SIST ETS 300 144 E2:2003
(Main)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
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
General Information
Standards Content (Sample)
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
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 in the transmit direction.6.4Gain, loss and recovery of multiframe alignmentMultiframe alignment is needed to number and synchronize two or more channels. Terminals such asthose having only single-channel capabilities which have no use for the multiframe structure shall transmitthe multiframe structure, but need not check for multiframe alignment on the incoming signal: they maytransmit outgoing A = 0 when frame alignment is recovered.NOTE:Such a terminal cannot recognize TEA (see table 4a).Multiframe alignment is defined to have been gained when the multiframe alignment signal is consistentover 16 consecutive frames.After multiframe alignment has been validated, the other functions represented by bit 1 of the SC can beused. When multiframe alignment of the distant terminal has been signalled (A=0 received), the distantterminal is expected to have validated BAS codes and to be able to interpret BAS codes.Multiframe alignment is defined to have been lost when three consecutive multiframe alignment signalshave been received with an error. It is defined to have been recovered when the multiframe alignmentsignal has been received with no error in the next multiframe. When multiframe alignment is required andhas been lost, even when an unframed mode is received, the A-bit of the next odd frame is set to 1 in thetransmit direction, and is reset to 0 when multiframe alignment is regained. It is reset in additionalchannels when multiframe alignment and synchronism with the initial channel is regained.6.5Procedure to recover octet timing from frame alignmentThe terminal shall recover octet timing in the receive direction from bit timing and from the framealignment.6.5.1General ruleThe receive octet timing is normally determined from the FAS position. At the start of the call and beforethe frame alignment is gained, the receive octet timing shall be taken from the network. As soon as a firstframe alignment is gained, the receive octet timing is initialized at the new bit position, but it is not yetvalidated. It shall be validated only when frame alignment is not lost during the next 16 frames.6.5.2Particular casesa)When frame alignment is lost after being gained, the receive timing shall not be changed until framealignment is recovered.b)As soon as frame and, if necessary, multiframe alignment have been gained once, the octet timingshall be considered as valid for the rest of the call, unless frame alignment is lost and a new framealignment is gained at another bit position.c)When the terminal switches from a framed mode to an unframed mode (by means of the BAS), theoctet timing previously gained shall be kept.SIST ETS 300 144 E2:2003
Page 15ETS 300 144: January 1996d)When a new frame alignment is gained on a new position, different from that previously validated,the receive octet timing is re-initialized to the new position but not yet validated and the previous bitposition is stored. If no loss of frame alignment occurs in the next 16 frames, the new position shallbe validated, otherwise the stored old bit position is re-utilized.e)At the start of the call and before the frame alignment is gained, if octet timing is not available fromthe network it may be taken to be the same as the internal transmit octet timing.6.5.3Search for Frame Alignment Signal (FAS)Two methods may be used: sequential or parallel. In the sequential method, each of the eight possible bitpositions for the FAS is tried. When FAS is lost after being validated, the search shall resume startingfrom the previously validated bit position. In the parallel method, a sliding window, shifting one bit for eachbit period, may be used. In that case, when frame alignment is lost, the search shall resume starting fromthe bit position next to the previously validated one.6.6Frame structure for interworking between a 64 kbit/s terminal and a 56 kbit/s terminal(optional)The ability to interwork with restricted networks is not a mandatory requirement.The sub-channel arrangement for this frame structure is given in tables 5a and 5b.Table 5a: Transmitter of the 64 kbit/s terminalBit number1234567(SC)811Octet numberSSSSSSFAS1:uuuuuu18bbbbbb19------BAS1:cccccc116hhhhhh117aaaaaa(ECS)1:nnnnnn124nnnnnnSub-125eeeeeechan-1·llllllnel1·#######1·1234567180SIST ETS 300 144 E2:2003
