SIST EN 300 937 V7.0.1:2003
(Main)Digital cellular telecommunications system (Phase 2+) (GSM); Data Link (DL) layer; General aspects (GSM 04.05 version 7.0.1 Release 1998)
- Abstract
Upgrade from Phase 2+ to Release 1998
- 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
SIST EN 300 937 V7.0.1:2003 is the Slovenian adoption of ETSI EN 300 937 V7.0.1 for the Global System for Mobile communications (GSM) data link (DL) layer. It specifies Link Access Procedures on the Dm channel, known as LAPDm, for transferring layer 3 signalling between the mobile station (MS) and the network on the GSM public land mobile network (PLMN) radio interface.
What does SIST EN 300 937 V7.0.1:2003 specify?
SIST EN 300 937 V7.0.1:2003 specifies the general aspects of LAPDm, the GSM data link protocol used on the Dm channel. It focuses on signalling transfer, channel use, and the service interface between the DL layer, layer 3, and the physical layer.
The scope says the protocol is described in general terms and that details are provided in GSM 04.06. The document is organized into clauses 1 to 6: references, abbreviations, concepts and terminology, an overview of LAPDm functions and procedures, service characteristics, data link layer structure, and specific requirements.
What are the key requirements of SIST EN 300 937 V7.0.1:2003?
Channel use and service modes
Clause 3 states that LAPDm supports multiple layer 3 entities, multiple physical layer entities, and signalling on BCCH, PCH + AGCH and DCCH. In practice, this means one protocol design must handle several signalling paths and channel types.
Clause 3 also distinguishes unacknowledged operation and acknowledged multiple frame operation. BCCH and PCH + AGCH use only unacknowledged operation, while SDCCH, SACCH and FACCH can support both. That choice determines whether the implementation needs acknowledgement, retransmission and flow control.
Transfer rules and priorities
Clause 4.2.2 sets priority handling. On SDCCH, SAPI = 0 has higher priority than SAPI = 3, and on SACCH the ordering must prevent SAPI = 3 traffic from starving SAPI = 0 traffic. This matters when signalling and short messages share capacity.
Clause 4.2.3 requires segmentation and concatenation only in acknowledged transfer. So long layer 3 message units may be split and reassembled there, but unacknowledged transfer has no segmentation service.
Clause 4.2.5 defines the main primitives for acknowledged transfer: data transfer, establishment, suspension, resumption, reconnection and release. For implementation and testing, these primitives are the control events that show how LAPDm starts, pauses, resumes and ends a connection.
Physical and administrative interaction
Clause 4.3 summarizes the services required from the physical layer: transparent frame transport, physical status indication, ordering, frame synchronization, error protection and random access burst handling. Clause 4.4 adds administrative services for error reporting and abnormal release. In practice, these clauses define what the DL layer expects from the radio bearer and how it reports unrecoverable failures.
Data link identification and limits
Clause 5.2 identifies data link endpoints with a Data Link Connection Identifier (DLCI), made from the Service Access Point Identifier (SAPI) and the control channel type. That is how the implementation routes each frame to the correct signalling relationship.
Clause 6.1 gives the allowed SAPI and mode combinations per channel, and clause 6.2 fixes the acknowledged-mode window size at 1 for SAPI = 0 and SAPI = 3. Clause 6.2.2 also requires enough processing capacity to avoid receiver busy state for SAPI = 0. In practice, LAPDm is designed for simple, tightly controlled signalling flow.
What terms does SIST EN 300 937 V7.0.1:2003 define?
- Dm channel - the collection of GSM signalling channels used by LAPDm between the MS and the network.
- Service Access Point (SAP) - the point where the DL layer offers service to layer 3.
- Service Access Point Identifier (SAPI) - the identifier of a SAP, carried in the frame address field.
- Data Link Connection Identifier (DLCI) - the identifier for a data link connection endpoint, combining SAPI and channel type.
- Unacknowledged operation - transfer using Unnumbered Information (UI) frames with no DL acknowledgement or recovery.
- Multiple frame operation - acknowledged transfer using numbered Information (I) frames, retransmission and flow control.
