VHF/FM sound broadcasts in the range 87,5 MHz to 108,0 MHz which may cary either stereophonic (pilot-tone system) or monophonic programmes. The main objectives of RDS are to enable improved functionality for FM receivers and to make them more user-friendly by using features such as Programme Identification, Programme Service name display and where applicable, automatic tuning for portable and car radios, in particular. The relevant basic tuning and switching information therefore has to be implemented by the type O group, and it is not optional unlike many of the other possible features in RDS.

Spezifikation des Radio-Daten-Systems (RDS) für den VHF/FM Tonrundfunk im Frequenzbereich 87,5 bis 108,0 MHz

Spécification du système de radiodiffusion de données (RDS) pour la radio à modulation de fréquence dans la bande 87,5 à 108,0 MHz

Specifikacija radijskega podatkovnega sistema (RDS) za VHF/FM zvokovno radiodifuzijo v frekvenčnem območju od 87,5 MHz do 108,0 MHz (IEC 62106:2000)

General Information

• Status: Withdrawn
• Publication Date: 31-Dec-2006
• Withdrawal Date: 21-Dec-2009
• ICS: 33.170 - Television and radio broadcasting
• Technical Committee: AVM - Audio, video and multimedia systems and equipment
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 22-Dec-2009
• Due Date: 14-Jan-2010
• Completion Date: 22-Dec-2009
• Ref Project: EN 62106:2001 - Specification of the radio data system (RDS) for VHF/FM sound broadcasting in the frequency range from 87,5 to 108,0 MHz

Relations

• Revised: SIST EN 62106:2010 - Specification of the radio data system (RDS) for VHF/FM sound broadcasting in the frequency range from 87,5 to 108,0 MHz (IEC 62106:2009)
• Effective Date: 04-Dec-2012
• Replaced By: SIST EN 62106:2010 - Specification of the radio data system (RDS) for VHF/FM sound broadcasting in the frequency range from 87,5 to 108,0 MHz (IEC 62106:2009)
• Effective Date: 29-Jan-2023
• Replaces: SIST EN 50067:1999 - Specification of the radio data system (RDS) for VHF/FM sound broadcasting in the frequency range from 87,5 to 108,0 MHz
• Effective Date: 28-Jan-2023
• Replaced By: SIST EN 62106:2010 - Specification of the radio data system (RDS) for VHF/FM sound broadcasting in the frequency range from 87,5 to 108,0 MHz (IEC 62106:2009)
• Effective Date: 01-Feb-2010
• Replaces: SIST EN 50067:1999 - Specification of the radio data system (RDS) for VHF/FM sound broadcasting in the frequency range from 87,5 to 108,0 MHz
• Effective Date: 01-Jan-2007

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EUROPEAN STANDARD EN 62106
NORME EUROPÉENNE
EUROPÄISCHE NORM December 2001
ICS 33.060.20;33.170;35.240.99 Supersedes EN 50067:1998
English version
Specification of the radio data system (RDS)
for VHF/FM sound broadcasting
in the frequency range from 87,5 to 108,0 MHz
(IEC 62106:2000)
Spécification du système de radiodiffusion Spezifikation des Radio-Daten-Systems
de données (RDS) pour la radio (RDS) für den VHF/FM Tonrundfunk
à modulation de fréquence im Frequenzbereich 87,5 bis 108,0 MHz
dans la bande 87,5 à 108,0 MHz (IEC 62106:2000)
(CEI 62106:2000)
This European Standard was approved by CENELEC on 2000-04-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands,
Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2001 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 62106:2001 E

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

EN 62106:2001 - 2 -
Foreword
The text of document 100A/134A/FDIS, future edition 1 of IEC 62106, prepared by SC 100A, Multimedia
end-user equipment, of IEC TC 100, Audio, video and multimedia systems and equipment, was
submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 62106 on
2000-04-01.
This European Standard supersedes EN 50067:1998.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2002-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2002-07-01
__________
Endorsement notice
The text of the International Standard IEC 62106:2000 was approved by CENELEC as a European
Standard without any modification.
In the official version, in annex Q, Bibliography, the following note has to be added for the standard
indicated:
IEC 60315-9 NOTE Harmonized as EN 60315-9:1996 (not modified).
__________