Page 16ETS 300 144: January 1996Table 5b: Receiver of the 64 kbit/s terminalBit number, synchronized with the octet timing of the network1234567811SS1SSSSFAS*uu1uuuubb1bbbb--1Frame structured----BAScc1by the 56 kbit/scccchh1terminalhhhhaa1aaaa(ECS)nn1nnnnnn1nnnnSub-ee1eeeechan-ll1llllnel##1#####121345671*FAS may appear at any of Bits 1 to 76.6.1Operation of the 64 kbit/s terminalThe transmitter fills the eighth sub-channel with "1", while the receiver searches FAS at everysub-channel. It should be noted that at the receiver side stuffing bits "1" always appear at Bit number 8,but FAS and BAS appear at any of Bit numbers 1 to 7.6.6.2Restriction against some communication modesSince the interworking bit rate becomes 56 kbit/s, the transmission modes using more than 56 kbit/s areforbidden (receivers ignore these command BAS codes). Facilities using the original seventh sub-channelmove to the sixth sub-channel. See subclause 10.1.1.2.7Multiple connectionsSome audiovisual terminals shall be able to communicate over multiple B or H0 connections. In this case,a single B or H0 initial connection is established, the possibility for more connections is determined fromthe transfer rate capability BAS of clause 10 and the additional connections are then established andsynchronized by the terminal using the multiframe structure.7.1Multiple B-connectionsFAS and BAS are transmitted in each B-channel.The actual bit-rates allowed by this ETS for audio codings within a 64 kbit/s I-channel are 64 kbit/s and 56kbit/s, commands (000)[4/5 and 18/19] respectively. Thus, in a 2B audiovisual call, it shall not bepermitted to transmit framed audio, coded according to CCITT Recommendation G.711 [4] and at the rateof 62,4 kbit/s occupying the whole I-channel except FAS and BAS positions, with only video in theadditional channel. The two channels shall be synchronized, the audio shall be set to 56 kbit/s, and whenthe video is ON it shall occupy the remaining 68,8 kbit/s.FAS operation is as follows:-multiframe numbering is used to determine relative transmission delay between B-channels or H0channels as described in subclause 6.2;-the channel numbers are transmitted in the FAS as described in subclause 6.2, the channel of theinitial connection being numbered 1 and there being up to 23 additional connections;SIST ETS 300 144 E2:2003
Page 17ETS 300 144: January 1996-the channel numbers of the additional channels are also transmitted in the BAS according to table12a;-the outgoing A-bit is set to 1 in the additional B-channel of the same connection whenever thereceived additional channel is not synchronized to the initial channel;-when receive synchronization is achieved between the initial and additional channels by introducingdelay to align their respective multiframe signals, the transmitted A-bit is set to 0;-the E-bit for each additional B-channel is transmitted in the additional B-channel in the sameconnection, because it relates to a physical condition of the transmission path.The BAS operation in additional connections is restricted to the transmission of the additional channelnumber according to table 12a and TIX* (see subclause 10.2.2.4). Thus the channel numbering of anyadditional connection shall be sent both in BAS according to subclause 10.4 and in the FAS, as insubclause 6.2, while channel numbering of the initial channel is sent only in FAS.The distant terminal, upon receiving the A-bit set to "0" with respect to sequentially numbered channels,can add their capacity to the initial connection by sending the appropriate transfer rate BAS in clause 10.The order of the bits transmitted in the channels is in accordance with the examples given in tables 14 to21.7.2Multiple H0-connectionsFAS and BAS are transmitted in the first time-slot of each H0.FAS operation is as stated in subclause 7.1 except that the channel number is used to order the six octetsreceived each 125 microseconds with respect to the six octet groups received in other channels.The BAS operation in additional channels is as specified in subclause 7.1.8Introduction to BAS8.1Encoding of the BASThe Bit-rate Allocation Signal (BAS) occupies bits 9 to 16 of the SC in every frame. An eight bit BAS code(b0, b1, b2, b3, b4, b5, b6, b7) is complemented by eight error correction bits (p0, p1, p2, p3, p4, p5, p6, p7)to implement a (16,8) double error correcting code. This error correcting code is obtained by shorteningthe (17,9) cyclic code with generator polynomial:g(x) = x8 + x7 + x6 + x4 + x2 + x + 1The error correction bits are calculated as coefficients of the remainder polynomial in the followingequation:p0x7 + p1x6 = p2x5 + p3x4 + p4x3 + p5x2 + p6x + p7= RESg(x) [b0x15 + b1x14 + b2x13 + b3x12 + b4x11 + b5x10 + b6x9 + b7x8]where RESg(x)[f(x)] represents the residue obtained by dividing f(x) by g(x).The BAS code is sent in the even-numbered frame, while the associated error correction bits are sent inthe subsequent odd-numbered frame. The bits of the BAS code or the error correction are transmitted inthe order shown in table 6 to avoid emulation of the FAW.SIST ETS 300 144 E2:2003
