ETSI EN 300 737 V6.0.1 (1999-09)

Digital cellular telecommunications system (Phase 2+) (GSM); In-band control of remote transcoders and rate adaptors for Enhanced Full Rate (EFR) and full rate traffic channels (GSM 08.60 version 6.0.1 Release 1997)

DEN/SMG-020860Q6

Digitalni celični telekomunikacijski sistem (faza 2+) – Znotrajpasovno krmiljenje oddaljenih prekodirnikov (transkoderjev) in prilagodilnikov hitrosti v kanalih za izboljšani polnohitrostni (EFR) govorni promet (GSM 08.60, različica 6.0.1, izdaja 1997)

General Information

• Status: Published
• Publication Date: 31-Aug-1999
• Technical Committee: SMG 2 - Radio
• Current Stage: 12 - Completion
• Due Date: 03-Sep-1999
• Completion Date: 01-Sep-1999
• Ref Project: SIST EN 300 737 V6.0.1:2003 - Digital cellular telecommunications system (Phase 2+) (GSM); In-band control of remote transcoders and rate adaptors for Enhanced Full Rate (EFR) and full rate traffic channels (GSM 08.60 version 6.0.1 Release 1997)

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); In-band control of remote transcoders and rate adaptors for Enhanced Full Rate (EFR) and full rate traffic channels (GSM 08.60 version 6.0.1 Release 1997)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 737 Version 6.0.1SIST EN 300 737 V6.0.1:2003en01-december-2003SIST EN 300 737 V6.0.1:2003SLOVENSKI
STANDARD



