ETSI ETS 300 144 ed.1 (1994-05)

Integrated Services Digital Network (ISDN); Audiovisual services Frame structure for a 64 kbit/s to 1 920 kbit/s channel and associated syntax for inband signalling

DE/TE-04117

Digitalno omrežje z integriranimi storitvami (ISDN) – Avdiovizualne storitve – Struktura okvirov za kanale s hitrostmi od 64 kbit/s do 1 920 kbit/s in pripadajočo skladnjo za znotrajpasovno krmiljenje

General Information

• Status: Published
• Publication Date: 28-Apr-1994
• Technical Committee: TE 4 - Audiovisual and Voice Terminals
• Current Stage: 12 - Completion
• Due Date: 07-Jan-1994
• Completion Date: 29-Apr-1994
• Ref Project: SIST ETS 300 144 E1:2003 - Integrated Services Digital Network (ISDN); Audiovisual services Frame structure for a 64 kbit/s to 1 920 kbit/s channel and associated syntax for inband signalling

Standards Content (Sample)

SLOVENSKI STANDARD
01-december-2003
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6WUXNWXUDRNYLURY]DNDQDOHVKLWURVWPLRGNELWVGRNELWVLQSULSDGDMRþR
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Integrated Services Digital Network (ISDN); Audiovisual services Frame structure for a
64 kbit/s to 1 920 kbit/s channel and associated syntax for inband signalling
Ta slovenski standard je istoveten z: ETS 300 144 Edition 1
ICS:
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 300 144
TELECOMMUNICATION May 1994
STANDARD
Source: ETSI TC-TE Reference: DE/TE-04117
ICS: 33.080
ISDN, audiovisual services, inband signalling
Key words:
Integrated Services Digital Network (ISDN);
Audiovisual services
Frame structure for a 64 kbit/s to 1 920 kbit/s channel
and associated syntax for inband signalling
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - [e-mail]
X.400: Internet:
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 1994. All rights reserved.
New presentation - see History box

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ETS 300 144: May 1994
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.

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ETS 300 144: May 1994
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions.8
4 Symbols and abbreviations .9
5 Description .10
5.1 Frame Alignment Signal (FAS) .10
5.2 Bit-rate Allocation Signal (BAS) .11
5.3 Encryption Control Signal (ECS) channel (optional) .11
5.4 Remaining capacity.11
6 Frame structure.12
6.1 General .12
6.2 Multiframe structure.12
6.3 Gain, loss and recovery of frame alignment .14
6.4 Gain, loss and recovery of multiframe alignment.14
6.5 Procedure to recover octet timing from frame alignment .14
6.5.1 General rule.14
6.5.2 Particular cases.14
6.5.3 Search for Frame Alignment Signal (FAS).15
6.6 Frame structure for interworking between a 64 kbit/s terminal and a 56 kbit/s terminal
(optional).15
6.6.1 Operation of the 64 kbit/s terminal .16
6.6.2 Restriction against some communication modes.16
7 Multiple connections.16
7.1 Multiple B-connections.16
7.2 Multiple H0-connections.17
8 Introduction to BAS .17
8.1 Encoding of the BAS.17
8.2 Values of the BAS.18
8.2.1 Single octet BAS.19
8.2.2 Two-octet BAS .19
8.2.3 Multi-octet BAS (optional).19
9 Connection quality monitoring (optional) .19
9.1 Computation of the CRC4 bits .20
9.1.1 Multiplication-division process.20
9.1.2 Encoding procedure .20
9.1.3 Decoding procedure (optional).20
9.2 Consequent actions .20
9.2.1 Action on the E-bit .20
9.2.2 Additional monitoring for incorrect frame alignment (optional).21
9.2.3 Monitoring for error performance (optional) .21
10 Definitions and tables of BAS values .21
10.1 Single/first octet BAS values.21
10.1.1 Audio command values (000) .21
10.1.1.1 Unrestricted case.21
10.1.1.2 Restricted case.22

