SIST ETS 300 481 E1:2003
(Main)Terminal Equipment (TE); Integrated Services Digital Network (ISDN); B-Channel Aggregation Unit (CAU); Procedures and terminal requirements
Terminal Equipment (TE); Integrated Services Digital Network (ISDN); B-Channel Aggregation Unit (CAU); Procedures and terminal requirements
To define protocols and related requirements whereby a number of ISDN B-channels may be synchronised and aggregated to represent a single bit stream for any application, whether audiovisual or more general data application. (Liaison with ETSI STC BTC4 required.)
Terminalska oprema (TE) – Enota za združevanje kanalov (CAU) B v digitalnem omrežju z integriranimi storitvami (ISDN) – Postopki in terminalske zahteve
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST ETS 300 481 E1:2003
01-december-2003
Terminalska oprema (TE) – Enota za združevanje kanalov (CAU) B v digitalnem
omrežju z integriranimi storitvami (ISDN) – Postopki in terminalske zahteve
Terminal Equipment (TE); Integrated Services Digital Network (ISDN); B-Channel
Aggregation Unit (CAU); Procedures and terminal requirements
Ta slovenski standard je istoveten z: ETS 300 481 Edition 1
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
35.180 Terminalska in druga IT Terminal and other
periferna oprema IT peripheral equipment
SIST ETS 300 481 E1:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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EUROPEAN ETS 300 481
TELECOMMUNICATION July 1996
STANDARD
Source: ETSI TC-TE Reference: DE/TE-04029
ICS: 33.080
Key words: ISDN, channel aggregation
Terminal Equipment (TE);
Integrated Services Digital Network (ISDN)
B-Channel Aggregation Unit (CAU);
Procedures and terminal requirements
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 92 94 42 00 - Fax: +33 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 1996. All rights reserved.
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Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.
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Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions.7
4 Symbols and abbreviations .8
4.1 Symbols .8
4.2 Abbreviations .9
5 General.10
5.1 Application of this ETS.10
5.1.1 Intercommunication of audiovisual equipments .10
5.1.1.1 Case A.10
5.1.1.2 Case B.11
5.1.1.3 Case C.11
5.1.2 Intercommunication of non-audiovisual equipments - Case D.12
5.2 Definition of the modes of transmission on the Multiple Channel (MC) side .12
5.3 General description of the aggregation process.15
5.4 CAU functionality .16
6 Choice of ISO Aggregation or H.244 Aggregation procedure .16
7 H.244 Aggregation procedure .19
7.1 Call control.19
7.1.1 Initial channel.19
7.1.2 Additional channels .19
7.2 Channel synchronisation.19
7.3 In-band procedure using ITU-T Recommendation H.221 BAS codes.19
7.3.1 Control of transfer rate .19
7.3.2 Determination of the transfer-rate capabilities to be transmitted on the MC
side.20
7.3.3 Determination of the transfer-rate capabilities to be transmitted on the SC
side.20
7.3.4 Capability sets transmitted from a CAU .20
7.3.4.1 Modification of SCE capset for forwarding towards MC
side .20
7.3.4.2 Modification of capset incoming from MC side for
forwarding towards SCE.21
7.3.5 Notification of change of N .21
a
7.3.6 Commands transmitted from a CAU.22
7.3.6.1 Substitution of transfer rate commands.22
7.3.6.2 Insertion and removal of [SM-comp] and [6B-H0-comp] .22
7.3.6.3 Insertion of [capex] .22
7.3.6.4 Insertion of [AggIN]*.22
7.4 Transmission of user information by a CAU .22
8 Initialisation, mode/rate changing and fault recovery .23
8.1 Initialisation .23
8.1.1 Single-channel side .23
8.1.2 Multi-channel Side, initial channel .23
8.1.3 Multi-channel side, additional channels.24
8.2 Change of transmission rate during a session.25
8.3 Recovery from fault conditions .25
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8.4 Further mode changes. 25
9 ISO Aggregation procedure. 25
Annex A (informative): Examples . 26
Annex B (informative): Example of SDL diagram for H.244 Aggregation initialisation. 30
Annex C (informative): Comments on the modification of capsets and commands. 31
Annex D (informative): Bibliography . 32
History. 33
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Foreword
This European Telecommunication Standard (ETS) has been produced by the Terminal Equipment (TE)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
Transposition dates
Date of adoption of this ETS: 17 May 1996
Date of latest announcement of this ETS (doa): 31 October 1996
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 30 April 1997
Date of withdrawal of any conflicting National Standard (dow): 30 April 1997
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1 Scope
This European Telecommunication Standard (ETS) defines protocols for the synchronisation and
aggregation of multiple ISDN channels at 64 kbit/s, these channels being with a differential delay in the
range of ± one second and with or without octet integrity structure. It also addresses the case of
interworking with a digital network restricted to a rate of 56 kbit/s. It is applicable to a wide range of user
data transport up to 63 channels using ISO/IEC 13871 [1], but special provision is made for audiovisual
systems according to ETS 300 144 [2], up to 24 channels; the aggregation may be network-based or
associated with Customer-Premises Equipment. The available operating modes (B1, B2, B3, H2) provide
options with/without transmission-management overhead and user-data rates at or less than the exact
multiples of 64 kbit/s or 56 kbit/s.