SIST EN 300 737 V6.0.1:2003



EN 300 737 V6.0.1 (1999-09)European Standard (Telecommunications series)Digital cellular telecommunications system (Phase 2+);In-band control of remote transcoders and rate adaptors forEnhanced Full Rate (EFR) and full rate traffic channels(GSM 08.60 version 6.0.1 Release 1997)GLOBAL SYSTEM
FOR MOBILE COMMUNICATIONSRSIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)2(GSM 08.60 version 6.0.1 Release 1997)ReferenceDEN/SMG-020860Q6 (6to0300o.PDF)KeywordsDigital cellular telecommunications system,Global System for Mobile communications (GSM)ETSIPostal addressF-06921 Sophia Antipolis Cedex - FRANCEOffice address650 Route des Lucioles - Sophia AntipolisValbonne - FRANCETel.: [phone]
Fax: [phone]Siret N° 348 623 562 00017 - NAF 742 CAssociation à but non lucratif enregistrée à laSous-Préfecture de Grasse (06) N° 7803/[e-mail] copies of this ETSI deliverablecan be downloaded fromhttp://www.etsi.orgIf you find errors in the present document, send yourcomment to: [e-mail] 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 1999.All rights reserved.SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)3(GSM 08.60 version 6.0.1 Release 1997)ContentsIntellectual Property Rights.5Foreword.51Scope.61.1References.61.2Abbreviations.72General Approach.73Frame Structure.103.1Speech Frames.103.2O&M Frames.113.3Data Frames.123.3.1Data Frame (for Synchronisation).123.3.2Extended data frame (E-TRAU : data transport).133.4Idle Speech Frames.143.5Coding.143.5.1Coding of Speech Frames.153.5.2Coding of O&M Frames.173.5.3Coding of Data Frames.173.5.4Coding of Extended Data Frames.173.5.5Coding of Idle Speech Frames.183.6Order of Bit Transmission.184Procedures.184.1Remote Control of Transcoders and Rate Adaptors.184.2Resource Allocation.184.3Resource Release.194.4In Call Modification.194.5Transfer of Idle Frames.204.5.1In Full rate data case:.204.5.2In Full rate speech case:.204.5.3In Enhanced Full rate speech case:.204.6Procedures for Speech Frames.204.6.1Time Alignment of Speech Frames.204.6.1.1Initial Time Alignment State.204.6.1.2The Static Time Alignment State.214.6.1.3Initiation at Resource Allocation.234.6.1.4Time Alignment During Handover.234.6.1.4.1BSS External Handover.234.6.1.4.2BSS Internal Handover.234.6.2Procedures for Discontinuous Transmission (DTX).234.6.2.1DTX procedures in the uplink direction.234.6.2.2DTX procedures in the downlink direction.234.7Procedures for Data Frames.244.7.19.6 and 4.8 kbit/s channel coding.244.7.1.1The RAA Function.244.7.1.2The RA1/RA1' Function.254.7.1.3The RA2 Function.254.7.1.4Procedures for 8 kbit/s intermediate rate adaption rate.254.7.1.5Procedures for 16 kbit/s intermediate rate adaption rate.254.7.1.6Support of Non-Transparent Bearer Applications.254.7.214.5 kbit/s channel coding.264.7.2.1The RAA’ Function.264.7.2.2The RA1’/RAA' Function.264.7.2.3The RA2 Function.264.8Frame Synchronization.264.8.1Search for Frame Synchronization.26SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)4(GSM 08.60 version 6.0.1 Release 1997)4.8.2Frame Synchronization After Performing Downlink Timing Adjustments.264.8.3Frame Synchronization Monitoring and Recovery.274.9Correction/detection of bit errors on the terrestrial circuits.284.9.1Error Detection on the Control Bits.284.9.1.1General Procedure.284.9.1.2Speech Frames.284.9.2Handling of frames received with errors.284.9.2.1In case of Full Rate:.284.9.2.2In case of Enhanced Full rate:.284.10Procedures for Operation & Maintenance.294.10.1Transfer of O&M Information Between the TRAU and the BSC.294.10.2Procedures in the TRAU.294.10.3Procedures in the BSC.294.10.3.1Use of O&M Frames.294.10.4Procedures in the BTS.30Annex A (informative):Change Request History.31History.32SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)5(GSM 08.60 version 6.0.1 Release 1997)Intellectual 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 SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respectof ETSI standards", which is available free of charge from the ETSI Secretariat. Latest updates are available on theETSI Web server (http://www.etsi.org/ipr).Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guaranteecan be given as to the existence of other IPRs not referenced in SR 000 314 (or the updates on the ETSI Web server)which are, or may be, or may become, essential to the present document.ForewordThis European Standard (Telecommunications series) has been produced by the Special Mobile Group (SMG).The present document specifies the inband control of remote transcoders and rate adaptors for full rate speech,Enhanced Full rate speech and full rate data within the Digital cellular telecommunications system (Phase 2+).The specification from which the present document has been derived was originally based on CEPT documentation,hence the presentation of the present document may not be entirely in accordance with the ETSI/PNE Rules.The contents of the present document is subject to continuing work within SMG and may change following formal SMGapproval. Should SMG modify the contents of the present document it will be re-released with an identifying change ofrelease date and an increase in version number as follows:Version 6.x.ywhere:6indicates Release 1997 of GSM Phase 2+xthe second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates,etc.ythe third digit is incremented when editorial only changes have been incorporated in the specification.Proposed national transposition datesDate of adoption of this EN:3 September 1999Date of latest announcement of this EN (doa):31 December 1999Date of latest publication of new National Standardor endorsement of this EN (dop/e):30 June 2000Date of withdrawal of any conflicting National Standard (dow):30 June 2000SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)6(GSM 08.60 version 6.0.1 Release 1997)1ScopeWhen 64 kbit/s traffic channels are used on the Abis interface, the speech shall be coded according to CCITTRecommendation G.711 and the data rate adaptation shall be as specified in GSM 04.21 and GSM 08.20.In the case where 16 kbit/s traffic channels are used for full rate speech or enhanced full rate speech or full rate dataservice, then the present document shall apply for frame structure and for control of remote transcoders and additionalrate adaptors.The use and general aspects of the Abis interface are given in GSM 08.51.NOTE:The present document should be considered together with the GSM 06 series of specifications, GSM04.21 (Rate Adaptation on the MS-BSS Interface) and GSM 08.20 (Rate Adaptation on the BS/MSCInterface).1.1ReferencesThe following documents contain provisions which, through reference in this text, constitute provisions of the presentdocument.