- Random Access Channel (RACH) - the access channel used for random access bursts in the LAPDm environment.
Who uses SIST EN 300 937 V7.0.1:2003?
The standard is used by GSM radio interface designers, mobile station and network implementers, and protocol test engineers. It is also relevant to quality and interoperability work where layer 2 signalling behaviour, channel selection, priority, and release handling must match the GSM specifications.
What changed in SIST EN 300 937 V7.0.1:2003 from the previous edition?
This version upgrades the Phase 2+ specification to Release 1998. The foreword also states the versioning rule used by ETSI: the first digit identifies Release 1998, the second digit marks substantive technical changes, and the third digit marks editorial changes.
Which standards are used with SIST EN 300 937 V7.0.1:2003?
The document relies on GSM01.04 for abbreviations, GSM04.01 for layering principles, GSM04.03 for channel structures and access capabilities, GSM04.04 for layer 1 requirements, and GSM04.06 for the detailed DL layer specification. GSM04.07, GSM04.08, GSM04.10 and GSM04.11 provide the layer 3 signalling context carried over LAPDm, while GSM07.01, GSM07.02, GSM07.03, GSM07.05 and GSM07.06 cover terminal adaptation and DTE-DCE interfaces. CCITT X.25, X.200, X.210, Q.920, Q.921, ISO 3309 and ISO/IEC 4335 provide the packet-mode, OSI, ISDN and HDLC concepts used in the protocol design.
What does the SIST EN 300 937 V7.0.1:2003 document contain?
The document contains figures showing the DL layer reference model, the relationship between SAPs and endpoints, and an example DL configuration in the MS. It also contains the service primitive lists for DL, MDL and PH interactions, the LAPDm functional overview, and the mode-and-channel support matrix in clause 6.1. Clause 5 describes the functional composition, endpoint identification, DL procedure, DL distribution procedure and random access procedure, which are the main implementation references for design and conformance work.
Get Certified
Connect with accredited certification bodies for this standard
ANCE
Mexican certification and testing association.
Intertek Slovenia
Intertek testing, inspection, and certification services in Slovenia.
LNE (Laboratoire National de Métrologie et d'Essais)
French national laboratory for metrology and testing.
Sponsored listings
Frequently Asked Questions
SIST EN 300 937 V7.0.1:2003 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "Digital cellular telecommunications system (Phase 2+) (GSM); Data Link (DL) layer; General aspects (GSM 04.05 version 7.0.1 Release 1998)". This standard covers: Upgrade from Phase 2+ to Release 1998
Upgrade from Phase 2+ to Release 1998
SIST EN 300 937 V7.0.1:2003 is classified under the following ICS (International Classification for Standards) categories: 33.070.50 - Global System for Mobile Communication (GSM). The ICS classification helps identify the subject area and facilitates finding related standards.
SIST EN 300 937 V7.0.1:2003 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Data Link (DL) layer; General aspects (GSM 04.05 version 7.0.1 Release 1998)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 937 Version 7.0.1SIST EN 300 937 V7.0.1:2003en01-december-2003SIST EN 300 937 V7.0.1:2003SLOVENSKI
STANDARD
ETSIEN300937V7.0.1(2000-01)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);DataLink(DL)layer;Generalaspects(GSM04.05version7.0.1Release1998)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 300 937 V7.0.1:2003
