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

To include in ETS 300 144 new code points allocated by ITU T

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

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Status
Published
Publication Date
30-Nov-2003
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Dec-2003
Due Date
01-Dec-2003
Completion Date
01-Dec-2003

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.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 signalling33.080Digitalno omrežje z integriranimi storitvami (ISDN)Integrated Services Digital Network (ISDN)ICS:Ta slovenski standard je istoveten z:ETS 300 144 Edition 2SIST ETS 300 144 E2:2003en01-december-2003SIST ETS 300 144 E2:2003SLOVENSKI

STANDARD
SIST ETS 300 144 E2:2003

EUROPEANETS 300 144TELECOMMUNICATIONJanuary 1996STANDARDSecond EditionSource: ETSI TC-TEReference: RE/TE-04037ICS:33.080Key words:ISDN, audiovisual services, inband signallingIntegrated Services Digital Network (ISDN);Audiovisual services;Frame structure for a 64 kbit/s to 1 920 kbit/s channeland associated syntax for inband signallingETSIEuropean Telecommunications Standards InstituteETSI SecretariatPostal address: F-06921 Sophia Antipolis CEDEX - FRANCEOffice address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCEX.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: secretariat@etsi.frTel.: +33 92 94 42 00 - Fax: +33 93 65 47 16Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and theforegoing restriction extend to reproduction in all media.© European Telecommunications Standards Institute 1996. All rights reserved.SIST ETS 300 144 E2:2003

Page 2ETS 300 144: January 1996Whilst 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.SIST ETS 300 144 E2:2003

Page 3ETS 300 144: January 1996ContentsForeword.......................................................................................................................................................51Scope..................................................................................................................................................72Normative references..........................................................................................................................73Definitions............................................................................................................................................84Abbreviations.......................................................................................................................................95Description........................................................................................................................................105.1Frame Alignment Signal (FAS)..........................................................................................105.2Bit-rate Allocation Signal (BAS).........................................................................................115.3Encryption Control Signal (ECS) channel (optional)..........................................................115.4Remaining capacity............................................................................................................116Frame structure.................................................................................................................................126.1General..............................................................................................................................126.2Multiframe structure...........................................................................................................126.3Gain, loss and recovery of frame alignment......................................................................146.4Gain, loss and recovery of multiframe alignment...............................................................146.5Procedure to recover octet timing from frame alignment..................................................146.5.1General rule...................................................................................................146.5.2Particular cases.............................................................................................146.5.3Search for Frame Alignment Signal (FAS)....................................................156.6Frame structure for interworking between a 64 kbit/s terminal and a 56 kbit/s terminal(optional)............................................................................................................................156.6.1Operation of the 64 kbit/s terminal................................................................166.6.2Restriction against some communication modes..........................................167Multiple connections..........................................................................................................................167.1Multiple B-connections.......................................................................................................167.2Multiple H0-connections.....................................................................................................178Introduction to BAS...........................................................................................................................178.1Encoding of the BAS..........................................................................................................178.2Values of the BAS..............................................................................................................188.2.1Single octet BAS............................................................................................198.2.2Two-octet BAS..............................................................................................198.2.3Multi-octet BAS (optional)..............................................................................199Connection quality monitoring (optional)...........................................................................................209.1Computation of the CRC4 bits...........................................................................................209.1.1Multiplication-division process.......................................................................209.1.2Encoding procedure......................................................................................209.1.3Decoding procedure (optional)......................................................................209.2Consequent actions...........................................................................................................219.2.1Action on the E-bit.........................................................................................219.2.2Additional monitoring for incorrect frame alignment (optional)......................219.2.3Monitoring for error performance (optional)..................................................2110Definitions and tables of BAS values................................................................................................2110.1Single/first octet BAS values in the initial channel.............................................................2110.1.1Audio command values (000).......................................................................2110.1.1.1Unrestricted case.................................................................2210.1.1.2Restricted case....................................................................23SIST ETS 300 144 E2:2003