· References are either specific (identified by date of publication, edition number, version number, etc.) ornon-specific.· For a specific reference, subsequent revisions do not apply.· For a non-specific reference, 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.· For this Release 1997 document, references to GSM documents are for Release 1997 versions (version 6.x.y).[1]GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations andacronyms".[2]GSM 04.06: "Digital cellular telecommunications system (Phase 2+); Mobile Station - BaseStation System (MS - BSS) interface; Data Link (DL) layer specification".[3]GSM 04.21: "Digital cellular telecommunications system (Phase 2+); Rate adaption on the MobileStation - Base Station System (MS - BSS) interface".[4]GSM 06.01: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Processingfunctions".[5]GSM 06.10: "Digital cellular telecommunications system (Phase 2+); Full rate speech;Transcoding".[6]GSM 06.11: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Substitutionand muting of lost frames for full rate speech channels".[7]GSM 06.12: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Comfortnoise aspect for full rate speech traffic channels".[8]GSM 06.31: "Digital cellular telecommunications system (Phase 2+); Full rate speech;Discontinuous Transmission (DTX) for full rate speech traffic channels".[9]GSM 06.32: "Digital cellular telecommunications system (Phase 2+); Voice Activity Detector(VAD)".[10]GSM 08.20: "Digital cellular telecommunications system (Phase 2+); Rate adaption on the BaseStation System - Mobile-services Switching Centre (BSS - MSC) interface".SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)7(GSM 08.60 version 6.0.1 Release 1997)[11]GSM 08.51: "Digital cellular telecommunications system (Phase 2+); Base Station Controller -Base Transceiver Station (BSC - BTS) interface; General aspects".[12]GSM 08.54: "Digital cellular telecommunications system (Phase 2+); Base Station Controller -Base Transceiver Station (BSC - BTS) interface; Layer 1 structure of physical circuits".[13]GSM 08.58: "Digital cellular telecommunications system (Phase 2+); Base Station Controller -Base Transceiver Station (BSC - BTS) interface; Layer 3 specification".[14]GSM 12.21: "Digital cellular telecommunications system (Phase 2+); Network Management (NM)procedures and message on the A-bis interface".[15]CCITT Recommendation G.711: "Pulse code modulation (PCM) of voice frequencies".[16]CCITT Recommendation I.460: "Multiplexing, rate adaption and support of existing interfaces".[17]CCITT Recommendation V.110: "Support of data terminal equipments (DTEs) with V-Seriesinterfaces by an integrated services digital network".[18]GSM 06.51: "Digital cellular telecommunications system (Phase 2+); Enhanced Full rate speechprocessing functions".[19]GSM 06.60: "Digital cellular telecommunications system (Phase 2+); Enhanced Full rate speechtranscoding".[20]GSM 06.61: "Digital cellular telecommunications system (Phase 2+); Substitution and muting oflost frames for Enhanced Full rate speech channels".[21]GSM 06.62: "Digital cellular telecommunications system (Phase 2+); Comfort noise aspect forEnhanced Full rate speech traffic channels".[22]GSM 06.81: "Digital cellular telecommunications system (Phase 2+); Discontinuous Transmission(DTX) for Enhanced Full rate speech traffic channel".[23]GSM 06.82: "Digital cellular telecommunications system (Phase 2+); Voice Activity Detection(VAD)".1.2AbbreviationsAbbreviations used in the present document are listed in GSM 01.04.2General ApproachWhen the transcoders/rate adaptors are positioned remote to the BTS, the information between the Channel Codec Unit(CCU) and the remote Transcoder/Rate Adaptor Unit (TRAU) is transferred in frames with a fixed length of 320 bits(20 mS). In the present document, these frames are denoted "TRAU frames". Within these frames, both the speech/dataand the TRAU associated control signals are transferred.The Abis interface should be the same if the transcoder is positioned 1) at the MSC site of the BSS or if it is positioned2) at the BSC site of the BSS. In case 1), the BSC should be considered as transparent for 16 kbit/s channels.In case of 4,8 and 9,6 kbit/s channel coding when data is adapted to the 320 bit frames, a conversion function is requiredin addition to the conversion/rate adaption specified in GSM 08.20. This function constitutes the RAA. In case of 14,5kbit/s channel coding, no RAA rate adaption is required because V.110 framing is not used.The TRAU is considered a part of the BSC, and the signalling between the BSC and the TRAU (e.g. detection of callrelease, handover and transfer of O&M information) may be performed by using BSC internal signals. The signallingbetween the CCU and the TRAU, using TRAU frames as specified in the present document, is mandatory when the Abisinterface is applied.SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)8(GSM 08.60 version 6.0.1 Release 1997)NOTE:If standard 64 kbit/s switching is used in the BSC, multiplexing according to CCITT RecommendationI.460 should apply at both sides of the switch.In figure 2.1, a possible configuration of the TRAU and the CCU is shown.The functions inside the TRAU are:-"Remote Transcoder and Rate Adaptor Control Function" (RTRACF);-"Remote Speech Handler Function" (RSHF);-The RAA function in case of 4.8 and 9.6 kbit/s channel coding;-The RAA’ function in case of 14.5 kbit/s channel coding;-The RA2 function;-The transcoder function.The functions inside the CCU are:-"Transcoder and Rate