ETSIETSIEN300937V7.0.1(2000-01)2(GSM04.05version7.0.1Release1998)ReferenceREN/SMG-030405Q7KeywordsDigitalcellulartelecommunicationssystem,GlobalSystemforMobilecommunications(GSM)ETSIPostaladdressF-06921SophiaAntipolisCedex-FRANCEOfficeaddress650RoutedesLucioles-SophiaAntipolisValbonne-FRANCETel.:+33492944200Fax:+33493654716SiretN°34862356200017-NAF742CAssociationàbutnonlucratifenregistréeàlaSous-PréfecturedeGrasse(06)N°7803/88Internetsecretariat@etsi.frIndividualcopiesofthisETSIdeliverablecanbedownloadedfromhttp://www.etsi.orgIfyoufinderrorsinthepresentdocument,sendyourcommentto:editor@etsi.frImportantnoticeThisETSIdeliverablemaybemadeavailableinmorethanoneelectronicversionorinprint.Inanycaseofexistingorperceiveddifferenceincontentsbetweensuchversions,thereferenceversionisthePortableDocumentFormat(PDF).Incaseofdispute,thereferenceshallbetheprintingonETSIprintersofthePDFversionkeptonaspecificnetworkdrivewithinETSISecretariat.CopyrightNotificationNopartmaybereproducedexceptasauthorizedbywrittenpermission.Thecopyrightandtheforegoingrestrictionextendtoreproductioninallmedia.©EuropeanTelecommunicationsStandardsInstitute2000.Allrightsreserved.SIST EN 300 937 V7.0.1:2003
ETSIETSIEN300937V7.0.1(2000-01)3(GSM04.05version7.0.1Release1998)ContentsIntellectualPropertyRights.4Foreword.41Scope.51.1References.61.2Abbreviations.72Conceptsandterminology.73OverviewdescriptionofLAPDmfunctionsandprocedures.103.1General.103.2Unacknowledgedoperation.113.3Acknowledgedoperation.113.4Informationtransfermode.113.4.1InformationtransferontheBCCH.113.4.2InformationtransferonthePCH+AGCH.113.4.3InformationtransferontheDCCHs.113.5Releaseofdatalinks.114Servicecharacteristics.124.1General.124.2Servicesprovidedtolayer3.124.2.1General.124.2.2Priority.124.2.3Segmentation.124.2.4Unacknowledgedinformationtransferservice.134.2.5Acknowledgedinformationtransferservices.134.2.6Randomaccessprocedure.144.3Servicesrequiredfromthephysicallayer.144.4Administrativeservices.154.4.1Generaldescriptionofadministrativeservices.154.4.2Definitionofprimitivesforadministrativeservices.165Overviewofdatalinklayerstructure.165.1Functionalcomposition.165.2Identificationofdatalinkendpoints.165.3Datalinkprocedure.175.4Datalinkdistributionprocedure.175.5Randomaccessprocedures.176Specificrequirements.186.1ModeofoperationandallowedSAPIs.186.2Acknowledgedmodeofoperation.196.2.1Windowsize.196.2.2Processingcapacity.19History.20SIST EN 300 937 V7.0.1:2003
ETSIETSIEN300937V7.0.1(2000-01)4(GSM04.05version7.0.1Release1998)IntellectualPropertyRightsIPRsessentialorpotentiallyessentialtothepresentdocumentmayhavebeendeclaredtoETSI.TheinformationpertainingtotheseessentialIPRs,ifany,ispubliclyavailableforETSImembersandnon-members,andcanbefoundinSR000314:"IntellectualPropertyRights(IPRs);Essential,orpotentiallyEssential,IPRsnotifiedtoETSIinrespectofETSIstandards",whichisavailablefromtheETSISecretariat.LatestupdatesareavailableontheETSIWebserver(http://www.etsi.org/ipr).PursuanttotheETSIIPRPolicy,noinvestigation,includingIPRsearches,hasbeencarriedoutbyETSI.NoguaranteecanbegivenastotheexistenceofotherIPRsnotreferencedinSR000314(ortheupdatesontheETSIWebserver)whichare,ormaybe,ormaybecome,essentialtothepresentdocument.ForewordThisEuropeanStandard(Telecommunicationsseries)hasbeenproducedbytheSpecialMobileGroup(SMG).Thepresentdocumentdefinesingeneraltermsthedatalinklayer(layer2)oftheMobileStation(MS)-networkinterfacewithinthedigitalcellulartelecommunicationssystem.TheETSfromwhichthepresentdocumenthasevolvedisPhase2GSMETS300554(GSM04.05version4.0.3).ThecontentsofthepresentdocumentissubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocument,itwillbere-releasedwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version7.x.ywhere:7 