SIST EN 300 481 V1.2.2:2003

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.]DKWHYHTerminal Equipment (TE); Integrated Services Digital Network (ISDN); B-Channel Aggregation Unit (CAU); Procedures and terminal requirements35.180Terminalska in druga periferna oprema ITIT Terminal and other peripheral equipment33.080Digitalno omrežje z integriranimi storitvami (ISDN)Integrated Services Digital Network (ISDN)ICS:Ta slovenski standard je istoveten z:EN 300 481 Version 1.2.2SIST EN 300 481 V1.2.2:2003en01-december-2003SIST EN 300 481 V1.2.2:2003SLOVENSKI
STANDARD
European Telecommunications Standards InstituteEN 300 481 V1.2.2 (1997-12)European Standard (Telecommunications series)Terminal Equipment (TE);Integrated Services Digital Network (ISDN);B-Channel Aggregation Unit (CAU);Procedures and terminal requirementsSIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)2ReferenceREN/MTA-004123 (4gc00ipc.PDF)KeywordsISDN, multichannel, terminalETSI SecretariatPostal addressF-06921 Sophia Antipolis Cedex - FRANCEOffice address650 Route des Lucioles - Sophia AntipolisValbonne - FRANCETel.: +33 4 92 94 42 00
Fax: +33 4 93 65 47 16Siret N° 348 623 562 00017 - NAF 742 CAssociation à but non lucratif enregistrée à laSous-Préfecture de Grasse (06) N° 7803/88X.400c= fr; a=atlas; p=etsi; s=secretariatInternetsecretariat@etsi.frhttp://www.etsi.frCopyright NotificationNo 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.SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)3ContentsIntellectual Property Rights.5Foreword.51Scope.62Normative references.63Definitions, symbols and abbreviations.73.1Definitions.73.2Symbols.83.3Abbreviations.84General.94.1Application of the present document.94.1.1Intercommunication of audiovisual equipments.94.1.1.1Case A.94.1.1.2Case B.94.1.1.3Case C.104.1.2Intercommunication of non-audiovisual equipments - Case D.104.2Definition of the modes of transmission on the Multiple Channel (MC) side.104.3General description of the aggregation process.144.4CAU functionality.145Choice of ISO Aggregation or H.244 Aggregation procedure.156H.244 Aggregation procedure.176.1Call control.176.1.1Initial channel.176.1.2Additional channels.176.2Channel synchronization.176.3In-band procedure using ITU-T Recommendation H.221 BAS codes.176.3.1Control of transfer rate.176.3.2Determination of the transfer-rate capabilities to be transmitted on the MC side.186.3.3Determination of the transfer-rate capabilities to be transmitted on the SC side.186.3.4Capability sets transmitted from a CAU.186.3.4.1Modification of SCE capset for forwarding towards MC side.196.3.4.2Modification of capset incoming from MC side for forwarding towards SCE.196.3.5Notification of change of Na.196.3.6Commands transmitted from a CAU.206.3.6.1Substitution of transfer rate commands.206.3.6.2Insertion and removal of [SM-comp] and [6B-H0-comp].206.3.6.3Insertion of [capex].206.3.6.4Insertion of [AggIN]*.206.4Transmission of user information by a CAU.207Initialization, mode/rate changing and fault recovery.217.1 Initialization.217.1.1Single channel side.217.1.1.1Incoming signal.217.1.1.2Outgoing signal.217.1.2Multi channel side, initial channel.227.1.2.1Incoming signal.227.1.2.2Outgoing signal.227.1.3Multi channel side, additional channels.227.2Change of transmission rate during a session.237.3Recovery from fault conditions.237.4Further mode changes.23SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)48ISO Aggregation procedure.23Annex A (informative):Examples.24Annex B (informative):Example of SDL diagram for H.244 Aggregation initialization.28B.1H.244 Aggregation operation selected.28Annex C (informative):Comments on the modification of capsets and commands.29Annex D (informative):Bibliography.30History.31SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)5Intellectual Property RightsIPRs essential or potentially essential to the present document may have been declared to ETSI. The informationpertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be foundin ETR 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect ofETSI standards", which is available free of charge from the ETSI Secretariat. Latest updates are available on the ETSIWeb server (http://www.etsi.fr/ipr).Pursuant to the ETSI Interim IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. Noguarantee can be given as to the existence of other IPRs not referenced in ETR 314 (or the updates onhttp://www.etsi.fr/ipr) which are, or may be, or may become, essential to the present document.ForewordThis European Standard (Telecommunications series) has been produced by ETSI Technical Committee TerminalEquipment (TE).National transposition datesDate of adoption of this EN: 5 December 1997Date of latest announcement of this EN (doa): 31 March 1997Date of latest publication of new National Standardor endorsement of this EN (dop/e): 30 September 1998Date of withdrawal of any conflicting National Standard (dow): 30 September 1998SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)61ScopeThe present document defines protocols for the synchronization and aggregation of multiple Integrated Services DigitalNetwork (ISDN) channels at 64 kbit/s, these channels having a differential delay in the range of one second and with orwithout octet integrity structure. It also addresses the case of interworking with a digital network restricted to a rate of56 kbit/s. It is applicable to a wide range of user data transport up to 63 channels using ISO/IEC 13871 [1], but specialprovision is made for audiovisual systems according to ETS 300 144 [2], up to 24 channels; the aggregation may benetwork-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 multiplesof 64/56 kbit/s.The number of aggregated channels may be varied dynamically during a session. Procedures are given for dealing withfaults, including loss of channels and slip.Call control is outside the scope of the present document.2Normative referencesReferences may be made to:a)specific versions of publications (identified by date of publication, edition number, version number, etc.), inwhich case, subsequent revisions to the referenced document do not apply; orb)all versions up to and including the identified version (identified by "up to and including" before the versionidentity); orc)all versions subsequent to and including the identified version (identified by "onwards" following the versionidentity); ord)publications without mention of a specific version, in which case the latest version applies.A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the samenumber.[1]ISO/IEC 13871: "Information Technology - Telecommunications and information exchangebetween systems - Private telecommunications networks - Digital channel aggregation".[2]ETS 300 144: "Integrated Services Digital Network (ISDN); Audiovisual services; Frame structurefor a 64 kbit/s to 1 920 kbit/s channel and associated syntax for inband signalling".[3]ETS 300 143: "Integrated Services Digital Network (ISDN); Audiovisual services; Inbandsignalling 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 terminalequipment".[5]ETS 300 145: "Integrated Services Digital Network (ISDN); Audiovisual services; Videotelephonesystems and terminal equipment operating on one or two 64 kbit/s channels".[6]ITU-T Recommendation H.242 (1993): "System for establishing communication betweenaudiovisual terminals using digital channels up to 2 Mbit/s".[7]ITU-T Recommendation H.221 (1993): "Frame structure for a 64 to 1 920 kbit/s channel inaudiovisual teleservices".SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)73Definitions, symbols and abbreviations3.1DefinitionsFor the purposes of the present document, the following definitions apply:called end: The Channel Aggregation Unit (CAU) or Multiple Channel Equipment (MCE) which accepts the first64/56 kbit/s channel connection request of the whole session, resulting in the establishment of the "initial channel". Ifduring fault-recovery procedures the initial channel is transferred to another connection, this does not affect thedefinition (see note 1).calling end: The CAU or MCE which requests the first 64/56 kbit/s channel connection of the whole session, resultingin the establishment of the "initial channel". If during fault-recovery procedures the initial channel is transferred toanother connection, this does not affect the definition (see note 1).Channel Aggregation Unit (CAU): A device having both multiple 64 kbit/s accesses and a single access at a higherbitrate. Reference in the present document to "CAU" or "aggregator" means equipment conforming to the presentdocument.compatibility bits: Bit 8 of the first sixteen octets in every time slot of a single channel except time slot 1.external setting: Term used to express operations outside the scope of the present document which determine thebehaviour of a CAU as to choice of option or timing of its action.H.221: See subclause 3.1, H.221 frame structure, H.221 framingH.221 frame structure, H.221 framing: Frame structure according to ITU-T Recommendation H.221 [7], as set out inETS 300 144 [2].H.244 aggregation: Terminal-Aggregator CommunicationH.320 terminal: A terminal that conforms to ITU-T Recommendation H.320 [4] (see note 2).ISO aggregation: No Terminal-Aggregator Communicationmode H2: Modes of aggregation by the method given in clauses 7 and 8 of the present document.modes B1, B2, B3: Modes of aggregation by the method of ISO/IEC 13871 [1], see subclause 4.2.