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ETS 300 144: May 1994
10.1.2 Transfer-rate command values (001) . 23
10.1.3 Video, encryption, loopback and other commands (010) . 24
(12)
10.1.4 LSD/MLP commands (011) . 26
10.1.5 Audio capabilities (100) . 27
10.1.6 Transfer-rate capabilities (100). 27
10.1.7 Video, MBE and encryption capabilities (101) . 28
(13)
10.1.8 LSD/MLP capabilities (101) . 28
10.1.9 Escape table values (111) . 29
10.2 Second octet ("escaped'') BAS values . 31
10.2.1 HSD/H-MLP (High speed Multi layer Protocol) (111)[16] . 31
10.2.1.1 Capabilities (111)[16]-(101). 31
10.2.1.2 Commands (111)[16]-(011) . 31
10.2.2 Control and Indication (C&I) - (111)[17]. 33
10.2.2.1 C&I related to video (111)[17]-(000). 33
10.2.2.2 C&I related to audio (111)[17]-(000) . 33
10.2.2.3 C&I related to simple multipoint conferences not using
MLP (111)[17]-(001). 34
10.2.2.4 SBE symbols used in multipoint working (111)[17]-(000),
(001), (010), (011). 34
10.2.3 Applications within LSD/HSD channels (111)[18]. 38
10.2.3.1 Capabilities (111)[18]-(101). 38
10.2.3.2 Commands (111)[18]-(011) . 39
10.2.4 General purpose SBE symbols: SBE numbers reached by (111)[19] . 40
10.2.5 General purpose SBE symbols: SBE characters reached by (111)[20] . 40
10.3 Multiple-byte extension BAS values . 40
10.4 Bit positions occupied by combinations of BAS commands. 40
Annex A (informative): Bibliography . 46
History. 47

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ETS 300 144: May 1994
Foreword
This European Telecommunication Standard (ETS) has been produced by the Terminal Equipment (TE)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
The attention of the user of this ETS is drawn to the possibility that compliance may require the use of
technology covered by patent or similar rights.
ETSI is not responsible for identifying patent or similar rights or for granting licences which may be
required and, as a result, ETSI is not in a position to give authoritative or comprehensive information
concerning the existence, validity or scope of patent or similar rights in connection with this ETS.

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ETS 300 144: May 1994
Blank page
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ETS 300 144: May 1994
1 Scope
This ETS specifies the frame structure and the syntax for end-to-end inband signalling for audiovisual
services and end-to-end data communication between equipment using single or multiple digital channels
(B, H0, H11 or H12) up to 1 920 kbit/s when connected by the pan-European Integrated Services Digital
Network (ISDN). Digital audiovisual services are provided by a transmission system in which the relevant
signals are multiplexed onto a digital path. This frame structure allows the best use of the total
transmission capacity for the various data flows as audio, video, user data, telematic information and
special applications. Additionally, signals for the proper functioning of the system are included.
This ETS allows the synchronisation of multiple 64 kbit/s or 384 kbit/s connections and the control of the
multiplexing of audio, video, data and other signals within the synchronised multiconnection structure in
the case of multimedia services, such as videoconference.
It provides the means to transmit end-to-end inband signalling according to the procedures described in
ETS 300 143 [2].
This ETS is applicable to terminals or other equipment (e.g. Multipoint Conference Units) supporting
audiovisual applications.
A separate ETS is under preparation (DE/TE-04120) which specifies the method of testing required to
identify conformance to this ETS.
2 Normative references
This ETS incorporates, by dated or 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 apply.
[1] ITU-T Recommendation H.261 (1993): "Video codec for audiovisual services at
p x 64 Kbit/s".
[2] ETS 300 143: "Integrated Services Digital Network (ISDN): Audiovisual services,
Inband signalling procedures for audiovisual terminals using digital channels up
to 2 048 kbit/s".
[3] ETS 300 145: "Integrated Services Digital Network (ISDN): Audiovisual
Services; Videotelephone Systems and Terminal Equipment Operating on one
or Two 64 kbit/s Channels".
[4] CCITT Recommendation G.711 (1988): "Pulse code modulation (PCM) of voice
frequencies".
[5] CCITT Recommendation G.722 (1988): "7 kHz audio-coding within 64 kbit/s".
[6] CCITT Recommendation G.725 (1988): "System aspects for the use of the 7
kHz audio codec within 64 kbit/s".
[7] CCITT Recommendation G.728 (1992): "Coding of speech at 16 kbit/s using
low-delay code-excited linear prediction".
[8] CCITT Recommendation H.200 (1988): "Framework for recommendations for
audiovisual services".
[9] CCITT Recommendation T.50 (1992): "International Alphabet No. 5".
[10] ITU-T Recommendation T.81 (1993): "Information technology - Digital
compression and coding of continuous-tone still images - Requirements and
guidelines".
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ETS 300 144: May 1994
[11] CCITT Recommendation H.221 (1992): "Frame structure for a 64 to 1 920 kbit/s
channel in audiovisual teleservices".
[12] CCITT Recommendation H.243 (1992): "Procedures for establishing
communication between three or more audiovisual terminals using digital
channels up to 2 Mbit/s".
[13] ISO/IEC 11172 (1993): "Information technology - Coding of moving pictures and
associated audio for digital storage media at up to about 1,5 Mbit/s".
[14] CCITT Recommendation T.35 (1991): "Procedure for the allocation of CCITT
defined codes for non-standard facilities".
3 Definitions
For the purposes of this ETS, the following definitions apply:
A-bit: Indicates the loss of frame or multiframe alignment.
Bit-rate allocation signal: Bit position within the frame structure to transmit, e.g. commands, control and
indication signals, capabilities.
Capability marker: The first code in a capability set.
Capability set: A sequence of capability codes started by the capability marker code.
Control and indication: End-to-end signalling between terminals consisting of control which causes a
state change in the receiver and indication which provides information as to the functioning of the system.
E-bit: Indication as to whether the most recent Cyclic Redundancy Check (CRC) block, received in the
incoming direction, contained errors or not.
ECS-channel: Optional 800 bit/s channel for use in encryption.
I-channel: The initial or only B channel, or TS1 of initial or only H0 channel, or TS1 of H11, H12 channels.
Mode: A term used to denote transmission of user information signals with a particular set of parameters.
Mode 0F: Applies only to the initial channel: there is frame structure in the Service Channel (SC), and
1)
audio is confined to the sub-channels 1 to 7 ; the audio is encoded in the same way as in CCITT
Recommendation G.711 [4] either in A-law or μ−law unless this law is also specified in brackets thus:
2)
Mode-0F(A), Mode-0F(μ), except that the Least Significant Bit (LSB) is not transmitted.
Mode 0U: Applies only to the initial channel; there is no frame structure, and audio is encoded according
3)
to CCITT Recommendation G.711 [4] , either in A-law or m−law unless this law is also specified in
brackets thus: Mode-0U(A), Mode-0U(u).
Multipoint Conference Unit: A piece of equipment located in a node of the network or in a terminal
connects several terminals and, according to certain criterions, processes audiovisual signals and
distributes them to the connected terminals.
Service Channel: The eighth sub-channel of a 64 kbit/s channel, or the seventh sub-channel when
communicating in restricted mode.