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INTERNATIONAL IEC
STANDARD
62106
First edition
2000-01
Specification of the radio data system (RDS)
for VHF/FM sound broadcasting
in the frequency range
from 87,5 to 108,0 MHz
 IEC 2000  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: [phone] e-mail: [e-mail] IEC web site http://www.iec.ch
Commission Electrotechnique Internationale
PRICE CODE
XF
International Electrotechnical Commission
For price, see current catalogue

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

62106 © IEC:2000 - 2 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
SPECIFICATION OF THE RADIO DATA SYSTEM (RDS) FOR VHF/FM SOUND
BROADCASTING IN THE FREQUENCY RANGE FROM 87,5 TO 108,0 MHZ
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising all national electrotechnical
committees (IEC National Committees). The object of the IEC is to promote international co-operation on all questions concerning standardization
in the electrical and electronic fields. To this end and in addition to other activities, the IEC publishes International Standards. Their preparation
is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work.
International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. The IEC collaborates
closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an international consensus of opinion on the
relevant subjects since each technical committee has representation from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form of standards, technical
specifications, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International Standards transparently to the
maximum extent possible in their national and regional standards. Any divergence between the IEC Standard and the corresponding national or
regional standard shall be clearly indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity
with one of its standards.
This International Standard IEC 62106 has been prepared by the IEC Subcommittee 100A: Multimedia end-user equipment,
of the Technical Committee 100: Audio, video and multimedia systems and equipment.
This standard is based on the European CENELEC Standard EN 50067:1998 prepared by the RDS Forum, using an earlier
specification [8] that was originally developed within the European Broadcasting Union. It was submitted to the National
Committees for voting under the Fast Track Procedure as the following documents:
FDIS Report on voting
100A/134A/FDIS 100A/139/RVD
Full information on the voting for the approval of this standard can be found in the report indicated in the above table.
Attention is drawn to the fact that there may be Intellectual Property Rights (IPR) in relation to certain provisions of this
standard. IPR holders should notify the IEC of their claims.
This publication has not been drafted in complete accordance with the ISO/IEC Directives, Part 3.
Annexes B, C, G, H, K, L and Q are for information only.
Annexes A, D, E, F, J, M, N, and P form an integral part of this standard.

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- 3 - 62106 © IEC:2000
CONTENTS
page
0 S cope . 6
1 Modulation characteristics of the data channel (physical layer) . 6
1.1 Subcarrier frequency . 6
1.2 Subcarrier phase . 6
1.3 Subcarrier level . 8
1.4 Method of modulation . 8
1.5 Clock-frequency and data-rate . 8
1.6 Differential coding . 8
1.7 Data-channel spectrum shaping . 9
2 Baseband coding (data-link layer) . 12
2.1 Baseband coding structure . 12
2.2 Order of bit transmission . 12
2.3 Error protection . 13
2.4 Synchronization of blocks and groups . 14
3 Message format (session and presentation layers) . 15
3.1 Addressing . 15
3.1.1 Design principles . 15
3.1.2 Principal features . 15
3.1.3 Group types . 17
3.1.4 Open data channel / Applications Identification . 19
3.1.4.1 Use of Open data applications . 19
3.1.4.2 Open data applications - Group structure . 20
3.1.5 Coding of the Group types . 21
3.1.5.1  Type 0 groups: Basic tuning and switching information . 21
3.1.5.2  Type 1 groups: Programme-item number and slow labelling codes . 23
3.1.5.3  Type 2 groups: RadioText . 25
3.1.5.4  Type 3A groups: Applications Identification for Open Data . 27
3.1.5.5  Type 3B groups: Open data application . 28
3.1.5.6  Type 4A groups: Clock-time and date . 28
3.1.5.7  Type 4B groups: Open data application . 29
3.1.5.8  Type 5 groups : Transparent data channels or ODA . 29
3.1.5.9  Type 6 groups : In house applications or ODA . 30
3.1.5.10 Type 7A groups: Radio paging or ODA . 31
3.1.5.11 Type 7B groups : Open data application . 31
3.1.5.12 Type 8 groups: Traffic Message Channel or ODA . 32
3.1.5.13 Type 9 groups: Emergency warning systems or ODA . 33
3.1.5.14 Type 10 groups: Programme Type Name (Group type 10A) and Open data
(Group type 10B)  . 34
3.1.5.15 Type 11 groups: Open data application . 35
3.1.5.16 Type 12 groups: Open data application . 36
3.1.5.17 Type 13A groups: Enhanced Radio paging or ODA . 36
3.1.5.18 Type 13B groups : Open data application . 37
3.1.5.19 Type 14 groups: Enhanced Other Networks information . 38
3.1.5.20 Type 15A groups . 39
3.1.5.21 Type 15B groups: Fast tuning and switching information . 39