Adaptor Control Function" (TRACF);-"Speech Handler Function" (SHF);-The RAA function in case of 4.8 and 9.6 kbit/s channel coding;-The RA1/RA1' function in case of 4.8 and 9.6 kbit/s channel coding;-The RA1’/RAA’ function in case of 14.5 kbit/s channel coding;-The channel codec function.The present document will not describe the procedures inside the TRAU and the CCU. The layout in figure 2.1 is onlyintended as a reference model.SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)9(GSM 08.60 version 6.0.1 Release 1997)Figure 2.1: Functional entities for handling of remote control of remote transcoders and rate adaptorsNOTE:This figure applies only for 4,8 and 9,6 kbit/s channel coding.SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)10(GSM 08.60 version 6.0.1 Release 1997)3Frame Structure3.1Speech FramesBit numberOctet no.1234567800000000010000000021C1C2C3C4C5C6C73C8C9C10C11C12C13C14C1541D1D2D3D4D5D6D75D8D9D10D11D12D13D14D1561D16D17D18D19D20D21D227D23D24D25D26D27D28D29D3081D31D32D33D34D35D36D379D38D39D40D41D42D43D44D45101D46D47D48D49D50D51D5211D53D54D55D56D57D58D59D60121D61D62D63D64D65D66D6713D68D69D70D71D72D73D74D75141D76D77D78D79D80D81D8215D83D84D85D86D87D88D89D90161D91D92D93D94D95D96D9717D98D99D100D101D102D103D104D105181D106D107D108D109D110D111D11219D113D114D115D116D117D118D119D120201D121D122D123D124D125D126D12721D128D129D130D131D132D133D134D135221D136D137D138D139D140D141D14223D143D144D145D146D147D148D149D150241D151D152D153D154D155D156D15725D158D159D160D161D162D163D164D165261D166D167D168D169D170D171D17227D173D174D175D176D177D178D179D180281D181D182D183D184D185D186D18729D188D189D190D191D192D193D194D195301D196D197D198D199D200D201D20231D203D204D205D206D207D208D209D210321D211D212D213D214D215D216D21733D218D219D220D221D222D223D224D225341D226D227D228D229D230D231D23235D233D234D235D236D237D238D239D240361D241D242D243D244D245D246D24737D248D249D250D251D252D253D254D255381D256D257D258D259D260C16C1739C18C19C20C21T1T2T3T4SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)11(GSM 08.60 version 6.0.1 Release 1997)3.2O&M FramesBit numberOctet no.1234567800000000010000000021C1C2C3C4C5C6C73C8C9C10C11C12C13C14C1541D1D2D3D4D5D6D75D8D9D10D11D12D13D14D1561D16D17D18D19D20D21D227D23D24D25D26D27D28D29D3081D31D32D33D34D35D36D379D38D39D40D41D42D43D44D45101D46D47D48D49D50D51D5211D53D54D55D56D57D58D59D60121D61D62D63D64D65D66D6713D68D69D70D71D72D73D74D75141D76D77D78D79D80D81D8215D83D84D85D86D87D88D89D90161D91D92D93D94D95D96D9717D98D99D100D101D102D103D104D105181D106D107D108D109D110D111D11219D113D114D115D116D117D118D119D120201D121D122D123D124D125D126D12721D128D129D130D131D132D133D134D135221D136D137D138D139D140D141D14223D143D144D145D146D147D148D149D150241D151D152D153D154D155D156D15725D158D159D160D161D162D163D164D165261D166D167D168D169D170D171D17227D173D174D175D176D177D178D179D180281D181D182D183D184D185D186D18729D188D189D190D191D192D193D194D195301D196D197D198D199D200D201D20231D203D204D205D206D207D208D209D210321D211D212D213D214D215D216D21733D218D219D220D221D222D223D224D225341D226D227D228D229D230D231D23235D233D234D235D236D237D238D239D240361D241D242D243D244D245D246D24737D248D249D250D251D252D253D254D255381D256D257D258D259D260D261D26239D263D264S1S2S3S4S5S6SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)12(GSM 08.60 version 6.0.1 Release 1997)3.3Data Frames3.3.1Data Frame (for Synchronisation)Bit numberOctet no.1234567800000000010000000021C1C2C3C4C5C6C73C8C9C10C11C12C13C14C1541.51.61.71Data frame position 18163 bits.91(72 bits including bit position 1)1011111211311411511611Data frame position 2171181191201211221231241251Data frame position 3261271281291301311321331Data frame position 4341351361371381391SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)13(GSM 08.60 version 6.0.1 Release 1997)3.3.2Extended data frame (E-TRAU : data transport)Bit numberOctet no.1234567800000000010000000021C1C2C3C4C5C6C73C8C9C10C11C12C13M1M24D1D2.567Data block of 288 data bits and M1, M2.89101112131415161718192021222324252627282930313233343536373839.D287D288SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)14(GSM 08.60 version 6.0.1 Release 1997)3.4Idle Speech FramesBit numberOctet no.1234567800000000010000000021C1C2C3C4C5C6C73C8C9C10C11C12C13C14C15411111111511111111611111111711111111811111111911111111101111111111111111111211111111131111111114111111111511111111161111111117111111111811111111191111111120111111112111111111221111111123111111112411111111251111111126111111112711111111281111111129111111113011111111311111111132111111113311111111341111111135111111113611111111371111111138111111C16C1739C18C19C20C21T1T2T3T43.5CodingIn the following sections, the coding of the frames is described. Any spare or not used control bits should be codedbinary "1".For all frame types the octet 0, 1 and the first bit of octets 2, 4, 6, 8, . 38 are used as frame sync.SIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)15(GSM 08.60 version 6.0.1 Release 1997)3.5.1Coding of Speech FramesControl bits (C-bits):DescriptionUplinkDownlinkC1C2C3C4 C5C1C2C3C4 C5Frame typeFRSpeech: 0
0
0
1
0.Speech: 1
1
1
0
0(Bits C1 - C5).
EFRSpeech: 1
1
0
1
0Speech: 1
1
0
1
0TimeBinary number indicating theBinary number indicatingAlignmentrequired timing adjustment tothe timing adjustment made.(Bits C6 - C11)be made in steps of 250/500 ms.The following values apply for the codingC6C7
. . .
C11 0
0
0
0
0
0
No change in frame timing 0
0
0
0
0
1
Delay frame 1 x 500 ms 0
0
0
0
1
0
Delay frame 2 x 500 ms
.
.
.
....
.
.
.
.... 1
0
0
1
1
1
Delay frame 39 x 500 ms 1
0
1
0
0
0
Not used
.
.
.
.... 1
1
1
1
0
1
Not used 1
1
1
1
1
0
Delay frame 1 x 250 ms 1
1
1
1
1
1
Advance frame 250 msFrame indicators. The definitionC12: BFIC12 - C15: Spareand coding of these indicators0
: BFI = 0are given in GSM 06.31.1
: BFI = 1IF FR. SpeechC13 C14: SIDELSEBits C12 - C16 0
0
:SID = 0C12: UFE 0
1
:SID = 1 0
:UFE=0 bad uplink frame 1
0
:SID = 21
:
UFE=1 good up-link frameDownlink Uplink Frame ErrorC15:
TAF(UFE) C12 0
:
TAF = 0(see subclause 4.8.3) 1
:
TAF = 1C13 - C15: spareC16: SpareC16: SP 0
:
SP = 0 1
:
SP = 1DTX indicator C17: DTXdC17: Spare0
:
DTX not applied1
:
DTX appliedBits C18 - C21SpareSpareSIST EN 300 737 V6.0.1:2003