1)
When in "restricted network" operation the number of bits per audio sample is reduced by one.
2)
When in "restricted network" operation, the LSB is not the bit 8, but the bit 7.
3)
When in "restricted network" operation the number of bits per audio sample is reduced by one.

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ETS 300 144: May 1994
Restricted network: A network consisting of multiples of 64 kbit/s links, but where only multiples of
56 kbit/s are usable for the terminals.
4 Symbols and abbreviations
For the purposes of this ETS, the following symbols and abbreviations apply:
BAS Bit-rate Allocation Signal
C&I Control and Indication
cap-mark capability marker
cap-set capability set
CIF Common Intermediate Format (picture format defined in ITU-T
Recommendation H.261 [1])
CRC4 Cyclic Redundancy Check 4-bit
ECS Encryption Control Signal
FAS Frame Alignment Signal
FAW Frame Alignment Word
4)
H-MLP High speed Multi Layer Protocol
H0 384 kbit/s channel
H11 1 536 kbit/s channel
H12 1 920 kbit/s channel
HSD High Speed Data
ISDN Integrated Services Digital Network
ITU-TS International Telecommunications Union - Telecommunication
Standardization Sector
LCA Loopback Command "Audio loop request"
LCD Loopback Command "Digital loop request"
LCO Loopback Command "Loop Off request"
LCV Loopback Command "Video loop request"
LSB Least Significant Bit
LSD Low Speed Data
MBE Multiple Byte Extension
MCU Multipoint Control Unit
5)
MLP Multi Layer Protocol
MSB Most Significant Bit
QCIF Quarter Common Intermediate Format (picture format defined in ITU-T
Recommendation H.261 [1])
SBE Single Byte Extension
SC Service Channel
SMF Sub-Multiframe
TEA Terminal Equipment Alarm
TS Time Slot
TS1 Time Slot 1
VCF Video Command "Freeze-picture request"
VCU Video Command "fast-Update request"

4)
MLP protocols are under discussion in the ITU-TS.
5)
MLP protocols are under discussion in the CCITT.