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62106 © IEC:2000 - 4 -
page
3.2 Coding of information . 40
3.2.1 Coding of information for control . 40
3.2.1.1 Programme Identification (PI) codes and Extended Country Codes (ECC) . 40
3.2.1.2 Programme-type (PTY) codes . 40
3.2.1.3 Traffic-programme (TP) and traffic-announcement (TA) codes . 40
3.2.1.4 Music Speech (MS) switch code . 40
3.2.1.5 Decoder Identification (DI) and Dynamic PTY Indicator (PTYI) codes . 41
3.2.1.6 Coding of Alternative Frequencies (AFs) in type 0A groups . 41
3.2.1.7 Programme-item number (PIN) codes . 46
3.2.1.8 Coding of Enhanced Other Networks information (EON) . 46
3.2.2 Coding and use of information for display . 50
3.2.3 Coding of clock-time and date (CT) . 50
3.2.4 Coding of information for Transparent data channels (TDC) . 50
3.2.5 Coding of information for In House applications (IH) . 50
3.2.6 Coding of Radio paging (RP) . 51
3.2.6.1 Introduction . 51
3.2.6.2 Identification of paging networks . 52
3.2.7 Coding of Emergency Warning Systems (EWS) . 53
44 D es cription of f eatures . 54
5 M arking . 57

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- 5 - 62106 © IEC:2000
ANNEXES
page
Annex A (normative) - Offset words to be used for group and block synchronization . 59
Annex B (informative) - Theory and implementation of the modified shortened cyclic code . 60
Annex C (informative) - Implementation of group and block synchronization using the modified shortened
cyclic code . 66
Annex D (normative) - Programme identification codes and Extended country codes . 69
Annex E (normative) - Character definition for Programme Service name, Programme Type Name,
RadioText and alphanumeric Radio paging . 73
Annex F (normative) - Programme Type codes . 77
Annex G (informative) - Conversion between time and date conventions . 81
Annex H (informative) - Specification of the ARI system . 83
Annex J (normative) - Language identification . 84
Annex K (informative) - RDS logo . 86
Annex L (informative) - Open data registration . 87
Annex M (normative) - Coding of Radio Paging . 90
Annex N (normative) - Country codes and Extended country codes for countries outside the
European Broadcasting Area . 126
Annex P (normative) - Index of abbreviations . 131
Annex Q (informative) - Bibliography . 132