ETSIEN 300 737 V6.0.1 (1999-09)16(GSM 08.60 version 6.0.1 Release 1997)Data Bits (D-bits):Bits D1 . D260:Speech block transferred in the same order as output from the transcoder (see GSM 06.10).For Enhanced Full Rate Speech:The speech block is subdivided in five subsets. The order within a given subset is the same as output from the transcoder(see ETS 300 726, GSM 06.60). Three parity bits are added at the end of each sub-set.These parity bits are added to the bits of the subset, according to a degenerate (shortened) cyclic code using thegenerator polynomial:g(D) = D3
+ D + 1The encoding of the cyclic code is performed in a systematic form which means that, in GF(2), the polynomial:d(m)Dn + d(m+1)Dn-1 + .+ d(m + n-3)D3 + p(0)D2 + p(1)D + p(2)where p(0), p(1), p(2) are the parity bits, when divided by g(D), yields a remainder equal to:1 + D + D2For every CRC, the transmission order is p(0) first followed by p(1) and p(2) successively.Bit D1:spare (binary "1").Bits D2.D39:Indexes of the LSF submatrices.Bits D40.D42:CRC over bits D1 to D22, D25 to D27 and D29.Bits D43.D95:Indexes of the parameters of first sub-frame.Bits D96.D98:CRC over bits D43 to D52, D91 and D92.Bits D99.D148:Indexes of the parameters of second sub-frame.Bits D149.D151:CRC over bits D99 to D103, D105, D144 and D145.Bits D152.D204:Indexes of the parameters of third sub-frame.Bits D205.D207:CRC over bits D152 to D161, D200 and D201.Bits D208.D257:Indexes of the parameters of fourth sub-frame.Bits D258.D260:CRC over bits D208 to D212, D214, D253 and D254.Time Alignment Bits:Bits T1 . T4:Bits positioned at the end of the downlink frames. If the timing of the frame is to be advanced250 µS, these 4 bits are not transferred in order to reduce the frame length accordingly. Whentransferred the bits are set to binary "1".SIST
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