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5 Description
This ETS provides for dynamically subdividing an overall transmission channel of 64 kbit/s to 1 920 kbit/s
into lower rates suitable for audio, video, data and telematic purposes. The overall transmission channel is
derived by synchronising and ordering transmissions over/from 1 to 6 B-connections, from 1 to 5 H0-
connections, or an H11 or H12 connection. The first connection established is the initial connection and
carries the initial channel in each direction. The additional connections carry additional channels.
The total rate of transmitted information is called the "transfer rate"; it is possible to fix the transfer rate at
less than the capacity of the overall transmission channel (values listed in Clause 10).
A single 64 kbit/s channel is structured into octets transmitted at 8 kHz. Each bit position of the octets may
be regarded as a sub-channel of 8 kbit/s (see table 1). The eighth sub-channel is called the Service
Channel (SC), consisting of several parts as described in subclauses 5.1 to 5.4 below.
An H0, H11 or H12 channel may be regarded as consisting of a number of 64 kbit/s Time Slots (TS) (see
table 2). The lowest numbered time-slot is structured exactly as described for a single 64 kbit/s channel,
while the other TS have no such structure. In the case of multiple B or H0 channels, all channels have a
frame structure; that in the initial channel controls most functions across the overall transmission, while
the frame structure in the additional channels is used for synchronisation, channel numbering and related
controls.
The term "I-channel" is applied to the initial or only B-channel, to TS1 of initial or only H0 channel, and to
TS1 of H11, H12 channels.
Table 1: Frame structure of a single 64 kbit/s channel (B-channel)
Bit number
1 2345 67 8 (SC)
Octet number
S SSSS SS FAS :
u uuuu uu 8
b bbbb bb 9
- ---- -- BAS :
c cccc cc 16
h hhhh hh 17
a aaaa aa ECS :
n nnnn nn 24
n nnnn nn Sub- 25
e eeee ee chan- ·
l llll ll nel ·
# #### ## # ·
1 2345 67 8 80
5.1 Frame Alignment Signal (FAS)
This signal structures the I-channel and other framed 64 kbit/s channels into frames of 80 octets each and
multiframes of 16 frames each. Each multiframe is divided into eight 2-frame sub-multiframes. The term
"Frame Alignment Signal" (FAS) refers to the bits 1-8 of the SC in each frame. In addition to framing and
multiframing information, control and alarm information may be inserted in the FAS, as well as error check
information to monitor end-to-end error performance and to check frame alignment validity. Other time-
slots in H0, H11 or H12 connections are aligned to the first.
The bits are transmitted to line in order, bit 1 first and Octet 1 first.
FAS shall be transmitted in the Least Significant Bit (LSB) of the octet (called "bit 8") within each 125
microsecond, e.g. in an ISDN basic or primary rate interface (see also tables 1 and 2 and subclause 6.6).
It should be noted that, where interworking between the audiovisual terminal and the telephone is
required, transmission using the network timing is essential; a transmitting terminal shall always use octet
timing, if this can be obtained from the network.

