SIST ETS 300 708 E1:2003
(Main)Television systems; Data transmission within Teletext
Television systems; Data transmission within Teletext
Specification of the use of Teletext to carry non-Teletext services. It includes the transportation of data which is intended to provide the means to carry an Electronic Programme Guide (EPG); see JTC work item DE/JTC-EPG (ETS 300 707).
Televizijski sistemi – Prenos podatkov v sistemu Teletext
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-december-2003
Televizijski sistemi – Prenos podatkov v sistemu Teletext
Television systems; Data transmission within Teletext
Ta slovenski standard je istoveten z: ETS 300 708 Edition 1
ICS:
33.050.30 Oprema za teleks, teletekst, Equipment for telex, teletext,
telefaks telefax
33.170 Televizijska in radijska Television and radio
difuzija broadcasting
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN ETS 300 708
TELECOMMUNICATION March 1997
STANDARD
Source: EBU/CENELEC/ETSI JTC Reference: DE/JTC-TTEXT-DT
ICS: 33.020
Key words: Broadcasting, data, TV, Teletext
Union Européenne de Radio-Télévision
European Broadcasting Union
Television systems;
Data transmission within Teletext
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 1997. All rights reserved.
Page 2
ETS 300 708: March 1997
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 300 708: March 1997
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions and abbreviations .7
3.1 Definitions .7
3.2 Abbreviations .8
4 Page Format - Clear.8
4.1 General points.8
4.2 Advantages.8
4.3 Disadvantages .8
4.4 Coding of the packets .8
4.4.1 Page header.9
4.4.2 Packets 1 to 23 (in future up to 25) .10
4.4.2.1 Transmission order.11
4.4.2.2 The Structure Header (SH).11
4.4.2.3 Packing the data into the pages .11
4.4.3 Packet 28 .12
4.5 Providing a service according to Page Format - Clear .12
4.5.1 General points on Page Format - Clear .13
4.5.2 Encoding scheme for electronic data transmission.13
5 Page Format - CA .13
5.1 General points.13
5.2 Advantages.13
5.3 Disadvantages .14
5.4 Method of coding .14
5.4.1 Teletext page data.15
5.4.1.1 Scrambled Data Pages.15
5.4.1.2 Pages containing Reformatted Data.15
5.4.2 The Page Key Packet.16
5.4.2.1 Service Mode bits .16
5.4.2.2 Service Identification.17
5.4.2.3 Continuity and Repeat Indicators.17
5.4.2.4 Packet Flags.17
5.4.2.5 Data Length .17
5.4.2.6 Scrambling Method.18
5.4.2.7 The Cyclic Redundancy Check (CRC) word.18
5.4.3 Terminal Equipment Addressing Pages.19
5.4.3.1 System Key Packet.19
5.4.3.2 Shared User Packets.19
5.4.3.3 Unique User Packets.20
5.4.3.4 Service/Page Link packets .21
5.4.3.5 Link to Independent Data Line Services.21
5.5 Security of Page Format - CA.21
5.5.1 Cipher feedback algorithm .21
5.5.2 One-way function.22
5.5.3 Text scrambling.23
6 Independent Data Lines (IDL) .23
6.1 General points.23
6.2 Advantages.23
6.3 Disadvantages .23
6.4 Methods of coding.23
Page 4
ETS 300 708: March 1997
6.4.1 Designation code . 23
6.4.1.1 Transmission multiplexing. 23
6.4.2 Data Channel addressing . 23
6.5 IDL Format A. 24
6.5.1 Format Type (FT) . 24
6.5.2 Interpretation and Address Length (IAL). 24
6.5.3 Service Packet Address (SPA). 25
6.5.4 Repeat Indicator (RI) . 25
6.5.5 Continuity Indicator (CI) . 25
6.5.6 Data Length (DL) byte. 25
6.5.7 User Data Group. 25
6.5.7.1 Dummy bytes . 26
6.5.8 Cyclic Redundancy Check (CRC) word. 26
6.5.8.1 Check word generation . 26
6.5.9 Transmission sequence. 27
6.6 Datavideo format. 27
6.6.1 Packet address. 27
6.6.2 Control Bytes (CB). 27
6.6.2.1 Packet Continuity Indicator (CI) . 27
6.6.3 Masking indicator. 27
6.6.4 Packet type indicator . 28
6.6.5 User data group. 28
6.6.6 Cyclic Redundancy Check (CRC) word. 28
6.6.6.1 Check word generation . 28
6.6.6.2 Check result . 28