Page 4ETS 300 144: January 199610.1.2Transfer-rate command values (001)...........................................................2310.1.3Video, encryption, loopback and other commands (010).............................2410.1.4LSD/MLP commands (011)(9)......................................................................2610.1.5Audio capabilities (100)................................................................................2710.1.6Transfer-rate capabilities (100).....................................................................2810.1.7Video, MBE and encryption capabilities (101)..............................................2810.1.8LSD/MLP capabilities (101) .........................................................................2910.1.9Escape table values (111)............................................................................3010.2Second octet ("escaped'') BAS values..............................................................................3210.2.1Escape table reached by first BAS octet (111) [16]......................................3210.2.1.1Capabilities (111)[16]-(101).................................................3210.2.1.2Commands (111)[16]-(011)................................................3310.2.1.3Au-ISO commands (111) [10000]-(001).............................3310.2.1.4Au-ISO capabilities (111) [10000]-(001).............................3510.2.2Control and Indication (C&I) - (111) [17].......................................................3610.2.2.1C&I related to video (111)[17]-(000)....................................3710.2.2.2C&I related to audio (111)[17]-(000)...................................3710.2.2.3C&I related to simple multipoint conferences not usingMLP (111)[17]-(001)............................................................3710.2.2.4SBE symbols used in multipoint working (111)[17]-(000),(001), (010), (011)...............................................................3810.2.2.5SBE symbols used in Channel Aggregation.......................4110.2.2.6SBE symbols used in the transfer of network addresses...4110.2.3Applications within LSD/HSD channels (111)[18].........................................4310.2.3.1Capabilities (111)[18]-(101).................................................4410.2.3.2Commands (111)[18]-(011)................................................4410.2.4General purpose SBE symbols: SBE numbers reached by (111)[19]..........4710.2.5General purpose SBE symbols: SBE characters reached by (111)[20].......4710.3Multiple-Byte Extension (MBE) BAS values......................................................................4810.4BAS used in additional channels.......................................................................................4911Tables illustrating bit occupancy.......................................................................................................50Annex A (informative):Bibliography.......................................................................................................58History.........................................................................................................................................................59SIST ETS 300 144 E2:2003

Page 5ETS 300 144: January 1996ForewordThis second edition European Telecommunication Standard (ETS) was produced by the TerminalEquipment (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 oftechnology covered by patent or similar rights.Transposition datesDate of adoption of this ETS:31 January 1996Date of latest announcement of this ETS (doa):30 April 1996Date of latest publication of new National Standardor endorsement of this ETS (dop/e):31 October 1996Date of withdrawal of any conflicting National Standard (dow):31 October 1996ETSI is not responsible for identifying patent or similar rights or for granting licences which may berequired and, as a result, ETSI is not in a position to give authoritative or comprehensive informationconcerning the existence, validity or scope of patent or similar rights in connection with this ETS.SIST ETS 300 144 E2:2003

Page 6ETS 300 144: January 1996Blank pageSIST ETS 300 144 E2:2003

Page 7ETS 300 144: January 19961ScopeThis second edition ETS specifies the frame structure and the syntax for end-to-end inband signalling foraudiovisual services and end-to-end data communication between equipment using single or multipledigital channels (B, H0, H11 or H12) up to 1 920 kbit/s when connected by the pan-European IntegratedServices Digital Network (ISDN). Digital audiovisual services are provided by a transmission system inwhich the relevant signals are multiplexed onto a digital path. This frame structure allows the best use ofthe total transmission capacity for the various data flows as audio, video, user data, telematic informationand special applications. Additionally, signals for the proper functioning of the system are included.This ETS allows the synchronization of multiple 64 kbit/s or 384 kbit/s connections and the control of themultiplexing of audio, video, data and other signals within the synchronized multiconnection structure inthe case of multimedia services, such as videoconferencing.It provides the means to transmit end-to-end inband signalling according to the procedures described inETS 300 143 [2].NOTE 1: Terminals conforming to this ETS and ETS 300 143 [2] are compatible with terminalsaccording to ITU-T Recommendations H.221 [9] and H.242.This ETS is applicable to terminals or other equipment (e.g. Multipoint Control Units) supportingaudiovisual applications.NOTE 2:A separate Interim European Telecommunication Standard (I-ETS) is underpreparation (DI/TE-04120, Parts 1 to 3) which specifies the method of testing requiredto identify conformance to this ETS.2Normative referencesThis ETS incorporates, by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text and the publications are listedhereafter. For dated references, subsequent amendments to or revisions of any of these publicationsapply to this ETS only when incorporated in it by amendment or revision. For undated references the latestedition of the publication referred to apply.[1]ITU-T Recommendation H.261: "Video codec for audiovisual services at p x64 kbit/s".[2]ETS 300 143: "Integrated Services Digital Network (ISDN): Audiovisual services,Inband signalling procedures for audiovisual terminals using digital channels upto 2 048 kbit/s".[3]ETS 300 145: "Integrated Services Digital Network (ISDN): AudiovisualServices; Videotelephone Systems and Terminal Equipment Operating on oneor Two 64 kbit/s Channels".[4]CCITT Recommendation G.711 (1988): "Pulse code modulation (PCM) of voicefrequencies".[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 the7 kHz audio codec within 64 kbit/s".[7]CCITT Recommendation G.728 (1992): "Coding of speech at 16 kbit/s usinglow-delay code-excited linear prediction".[8]CCITT Recommendation T.61 (1992): "International Alphabet No. 5".[9]ITU-T Recommendation H.221 (1993): "Frame structure for a 64 to 1 920 kbit/schannel in audiovisual teleservices".SIST ETS 300 144 E2:2003