indicates Release 1998 of GSM Phase 2+.xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.ThespecificationfromwhichthepresentdocumenthasbeenderivedwasoriginallybasedonCEPTdocumentation,hencethepresentationofthepresentdocumentmaynotbeentirelyinaccordancewiththeETSIdraftingrules.NationaltranspositiondatesDateofadoptionofthisEN:31December1999DateoflatestannouncementofthisEN(doa):31March2000DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):30September2000DateofwithdrawalofanyconflictingNationalStandard(dow):30September2000SIST EN 300 937 V7.0.1:2003
ETSIETSIEN300937V7.0.1(2000-01)5(GSM04.05version7.0.1Release1998)1ScopeThepresentdocumentdescribesingeneraltermstheLinkAccessProceduresontheDmchannel,LAPDm.Theapplicationofthisprotocoltootherchanneltypesisforfurtherstudy.DetailsareprovidedinGSM04.06.ThepurposeofLAPDmistoconveyinformationbetweenlayer3entitiesacrosstheGSMPLMNradiointerface(MStonetworkinterface)usingtheDmchannel.NOTE1:ThetermDmchannelisusedforconveniencetodesignatethecollectionofallthevarioussignallingchannelsrequiredintheGSMsystem.SeealsoGSM04.03.ThedefinitionofLAPDmisbasedontheprinciplesandterminologyof:-CCITTRecommendationsX.200andX.210:thereferencemodelforOpenSystemsInterconnection(OSI);-CCITTRecommendationsQ.920andQ.921:thespecificationofLAPDfortheuser-networkinterfaceinISDN;-CCITTRecommendationX.25LAPB:user-networkinterfaceforpacketmodeterminals;and-ISO3309andISO4335:High-levelDataLinkControl(HDLC)standardsforframestructureandelementsofprocedures.LAPDmisaprotocolthatoperatesatthedatalinklayeroftheOSIarchitecture.Therelationshipbetweenthedatalinklayerandotherprotocollayersisdefinedbelow.NOTE2:Theinterfacebetweenthemobilestationandexternalterminalequipment/terminaladaptersisdefinedintheTechnicalSpecificationsoftheGSM07-series.NOTE3:ThephysicallayerontheradiointerfaceisdefinedinGSM04.04andlayer3isdefinedinGSM04.07,04.08,04.10and04.11.ReferenceshouldbemadetotheseTechnicalSpecificationsforthecompletedefinitionsoftheprotocolsandproceduresacrosstheGSMPLMNradiointerface.NOTE4:Theterm"datalinklayer"isusedinthemaintextofthepresentdocument.However,mainlyinfiguresandtables,theterms"layer2"and"L2"areusedabbreviations.Furthermore,inaccordancewithGSM04.07and04.08theterm"layer3"isusedtoindicatethelayerabovethedatalinklayer.LAPDmisindependentofthetransmissionbitrate.ItrequiresphysicalchannelswithcharacteristicsasdefinedinGSM04.03.Section2belowdescribesbasicconceptsusedinthepresentdocumentandGSM04.06.Section3givesanoverviewdescriptionofLAPDmfunctionsandprocedures.Section4summarizestheservicesthatthedatalinklayerprovidestolayer3andtheservicesthatthedatalinklayerrequiresfromthephysicallayer.Section5providesanoverviewofthedatalinklayerstructure.SIST EN 300 937 V7.0.1:2003