6.7 Low bit-rate audio. 28
6.7.1 Method of coding . 29
6.7.1.1 Decoder action. 29
6.7.2 Programme-related audio service . 29
6.7.2.1 Service Byte (SB). 29
6.7.2.2 Control Byte (CB) . 29
6.7.2.3 Audio data. 30
6.7.3 Programme independent audio service. 30
6.7.3.1 Service Byte (SB). 30
6.7.3.2 Control Byte (CB) . 30
6.7.3.3 Audio data. 30
7 IDL - CA (type A) . 30
7.1 General points. 30
7.2 Advantages . 31
7.3 Disadvantages. 31
7.4 Methods of coding. 31
7.4.1 Block Separator . 31
7.4.2 Block Formats. 31
7.4.3 Block Format A . 31
7.4.3.1 Block Types. 31
7.4.3.2 Primary Block Key Messages . 32
7.4.3.3 Secondary Block Messages and Scrambled User Data . 32
7.4.3.4 System-Key Message Block . 32
7.4.3.5 Shared-User Message Block . 32
7.4.3.6 Unique User Message Block. 33
7.4.3.7 Service Address Message Block - Independent Data
Service . 33
7.4.3.8 Service Address Message Block - Link to Page Format -
CA . 33
History. 34
Page 5
ETS 300 708: March 1997
Foreword
This European Telecommunication Standard (ETS) has been produced by the Joint Technical Committee
(JTC) of the European Broadcasting Union (EBU), Comité Européen de Normalisation ELECtrotechnique
(CENELEC) and the European Telecommunications Standards Institute (ETSI).
NOTE: The EBU/ETSI JTC was established in 1990 to co-ordinate the drafting of ETSs in the
specific field of broadcasting and related fields. Since 1995 the JTC became a tripartite
body by including in the Memorandum of Understanding also CENELEC, which is
responsible for the standardization of radio and television receivers. The EBU is a
professional association of broadcasting organizations whose work includes the
co-ordination of its Members' activities in the technical, legal, programme-making and
programme-exchange domains. The EBU has Active Members in about 60 countries
in the European Broadcasting Area; its headquarters is in Geneva *.
* European Broadcasting Union
Case Postale 67
CH-1218 GRAND SACONNEX (Geneva)
Switzerland
Tel: +41 22 717 21 11
Fax: +41 22 717 24 81
Transposition dates
Date of adoption: 7 March 1997
Date of latest announcement of this ETS (doa): 30 June 1997
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 December 1997
Date of withdrawal of any conflicting National Standard (dow): 31 December 1997
Page 6
ETS 300 708: March 1997
Blank page
Page 7
ETS 300 708: March 1997
1 Scope
This European Telecommunication Standard (ETS) describes the various ways in which Teletext may be
used to carry non-Teletext services. It should be used in conjunction with ETS 300 706 [1]. An example is
fully described in ETS 300 707 [2]. This ETS includes additional practical information on implementing a
data service of this type.
Hooks into existing Teletext services may be provided from within the application which is carried as a
non-Teletext service. A data broadcast application may be pointed to from the Magazine Inventory Page
(MIP) or it may be allocated a specific page number. A Code of Practice (CoP) shall ensure that services
destined for the consumer may be found quickly by "low-end" Teletext decoders but this is outside the
scope of this ETS.
There are two methods available for carrying data services. The first method carries the data within
Teletext pages. The data in these pages is not sui for direct display by a Teletext decoder and shall
normally be allocated a special page number and/or have the display inhibited. The second method
carries the data within Independent Data Lines (IDL) and these are independent of the page service.
With both Page and IDL formats there exist versions which offer Conditional Access (CA).
There are other specific IDL data services which have been defined but it is beyond the scope of this ETS
to cover all of these.