Page 8ETS 300 144: January 1996[10]ITU-T Recommendation H.243 (1993): "Procedures for establishingcommunication between three or more audiovisual terminals using digitalchannels up to 2 Mbit/s".[11]ISO/IEC 11172 (1993): "Information technology - Coding of moving pictures andassociated audio for digital storage media at up to about 1,5 Mbit/s".[12]CCITT Recommendation T.35 (1991): "Procedure for the allocation of ITU-Tdefined codes for non-standard facilities".[13]ITU-T Recommendation H.244 (1995): "Synchronized Aggregation of ISDNChannels".3DefinitionsFor the purposes of this ETS, the following definitions apply:A-bit: Indicates the loss of frame or multiframe alignment.Bit-rate Allocation Signal (BAS): 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.channel: The signal structure used to transmit the information over a connection.connection: A physical path between the end-points.Control and Indication (C&I): End-to-end signalling between terminals consisting of Control whichcauses a state change in the receiver and Indication which provides information as to system functioning.E-bit: Indication as to whether the most recent Cyclic Redundancy Check (CRC) block, received in theincoming 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), andaudio is confined to the sub-channels 1 to 7 1); the audio is encoded in the same way as in CCITTRecommendation G.711 [4] either in A-law or µ-law unless this law is also specified in brackets thus:Mode-0F(A), Mode-0F(µ), except that the Least Significant Bit (LSB) 2) is not transmitted.Mode 0U: Applies only to the initial channel; there is no frame structure, and audio is encoded accordingto CCITT Recommendation G.711 [4] 3), either in A-law or µ-law unless this law is also specified inbrackets thus: Mode-0U(A), Mode-0U(u).Multipoint Conference Unit (MCU): A piece of equipment located in a node of the network or in aterminal which connects several terminals and, according to certain criterions, processes audiovisualsignals and distributes them to the connected terminals.

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.SIST ETS 300 144 E2:2003

Page 9ETS 300 144: January 1996Service Channel (SC): The eighth sub-channel of a 64 kbit/s channel, or the seventh sub-channel whencommunicating in restricted mode.restricted network: A network consisting of multiples of 64 kbit/s links, but where only multiples of56 kbit/s are usable for the terminals.4AbbreviationsFor the purposes of this ETS, the following abbreviations apply:NOTE:Numerous other specific C&I codepoint abbreviations are listed in subclause 10.1.3and subclause 10.2.2.BASBit-rate Allocation SignalC&IControl and Indicationcap-markcapability markercap-setcapability setCIFCommon Intermediate Format (picture format defined in ITU-TRecommendation H.261 [1])CRC4Cyclic Redundancy Check 4-bitECSEncryption Control SignalFASFrame Alignment SignalFAWFrame Alignment WordH-MLPHigh speed MLP logical subchannel 4)H0384 kbit/s channelH111 536 kbit/s channelH121 920 kbit/s channelHSDHigh Speed DataISDNIntegrated Services Digital NetworkITU-TSInternational Telecommunications Union - TelecommunicationStandardization SectorLSBLeast Significant BitLSDLow Speed DataMBEMultiple Byte ExtensionMCUMultipoint Control UnitMLPLogical data subchannel named "MLP" 4)MSBMost Significant BitQCIFQuarter Common Intermediate Format (picture format defined in ITU-TRecommendation H.261 [1])SBESingle Byte ExtensionSCService ChannelSMFSub-MultiframeTEATerminal Equipment AlarmTSTime SlotTS1Time Slot 1