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In the receiver side, FAS shall be sought in all bit positions. If the received FAS position conflicts with the
network octet timing, the FAS position is given priority. This may happen when the receiver utilises
network octet timing while the transmitter does not, as in a terminal using codecs with separate ISDN
terminal adaptor, or when interworking between 64 kbit/s and 56 kbit/s terminals takes place.
Table 2: Frame structure of higher-rate single channels (H , H , H channels)
0 11 12
125 microseconds
_______________________________________________________________________________
< >p
TS
12 3456 7 · · · · · · 6n-2 6n-1 6n
H n = 1
H n = 4
H n = 5
Audio + service channel
1 2345 67 8
1 Octet number
S SSSS SS FAS :
u uuuu uu 8
b bbbb bb 9
- ---- -- BAS :
c cccc cc 16
h hhhh hh 17
a aaaa aa ECS :
n nnnn nn 24
n nnnn nn
e eeee ee Sub- ·
chan-
l llll ll
nel
·
# #### ## #
1 2345 67 8 80
5.2 Bit-rate Allocation Signal (BAS)
Bits 9 to 16 of the SC in each frame are referred to as the BAS. This signal allows the transmission of
codewords to describe the capability of a terminal to structure the capacity of the channel or synchronised
multiple channels in various ways, and to command a receiver to demultiplex and make use of the
constituent signals in such structures. This signal is also used for controls and indications.
NOTE: For some countries having 56 kbit/s channels, the net available bit rates are 8 kbit/s
fewer. Interworking between a 64 kbit/s terminal and a 56 kbit/s terminal is established
according to the frame structure in subclause 6.6.
5.3 Encryption Control Signal (ECS) channel (optional)
The ECS channel is optional and can be used in single B or H0 channels as well as H11 and H12
channels, or in the initial channel of multiple-channel calls.
When switched on, the ECS channel occupies the bits 17 to 24 of the SC, a rate of 800 bit/s, and any
video or variable data channel which would otherwise occupy these bits is accordingly reduced in rate by
800 bit/s.
5.4 Remaining capacity
The remaining capacity may convey a variety of signals within the framework of a multimedia service,
under the control of the BAS. It is carried in bits 1 to 8 of each octet in the case of a single 64 kbit/s
connection, and it includes the rest of the SC. The facilities provided can be found in the list given in
subclause 8.2.
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6 Frame structure
6.1 General
An 80-octet frame length produces 80 bits in the SC. These 80 bits are numbered 1 to 80. Bits 1 to 8 of
the SC in every frame constitute the FAS (see table 3), whose content is as follows:
- multiframe structure (see subclause 6.2 and table 4a);
- Frame Alignment Word (FAW);
- A-bit;
- E-bit and C-bits (see Clause 9).
The first seven bits of the Frame Alignment Word (FAW) are formed by bits 2 to 8 of the FAS in the even
frames of a sub-multiframe. Their value is "0011011". They are complemented by a "1" in bit 2 of the
succeeding odd frame. This eighth bit of the FAW is necessary in order to avoid simulation of the FAW by
a frame-repetitive pattern elsewhere in a frame.
The A-bit of the I-channel indicates the loss of frame- or multiframe alignment. It is set to "0" whenever
frame- and multiframe is aligned (if multiframe alignment is evaluated, see subclause 6.4, otherwise only if
it is frame aligned), and is set to "1" otherwise (see subclause 6.3; for additional channels, see subclause
7.1).
When the optional Cyclic Redundancy Check 4-bit (CRC4) procedure, as defined in Clause 9, is not used,
the E-bit shall be set to 0, and bits C1, C2, C3 and C4 shall be set to 1 by the transmitter.
Table 3: Assignment of bits 1 to 8 of the service channel in each frame
Bit number 1 2 34 5 6 78
Successive frames
Even frames See subclause
0 0 1 1 0 1 1
6.2
Odd frames See subclause
1 A E C1 C2 C3 C4
6.2
FAW
6.2 Multiframe structure
The multiframe structure is shown in table 4a.
Each multiframe contains 16 consecutive frames numbered 0 to 15 divided into eight sub-multiframes of
two frames each. The multiframe alignment signal is located in bit 1 of frames 1-3-5-7-9-11 and has the
form 001011.
Bit 1 of frame 15 remains reserved ("R") for future use. The value is fixed at 0.
Bit 1 of frames 0-2-4-6 (N1 - N4) may be used for a modulo 16 counter to number multiframes in
descending order. The LSB is transmitted in frame 0, and the Most Significant Bit (MSB) in frame 6. The
receiver uses the multiframe numbering to share out the differential delay of separate connections, and to
synchronise the received signals.
The multiframe numbering shall be mandatory in both the initial and additional channels for multiple B or
multiple H0 communications, but it may or may not be inserted for single B or single H0 or H11/H12 or
other communications where synchronisation between multiple channels is not required. In this case, N1
to N4 are set to "0".
Bit 1 of frame 8 (N5) indicates whether multiframe numbering is active or inactive. It is set to 1 when
multiframes are numbered and is set to 0 when they are not.
Bit 1 of frames 10-12-13 (L1 - L3) form the channel number; the LSB is L1. This number shall be used to
number each channel in a multiconnection structure so that the distant receiver can place the octets
received in each 125 microseconds in the correct order.