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 communicationbetween Single Channel Equipment (SCE) and CAU takes place - the single channel is only a clear path for the datawhich will be wholly transmitted to the remote party; any communication between the terminal and the CAU is bymeans not specified in the present document (see clause 8).redundant command: A Bit Allocation Signal (BAS) command which repeats, unchanged, a previously transmittedmode 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 RecommendationH.221 BAS codes (see clauses 7 and 8 of the present document).user information: The application data streams passing (in both directions) between CAU and SCE (see note 3).NOTE 1:The significance of "calling" and "called" end-points is mentioned in subclause 7.1.3.NOTE 2:ETS 300 145 [5] is the ETSI equivalent to ITU-T Recommendation H. 320 [4]. The scope ofETS 300 145 [5] is, however, restricted to systems supporting 1B or 2B access.SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)8NOTE 3:In the audiovisual cases, the application data stream includes the ITU-T Recommendation H.221 [7]frame structure.3.2SymbolsFor the purposes of the present document, the following symbols apply:NOTE:For readability, the capability and command values listed in ETS 300 144 [2] are referred to in the presentdocument by their names rather than codepoint byte values; the use of {name} for capabilities and [name]for commands serves to distinguish between these.Nan integer, applied to 64/56 kbit/s channels to define a parallel (un-aggregated) bitstream of rateN×64 kbit/s.nan integer, applied to 64 kbit/s to define a serial (or otherwise aggregated) bitstream of raten*64 kbit/s.Nathe number of active 64/56 kbit/s channels between CAU and MCE or between two CAUs.Nmthe maximum number of 64/56 kbit/s channels which can be accepted by a CAU transmitting thevalue {Nm×B}.N'mused to denote the incoming value of Nm from the remote CAU, or equivalent from an MCE.Ndthe number of connections requested by the calling end, the lower of Nm and N'm.{N×64k}capabilities in the series {1B}, {2B}, {3B}. corresponding to N=1, 2, 3., (applies to Mode H2only).{n*64k}capabilities in the series {64k}, {128k}, {192k}. corresponding to n=1, 2, 3.nmsuch that {nm*64k} is the highest transfer-rate capability incoming from the SCE for which thecontinuous series of rate capabilities {(nm-1)*64k}, {(nm-2)*64k},.{2*64k} is also present inthe capability set (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 6.3.6.3) to an SCE to stimulate a capability exchange.[AggIN]*a double Single Byte Extension (SBE) symbol indicating the number n as determined by theprocess of subclause 6.3.4.2; see the procedure described in clause 7 (see ETS 300 144 [2]).{null}capability having no significance other than as a filler; only ever transmitted by a CAU, andtherefore it identifies the capset as having last come from, or been forwarded by, a CAU; SCEignores 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, settingthese 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 bitsin the reverse direction either). See ETS 300 144 [2]. SAudible signal (to be defined), which would be recognized by a human user as a call progress tone(he would not hang up).3.3AbbreviationsFor the purposes of the present document, the following abbreviations apply:AVAudiovisualBASBit Allocation Signalcapexcapability exchangecapsetCapability setCAUChannel Aggregation UnitFASFrame Alignment SignalISDNIntegrated Services Digital NetworkLANLocal Area NetworkMBEMulti Byte ExtensionMC (side)Multiple Channel (side, of a CAU)MCMultiple ChannelMCEMultiple Channel EquipmentNIINetwork Indicate Incompatible - aggregatorsSBESingle Byte ExtensionSC (side)Single Channel (side, of a CAU)SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)9SCESingle Channel EquipmentSM-compSingle Multiple compatibilityUDUnspecified Data4General4.1Application of the present documentOn the single channel connections, which may be very short if the terminal and Channel Aggregation Unit (CAU) areco-located, or much longer if a telecommunications link is involved, two options are covered by the