4 )MLP previously referred to the ITU-T Recommendation T.120 Multilayer Protocol, but now is just a name for the logicalsubchannel which may contain T.120 or H.224 protocol, or Dummy data - see

ETS 300 143 [2].SIST ETS 300 144 E2:2003

Page 10ETS 300 144: January 19965DescriptionThis ETS provides for dynamically subdividing an overall transmission channel of 64 kbit/s to 1 920 kbit/sinto lower rates suitable for audio, video, data and telematic purposes. The overall transmission channel isderived by synchronising and ordering transmissions in 1 to 24 B-connections, or 1 to 5 H0-connections,or a 1 536 kbit/s or 2 048 kbit/s connection. The first connection established is the initial connection andcarries the initial channel in each direction. The additional connections carry additional channels.The total rate of transmitted information is called the "transfer rate"; the transfer rate can be fixed at lessthan 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 maybe regarded as a sub-channel of 8 kbit/s (see table 1). The eighth sub-channel is called the ServiceChannel (SC), consisting of several parts as described in subclauses 5.1 to 5.4 below.A 384 kbit/s (H0), 1 536 kbit/s (H11) or 1 920 kbit/s (H12) channel may be regarded as consisting of anumber of 64 kbit/s Time Slots (TS) (see table 2). The lowest numbered TS is structured exactly asdescribed for a single 64 kbit/s channel, while the other TS have no such structure. In the case of multipleB or H0 channels, all channels have a frame structure; that in the initial channel controls most functionsacross the overall transmission, while the frame structure in the additional channels is used forsynchronization, 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 toTS1 of H11, H12 channels.Table 1: Frame structure of a single 64 kbit/s channel (B-channel)Bit number12345678 (SC)1Octet numberSSSSSSSFAS:uuuuuuu8bbbbbbb9-------BAS:ccccccc16hhhhhhh17aaaaaaaECS:nnnnnnn24nnnnnnnSub-25eeeeeeechan-·lllllllnel·########·12345678805.1Frame Alignment Signal (FAS)This signal structures the I-channel and other framed 64 kbit/s channels into frames of 80 octets each andmultiframes 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 to 8 of the SC in each frame. In addition to framingand multiframing information, control and alarm information may be inserted in the FAS, as well as errorcheck information to monitor end-to-end error performance and to check frame alignment validity. Othertime-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 each125 microsecond, e.g. in an ISDN basic or primary rate interface (see also tables 1 and 2 andsubclause 6.6). It should be noted that, where interworking between the audiovisual terminal and thetelephone is required, transmission using the network timing is essential; a transmitting terminal shallalways use octet timing, if this can be obtained from the network.SIST ETS 300 144 E2:2003

Page 11ETS 300 144: January 1996At the receiver side, FAS shall be sought in all bit positions. If the received FAS position conflicts with thenetwork octet timing, the FAS position is given priority. This may happen when the receiver utilisesnetwork octet timing while the transmitter does not, as in a terminal using codecs with separate ISDNterminal adaptor, or when interworking between 64 kbit/s and 56 kbit/s terminals takes place.Table 2: Frame structure of higher-rate single channels (H0, H11, H12 channels)125 microseconds<_______________________________________________________________________________>pTS1234567· · ·· · ·6n-26n-16nH0n = 1H11n = 4H12n = 5Audio + service channel123456781Octet numberSSSSSSSFAS:uuuuuuu8bbbbbbb9-------BAS:ccccccc16hhhhhhh17aaaaaaaECS:nnnnnnn24nnnnnnneeeeeeeSub-·lllllllchan-nel·########12345678805.2Bit-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 ofcodewords to describe the capability of a terminal to structure the capacity of the channel or synchronizedmultiple channels in various ways, and to command a receiver to demultiplex and make use of theconstituent 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/sfewer. Interworking between a 64 kbit/s terminal and a 56 kbit/s terminal is establishedaccording to the frame structure in subclause 6.6.5.3Encryption 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 H12channels, or in the initial channel of multiple-channel calls.When switched on, the ECS channel occupies bits 17 to 24 of the SC, a rate of 800 bit/s, and any video orvariable data channel which would otherwise occupy these bits is accordingly reduced in rate by 800 bit/s.5.4Remaining capacityThe remaining capacity may convey a variety of signals multiplexed in a way which is defined by the BAScommands; each command defined in clause 10 specifies the explicit bit occupancy, but, additionallycertain procedural rules stated in ETS 300 143 [2], subclause 5.2 shall be obeyed. The facilities providedcan be found in the list given in subclause 8.2.SIST ETS 300 144 E2:2003