2 Normative references
This ETS incorporates, by dated or undated references, 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] ETS 300 706: "Enhanced Teletext specification".
[2] ETS 300 707: "Electronic Programme Guide (EPG); Protocol for a TV Guide
using electronic data transmission".
[3] ETS 300 231: "Television systems; Specification of the domestic video
Programme Delivery Control system (PDC)".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this ETS, the following definitions apply:
data stream: The sequence of bytes carried in a uniquely addressable data service.
encryption: The process whereby a sequence of data is made secret. See subclause 5.5 for further
information.
network operator: The organization responsible for the compilation of the Teletext service for insertion
into the available Vertical Blanking Interval (VBI) lines.
scrambling: The process whereby a sequence of data is made unintelligible. See subclause 5.5 for
further information.
service provider: The organization responsible for the creation and supply of the data service application.
Page 8
ETS 300 708: March 1997
3.2 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
AUDETEL AUdio DEscription of TELevision
BL Block Length
BP Block Pointer
BS Block Separator
BT Block Type
CA Conditional Access
CI Continuity Index
CoP Code of Practice
EPG Electronic Programme Guide
FB Filler Bytes
IDL Independent Data Lines
LSB Least Significant Bit
MIP Magazine Inventory Page
MSB Most Significant Bit
RI Repeat Indicator
SH Structure Header
VBI Vertical Blanking Interval (fully defined in this ETS)
4 Page Format - Clear
4.1 General points
A page number which includes at least one hexadecimal digit should be chosen for this type of service.
For an Electronic Programme Guide (EPG) service this will generally be page 1DF as fully described in
ETS 300 707 [2]. The value nFF is not permitted for any data service, where n can take the value from
1 to 8 inclusive. The page number is defined in the Magazine Inventory Page (MIP), ETS 300 706 [1].
The user data is divided into blocks, each of whose length is defined. An additional check of where the
block boundaries are located is provided by means of a block pointer placed in the first byte in each
packet. The data stream is further identified by means of additional data provided in the page header. It is
possible to carry several independent data services within the same page number.
4.2 Advantages
This mode is appropriate for reception by all existing Teletext decoders. A default coding method is
defined in order that services may be offered using existing Teletext systems. Synchronization of the user
data blocks is assured by means of a simple robust method of dual pointing to each block start location.
Future possibilities exist by providing an additional packet 28 which will further define the coding system in
use. It is left up to the service provider to apply any additional protection to those parts of his service which
require it. It is possible to sub-divide the service into those parts which will be required by all decoders and
those parts which will only be required by the more sophisticated decoders.
4.3 Disadvantages
This mode is not efficient for sending a small amount of data as there is always the overhead of including
a page header and the optional, but useful, packet 28. Another disadvantage of this mode is that the data
transmission efficiency is further reduced when the Teletext broadcaster wishes to send the data in a
fragmented way in order to interleave the data service with his primary Teletext service.
4.4 Coding of the packets
In order to provide greater flexibility for the network operator it is not necessary to fill each data page.
Several separated headers, each with some data packets, may be required to provide the data service
and this technique is covered fully in ETS 300 706 [1]. In the case of a data service it is possible to send
full but fragmented pages as well as to simply send shorter pages.
Page 9
ETS 300 708: March 1997
Fragmented pages are usually interleaved with one or more other pages. Each fragmented page contains,
in row order, parts of a full page. Fragmented pages transmitted in stream 1 shall obey the 20 ms rule for
each fragment.
4.4.1 Page header
This is necessary but shall not generally contain any of the application data. It may be identical to all
others in the same magazine. The use of the Teletext page sub-code is defined as shown in figure 1.
S4 S3 S2 S1
(2 bits) (4 bits) (3 bits) (4 bits)
Number of packets Transmission Rule Continuity Index (CI)
1 to 23 normally but 25 LSB = 0 then 20 ms 0 to 15
possible in future
rule applies else it does
services
not.