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ETS 300 144: May 1994
The bits N1 - N5 and L1 - L3 in the multiframe shall be considered valid, as long as they are received
consistently in three consecutive multiframes.
Bit 1 of frame 14, the Terminal Equipment Alarm (TEA) may be set to 1 in the outgoing signal, when one
or more of the following conditions holds:
- an internal terminal equipment fault exists such that it cannot receive and act on the incoming
signal;
- an internal terminal equipment fault exists such that it can no longer transmit user information in the
form previously transmitted.
Otherwise it is set to 0.
For a description of the A-bit see subclause 6.1; the use of the bits C1 to C4 and of the E-bit is described
in Clause 9.
Table 4a: Assignment of bits 1 to 8 of the SC in each frame in a multiframe
Sub- Frame Bits 1 to 8 of the service channel in every frame
multiframe
(SMF) 1 2 3 4 5 6 7 8
0N1 0 0 1 1 0 1 1
SMF1 1 0 1 A E C1C2 C3C4
2N2 0 0 1 1 0 1 1
SMF2 3 0 1 A E C1C2 C3C4
4N3 0 0 1 1 0 1 1
SMF3 5 1 1 A E C1C2 C3C4
6N4 0 0 1 1 0 1 1
Multi- SMF4 7 0 1 A E C1C2 C3C4
frame 8 N5 0 0 1 1 0 1 1
SMF5 9 1 1 A E C1C2 C3C4
10 L1 0 0 1 1 0 1 1
SMF6 11 1 1 A E C1C2 C3C4
12 L2 0 0 1 1 0 1 1
SMF7 13 L3 1 A E C1C2 C3C4
14 TEA 0 0 1 1 0 1 1
SMF8 15 R 1 A E C1C2 C3C4
Table 4b: Channel numbering with bits L3, L2, L1
Channel L3 L2 L1
Initial 0 0 1
Second 0 1 0
Third 0 1 1
· · · · · · · · ·
Sixth 1 1 0
Table 4c: Multiframe numbering with bits N4, N3, N2, N1
Multiframe Number N4 N3 N2 N1
0 0 0 0 0 (or numbering inactive)
· · · · · · · · · ·
15 1 1 1 1
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6.3 Gain, loss and recovery of frame alignment
Frame alignment is defined as being gained when the following sequence is detected:
- for the first time, the presence of the correct first seven bits of the FAW;
- the eighth bit of the FAW in the following frame is detected by verifying that bit 2 is a 1;
- for the second time, the presence of the correct first seven bits of the FAW in the next frame.
Frame alignment is defined to have been lost when three consecutive FAWs have been received with an
error.
Frame alignment is defined to have been recovered when the same sequence as described above is
detected.
When the frame alignment is lost, the A-bit of the next odd frame is set to 1 in the transmit direction.
6.4 Gain, loss and recovery of multiframe alignment
Multiframe alignment is needed to number and synchronise two or more channels. Terminals such as
those having only single-channel capabilities which have no use for the multiframe structure shall transmit
the multiframe structure, but need not check for multiframe alignment on the incoming signal: they may
transmit outgoing A = 0 when frame alignment is recovered.
NOTE: Such a terminal cannot recognise TEA (see table 4a).
Multiframe alignment is defined to have been gained when the multiframe alignment signal is consistent
over 16 consecutive frames.
After multiframe alignment has been validated, the other functions represented by bit 1 of the SC can be
used. When multiframe alignment of the distant terminal has been signalled (A=0 received), the distant
terminal is expected to have validated BAS codes and to be able to interpret BAS codes.
Multiframe alignment is defined to have been lost when three consecutive multiframe alignment signals
have been received with an error. It is defined to have been recovered when the multiframe alignment
signal has been received with no error in the next multiframe. When multiframe alignment is required and
has been lost, even when an unframed mode is received, the A-bit of the next odd frame is set to 1 in the
transmit direction, and is reset to 0 when multiframe alignment is regained. It is reset in additional
channels when multiframe alignment and synchronism with the initial channel is regained.
6.5 Procedure to recover octet timing from frame alignment
The terminal shall recover octet timing in the receive direction from bit timing and from the frame
alignment.
6.5.1 General rule
The receive octet timing is normally determined from the FAS position. At the start of the call and before
the frame alignment is gained, the receive octet timing may be taken to be the same as the internal
transmit octet timing. As soon as a first frame alignment is gained, the receive octet timing is initialised at
the new bit position, but it is not yet validated. It shall be validated only when frame alignment is not lost
during the next 16 frames.
6.5.2 Particular cases
a) When, at the initiation of a call, the terminal is in a forced reception mode (i.e. searching for frame
alignment), or when the frame alignment has not yet been gained, the terminal may temporarily use
the transmit octet timing.
b) When frame alignment is lost after being gained, the receive timing shall not be changed until frame
alignment is recovered.
c) As soon as frame and, if necessary, multiframe alignment have been gained once, the octet timing
shall be considered as valid for the rest of the call, unless frame alignment is lost and a new frame
alignment is gained at another bit position.