ETSIETSIEN300937V7.0.1(2000-01)6(GSM04.05version7.0.1Release1998)1.1ReferencesThefollowingdocumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthepresentdocument.•Referencesareeitherspecific(identifiedbydateofpublication,editionnumber,versionnumber,etc.)ornon-specific.•Foraspecificreference,subsequentrevisionsdonotapply.•Foranon-specificreference,thelatestversionapplies.•Anon-specificreferencetoanETSshallalsobetakentorefertolaterversionspublishedasanENwiththesamenumber.•ForthisRelease1998document,referencestoGSMdocumentsareforRelease1998versions(version7.x.y).[1]GSM01.04:"Digitalcellulartelecommunicationssystem(Phase2+);Abbreviationsandacronyms".[2]GSM04.01:"Digitalcellulartelecommunicationssystem;MobileStation-BaseStationSystem(MS-BSS)interfaceGeneralaspectsandprinciples".[3]GSM04.03:"Digitalcellulartelecommunicationssystem(Phase2+);MobileStation-BaseStationSystem(MS-BSS)interfaceChannelstructuresandaccesscapabilities".[4]GSM04.04:"Digitalcellulartelecommunicationssystem;Layer1Generalrequirements".[5]GSM04.06:"Digitalcellulartelecommunicationssystem;MobileStation-BaseStationSystem(MS-BSS)interfaceDataLink(DL)layerspecification".[6]GSM04.07:"Digitalcellulartelecommunicationssystem(Phase2);Mobileradiointerfacesignallinglayer3Generalaspects".[7]GSM04.08:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacelayer3specification".[8]GSM04.10:"Digitalcellulartelecommunicationssystem;Mobileradiointerfacelayer3SupplementaryservicesspecificationGeneralaspects".[9]GSM04.11:"Digitalcellulartelecommunicationssystem(Phase2+);Point-to-Point(PP)ShortMessageService(SMS)supportonmobileradiointerface".[10]GSM07.01:"Digitalcellulartelecommunicationssystem(Phase2+);GeneralonTerminalAdaptationFunctions(TAF)forMobileStations(MS)".[11]GSM07.02:"Digitalcellulartelecommunicationssystem(Phase2+);TerminalAdaptationFunctions(TAF)forservicesusingasynchronousbearercapabilities".[12]GSM07.03:"Digitalcellulartelecommunicationssystem(Phase2+);TerminalAdaptationFunctions(TAF)forservicesusingsynchronousbearercapabilities".[13]GSM07.05:"Digitalcellulartelecommunicationssystem(Phase2+);UseofDataTerminalEquipment-DataCircuitterminatingEquipment(DTE-DCE)interfaceforShortMessageService(SMS)andCellBroadcastService(CBS)".[14]GSM07.06:"Digitalcellulartelecommunicationssystem(Phase2);UseoftheVseriesDataTerminalEquipment-DataCircuitterminatingEquipment(DTE-DCE)interfaceattheMobileStation(MS)forMobileTermination(MT)configuration".[15]CCITTRecommendationX.25:"Interfacebetweendataterminalequipment(DTE)anddatacircuit-terminatingequipment(DCE)forterminalsoperatinginthepacketmodeandconnectedtopublicdatanetworksbydedicatedcircuit".SIST EN 300 937 V7.0.1:2003
ETSIETSIEN300937V7.0.1(2000-01)7(GSM04.05version7.0.1Release1998)[16]CCITTRecommendationX.200:"ReferenceModelofOpenSystemsInterconnectionforCCITTApplications".[17]CCITTRecommendationX.210:"OpenSystemsInterconnectionlayerservicedefinitionconventions".[18]CCITTRecommendationQ.920:"Integratedservicesdigitalnetwork(ISDN)user-networkinterface-DatalinklayerGeneralaspects".[19]CCITTRecommendationQ.921:"Integratedservicesdigitalnetwork(ISDN)user-networkinterface-Datalinklayerspecification".[20]ISO3309:"Informationtechnology-Telecommunicationsandinformationexchangebetweensystems-Highleveldatalinkcontrol(HDLC)procedures-Framestructure".