(see table 1)
Figure 1: The use of the Teletext page sub-code
The default valid range for the number of packets is 1 to 23 where this value provides the last row
which is being transmitted for the page with this particular value for the Continuity Index (CI). The packets
of the page are transmitted in ascending address order. There are no missing rows and where a new
header is required to complete the page then this shall be provided with the same CI. The maximum
number of packets per page is 25 and as a result S2 and S4 will never have values of 7 and 3
simultaneously. Thus the reserved sub-code value of 3F7F defined in ETS 300 706 [1] can never occur.
As expected the Least Significant Bit (LSB) of each parameter in the page sub-code is transmitted first.
S2 contains least significant 3 bits of the "Number of packets".
The 20 ms rule requires that the header packet 0 is sent during a previous field. This rule shall be
followed when the LSB of S3 is set to 0. When this bit is set to 1 then the header may be followed
immediately by the packets associated with this header. The following values have been defined in
table 1.
Table 1: Values of S3
Hex value of S3 Interpretation
0 20 ms rule applies - data stream 1
1 no 20 ms rule - data stream 2
2 20 ms rule applies - data stream 3
3 no 20 ms rule - data stream 4
4, 6, 8, A, C & E 20 ms rule applies - data stream 5, 7, 9, 11, 13 & 15 respectively
5,7,9,B & D no 20 ms rule - data stream 6, 8, 10, 12 & 14 respectively
F reserved for future use, no 20 ms rule applies
In each stream the CI value increments modulo 16 for each page which contains different application
data.
Page control bytes C4 to C14; their action is as follows:
The values for C5, C6, C7, C8, C11, C12, C13 and C14 depend upon the type of service which the
network provider is offering and have the same meaning as for normal Teletext pages. The following
control bytes in table 2 have a recommended value.
Page 10
ETS 300 708: March 1997
Table 2: Page Control Bits
C4 C9 C10
Erase Page Interrupted Sequence Inhibit Display
01 1
The next 24 bytes should normally match those of the other pages in the same magazine. This is to avoid
possible display problems with viewers of the normal Teletext service which shares this Magazine.
The last 8 bytes of the header shall be used in a way which takes account of the rest of the Teletext
service. Where the time can be the same as that on the normal Teletext service it shall be presented in
the same format. Where this is not possible these 8 bytes should be filled with spaces. In the case where
there is no other Teletext service then the local time shall be placed in these 8 bytes according to the
Enhanced Teletext Specification ETS 300 706 [1].
4.4.2 Packets 1 to 23 (in future up to 25)
These packets may carry the data service. The page sub-code indicates to the decoder how many
packets to expect. The default maximum number of packets is 23 although future services may be able to
use up to 25. Each Teletext packet is constructed in the manner shown in figure 2.
Structure Header (SH) comprises the Block Type (BT)
Block Separator (BS)
followed by the Block length (BL)
Hamming 8/4 coded
Hamming 8/4 coded 4 bytes = 16 data bits
C hex = A1 hex
5 LSB provide BT, 11 MSB provide BL (see figure 3)
Packet 0
8 bytes 24 bytes text (normal magazine contents) 8 bytes (see text)
Packet 1
BP
Points to BS
Packet 2
BP FB? BS SH
Packet
BP
last -1
Last
FB?
packet
Block Pointer (BP) Hamming 8/4 coded Possible Filler Bytes (FB) Hamming 8/4
See text below for options & meaning coded 3 hex = 5E hex. See text below
Figure 2: Example of a page according to Page Format - Clear
Page 11
ETS 300 708: March 1997
4.4.2.1 Transmission order
This follows the normal Teletext format where the LSB is transmitted first. For example in the Structure
Header (SH) the least significant 4 bits of the Block Type shall be placed in the byte which is transmitted
first. The most significant bit of BT shall be placed in the least significant position of the next byte.
The Hamming 8/4 coding is carried out in the same way as fully described in ETS 300 706 [1]. The bytes
defined above are all transmitted in the same way. It is up to the data service provider how he codes
the bytes which constitute the "user data". The values for BP are given in table 3.
Table 3: Values for Block Pointer (BP)
Hex value for BP Interpretation
0 to C point to BS in byte position (BP x 3) + 1
D means that there is no BS in this packet
E and F reserved for future use
4.4.2.2 The Structure Header (SH)
The SH comprises four Hamming 8/4 coded bytes. This is put in by the data service provider and the 16
available data bits are used in the following way.