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d) When the terminal switches from a framed mode to an unframed mode (by means of the BAS), the
octet timing previously gained shall be kept.
e) When a new frame alignment is gained on a new position, different from that previously validated,
the receive octet timing is re-initialised to the new position but not yet validated and the previous bit
position is stored. If no loss of frame alignment occurs in the next 16 frames, the new position shall
be validated, otherwise the stored old bit position is ritualised.
6.5.3 Search for Frame Alignment Signal (FAS)
Two methods may be used: sequential or parallel. In the sequential method, each of the eight possible bit
positions for the FAS is tried. When FAS is lost after being validated, the search shall resume starting
from the previously validated bit position. In the parallel method, a sliding window, shifting one bit for each
bit period, may be used. In that case, when frame alignment is lost, the search shall resume starting from
the bit position next to the previously validated one.
6.6 Frame structure for interworking between a 64 kbit/s terminal and a 56 kbit/s terminal
(optional)
The ability to interwork with restricted networks is not a mandatory requirement.
The sub-channel arrangement for this frame structure is given in tables 5a and 5b.
Table 5a: Transmitter of the 64 kbit/s terminal
Bit number
123456 7(SC) 8
Octet number
SSSSSS FAS 1 :
uuuuuu 1 8
bbbbbb 1 9
------ BAS 1 :
cccccc 1 16
hhhhhh 1 17
aaaaaa (ECS) 1 :
nnnnnn 1 24
nnnnnn Sub- 1 25
eeeeee chan- 1 ·
llllll nel 1 ·
#######1 ·
12345671 80
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Table 5b: Receiver of the 64 kbit/s terminal
Bit number, synchronised with the octet timing of the network
SS 1
S S S S FAS* u u 1
u uuu bb 1
Frame structured
b bbb - - 1
by the 56 kbit/s
- --- BAS c c 1
terminal
c ccc h h 1
h hhh aa 1
a a a a (ECS) n n 1
n nnn nn 1
n n n n Sub- e e 1
e e e e chan- l l 1
l lll nel # # 1
# ####12 1
3 4567
*FAS may appear at any of Bits 1 to 7
6.6.1 Operation of the 64 kbit/s terminal
The transmitter fills the eighth sub-channel with "1", while the receiver searches FAS at every sub-
channel. It should be noted that at the receiver side stuffing bits "1" appear always at Bit number 8, but
FAS and BAS appear at any of Bit numbers 1 to 7.
6.6.2 Restriction against some communication modes
Since the interworking bit rate becomes 56 kbit/s, the transmission modes using more than 56 kbit/s are
forbidden (receivers ignore these command BAS codes). Facilities using the original seventh sub-channel
move to the sixth sub-channel. See subclause 10.1.1.2.
7 Multiple connections
Some audiovisual terminals shall be able to communicate over multiple B or H0 connections (see NOTE).
In this case, a single B or H0 initial connection is established, the possibility for more connections is
determined from the transfer rate capability BAS of Clause 10 and the additional connections are then
established and synchronised by the terminal using the multiframe structure.
NOTE: A connection is a physical path between the terminals. A channel is the transmission in
one direction over the connection.
7.1 Multiple B-connections
FAS and BAS are transmitted in each B-channel.
The actual bit-rates allowed by this ETS for audio codings within a 64 kbit/s I-channel are 64 kbit/s and 56
kbit/s, commands (000)[4/5 and 18/19] respectively. Thus, in a 2B audiovisual call, it shall not be
permitted to transmit framed audio, coded according to CCITT Recommendation G.711 [4] in the I-
channel and video only in the additional channel. The two channels shall be synchronised, the audio shall
be set to 56 kbit/s, and, when the video is ON, it shall occupy the remaining 68,8 kbit/s.

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FAS operation is as follows:
- multiframe numbering is used to determine relative transmission delay between B-channels as
described in Subclause 6.2;
- the channel numbers are transmitted, as described in subclause 6.2, with the channel of the initial
connection being numbered 1 and there being up to five additional connections;
- the outgoing A-bit is set to 1 in the additional B-channel of the same connection whenever the
received additional channel is not synchronised to the initial channel;
- when receive synchronisation is achieved between the initial and additional channels by introducing
delay to align their respective multiframe signals, the transmitted A-bit is set to 0;
- the E-bit for each additional B-channel is transmitted in the additional B-channel in the same
connection, because it relates to a physical condition of the transmission path.
The BAS operation in additional connections is restricted to the transmission of the additional channel
number (thus the channel numbering of any additional connection shall be sent both in BAS according to
Clause 10 and in the FAS, as in subclause 6.2), while channel numbering of the initial channel is sent only
in FAS.
The distant terminal, upon receiving the A-bit set to "0" with respect to sequentially numbered channels,
can add their capacity to the initial connection by sending the appropriate transfer rate BAS in Clause 10.
The order of the bits transmitted in the channels is in accordance with the examples given in tables 14 to
21.
7.2 Multiple H0-connections
FAS and BAS are transmitted in the first time-slot of each H0.
FAS operation is as stated in subclause 7.1 except that the channel number is used to order the six octets
received each 125 microseconds with respect to the six octet groups received in other channels.
The BAS operation in additional channels is as specified in subclause 7.1.
8 Introduction to BAS
8.1 Encoding of the BAS
The Bit-rate Allocation Signal (BAS) occupies the bits 9 to 16 of the SC in every frame. An eight bit BAS
code (b , b , b , b , b , b , b , b ) is complemented by eight error correction bits (p , p , p , p , p , p , p ,
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6
p ) to implement a (16,8) double error correcting code. This error correcting code is obtained by
shortening the (17,9) cyclic code with generator polynomial:
8 7 6 4 2
g(x) = x + x + x + x + x + x + 1
The error correction bits are calculated as coefficients of the remainder polynomial in the following
equation:
7 6 5 4 3 2
p x + p x = p x + p x + p x + p x + p x + p
0 1 2 3 4 5 6 7
15 14 13 12 11 10 9 8
= RES [b x + b x + b x + b x + b x + b x + b x + b x ]
g(x) 0 1 2 3 4 5 6 7
where RES [f(x)] represents the residue obtained by dividing f(x) by g(x).
g(x)
The BAS code is sent in the even-numbered frame, while the associated error correction bits are sent in
the subsequent odd-numbered frame. The bits of the BAS code or the error correction are transmitted in
the order shown in table 6 to avoid emulation of the FAW.