present document:a)no in-band management communication on the single channel, this being only a clear path for the data which willbe wholly transmitted to the remote party; any communication between the terminal and the CAU is by means notspecified in the present document; this is referred to as the "ISO Aggregation" case - No Terminal-AggregatorCommunication;b)in-band communication as specified in the present document, using the Bit Allocation Signal (BAS) codesdefined in ETS 300 144 [2] and the procedures of ETS 300 143 [3]; this is referred to as the "H.244Aggregation" case - Terminal­Aggregator Communication. This corresponds to the use of Mode H2 (seesubclause 4.2, figure 8 and associated text).4.1.1Intercommunication of audiovisual equipmentsFor audiovisual terminals conforming to ETS 300 144 [2] and ETS 300 143 [3], the present document provides forsynchronization and aggregation of up to 24 channels of 64/56 kbit/s, each being with or without octet integrity andrelative transmission delay in the range ±1 second.Provision is made for the following intercommunication Cases A to C.4.1.1.1Case AFor 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.MCESCECAUISDNH.244AggregationFigure 1: Case A4.1.1.2Case BThis case provides for interconnection between two single channel audiovisual end-points which see the aggregated linkpurely as a clear data channel; each has a CAU associated with it, but there is no in-band control communicationbetween the end-point and its associated CAU (see figure 2); this is the ISO Aggregation approach. The system isexactly the same as for unspecified data applications (see subclause 4.1.2); the CAU-ISDN-CAU combination providesa clear channel at one of the transfer rates specified in ETS 300 144 [2], and, therefore, shall use Mode B1 or B3 (seesubclause 4.2).SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)10SCECAUISDNSCECAUISOAggregationISOAggregationoptional external communicationFigure 2: Cases B and D4.1.1.3Case CThis provides for the interconnection of two single channel end-points both conforming to ETS 300 144 [2] andETS 300 143 [3] and capable of the operation described in clauses 7 to 8, the H.244 Aggregation approach (seefigure 3); this involves two CAUs, which may be within the network or close to the single­channel end-points.NOTE: H.244 Aggregation cannot be used at one end and ISO Aggregation at the other, see clause 5.SCECAUISDNSCECAUH.244AggregationH.244AggregationFigure 3: Case C4.1.2Intercommunication of non-audiovisual equipments - Case DThe present document provides for synchronization and aggregation of up to 63 channels of 64/56 kbit/s, each beingwith or without octet integrity and relative transmission delay in the range ± one second. It is applicable to a wide rangeof 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 sees theaggregated link purely as a clear data channel, and the structure or content of the data streams is of no concern to theaggregating equipment.The ISO Aggregation approach is appropriate (see figure 2); the CAU-ISDN-CAU combination provides a clear channelat one of the transfer rates specified in ISO/IEC 13871 [1] using Mode B1, B2 or B3 (see subclause 4.2).4.2Definition of the modes of transmission on the MultipleChannel (MC) sideThe four modes of transmission are defined below, the accompanying figures being given by way of example for thecase of about 192 kbit/s on the Single Channel (SC) side.Mode B1: the user information occupies an integral number of 64/56 kbit/s channels (usually the N available andaligned channels); only unframed signals are transmitted (see figure 4), alignment of the channels has previously beenSIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)11achieved using a framed mode, and it is assumed that no slip or other network fault has occurred since then. There areno management bits multiplexed into the stream on either Multiple Channel (MC) or SC sides, and the total bitrates areequal; the mode is therefore confined to ISO Aggregation cases, and rate change cannot occur.CAU192 kbit/s64 kbit/s64 kbit/s64 kbit/sFigure 4: Mode B1 - applicable to the ISO Aggregation case onlyAudiovisual signals according to ETS 300 144 [2] can be transmitted, but the ITU-T Recommendation H.221 [7]framing plays no part in the aggregation process, and shall appear at a random position within one of the B-channels asshown in black in figure 5.CAU64 kbit/s64 kbit/s64 kbit/s192 kbit/sFigure 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 userinformation rate being about 