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶„
•6WUXFWXUH+HDGHU•
•+DPPLQJSURWHFWHGE\WHV•
”¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶»
•••••”¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶„
••••”¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶„•
‚¶¶¶¶¶¶¶¶¶»••”¶¶¶¶¶¶¶¶¶¶¶¶¶¶„••
•‚¶¶¶¶»”¶¶¶¶¶„•••
••••••
••••••
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶„
•%ORFN7\SH•%ORFN7\SH•%ORFNOHQJWK•%ORFNOHQJWK•%ORFNOHQJWK•
••••••
•ELWVWR•ELW•ELWVWR•ELWVWR•ELWVWR•
”¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¶»
Shown in transmission order from left to right. LSB transmitted first. Only the data bytes are shown.
Figure 3: The Structure Header
The first 5 bits (BT) provide the Application ID. This gives the data application provider the possibility of
providing up to 31 different categories of data within one page service. This is addition to the separation
into a number of streams which is possible by means of the page sub-code value for S3. The actual value
for the Application ID is up to the application provider. When the Application ID has the value 0 this is used
to provide the system with information about which services are carried in this data channel. This is fully
covered in ETS 300 707 [2].
The remaining 11 bits define the block length which permits block lengths of up to 2 048 bytes long.
4.4.2.3 Packing the data into the pages
The network operator packs the available data into the Teletext packets. He has to read the block
lengths in order to put in the Block Pointer (BP) values. The BP may point to 1 of 13 locations in a Teletext
packet according to table 3. Where a data block does not fill up to 1 of the 13 possible start locations the
free bytes are filled with Filler Bytes (FB). Filler bytes are also used to pad out the end of a packet if the
broadcaster has no data available to fill it. The benefit of this process is that each block start is not only
pointed to from the previous block length but also from the BP. It provides a robust method of
synchronizing the application data stream. Block Pointer (BP), Block Separator (BS) and Block Length
(BL) are all Hamming 8/4 coded. Even with bit errors it should be possible for the reception device to have
a high confidence that it is in correct synchronization. The BL may not point precisely to the next BS as
these may only be placed in every third byte, when pointed to from the BP. The existence of the FB
informs the decoder to look forward to find the next BS.
Page 12
ETS 300 708: March 1997
Where the Service Operator provides very short data blocks it is possible that 2 blocks may commence in
the same Teletext Packet. Where this occurs the BP shall point to the first BS. The second BS shall be
placed immediately after the end of the first block, as indicated by the BL in the previous SH. There is no
requirement for Filler Bytes between the two data blocks as the second BS will not be pointed to from a
BP.
The Filler Byte (FB) (5E hex = 01011110 binary) has the inverted value of the Block Separator (BS)
(A1 hex = 10100001 binary).
Where the broadcaster starts from no data then the first Block Separator (BS) shall occur at the start of
the page. Data Blocks may start within one page and finish in a different one. The network operator
requires no knowledge of the data which he is transporting apart from knowing where each block
commences and how long it is. Each of the user data bytes contains 8 usable bits and it is up to the Data
service provider to determine how he uses them. The packets shall be sent in ascending sequence
through from 1 to n (given by the n value in the page sub-code provided by S4 and S2). In this way any
lost packets can be detected.
The employment of a packet 28 permits these data bytes to be encoded in various different ways but
currently only the one mode is defined. When the service provider requests the use of more than one data
stream then the network operator shall treat each stream as an independent data service. In the case of
an EPG there are some restrictions and these shall be checked in each circumstance as they will vary
according to the capabilities of the reception equipment.
4.4.3 Packet 28
Packet 28 is optionally required to unambiguously define the format and purpose of the data contained in
the following packets which comprise the page. It should be sent, as soon as possible, following the
header. Some Teletext decoders do not acquire the packet 28 and so it should be employed only for
applications which are aimed at newer decoders. The designation code should be set to 0000 and the
page function set to 0001. The contents of the packet is given in table 4.