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62106 © IEC:2000 - 6 -
0  Scope
The Radio Data System, RDS, is intended for application to VHF/FM sound broadcasts in the range 87.5 MHz
to 108.0 MHz which may carry either stereophonic (pilot-tone system) or monophonic programmes. The main objectives
of RDS are to enable improved funtionality for FM receivers and to make them more user-friendly by using features such
as Programme Identification, Programme Service name display and where applicable, automatic tuning for portable and
car radios, in particular. The relevant basic tuning and switching information therefore has to be implemented by the type
0 group (see 3.1.5.1), and it is not optional unlike many of the other possible features in RDS.
1 Modulation characteristics of the data channel (physical layer)
The Radio Data System is intended for application to VHF/FM sound broadcasting transmitters in the range 87.5
to 108.0 MHz, which carry stereophonic (pilot-tone system) or monophonic sound broadcasts (see ITU-R
Recommendation BS.450-2).
It is important that radio-data receivers are not affected by signals in the multiplex spectrum outside the data
channel.
The system can be used simultaneously with the ARI (Autofahrer-Rundfunk-Information) system (see annex H),
even when both systems are broadcast from the same transmitter. However, certain constraints on the phase and injection
levels of the radio-data and ARI signals must be observed in this case (see 1.2 and 1.3).
The data signals are carried on a subcarrier which is added to the stereo multiplex signal (or monophonic signal
as appropriate) at the input to the VHF/FM transmitter. Block diagrams of the data source equipment at the transmitter and
a typical receiver arrangement are shown in figures 1 and 2, respectively.
1.1 Subcarrier frequency
During stereo broadcasts the subcarrier frequency will be locked to the third harmonic of the 19-kHz pilot-tone.
Since the tolerance on the frequency of the 19-kHz pilot-tone is ± 2 Hz (see ITU-R Recommendation BS.450-2), the
tolerance on the frequency of the subcarrier during stereo broadcasts is ± 6 Hz.
During monophonic broadcasts the frequency of the subcarrier will be 57 kHz ± 6 Hz.
1.2 Subcarrier phase
During stereo broadcasts the subcarrier will be locked either in phase or in quadrature to the third harmonic of
the 19 kHz pilot-tone. The tolerance on this phase angle is ± 10(, measured at the modulation input to the FM transmitter.
In the case when ARI and radio-data signals are transmitted simultaneously, the phase angle between the two
subcarriers shall be 90( ± 10(.

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- 7 - 62106 © IEC:2000
Figure 1 - Block diagram of radio-data equipment at the transmitter
*
The overall data-shaping in this decoder comprises the filter F and the data-shaping inherent in the biphase symbol decoder. The
1
amplitude/frequency characteristic of filter F is, therefore, not the same as that given in figure 3.
1
Figure 2 - Block diagram of a typical radio-data receiver/decoder

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62106 © IEC:2000 - 8 -
1.3 Subcarrier level
The deviation range of the FM carrier due to the unmodulated subcarrier is from ± 1.0 kHz to ± 7.5 kHz. The
1
recommended best compromise is ± 2.0 kHz ). The decoder/demodulator shall also operate properly when the deviation
of the subcarrier is varied within these limits during periods not less than 10 ms.
In the case when ARI (see annex H) and radio-data signals are transmitted simultaneously, the recommended
maximum deviation due to the radio-data subcarrier is ± 1.2 kHz and that due to the unmodulated ARI subcarrier shall be
reduced to ± 3.5 kHz.
The maximum permitted deviation due to the composite multiplex signal is ± 75 kHz.
1.4 Method of modulation
The subcarrier is amplitude-modulated by the shaped and biphase coded data signal (see 1.7). The subcarrier
is suppressed. This method of modulation may alternatively be thought of as a form of two-phase phase-shift-keying (psk)
with a phase deviation of ± 90(.
1.5 Clock-frequency and data-rate
The basic clock frequency is obtained by dividing the transmitted subcarrier frequency by 48. Consequently,
the basic data-rate of the system (see figure 1) is 1187.5 bit/s ± 0.125 bit/s.
1.6 Differential coding
The source data at the transmitter are differentially encoded according to the following rules:
Table 1 - Encoding rules
Previous output New input New output
(at time t ) (at time t ) (at time t )
i-1 i i
0 0 0
0 1 1
1 0 1
1 1 0
where t is some arbitrary time and t is the time one message-data clock-period earlier, and where the message-data clock-
i i-1
rate is equal to 1187.5 Hz.
1
) With this level of subcarrier, the level of each sideband of the subcarrier corresponds to half the
nominal peak deviation level of ± 2.0 kHz for an "all-zeroes" message data stream (i.e. a
continuous bit-rate sine-wave after biphase encoding).