1,5 % less than an integral multiple of 64/56 kbit/s due to the overhead of the framestructure. There is no provision for management bits on the SC side, so the use of this mode is confined to theISO Aggregation case.SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)12CAU(192-3x) kbit/s(64-x) kbit/s(64-x) kbit/s(64-x) kbit/sFigure 6: Mode B2 - applicable to the ISO Aggregation case onlyMode B3: signals are transmitted with framing in all N channels according to ISO/IEC 13871 [1], the user informationrate being an integral multiple (such as N-1) of 64/56 kbit/s; thus there is a management overhead of about 1,5 % andgenerally some unused capacity, as illustrated in figure 7. The exact bit positions occupied by user information aredefined in ISO/IEC 13871 [1].CAU192 kbit/s(64-x)kbit/s(64-x)kbit/s(64-x)kbit/s(3x) kbit/sunusedcapacityFigure 7: Mode B3 - applicable to the ISO Aggregation case onlyMode 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 64/56 kbit/s channels (usually the N available and alignedchannels), including the Frame Alignment Signal (FAS) and BAS within this rate. On the MC side all channels areframed; on the SC side only the I-channel (Time-Slot 1) carries H.221 framing, but the corresponding bits (shown withdashed outline) in the other time-slots shall be vacated, so that framing can be inserted at the CAU in the SC to MCdirection (and removed in the other): this is done under the Single Multiple compatibility ([SM-comp]) command.SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)13CAU64 kbit/s64 kbit/s64 kbit/s192 kbit/sFigure 8: Mode H2 - applicable to the H.244 Aggregation case onlyMode propertiesThe properties of the four modes are summarized in table 1. "Dynamic rate change" refers to dynamic variation of thenumber N of aggregated channels during a session: rate changes within available connection capacity can normally bemade in less than 40 ms for Modes H2 and B3; when new connections need to be added, the response depends on callset-up time; for Mode B1, interruption of the application is inevitable.Table 1: Mode propertiesMode B1Mode H2Mode B2Mode B3Aggregation overheadNone2,5 % in the additionalchannels1,5 %64/56 kbit/sDynamic rate changesNoYesYesYesExact multiples of64/56 kbit/sYesYes (H.221 - framed only)NoYesInterworking with MCE(audiovisual)NoYesnot applicableNoThe applicability of the Modes is summarized in table 2.Table 2: Mode applicabilityModeAV/non-AVMode applicable when.B1Audiovisualthe remote end is not an MCE, and the remote CAU does not support Mode H2, andMode B3 is considered too inefficient or is not available; bitstream treated as UDonly; ISO Aggregation case, so external means shall be used to set bitrate.Non-audiovisualexact multiple of 64/56 kbit/s required, absence of dynamic rate change tolerable,B3 considered too inefficient.B2Audiovisualnot applicable - B2 does not provide suitable bitrates.Non-audiovisualexact multiple of 64/56 kbit/s not essential, dynamic rate change desired.B3Audiovisualthe 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-audiovisualexact multiple of 64/56 kbit/s required, dynamic rate change more important thanefficiency.H2Audiovisualremote end is an MCE, or a CAU supporting Mode H2; H.244 Aggregation case, sono external control needed.Non-audiovisualnot applicable (unless conformant to ETS 300 144 [2]).SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)144.3General description of the aggregation processCAU is a device having, on the one side, a single channel port and on the other side a multiplicity of 64/56 kbit/schannel ports. The present document defines the behaviour of the CAU in respect of the input and output signals at thetwo sides.When new multiple channels are active, the CAU buffers the incoming signals in order to synchronize them, and thenreads the user information to the SC side. In the reverse direction, the CAU takes the serial input into the SC side andloads it into those parallel channels which it knows to be in synchronism at the remote end. However, according to thetwo quite different conditions described at the beginning of subclause 4.1, 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 correctprocess is described in clause 5.When there is such communication (this applies only to audiovisual terminals), effectively it is the terminal which iscommunicating with the other terminal at the remote end of the connection, by capability sets and commands; the CAUmerely moderates this communication in order to assure satisfactory conditions on the