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Table 6
Bit position Even frame Odd frame
9b p
0 2
10 b p
3 1
11 b p
2 0
12 b p
1 4
13 b p
5 3
14 b p
4 5
15 b p
6 6
16 b p
7 7
The decoded BAS value is valid if:
- the receiver is in frame alignment, and
- the FAW, in the same sub-multiframe, was received with two or fewer bits in error.
Otherwise the decoded BAS value is ignored.
8.2 Values of the BAS
The encoding of BAS is made according to an attribute method. This consists of attribute (8 attributes)
and value (32 values). The first three bits of a BAS represent the attribute, describing the general
command or capability, and the other five bits identify the "value" - the specific command or capability (see
table 7).
Table 7
Attribute Significance
000 Audio coding command
001 Transfer rate command
010 Video, encryption, loops and other command
011 LSD/MLP commands
100 Audio / Transfer Rate capabilities
101 Video, MBE, encryption and LSD/MLP capabilities
110 Reserved
111 Escape codes
The values of these attributes are listed and defined in Clause 10. They provide for the following facilities:
- transmission at various total rates and on single and multiple channels, on clear channels and on
networks subject to restrictions to 56 kbit/s and its multiples;
- audio transmission, digitally encoded to various recommended algorithms, e.g.:
- voice encoded at 56 kbit/s using a truncated form of PCM of CCITT Recommendation G.711
[4] (A-law or μ- law);
- voice encoded at 16 kbit/s and video at 46,4 kbit/s;
- voice encoded at 56 kbit/s with a bandwidth 50 Hz to 7 000 Hz (sub-band ADPCM according
to CCITT Recommendation G.722 [5]); the coding algorithm is also able to work at 48 kbit/s -
data can then be dynamically inserted at up to 14,4 kbit/s;
- video transmission, digitally encoded to a recommended algorithm, with provision for future
recommended improvement;
- still pictures;
- Low Speed Data (LSD) within the I-channel, or TS1 of a higher rate initial channel, e.g. data at 56
kbit/s inside an audiovisual session for, inter alia, file transfer for communicating between personal
computers;
- High Speed data (HSD) in the highest-numbered 64 kbit/s channel or Time Slots;
6)
- data transmission within a multilayer protocol, either in the I-channel Multi Layer Protocol (MLP )
or in capacity other than the I-channel High speed Multi Layer Protocol (H-MLP);

6)
MLP protocols are under discussion in the ITU-TS.

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- an encryption control signal;
- loopback towards the network for maintenance purposes;
- signalling for control and indications;
- a message system for, inter alia, conveying information concerning equipment manufacturer and
type.
8.2.1 Single octet BAS
The command BAS attributes have the following significance: on receipt of a BAS command code in one
(even) frame and its error-correcting code in the next (odd), the receiver prepares to accept the stated
mode (or mode change) beginning from the subsequent (even) frame; thus a mode change can be
effected in 20 milliseconds. The command remains in force until countermanded (see ETS 300 143 [2]).
The bit positions occupied as a result of combinations of BAS commands are exemplified in Clause 10,
tables 14 to 21.
The capability BAS attributes have the following significance: they indicate the ability of a terminal to
receive and properly treat the various types of signal. It follows that having received a set of capability
values from the remote terminal Y, terminal X shall not transmit signals lying outside that declared range.
The value (111)[24] is the capability marker which is followed by normal BAS codes, not by any escape
values (see ETS 300 143 [2]).
8.2.2 Two-octet BAS
The attribute (111) provides means for extension of the use of the
...