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- 9 - 62106 © IEC:2000
Thus, when the input-data level is 0, the output remains unchanged from the previous output bit and when an
input 1 occurs, the new output bit is the complement of the previous output bit.
In the receiver, the data may be decoded by the inverse process:
Table 2 - Decoding rules
Previous input New input New output
(at time t ) (at time t ) (at time t )
i-1 i i
0 0 0
0 1 1
1 0 1
1 1 0
The data is thus correctly decoded whether or not the demodulated data signal is inverted.
1.7 Data-channel spectrum shaping
The power of the data signal at and close to the 57 kHz subcarrier is minimized by coding each source data bit
as a biphase symbol.
This is done to avoid data-modulated cross-talk in phase-locked-loop stereo decoders, and to achieve
compatibility with the ARI system. The principle of the process of generation of the shaped biphase symbols is shown
schematically in figure 1. In concept each source bit gives rise to an odd impulse-pair, e(t), such that a logic 1 at source
gives:
e(t)/(t)/(tt /2)
(1)
d
and a logic 0 at source gives:
e(t) /(t)/(tt /2)
(2)
d
These impulse-pairs are then shaped by a filter H (f), to give the required band-limited spectrum where:
T
ft
d
cos if 0f2/t
d
(3)
H (f)4
T
0 if f > 2/t
d
and here
1
s
t
d
1187.5
The data-spectrum shaping filtering has been split equally between the transmitter and receiver (to give optimum
performance in the presence of random noise) so that, ideally, the data filtering at the receiver should be identical to that
of the transmitter, i.e. as given above in equation (3). The overall data-channel spectrum shaping H (f) would then be 100%
o
cosine roll-off.

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62106 © IEC:2000 - 10 -
The specified transmitter and receiver low-pass filter responses, as defined in equation (3) are illustrated in
figure 3, and the overall data-channel spectrum shaping is shown in figure 4.
The spectrum of the transmitted biphase-coded radio-data signal is shown in figure 5 and the time-function of
a single biphase symbol (as transmitted) in figure 6.
The 57 kHz radio-data signal waveform at the output of the radio-data source equipment may be seen in the
photograph of figure 7.
1.0
0.8
0.6
0.4
0.2
0
0 480 960 1440 1920 2400 Hz
Frequency
Figure 3 - Amplitude response of the specified transmitter or receiver data-shaping filter
1.0
0.8
0.6
0.4
0.2
0
0 480 960 1440 1920 2400 Hz
Frequency
Figure 4 - Amplitude response of the combined transmitter and receiver data-shaping filters
H
H ,
,
Relative amplitude (f)
O
Relative amplitude (f)
T

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- 11 - 62106 © IEC:2000
Figure 5 - Spectrum of biphase coded radio-data signals
Figure 6 - Time-function of a single biphase symbol
Figure 7 - 57 kHz radio-data signals

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62106 © IEC:2000 - 12 -
2  Baseband coding (data-link layer)
2.1 Baseband coding structure
Figure 8 shows the structure of the baseband coding. The largest element in the structure is called a "group" of
104 bits each. Each group comprises 4 blocks of 26 bits each. Each block comprises an information word and a
checkword. Each information word comprises 16 bits. Each checkword comprises 10 bits (see 2.3).
Group = 4 blocks = 104 bits
Block 1 Block 2 Block 3 Block 4
Block = 26 bits
Information word Checkword + offset word
Information word = 16 bits Checkword = 10 bits
m m m m m m m m m m m m m m m m c' c' c' c' c' c' c' c' c' c'
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
Figure 8 - Structure of the baseband coding
2.2 Order of bit transmission
All information words, checkwords, binary numbers or binary address values have their most significant bit
o
(m.s.b.) transmitted first (see figure 9). Thus the last bit transmitted in a binary number or address has weight 2 .
The data transmission is fully synchronous and there are no gaps between the groups or blocks.

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- 13 - 62106 © IEC:2000
One group = 104 bits   87.6 ms
Block 1 Block 2 Block 3 Block 4
First transmitted bit of group B TP Last transmitted bit of group
o
t t
1 2
Checkword Checkword Checkword Checkword
Group
+ + + +
PI code type PTY     PI
offset A offset B offset C or C' offset D
code