multiple 64/56 kbit/s channelsubclause. The CAU informs the terminal about the upper limit of transmission rate, which depends on the number ofchannels available, or what the other end can accept, whichever is the lower; it does this by suitably modifying thecapability sets exchanged. The synchronization process is based on ETS 300 144 [2], which also provides for numberingof the channels. Negotiation of appropriate conditions is based on ETS 300 143 [3]; the capability sets emanating fromthe CAU define the range of signals that could be sent to it, while commands define the actual signal structure beingtransmitted from the CAU. See clauses 7 to 8 of the present document.When there is no in-band communication between the CAU and SCE, the CAU is totally responsible for itscommunication with the remote CAU, presenting on its SC side a clear digital channel at a specified bit rate, which canbe used for any purpose whatsoever (including audiovisual systems). Here again the CAU needs to control thetransmission rate from the terminal - this can be done by clocking if the application rate can be varied in this way (andthis does not apply to terminals conforming to ETS 300 145 [5]), or by other external signalling. In this("ISO Aggregation") case, the synchronization and communication processes are fully described in ISO/IEC 13871 [1] -see clause 8 of the present document.4.4CAU functionalityThe CAU functionality can be summarized as follows:1)all modesMC-to-SC direction: synchronization and aggregation of N incoming 64/56 kbit/s channels into one outgoingsingle channel; SC-to-MC direction: partition of incoming user information onto N outgoing 64/56 kbit/schannels, with framing as appropriate.H2 modeIgnore the compatibility bits incoming on the SC side, putting FAS/BAS into the corresponding outgoing bits onthe MC side; remove FAS/BAS in additional channels incoming on the MC side, putting "ones" into thecorresponding outgoing bits on the SC side.2)all modesControl the aggregated bitrate according to application requirements and the available MC capacity.H2 modeModify capability sets and commands to ensure correct operation of the system; detect changes to capacityrequirements from incoming capability sets.3)all modesDetect fault conditions and take appropriate action.4)all modes(Optionally) transfer the call-control signalling between the ISDN and single channel networks.SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)15The action of the CAU is not completely specified, some matters being left to the choice of the implementer or serviceprovider. For example, requests for channels will not all mature simultaneously, and it is a matter of choice whether eachshould be added in to the communication as soon as available (increasing the bit rate in a series of many steps), oralternatively held back until all or most are available (increasing the bit rate in one single step).5Choice of ISO Aggregation or H.244 AggregationprocedureThe procedure at the start of the call is as depicted in figure 9 and described as follows. It is mandatory that all CAUsintended for use with audiovisual terminals conforming to ETS 300 144 [2] shall be able to operate in Mode H2.There are two alternatives for the choice between ISO Aggregation and H.244 Aggregation processes at each CAU:1)the CAU may be pre-set to operate in the ISO Aggregation procedure or the H.244 Aggregation procedure only,according to the environment for which the CAU is intended;2)if 1) has not been applied, a decision shall be taken on the basis of incoming signals on both SC and MC sides, asdescribed below.Reference is made to figure 9. The CAU operation is essentially the same whether it is the originating (calling) end orthe destination (called) end (the setting of Flag1 is for possible later use when the additional channels are to berequested).First, three local conditions need to be tested, and if any of the three are not met then ISO Aggregation (clause 8) shallbe used. These conditions are:a)there has been no pre-set to specify ISO Aggregation only; note that if the connected SCE is an ITU­TRecommendation H.320 [4] terminal, then specifying ISO Aggregation means that only modes B1 or B3 may beused - B2 does not provide valid bitrates;b)H.221 framing is detected, coming from the SCE; note that a time-out is involved here;c)the capability set (capset) in that H.221 frame contains the value {SM-comp} and/or {6B-H0-comp}.Only under these three conditions is the H.221-framed signal forwarded from the SCE on the initial