[21]ISO/IEC4335:"Informationtechnology-Telecommunicationsandinformationexchangebetweensystems-Highleveldatalinkcontrol(HDLC)procedures-Elementsofprocedures".1.2AbbreviationsAbbreviationsusedinthepresentdocumentarelistedinGSM01.04.2ConceptsandterminologyThegenerallayeringprinciplesusedinthepresentdocumentandotherspecificationsinthe04seriesaregiveninGSM04.01.ThedatalinklayeristhenexttolowestlayeroftheOSIreferencemodel.Thedatalinklayerreceivesservicesfromthephysicallayerandprovidesservicestolayer3.Theservicesprovidedbythedatalinklayerarethecombinationoftheservicesandfunctionsprovidedbyboththedatalinklayerandthephysicallayer.AdatalinklayerServiceAccessPoint(SAP)isthepointatwhichthedatalinklayerprovidesservicestolayer3.TheServiceAccessPointisidentifiedbyaServiceAccessPointIdentifier(SAPI).OneormoredatalinkconnectionendpointscanbeassociatedwitheachdatalinklayerSAP.Seefigure1.Adatalinkconnectionendpointisidentifiedbyadatalinkconnectionendpointidentifier(asseenfromlayer3)andbyaDataLinkConnectionIdentifierDLCI(asseenfromthedatalinklayer).SAPIsandDLCIsusedbyLAPDmaredefinedinsection5.2.Layer3Layer3entityDatalinklayerserviceaccesspointDatalinkconnectionendpointDatalinklayerDatalinklayerentity*Figure1:Entities,serviceaccesspointsandendpointsSIST EN 300 937 V7.0.1:2003
ETSIETSIEN300937V7.0.1(2000-01)8(GSM04.05version7.0.1Release1998)Co-operationbetweendatalinklayerentitiesisgovernedbyapeer-to-peerprotocolspecifictothelayer.Forinformationexchangebetweentwoormorelayer3entities,anassociationmustbeestablishedbetweenthelayer3entitiesinthedatalinklayerusingadatalinklayerprotocol.Thisassociationiscalledadatalinkconnection.DatalinkconnectionsareprovidedbythedatalinklayerbetweentwoormoreSAPs(seefigure2).Layer3entityLayer3entityDatalinklayerserviceaccesspointDatalinkconnectionendpointDatalinkrelationshipFigure2:Peer-to-peerrelationshipDatalinklayermessageunitsareconveyedbetweendatalinklayerentitiesbymeansofphysicalconnection.Layer3requestsservicesfromthedatalinklayerviaserviceprimitives.Thesameappliesfortheinteractionbetweenthedatalinklayerandthephysicallayer.Theprimitivesrepresent,inanabstractway,thelogicalexchangeofinformationandcontrolbetweenthedatalinklayeranditsadjacentlayers.Theydonotspecifyorconstrainimplementations.Theprimitivesthatareexchangedbetweenthedatalinklayerandadjacentlayersareofthefollowingfourtypes(seealsofigure3).**Layer3ConfirmIndicationSAPDatalinklayerLayer2peer-to-peerprotocolRequestResponseNOTE:Thesameprincipleappliesfordatalinklayer-physicallayerinteractions.Figure3:PrimitiveactionsequenceSIST EN 300 937 V7.0.1:2003
ETSIETSIEN300937V7.0.1(2000-01)9(GSM04.05version7.0.1Release1998)TheREQUESTprimitivetypeisusedwhenahigherlayerisrequestingaservicefromthenextlowerlayer.TheINDICATIONprimitivetypeisusedbyalayerprovidingaservicetonotifythenexthigherlayerofactivitiesrelatedtotheprimitivetypeREQUEST.TheRESPONSEprimitivetypeisusedbyalayertoacknowledgereceipt,fromalowerlayer,oftheprimitivetypeINDICATION.TheCONFIRMprimitivetypeisusedbythelayerprovidingtherequestedservicetoconfirmthattheactivityhasbeencompleted.TheprecisespecificationofLayer-to-layerinteractionsisgiveninGSM04.06.InformationbetweenpeerentitiesandbetweenentitiesinadjacentlayersattachedtothesameSAPistransferredintwodifferenttypesofmessageunits:-messageunitsofapeer-to-peerprotocol;and-messageunitsthatcontainlayer-to-layerinformationconcerningstatusandspecializedservicerequests.Themessageunitsofthelayer3peer-to-peerprotocolarecarriedbythedatalinkconnection.Themessageunitscontaininglayer-to-layerinformationconcerningstatusandspecializedservicerequestsareneverconveyedoveradatalinkconnectionoraphysicalconnection.Thepresentdocumentintroduces(seealsofigure4):a)thepeer-to-peerprotocolforthetransferofinformationandcontrolbetweenanypairofdatalinklayerserviceaccesspoints;b)theinteractionsbetweenthedatalinklayerandlayer3,andbetweenthedatalinklayerandthephysicallayer.Layer3entityLayer3entityDa
...