The number of aggregated channels may be varied dynamically during a session. Procedures are given
for dealing with faults, including loss of channels and slip.
Call control is outside the scope of 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 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] ISO/IEC 13871: "Information Technology - Telecommunications and information
exchange between systems - Private telecommunications networks - Digital
channel aggregation".
[2] ETS 300 144: "Integrated Services Digital Network (ISDN); Audiovisual services;
Frame structure for a 64 to 1 920 kbit/s channel and associated syntax for
inband signalling".
[3] 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".
[4] ITU-T Recommendation H.320 (1993): "Narrow-band visual telephone systems
and terminal equipment".
[5] ETS 300 145: "Integrated Services Digital Network (ISDN); Audiovisual services;
Videotelephone systems and terminal equipment operating on one or two
64 kbit/s channels".
[6] ITU-T Recommendation H.242 (1993): "System for establishing communication
between audiovisual terminals using digital channels up to 2 Mbit/s".
3 Definitions
For the purposes of this ETS, the following definitions apply:
called end: The Channel Aggregation Unit (CAU) or Multiple Channel Equipment (MCE) which accepts
the first 64/56 channel connection request of the whole session, resulting in the establishment of the
"initial channel". If during fault-recovery procedures the initial channel is transferred to another connection,
this does not affect the definition (see note 1).
calling end: The CAU or MCE which requests the first 64/56 channel connection of the whole session,
resulting in the establishment of the "initial channel". If during fault-recovery procedures the initial channel
is transferred to another connection, this does not affect the definition (see note 1).
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Channel Aggregation Unit (CAU): A device having both multiple 64 kbit/s accesses and a single access
at a higher bitrate. Reference in this ETS to "CAU" or "aggregator" means equipment conforming to this
ETS.
compatibility bits: Bit 8 of the first sixteen octets in every timeslot of a single channel except Time-slot 1.
external setting: Term used to express operations outside the scope of this ETS which determine the
behaviour of a CAU as to choice of option or timing of its action.
H.221 frame structure, H.221 framing: Frame structure according to ITU-T Recommendation H.221, as
set out in ETS 300 144 [2].
H.320 terminal: A terminal that conforms to ITU-T Recommendation H.320 [4] (note 2).
Mode H2: Modes of aggregation by the method given in clauses 7 and 8 of this ETS.
Modes B1, B2, B3: Modes of aggregation by the method of ISO/IEC 13871 [1], see subclause 5.2.
Multiple Channel Equipment (MCE): A terminal or other unit (such as a Local Area Network (LAN)
gateway) directly attached to an ISDN (through one or more ISDN accesses, whether basic accesses or
primary rate access(es)).
No Terminal Aggregator Communication case (ISO Aggregation case): No in-band management
communication between Single Channel Equipment (SCE) and CAU takes place - the single channel is
only a clear path for the data which will be wholly transmitted to the remote party; any communication
between the terminal and the CAU is by means not specified in this ETS (see clause 9).
redundant command: A Bit Allocation Signal (BAS) command which repeats, unchanged, a previously
transmitted mode value which is still in force.
Single Channel Equipment (SCE): A terminal or other unit (such as a LAN interface) having a single
serial bi-directional digital interface.
H.244 Aggregation case: In-band communication between SCE and CAU takes place using ITU-T
Recommendation H.221 BAS codes (see clauses 7 and 8 of this ETS).
user information: The application data streams passing (in both directions) between CAU and SCE
(note 3).
NOTE 1: The significance of "calling" and "called" end-points is mentioned in subclause 8.1.3.
NOTE 2: ETS 300 145 [5] is the ETSI equivalent to ITU-T Recommendation H. 320 [4]. The
scope of ETS 300 145 [5] is, however, restricted to systems supporting 1B or 2B
access.