Table 4: The Packet 28 for Page Format - Clear
Triplet Bits Function
Page Function
0001 Page used to carry general purpose data
15 Page Coding
These bits define the coding of packets X1 to X25, if present, of the associated page.
Where these bits are set to 000 then the packets are defined as for Page Format -
Clear.
All other values are reserved for future use.
18 Reserved for future use
2 1 Reserved for future use
13 18
4.5 Providing a service according to Page Format - Clear
The following lists lay down the conditions which are necessary for a satisfactory transmission and
reception of a data broadcast application which employs this method for transporting data.
Page 13
ETS 300 708: March 1997
4.5.1 General points on Page Format - Clear
1) The 20 ms rule applies between transmission of the header and any following packets when the
received data is required to be processed by all "low end" decoders. The value for the LSB of the
S3 value in the page header shall be set to 0. Enhanced data which is destined for use by new "high
end" decoders does not need to follow the 20 ms rule (LSB of S3 = 1).
2) The maximum number of packets following the header shall be limited to 23.
3) The data within the packets shall be treated by the Teletext decoder as 8-bit data.
4) The data shall all be transmitted using the method described in Page Format - Clear.
5) The user data shall not necessarily be synchronized to the page format.
6) The block structure shall be as indicated under Page Format - Clear.
7) Where the service is constructed from more than one data stream then each stream shall be dealt
with as an independent data service. It is up to the application to make intelligent use of the data
extracted from more than one stream.
8) The implication of 7) is that the decoder may have to simultaneously build up two separate data
pages. This may happen if fragmented pages from two streams are interleaved with each other.
This can be managed by a Code of Practice (CoP) document for the data service.
4.5.2 Encoding scheme for electronic data transmission
This subclause shows how to take the application to the transport system. The main issues are:
1) The application data is encoded in a way appropriate to its purpose. Critical data is better protected.
This function is left to the data service provider, or his agent, and is of no concern to the
transportation layer. He may group together items or divide them but the end result shall be blocks
of data which he wishes to deliver to the network operator.
2) The user data blocks are linked together into one data stream by means of the Block Separators
(BS). The Data service provider puts in the Application ID the Block Type (BT) and the Block
Lengths (BL) as defined in Page Format - Clear.
3) The resulting data stream is fitted into pages by the network operator who shall shift through the
data in order to put in the Block Pointers (BP) and the Filler Bytes (FB). Apart from this the network
operator has no interest in the data.
4) Where 2 Blocks start in the same Teletext Packet the network operator inserts the BP for the first
one only as described in subclause 4.4.2.3.
5) Where the data is destined to be transmitted in more than one data stream then the data for each
stream shall be supplied separately and considered as an independent and separate service.
6) The network operator shall take account of the capabilities of the receiving equipment when he
inserts the data streams into the Teletext service (see subclause 4.5.1, point 8).
5 Page Format - CA
5.1 General points
This mode provides the means for subscription data services where the subscriber management centre is
under the control of the network operator.
5.2 Advantages
This mode enables many service providers the means to transmit large amounts of data efficiently to
subscriber groups. As the network operator is providing a value added service it potentially provides him
Page 14
ETS 300 708: March 1997
with additional revenue. The service provider does not need to concern himself with the complex issues of
Conditional Access (CA).
An efficient scheme has been defined which provides an effective way of managing large numbers of
subscribers with varying requirements. It achieves this by employing a hierarchical approach to handling
the required encryption keys.
5.3 Disadvantages
This method requires the use of special Teletext decoders which incorporate the appropriate CA
sub-system. It is not a very efficient way to transmit short blocks of data in view of the essential overhead
of the page header and the packet 28. Error checking, at the transport level, is only possible on a per page
basis.
5.4 Method of coding
There may be an introductory page of non-scrambled text. When no introductory text for display is
required, this page shall at least include the header packet with Y = 0 and a packet or packets with Y = 27
to provide links to the conditional access service. The links are provided in a packet with Y = 27,
designation codes 0100 to 0111 (see ETS 300 706 [1]). Figure 4 shows how the system works.