Page 12ETS 300 144: January 19966Frame structure6.1GeneralAn 80-octet frame length produces 80 bits in the SC. These 80 bits are numbered 1 to 80. Bits 1 to 8 ofthe 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 evenframes of a sub-multiframe. Their value is "0011011". They are complemented by a "1" in bit 2 of thesucceeding odd frame. This eighth bit of the FAW is necessary in order to avoid simulation of the FAW bya 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" wheneverframe- and multiframe is aligned (if multiframe alignment is evaluated, see subclause 6.4, otherwise only ifit is frame aligned), and is set to "1" otherwise (see subclause 6.3; for additional channels, seesubclause 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 frameBit numberSuccessive frames12345678Even framesSeesubclause 6.20011011Odd framesSeesubclause 6.21AEC1C2C3C4FAW6.2Multiframe structureThe multiframe structure is shown in table 4a.Each multiframe contains 16 consecutive frames numbered 0 to 15 divided into eight sub-multiframes oftwo frames each. The multiframe alignment signal is located in bit 1 of frames 1-3-5-7-9-11 and has theform 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 indescending order. The LSB is transmitted in frame 0, and the Most Significant Bit (MSB) in frame 6. Thereceiver uses the multiframe numbering to share out the differential delay of separate connections, and tosynchronize the received signals.The multiframe numbering shall be mandatory in both the initial and additional channels for multiple B ormultiple H0 communications, but it may or may not be inserted for single B or single H0 or H11/H12 orother communications where synchronization between multiple channels is not required. In this case, N1to N4 are set to "0".Bit 1 of frame 8 (N5) indicates whether multiframe numbering is active or inactive. It is set to 1 whenmultiframes 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 tonumber each channel in a multiconnection structure so that the distant receiver can place the octetsreceived in each 125 microseconds in the correct order.SIST ETS 300 144 E2:2003

Page 13ETS 300 144: January 1996The bits N1 - N5 and L1 - L3 in the multiframe shall be considered valid, as long as they are receivedconsistently in three consecutive multiframes.Bit 1 of frame 14, the Terminal Equipment Alarm (TEA) may be set to 1 in the outgoing signal, when oneor more of the following conditions holds:-an internal terminal equipment fault exists such that it cannot receive and act on the incomingsignal;-an internal terminal equipment fault exists such that it can no longer transmit user information in theform 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 describedin clause 9.Table 4a: Assignment of bits 1 to 8 of the SC in each frame in a multiframeSub-multiframeFrameBits 1 to 8 of the service channel in every frame(SMF)123456780N10011011SMF1101AEC1C2C3C42N20011011SMF2301AEC1C2C3C44N30011011SMF3511AEC1C2C3C46N40011011Multi-SMF4701AEC1C2C3C4frame8N50011011SMF5911AEC1C2C3C410L10011011SMF61111AEC1C2C3C412L20011011SMF713L31AEC1C2C3C414TEA0011011SMF815R1AEC1C2C3C4Table 4b: Channel numbering with bits L3, L2, L1ChannelL3L2L1Initial001Second010Third011· · ·· ·· ·· ·Sixth110Seventh and higher111Table 4c: Multiframe numbering with bits N4, N3, N2, N1Multiframe NumberN4N3N2N100000(or numbering inactive)1000120010· ·· ·· ·· ·· ·151111SIST ETS 300 144 E2:2003

Page 14ETS 300 144: January 19966.3Gain, loss and recovery of frame alignmentFrame 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 anerror.Frame alignment is defined to have been recovered when the same sequence as described above isdetected.When the frame alignment is lost, the A-bit of the next odd frame is set to 1 i

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