channel, otherwisethe CAU generates the signal defined in section 7.1 of ISO/IEC 13871 [1].Second, the incoming signal is searched for H.221 framing and ISO/IEC 13871 [1] signal. If ISO/IEC 13871 [1] signalis detected, then ISO Aggregation procedure of clause 8 shall be used - if previously following clauses 7 to 8 becausethe above three conditions were met, this means switching to ISO/IEC 13871 [1] signal on the outgoing transmission. Atime-out of 10 seconds is applied to the detection of the ISO/IEC 13871 [1] signal to allow for the possibility thatclauses 7 to 8 is initially being followed at the remote end. Only if the transmissions in both directions are H.221-framed with {SM-comp} or {6B-H0-comp} the procedures of clauses 7 to 8 apply.Failure statesIf no incoming framing, either of ITU-T Recommendation H.221 [7] or ISO/IEC 13871 [1] type, Failure State 1 isreached, it shall be presumed that the remote end-point is neither a CAU nor an audiovisual MCE (in some applications,speech communication using PCM according to CCITT Recommendation G.711 may still be possible).If one end is transmitting according to ISO Aggregation operation (clause 8), one of the above three conditions nothaving been fulfilled, and the remote end is sending H.221 framing but without {SM-comp} or {6B-H0-comp}, FailureState 2 shall be reached, reflecting the technical impossibility of interconnecting to an MCE at the remote end.Failure State 3 shall be reached if the CAU is set to operate in the H2 mode but the connected SCE is not sending H.221framing.The action to be taken on reaching any of the failure states shall be an implementation matter. The Single ByteExtension (SBE) symbol NII (Network Indicate Incompatible-aggregators), indicating incompatible aggregators, may beused in appropriate fault conditions.SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)16standbySet Flag1 =0Set Flag1 =1Search for H.221 framingincoming on SC side*Look for {SM-comp} from SCESend ISO 13871signal - §9Near-endfavourable forH.244 AggregationSwitch transmittedsignal to ISO 13871Await incomingchange to ISO 13871signal structureForward framed PCMfrom SC side to MC sideCapset_mod_1 (§7.3.4.1)CONN_ACKreceivedCONNECTreceiveddetected (note)H.221 framingpresent?YN12{SM-comp}present*{SM-comp}present*Nfailurestate 1failurestate 2NAll conditions met forNOTE: ISO 13871 aggregation selected in all other cases - §9 appliesH.221 framingdetectedH.221 framingdetectedISO 13871 signaldetected (Note)failurestate 1Nfailurestate 3preset?Ydestinationterminaloriginatingterminal §6, §7 apply*alternative: {6B-H0-comp}incoming on MC sideExamine signalsincoming on MC sideFlag is used in ISO 13871Aggregation to distinguishCalling/Answering EndpointsISOaggregationpresent?H.244AggregationExamine signalsISO 13871 signalNeither H.221 framingnor ISO 13871 signalsdetected within 10 sH.244 aggregationCondition 3Condition 2Condition 1Neither H.221 framingnor ISO 13871 signalsdetected within 10 s34Figure 9: Procedure for selection between H.244 Aggregation and ISO Aggregation processesSIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)176H.244 Aggregation procedure6.1Call controlThe signalling for call control is outside the scope of the present document. It is assumed that external signalling isavailable to set up the appropriate paths between the equipments - for example, the "D-channel" in the case of ISDN.Means are described in subclause 7.1.3 for the in-band transfer of network address information where this is needed forcall control.6.1.1Initial channelThe initial 64/56 kbit/s channel is requested when communication has been established between the calling-end SCE andits CAU and any necessary checking has been carried out (for example, presence of {SM-comp} if required; presence of{n*64k} with n > 1.). During establishment of the initial channel, the value of Nm shall be calculated from the SCEcapset (see subclause 6.3.2).SCE terminals conforming to ETS 300 145 [5] should include the 6B-H0 compatibility mode; if this capability and{SM-comp} are both absent, the CAU shall adopt ISO Aggregation working - see clause 5.6.1.2Additional channelsAdditional-channel requests are made by a CAU when:-the total of channels already requested is less than the lower of Nm and N'm, and (in dial-up cases) the CAU is thecalling end.Additional channels may be dropped by a CAU when the total of channels already requested exceeds the lower of Nmand N'm.6.2Channel synchronizationOn the multiple-channel side, CAUs shall always synchronize all