NOTE 3: In the audiovisual cases, the application data stream includes the ITU-T
Recommendation H.221 frame structure.
4 Symbols and abbreviations
4.1 Symbols
For the purposes of this ETS, the following symbols apply:
NOTE: For readability, the capability and command values listed in ETS 300 144 [2] are
referred to in this ETS by their names rather than codepoint byte values; the use of
{name} for capabilities and [name] for commands serves to distinguish between these.
N an integer, applied to 64/56 channels to define a parallel (un-aggregated)
bitstream of rate N×64 kbit/s.
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n an integer, applied to 64 kbit/s to define a serial (or otherwise aggregated)
bitstream of rate n*64 kbit/s.
N the number of active 64/56 channels between CAU and MCE or between two
a
CAUs.
N the maximum number of 64/56 channels which can be accepted by a CAU
m
transmitting the value {N ×B}.
m
N' used to denote the incoming value of N from the remote CAU, or equivalent
m m
from an MCE.
N the number of connections requested by the calling end, the lower of N and
d m
N' .
m
{N×64k} capabilities in the series {1B}, {2B}, {3B}. corresponding to N=1, 2, 3.,
(applies to Mode H2 only).
{n*64k} capabilities in the series {64k}, {128k}, {192k}. corresponding to n=1, 2, 3.
n such that {n *64k} is the highest transfer-rate capability incoming from the SCE
m m
for which the continuous series of rate capabilities {(n -1)*64k}, {(n -
m m
2)*64k},.{2*64k} is also present in the capset.
[N×64] Multiple-channel commands (as defined in ETS 300 144 [2]).
[n*64k] Single-channel commands (as defined in ETS 300 144 [2]).
[capex] command issued by a CAU (see subclause 7.3.6.3) to an SCE to stimulate a
capability exchange.
[AggIN]* a double SBE symbol indicating the number n as determined by the process of
subclause 7.3.4.2; see the procedure described in clause 8 (see ETS 300 144
[2]).
{null} capability having no significance other than as a filler; only ever transmitted by a
CAU, and therefore it identifies the capset as having last come from, or been
forwarded by, a CAU; SCE ignores any number of these in an incoming capset
(see ETS 300 144 [2]).
{SM-comp} capability to transmit and receive user information without using any
compatibility bits, setting these to 1 (see ETS 300 144 [2]).
[SM-comp] user information is not contained in the compatibility bits (and is not sent in the
compatibility bits in the reverse direction either). See ETS 300 144 [2].
Σ Audible signal (to be defined), which would be recognised by a human user as a
call progress tone (he would not hang up).
4.2 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
BAS Bit Allocation Signal
Capset Capability set
CAU Channel Aggregation Unit
FAS Frame Alignment Signal
H.221 See subclause 3.1, H.221 frame structure, H.221 framing
MC (side) Multiple Channel (side, of a CAU)
MCE Multiple-Channel Equipment
NII Network Indicate Incompatible - aggregators
ISO Aggregation No Terminal-Aggregator Communication
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SC (side) Single Channel (side, of a CAU)
SCE Single-Channel Equipment
SM-comp Single-Multiple compatibility
H.244 Aggregation Terminal-Aggregator Communication
UD Unspecified Data
5 General
5.1 Application of this ETS
On the single-channel connections, which may be very short if the terminal and CAU are co-located, or
much longer if a telecommunications link is involved, two options are covered by this ETS:
a) no in-band management communication on the single channel, this being only a clear path for the
data which will be wholly transmitted to the remote party; any communication between the terminal
and the CAU is by means not specified in this ETS; this is referred to as the "ISO Aggregation" case
- No Terminal-Aggregator Communication;
b) in-band communication as specified in this ETS, using the BAS codes defined in ETS 300 144 [2]
and the procedures of ETS 300 143 [3]; this is referred to as the "H.244 Aggregation" case -
Terminal-Aggregator Communication. This corresponds to the use of Mode H2 (see subclause 5.2,
figure 8 and associated text).
5.1.1 Intercommunication of audiovisual equipments
For audiovisual terminals conforming to ETS 300 144 [2] and ETS 300 143 [3], this ETS provides for
synchronisation and aggregation of up to 24 channels of 64 kbit/s or 56 kbit/s, each being with or without
octet integrity and relative transmission delay in the range ± 1 second.
Provision is made for the following intercommunication Cases A to C.