-1
-1
TRANSMISSION E = ENCRYPTION RECEPTION E = DECRYPTION
E
-1
-1
S = SCRAMBLING SS = SCRAMBLING
TELETEXT
TELETEXT
-1
S
S
PAGE DATA PAGE DATA
SCRAMBLED TELETEXT PAGE
Un
PAGE KEY
PAGE KEY
SERVICE Sn
NUMBER
E -1
Sn E
ENCRYPTED PAGE KEY PACKET
SYSTEM KEY
YES/NO
SYSTEM KEY
SERVICE
TABLE
USER
-1
ENABLE E
E
Un
SHARED USER PACKET
DISTRIBUTION KEY
DISTRIBUTION KEY
SERVICE
TABLE
-1
E
E
UNIQUE USER PACKET
USER EQUIPMENT
USER EQUIPMENT
UNIQUE KEY
UNIQUE KEY
Figure 4: Component parts required for the service
Figure 4 helps to understand the operation of a service operating to the Page Format - CA standard.
Page 15
ETS 300 708: March 1997
5.4.1 Teletext page data
For the purpose of scrambling, two types of pages are defined.
1) Scrambled Data Pages are essentially normal Teletext pages but with each byte scrambled to
make it unintelligible. The scrambling process is initialized at the start of each packet. Unused
packets need not be transmitted. See subclause 5.4.1.1.
2) Pages containing Reformatted Data shall be signalled by means of the packet X/28 as shown in
table 5. In this case the scrambling process is initialized at the start of each page. See
subclause 5.4.1.2.
Page Mode Definition is achieved by means of a Packet X/28. The first 8 bits in the first triplet define the
type of page data which follows. Table 5 below provides the relevant values but for more detail see
ETS 300 706 [1]. Note that this table only refers to packets X/28 with designation codes of 0000 & 0010.
Table 6 provides details on how to interpret bits 15 to 18 in this packet X/28.
Table 5: Coding of Packets X/28 - interpretation of the following page
8 7 6 5 4 3 2 1 Bit Numbers
1 0 0 0 0 1 0 0 Reformatted Data
1 0 0 0 0 1 0 1 Terminal Equipment Addressing page
0 * * 0 0 0 0 0 Page has standard character position and row format
* = don’t care value
Table 6: Coding of Packets X/28 - data bit organization and protection
18 17 16 15 Bit Numbers
0 0 0 0 Data coded as 8-bit bytes, 7 bits data plus 1 parity bit
0 0 0 1 Data coded as 8-bit bytes, with 8 data bits each
0 0 1 0 Data coded as 3 groups of 8-bit bytes, 18 data bits Hamming protected 24/18
0 0 1 1 Data coded as 8-bit bytes, 4 data bits Hamming protected 8/4
This interpretation is only defined when the remaining bits in this 18 bit group, bits 9 through to 14 all have
the value 0.
5.4.1.1 Scrambled Data Pages
The data for transmission in bytes 6 to 45 of packets with Y = 1 to Y = 25, plus the 18 data bits in each
three byte data group for transmission in packets with Y = 26, is scrambled, using a suitable scrambling
algorithm. Subclause 5.5 provides an example of a suitable algorithm. The numbers of the packets
included in a scrambled text page are specified as in subclause 5.4.2.4.
Parity protected 7-bit data
To provide a sequence of complete bytes for scrambling when 7-bit data is used, a most significant bit is
added. The resulting bytes are scrambled and the respective bit masked before the odd parity bit added.
Data in Packets with Y = 26
To provide a sequence of complete bytes for scrambling, the 18 data bits have the 6 most significant bits
added. The resulting 3 bytes are scrambled and the respective 6 bits masked before Hamming
protection bits are calculated and added.
5.4.1.2 Pages containing Reformatted Data
The data for transmission in bytes 14 to 37 of packets with Y = 0 and bytes 6 to 45 of packets with Y = 1 to
Y = 25 are scrambled using an encryption algorithm. The number of bytes included in the page of
scrambled data is indicated by the Data Length parameter according to subclause 5.4.2.5.
Parity protected 7-bit data
Page 16
ETS 300 708: March 1997
To provide a sequence of complete bytes for scrambling when 7-bit data is used, a most significant bit is
added. The resulting bytes are scrambled and the respective bit masked before the odd parity bit is
added.