Page 18ETS 300 144: January 1996Table 6Bit positionEven frameOdd frame9b0p210b3p111b2p012b1p413b5p314b4p515b6p616b7p7The decoded BAS value is valid if:-the receiver is in frame alignment, and-the FAW, in the same sub-multiframe, was received with two or fewer bits in error.Otherwise the decoded BAS value is ignored.8.2Values of the BASThe encoding of BAS is made according to an attribute method. This consists of attribute (8 attributes)and value (32 values). The first three bits of a BAS represent the attribute, describing the generalcommand or capability, and the other five bits identify the "value" - the specific command or capability (seetable 7).Table 7AttributeSignificance (in initial channel only)000Audio coding command001Transfer rate command010Video, encryption, loops and other commands011LSD/MLP commands100Audio and Transfer Rate capabilities101Video, MBE, encryption and LSD/MLP capabilities110Reserved111Escape codesThe values of these attributes are listed and defined in clause 10. They provide for the following facilities:-transmission at various total rates and on single and multiple channels, on clear channels and onnetworks subject to restrictions to 56 kbit/s and its multiples;-audio transmission, digitally encoded to various recommended algorithms, e.g.:-voice encoded at 56 kbit/s using a truncated form of PCM of CCITT Recommendation G.711[4] (A-law or µ- law);-voice encoded at 16 kbit/s and video at 46,4 kbit/s;-voice encoded at 56 kbit/s with a bandwidth 50 Hz to 7 000 Hz (sub-band ADPCM accordingto CCITT Recommendation G.722 [5]); the coding algorithm is also able to work at 48 kbit/s -data can then be dynamically inserted at up to 14,4 kbit/s;-video transmission, digitally encoded to a recommended algorithm, with provision for futurerecommended improvement;-still pictures;-Low Speed Data (LSD) within the I-channel, or TS1 of a higher rate initial channel, e.g. data at56 kbit/s inside an audiovisual session for, inter alia, file transfer for communicating betweenpersonal computers;SIST ETS 300 144 E2:2003
Page 19ETS 300 144: January 1996-High Speed data (HSD) in the highest-numbered 64 kbit/s channel or Time Slots;-data transmission within a standardized protocol, either in the I-channel (MLP subchannel 5)) or incapacity other than the I-channel (H-MLP subchannel);-an encryption control signal;-loopback towards the network for maintenance purposes;-signalling for control and indications;-a message system for, inter alia, conveying information concerning equipment manufacturer andtype.8.2.1Single octet BASThe command BAS attributes have the following significance: on receipt of a BAS command code in one(even) frame and its error-correcting code in the next (odd), the receiver prepares to accept the statedmode (or mode change) beginning from the subsequent (even) frame; thus a mode change can beeffected in 20 milliseconds. The command remains in force until countermanded (see ETS 300 143 [2]).The bit positions occupied as a result of combinations of BAS commands are exemplified in clause 10,tables 14 to 21.The capability BAS attributes have the following significance: they indicate the ability of a terminal toreceive and properly treat the various types of signal. It follows that having received a set of capabilityvalues from the remote terminal Y, terminal X shall not transmit signals lying outside that declared range.The value (111)[24] is the capability marker which is followed by normal BAS codes, not by any escapevalues (see ETS 300 143 [2]).8.2.2Two-octet BASThe attribute (111) provides means for extension of the use of the BAS position in the subsequent sub-multiframe(s) for other purposes.Values [15] to [23] of the attribute (111) are temporary escape BAS codes of Single Byte Extension (SBE).The last three bits of the temporary escape BAS form a pointer to one of eight possible escape BAStables of 224 entries each (codes beginning with 111 are not used in the escape BAS tables). Then thenext received BAS indicates the specific entry in the escape BAS table.Value [15] gives access to the values in table 12b, specifying transfer-rate capabilities and commandsused in aggregation of seven or more B-channels.Value [16] gives access to the values in table 10, specifying capabilities and commands for data channels(MLP, H-MLP, LSD or HSD).Value [17] gives access to the values in table 11, specifying SBE values for C&I.Value [18] gives access to the values in table 12, specifying applications of a data channel (MLP, H-MLP,LSD or HSD).8.2.3Multi-octet BAS (optional)NOTE:The ability to work with multi-octet BAS is not a mandatory requirement.The last seven attribute values [25] to [31] of the attribute (111) are of Multiple Byte Extension (MBE) andare used to send messages as specified in clause 10.SIST ETS 300 144 E2:2003
Page 20ETS 300 144: January 19969Connection quality monitoring (optional)NOTE:The use of the connection quality monitoring procedure is not a mandatoryrequirement.To provide an end-to-end quality monitoring of the connection, a 4-bit Cyclic Redundancy Check (CRC4)procedure may be used and the four bits C1, C2, C3 and C4 computed at the source location are insertedin bit positions 5 to 8 of the odd frames. In addition, bit 4 of the odd frames, the E-bit, is used to transmitan indication whether the most recent CRC block, received in the incoming direction, contained errors ornot.When the optional CRC4 procedure is not used, the E-bit shall be set to 0, and bits C1, C2, C3 and C4shall be set to 1 by the transmitter. The receiver may disable
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