Offset C = version A
Offset C' = version B
Least signifiant bit
Most signifiant bit
Traffic
A A A A B prog. PT PT PT PT PT
3 2 1 0 0 4 3 2 1 0
code
4 - bit group type code 0 = version A
1 = version B
Notes to figure 9:
1. Group type code = 4 bits (see 3.1)
2. B = version code = 1 bit (see 3.1)
o
3. PI code = Programme Identification code = 16 bits (see 3.2.1.1 and annex D)
4. TP = Traffic Programme Identification code = 1 bit (see 3.2.1.3)
5. PTY = Programme Type code = 5 bits (see 3.2.1.2 and annex F)
6. Checkword + offset "N" = 10 bits added to provide error protection and block and group synchronization
information (see 2.3 and 2.4 and annexes A,B and C)
7. t ‹ t : Block 1 of any particular group is transmitted first and block 4 last
1 2
Figure 9 - Message format and addressing
2.3 Error protection
Each transmitted 26-bit block contains a 10-bit checkword which is primarily intended to enable the
receiver/decoder to detect and correct errors which occur in transmission. This checkword (i.e. c' , c' , . c' in figure 8)
9 8 o
is the sum (modulo 2) of:
10
a) the remainder after multiplication by x and then division (modulo 2) by the generator polynomial g(x), of
the 16-bit information word,
b ) a 10-bit binary string d(x), called the "offset word",
where the generator polynomial, g(x) is given by:
10 8 7 5 4 3
g(x) = x + x + x + x + x + x + 1
and where the offset values, d(x), which are different for each block within a group (see 2.4) are given in annex A.
The purpose of adding the offset word is to provide a group and block synchronisation system in the
receiver/decoder (see 2.4). Because the addition of the offset is reversible in the decoder the normal additive error-
correcting and detecting properties of the basic code are unaffected.
The checkword thus generated is transmitted m.s.b. (i.e. the coefficient of c' in the checkword) first and is
9
transmitted at the end of the block which it protects.

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62106 © IEC:2000 - 14 -
The above description of the error protection may be regarded as definitive, but further explanatory notes on the
generation and theory of the code are given in annexes B and C .
The error-protecting code has the following error-checking capabilities [3, 4] :
a) Detects all single and double bit errors in a block.
b) Detects any single error burst spanning 10 bits or less.
c) Detects about 99.8% of bursts spanning 11 bits and about 99.9% of all longer bursts.
The code is also an optimal burst error correcting code [5] and is capable of correcting any single burst of span
5 bits or less.
2.4 Synchronisation of blocks and groups
The blocks within each group are identified by the offset words A, B, C or C' and D added to blocks 1, 2, 3, and
4 respectively in each group (see annex A).
The beginnings and ends of the data blocks may be recognized in the receiver decoder by using the fact that the
error-checking decoder will, with a high level of confidence, detect block synchronisation slip as well as additive errors.
This system of block synchronisation is made reliable by the addition of the offset words (which also serve to identify the
blocks within the group). These offset words destroy the cyclic property of the basic code so that in the modified code,
cyclic shifts of codewords do not give rise to other codewords [6, 7].
Further explanation of a technique for extracting the block synchronisation information at the receiver is given
in annex C.

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- 15 - 62106 © IEC:2000
3  Message format (session and presentation layers)
3.1 Addressing
3.1.1 Design principles
The basic design principles underlying the message format and addressing structure are as follows:
a) The messages which are to be repeated most frequently, and for which a short acquisition time is required e.g.
Programme Identification (PI) codes, in general occupy the same fixed positions within every group. They
can therefore be decoded without reference to any block outside the one which contains the information.
b) There is no fixed rhythm of repetition of the various types of group, i.e. there is ample flexibility to interleave
the various kinds of message to suit the needs of the users at any given time and to allow for future
developments.
c) This requires addressing to identify the information content of those blocks which are not dedicated to the
high-repetition-rate information.
d) Each group is, so far as possible, fully addressed to identify the information content of the various blocks.
e) The mixture of different kinds of message within any one group is minimized, e.g. one group type is reserved
for basic tuning information, another for RadioText, etc. This is important so that broadcasters who do not
wish to transmit messages of certain kinds are not forced to waste channel capacity by transmitting groups
with unused blocks. Instead, they are able to repeat more frequently those group types which contain the
messages they want to transmit.
f) To allow for future applications the data formatting has been made flexible. For example, a number of group
types (see ta
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