5.4.2 The Page Key Packet
Descrambling of a Scrambled Teletext Page Data is by means of a Page Key contained in a packet with
Y = 28 of a scrambled page. The Page Key Packet also provides details concerning the scrambled data
which is carried by the Teletext page. Byte 6, 4 bits data plus 4 bits Hamming protection, carries the
Designation Code with the data bits set to 0010. Bytes 7 to 45 are used as 13 groups of 18 data bits plus
6 bits Hamming protection as shown in figure 5.
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶„
•&ORFNUXQLQ•)UDPLQJ•0DJD]LQHDQG•’HVLJQDWLRQ•)LUVW7KUHH•
••&RGH•3DFNHW$GGUHVV•&RGH•%\WH’DWD*URXS•
”¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶»
••
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶»’$7$127(1&5<37(’”¶¶¶¶¶„
••
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶„
•3’3’3’3’•33’3’’’3’’’’’’’3’’’’’’’3•
•’HVLJQDWLRQ&RGH••
”¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶»
•
•
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶»
•
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶„
•6HUYLFH•6HW•&XUUHQW•6HUYLFH•3DJH•.H\9DOXH•
•0RGHV•WR•6\VWHP.H\•,GHQWLILFDWLRQ•.H\•&UHGLW7RNHQV•
•%LWV•%LWV•%LWV•%LWV•%LWV•%LWV•
…¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶»
•(1&5<37(’:,7+&855(176<67(0.(<•
”¶¶¶¶¶¶»
•
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶»
•‚¶¶¶¶¶¶ELWV¶¶¶¶„
‚¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶¶„
•&RQWLQXLW\•5HSHDW•3DFNHW•6HW•6FUDPEOLQJ•,Q8VH•6HWWR•&\FOLF•
•,QGLFDWRU•,QGLFDWRU•)ODJV•WR•0HWKRG•6\VWHP••5HGXQGDQF\•
•%LWV•%LW•%LWV•%LW•%LWV•.H\•%LWV•&KHFN•
•••RU•RU••/DEHO••%LWV•
•••’DWD•6HW••%LWV•••
•••/HQJWK•WR•••••
•••%LWV•%LWV•••••
…¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¿¶¶¶¶¶¶¶¶¶¶¶¶¶‰
•’$7$127(1&5<37(’•
”¶¶¶¶¶¶»
Figure 5: Format of Page Key Packet (X/28)
The first group of 18 data bits is not encrypted and shall be set to designate the page type as provided in
table 5 and table 6. The next 144 bits of data are encrypted with the Current System Key. The following
subclauses provide additional detail which is not included in figure 5.
5.4.2.1 Service Mode bits
The two Service Modes bits are interpreted as shown in table 7.
Table 7: Service Mode Bits
Bit 2 Bit 1 Service Mode Mode Description
0 0 1 256 Services Non-Tiered
0 1 2 64 Services Tiered
1 0 3 256 Services with Credit Tokens
1 1 4 Not Assigned
Page 17
ETS 300 708: March 1997
5.4.2.2 Service Identification
The 9-bit Service Identification Number is used in the following way dependent on the Service Mode:
Service Mode 1 or 3: 8 bits define service number, 0 to 255;
or
Service Mode 2: 6 most significant bits of 8-bit group define service number 0 to 63.
2 least significant bits define the service tier as shown in table 8.
Table 8: Service Tiers
Bit 2 Bit 1 Service Tier
0 0 Basic Tier
0 1 Basic + Premium Tier
1 0 Basic + Premium + Extra Tier
1 1 Not Assigned
The 16-bit Key Value Credit Tokens are defined as shown below:
8 bits: fraction part;
8 bits: whole part.
The remaining 72 bits of data are not encrypted. The following subclauses provide additional detail on
these.
5.4.2.3 Continuity and Repeat Indicators
The Continuity Indicator is incremented by 1, modulo 127, for each subsequent page with the same
service number.
The Repeat Indicator is set to 1 when it is expected that the page will be repeated. It is set to 0 when
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...