5.1.1.1 Case A
For interconnection of a Single-Channel Equipment (SCE) and a Multiple-Channel Equipment (MCE)
audiovisual end-point, both conforming to ETS 300 144 [2] and ETS 300 143 [3], only the H.244
Aggregation approach can be followed (see figure 1); this involves only one CAU, which may be within the
network or close to the single-channel end-point.
CAU ISDN
SCE
MCE
TAC
Figure 1: Case A
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5.1.1.2 Case B
This case provides for interconnection between two single-channel audiovisual end-points which see the
aggregated link purely as a clear data channel; each has a CAU associated with it, but there is no in-band
control communication between the end-point and its associated CAU (see figure 2); this is the ISO
Aggregation approach. The system is exactly the same as for unspecified data applications (see
subclause 5.1.2); the CAU-ISDN-CAU combination provides a clear channel at one of the transfer rates
specified in ETS 300 144 [2], and, therefore, shall use Mode B1 or B3 (see subclause 5.2).
CAU ISDN CAU
SCE SCE
(NoTAC) (NoTAC)
optional external communication
Figure 2: Cases B and D
5.1.1.3 Case C
This provides for the interconnection of two single-channel end-points both conforming to ETS 300 144 [2]
and ETS 300 143 [3] and capable of the operation described in clauses 7 to 8, the H.244 Aggregation
approach (see figure 3); this involves two CAUs, which may be within the network or close to the
single-channel end-points.
NOTE: H.244 Aggregation cannot be used at one end and ISO Aggregation at the other, see
clause 6.
CAU ISDN CAU
SCE SCE
TAC TAC
Figure 3: Case C
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5.1.2 Intercommunication of non-audiovisual equipments - Case D
This ETS provides for synchronisation and aggregation of up to 63 channels of 64 kbit/s or 56 kbit/s, each
being with or without octet integrity and relative transmission delay in the range ± one second. It is
applicable to a wide range of user information transport, including LAN-LAN interconnect, private circuit
back-up, and other "unspecified data" applications. No in-band control communication takes place on the
single-channel side. The equipment see the aggregated link purely as a clear data channel, and the
structure or content of the data streams is of no concern to the aggregating equipment.
The ISO Aggregation approach is appropriate (see figure 2); the CAU-ISDN-CAU combination provides a
clear channel at one of the transfer rates specified in ISO/IEC 13871 [1] using Mode B1, B2 or B3 (see
subclause 5.2).
5.2 Definition of the modes of transmission on the Multiple Channel (MC) side
The four modes of transmission are defined below, the accompanying figures being given by way of
example for the case of about 192 kbit/s on the Single Channel (SC) side.
Mode B1: the user information occupies an integral number of 64k/56k channels (usually the N available
and aligned channels); only unframed signals are transmitted (see figure 4), alignment of the channels
has previously been achieved using a framed mode, and it is assumed that no slip or other network fault
has occurred since then. There are no management bits multiplexed into the stream on either Multiple
Channel (MC) or SC sides, and the total bitrates are equal; the mode is therefore confined to ISO
Aggregation cases, and rate change cannot occur.
CAU
192 kbit/s
64 kbit/s 64 kbit/s 64 kbit/s
Figure 4: Mode B1 - applicable to the ISO Aggregation case only
Audiovisual signals according to ETS 300 144 [2] can be transmitted, but the ITU-T Recommendation
H.221 framing plays no part in the aggregation process, and shall appear at a random position within one
of the B-channels as shown in black in figure 5.
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CAU
192 kbit/s
64 kbit/s 64 kbit/s
64 kbit/s
Figure 5: Mode B1 - framed audiovisual signal carried as Unspecified Data (UD)
Mode B2: signals are transmitted with framing according to ISO/IEC 13871 [1] (depicted as white in
figure 6), the user information rate being about 1,5 % less than an integral multiple of 64 kbit/s or 56 kbit/s
due to the overhead of the frame structure. There is no provision for management bits on the SC side, so
the use of this Mode is confined to the ISO Aggregation case.
CAU
(192-3x) kbit/s
(64-x) kbit/s (64-x) kbit/s (64-x) kbit/s
Figure 6: Mode B2 - applicable to the ISO Aggregation case only
Mode B3
: signals are transmitted with framing in all N channels according to ISO/IEC 13871 [1], the user
information rate being an integral multiple (such as N-1) of 64 kbit/s or 56 kbit/s; thus there is a
management overhead of about 1,5 % and generally some unused capacity, as illustrated in figure 7. The
exact bit positions occupied by user information are defined in ISO/IEC 13871 [1].