connected channels (in the ISDN case, those for whichCONNECT has been sent or received). The value of Na shall be determined according to the channels for which:-the incoming A-bit is set to zero;-the channel numbers in BAS position (see annex A) form a continuous series from 1 to Na.6.3In-band procedure using ITU-T Recommendation H.221BAS codesIn-band signalling shall follow ETS 300 143 [3] to ensure correct operation between the equipments. H.221 framingshall be used on all the multiple channels, and also on the single channel side. All BAS commands shall be consideredeffective from the start of the following submultiframe, and shall remain in force until countermanded, seeETS 300 143 [3].CAUs shall remain responsive to incoming H.221 framing throughout the call, on the MC side on all channels, and onthe SC side. This means that when no framing is detected, the equipment will nevertheless respond rapidly when theincoming signal is switched to a framed mode, and will also respond quickly (if required) to fault conditions.6.3.1Control of transfer rateThe main function of the CAU is to match the effective transfer rates on its two sides. To do this it shall be able tocontrol the user information which is sent to it: it does this in-band on the MC side, and in the H.244 Aggregation casealso on the SC side. The in-band method is by means of the capability set (see ETS 300 143 [3]) which it transmits orSIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)18forwards; this shall always contain transfer-rate capability values no higher than the available rate on the other side ofthe CAU.NOTE:There can be other in-band signalling between SCE and CAU, however, this is outside the scope of thepresent document, and should be treated in the same way as "out-of-band" signalling - seeISO Aggregation case.6.3.2Determination of the transfer-rate capabilities to be transmitted onthe MC sideReference is made to the in-band streams (1) and (2) in figure 10.Transfer-rate capabilities transmitted on the MC side (2) are decided on the basis of the capset received from the SCE(1).If nm > 1, an {N×64k} type value, with N = nm shall be sent - this is required for communication with an MCE, and alsoprovides for communication with an SCE with fallback to all lesser multiples of 64/56 kbit/s.If an SCE-transmitted capset contains values of {n*64k} for which n is higher than nm, these also shall be included (seesubclause 6.3.4.2) for potential communication with another SCE, though fallback to lesser rates shall be limited.CAUin-band information(H.244 aggregation case)in-band information(4)(2)(1)(3)(initial B-channel)Figure 106.3.3Determination of the transfer-rate capabilities to be transmitted onthe SC sideReference is made to the in-band streams (3) and (4) in figure 10.Transfer-rate capabilities transmitted on the SC side (4) are decided on the basis of the capset received from the MCside (3) and the number of channels currently available, Na.The incoming capability set on the MC side contains a single transfer-rate value of {N'm×64k} type: this value shall bereplaced by a {n*64k}-type transfer-rate value, corresponding either to the incoming value (i.e. such that n = N'm), or tothe available number of channels (i.e. such that n = Na), whichever is the lesser. In general, the highest {n*64k}-typetransfer-rate capability value transmitted from CAU on the SC side (4) is that which indicates the maximum bitrate thatcan be accepted, including both user information and management.6.3.4Capability sets transmitted from a CAUCapsets are not generated by the CAU itself; they are generated only in the terminals, and shall be forwarded, in both SCand MC directions, by the CAUs with modifications as described in subclauses 6.3.4.1 and 6.3.4.2. No changes in thelength of a capset are made by a CAU, the value {null} being used to fill any unused positions.The capsets outgoing from CAUs shall not violate the rules set out in ETS 300 143 [3]; in particular, all capsets whichfollow one another in succession without intervening commands shall be identical. Thus when circumstances require thata new modification be made, this shall always be done on a new capset, which shall be stimulated by the procedure ofsubclause 6.3.5.SIST EN 300 481 V1.2.2:2003

EN 300 481 V1.2.2 (1997-12)196.3.4.1Modification of SCE capset for forwarding towards MC sideThe CAU modifies the SCE capset changing the lowest transfer-rate capability value to {Nm×64k}; here Nm isdeterm
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