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CAU
(3x) kbit/s
(64-x) (64-x) (64-x)
unused
192 kbit/s
capacity
kbit/s kbit/s kbit/s
Figure 7: Mode B3 - applicable to the ISO Aggregation case only
Mode H2: only ITU-T Recommendation H.221-framed signals are transmitted (framing is shown as white
in figure 8), the user information rate being an integral number of 64k/56k channels (usually the N
available and aligned channels), including the Frame Alignment Signal (FAS) and BAS within this rate. On
the MC side all channels are framed; on the SC side only the I-channel (Time-Slot 1) carries H.221
framing, but the corresponding bits (shown with dashed outline) in the other time-slots shall be vacated,
so that framing can be inserted at the CAU in the SC to MC direction (and removed in the other): this is
done under the [SM-comp] command.
CAU
192 kbit/s
64 kbit/s 64 kbit/s 64 kbit/s
Figure 8: Mode H2 - applicable to the H.244 Aggregation case only
Mode properties
The properties of the four modes are summarised in table 1. "Dynamic rate change" refers to dynamic
variation of the number N of aggregated channels during a session: rate changes within available
connection capacity can normally be made in less than 40 ms for Modes H2 and B3; when new
connections shall be added, the response depends on call set-up time; for Mode B1 interruption of the
application is inevitable.
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Table 1: Mode properties
Mode B1 Mode H2 Mode B2 Mode B3
Aggregation overhead None 2,5 % in the additional 1,5 % 64 kbit/s or
channels 56 kbit/s
Dynamic rate changes No Yes Yes Yes
Exact multiples of Yes Yes (H.221 - framed No Yes
64 kbit/s/56 kbit/s only)
Interworking with MCE No Yes not applicable No
(audiovisual)
The applicability of the Modes is summarised in table 2.
Table 2: Mode applicability
Mode AV/non-AV Mode applicable when.
B1 Audiovisual the remote end is not an MCE, and the remote CAU does not support Mode
H2, and Mode B3 is considered too inefficient or is not available; bitstream
treated as UD only; ISO Aggregation case, so external means shall be used
to set bitrate.
Non-audiovisual exact multiple of 64 kbit/s or 56 kbit/s required, absence of dynamic rate
change tolerable, B3 considered too inefficient.
B2 Audiovisual not applicable - B2 does not provide suitable bitrates.
Non-audiovisual exact multiple of 64 kbit/s or 56 kbit/s not essential, dynamic rate change
desired.
B3 Audiovisual the remote end is not an MCE, and the remote CAU does not support Mode
H2; dynamic rate change more important than efficiency; bitstream treated
as UD only; ISO Aggregation case, so external means shall be used to set
bitrate.
Non-audiovisual exact multiple of 64 kbit/s or 56 kbit/s required, dynamic rate change more
important than efficiency.
H2 Audiovisual remote end is an MCE, or a CAU supporting Mode H2; H.244 Aggregation
case, so no external control is needed.
Non-audiovisual not applicable (unless conformant to ETS 300 144 [2]).
5.3 General description of the aggregation process
CAU is a device having, on the one side, a single-channel port and on the other side a multiplicity of 64/56
channel ports. This ETS defines the behaviour of the CAU in respect of the input and output signals at the
two sides.
When new multiple channels are active, the CAU buffers the incoming signals in order to synchronise
them, and then reads the user information to the SC side. In the reverse direction, the CAU takes the
serial input into the SC side and loads it into those parallel channels which it knows to be in synchronism
at the remote end. However, according to the two quite different conditions described at the beginning of
subclause 5.1, the CAU has two different processes, that is, depending on whether or not it is
communicating in-band with the single-channel terminal; selection of the correct process is described in
clause 6.
When there is such communication (this applies only to audiovisual terminals), effectively it is the terminal
which is communicating with the other terminal at the remote end of the connection, by capability sets and
commands; the CAU merely moderates this communication in order to assure satisfactory conditions on
the multiple 64/56 channel subclause. The CAU informs the terminal about the upper limit of transmission
rate, which depends on the number of channels available, or what the other end can accept, whichever is
the lower; it does this by suitably modifying the capability sets exchanged. The synchronisation process is
based on ETS 300 144 [2], which also provides for numbering of the channels. Negotiation of appropriate
conditions is based on ETS 300 143 [3]; the capability sets emanating from the CAU define the range of
signals that could be sent to it, while commands define the
...
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