ETSI ETS 300 742 ed.1 (1997-04)
Transmission and Multiplexing (TM); Physical layer User Network Interface (UNI) for 2 048 kbit/s Asynchronous Transfer Mode (ATM) signals
Transmission and Multiplexing (TM); Physical layer User Network Interface (UNI) for 2 048 kbit/s Asynchronous Transfer Mode (ATM) signals
DE/TM-03064
Prenos in multipleksiranje (TM) – Vmesnik uporabnik-omrežje (UNI) na fizični plasti za signale hitrosti 2 048 kbit/s v asinhronem prenosnem načinu (ATM)
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.70Transmission and Multiplexing (TM); Physical layer User Network Interface (UNI) for 2 048 kbit/s Asynchronous Transfer Mode (ATM) signals33.040.20Prenosni sistemTransmission systemsICS:Ta slovenski standard je istoveten z:ETS 300 742 Edition 1SIST ETS 300 742 E1:2003en01-december-2003SIST ETS 300 742 E1:2003SLOVENSKI
STANDARD
SIST ETS 300 742 E1:2003
EUROPEANETS 300 742TELECOMMUNICATIONApril 1997STANDARDSource: ETSI TC-TMReference: DE/TM-03064ICS:33.020Key words:Broadband, ISDN, access, interface, UNI, ATMTransmission and Multiplexing (TM);Physical layer User Network Interface (UNI)for 2 048 kbit/s Asynchronous Transfer Mode (ATM) signalsETSIEuropean 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 4 92 94 42 00 - Fax: +33 4 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 1997. All rights reserved.SIST ETS 300 742 E1:2003
Page 2ETS 300 742: April 1997Whilst 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 300 742 E1:2003
Page 3ETS 300 742: April 1997ContentsForeword.51Scope.72Normative references.73Definitions and abbreviations.83.1Definitions.83.2Abbreviations.84Reference configuration at the user-network interface.94.1Functional groups and reference points.94.2Examples of physical realizations.104.3Basic characteristics of the interfaces at TB and SB reference points for 2 048 kbit/s.144.3.1Interface at TB reference point.144.3.2Interface at the SB reference point.144.3.3Relationship between interfaces at SB and TB.144.4Relationship between ISDN interfaces.144.5Functional groups characteristics.144.5.1Network termination 1 for B-ISDN (B-NT1).144.5.2Network termination 2 for B-ISDN (B-NT2).144.5.3Terminal equipment for B-ISDN (B-TE).154.5.3.1Terminal equipment type 1 for B-ISDN (B-TE1).154.5.3.2Terminal equipment type 2 for B-ISDN (B-TE2).154.5.4Terminal adapter for B-ISDN (B-TA).155UNI specifications.155.1Interface location with respect to reference configuration.155.2Interface location with respect to the wiring configuration.156Service and layering aspects of the physical layer.166.1Services provided to the ATM-layer.166.2Service primitives exchanged with the ATM layer.166.3Sublayering of the physical layer.167Physical medium characteristics at the TB and SB reference point of the UNI for 2 048 kbit/s.167.1Bit rate and interface symmetry.167.2Physical characteristics.177.2.1Electrical interface.177.2.1.1Interface range.177.2.1.2Transmission medium.177.2.1.3Electrical parameters at interface points Ia and Ib.177.2.1.4Electrical connectors.177.2.1.5Line coding.187.2.1.6Electromagnetic compatibility and electromagneticinterference requirements.187.2.1.7Jitter and Wander.188Power feeding.188.1Provision of power.188.2Power available at B-NT1.188.3Feeding voltage.188.4Safety requirements.199Functions provided by the transmission convergence sublayer.199.1Transfer capability for 2 048 kbit/s.19SIST ETS 300 742 E1:2003
Page 4ETS 300 742: April 19979.2Physical Layer aspects.199.2.1Timing.199.2.2Interface structure for 2 048 kbit/s.199.3Header error control.219.3.1Header error control functions.219.3.2Header error control sequence generation.239.4Idle cells.239.5Cell delineation and scrambling.239.5.1Cell delineation and scrambling objectives.239.5.2Cell delineation algorithm.249.5.3Cell delineation performance.259.5.4Scrambler operation.2510UNI related OAM and operational functions.2510.1Operational functions.2510.1.1Definition of signals.2510.1.2Definitions of state tables at network and user sides.2710.1.2.1Layer 1 states on the user side of the interface.2710.1.2.2Layer 1 states at the network side of the interface.2810.1.2.3Definition of primitives.2910.1.2.4State tables.30Annex A (informative):Bibliography.35History.36SIST ETS 300 742 E1:2003
Page 5ETS 300 742: April 1997ForewordThis European Telecommunication Standard (ETS) defines the user network access physical layerinterface to be applied to the TB, SB reference points of the reference configurations of the B-ISDN UserNetwork Interface (UNI) for Broadband Integrated Services Digital Network (B-ISDN) applications. Itaddresses the structure of the transmission system that is used at these interfaces as well as theimplementation of the UNI related Operation Administration and Maintenance (OAM) functions at thephysical layer.This ETS has been produced by the Transmission and Multiplexing Technical Committee of the EuropeanTelecommunications Standards Institute (ETSI) taking into account the recommendations given in ITU-TRecommendations I.413 [7] and I.432 [8].Transposition datesDate of adoption:4 April 1997Date of latest announcement of this ETS (doa):31 July 1997Date of latest publication of new National Standardor endorsement of this ETS (dop/e):31 January 1998Date of withdrawal of any conflicting National Standard (dow):31 January 1998SIST ETS 300 742 E1:2003
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Page 7ETS 300 742: April 19971ScopeThis European Telecommunication Standard (ETS) defines the physical layer interface to be applied tothe SB and TB reference points of the reference configurations of the Broadband Integrated ServicesDigital Network (B-ISDN) User Network Interface (UNI) at 2 048 kbit/s. It addresses separately thephysical media and the transmission system used at these interfaces and addresses also theimplementation of UNI related Operation Administration and Maintenance (OAM) functions.The physical medium for the interfaces at the SB and TB reference points should take into account thatonly electrical wires are to be used to cable customer equipment.This ETS mainly is based on ETS 300 300 [13], being responsible for the bit rates 155 520 kbit/s and622 080 kbit/s and the ITU-T Recommendation I.432 [8] being responsible for the bit rates 622 080 kbit/s,155 520 kbit/s, 2 048 kbit/s and 1 544 kbit/s.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 applies.[1]ITU-T Recommendation G.804: "ATM cell mapping into Plesiochronous DigitalHierarchy (PDH)".[2]ETS 300 166 (1993): "Transmission and Multiplexing (TM); Physical andelectrical characteristics of hierarchical digital interfaces for equipment using the2048 kbit/s - based plesiochronous or synchronous digital hierarchies".[3]ITU-T Recommendation I.431: "Primary rate user-network interface - Layer 1specification".[4]ITU-T Recommendation G.823 (1993): "The control of jitter and wander withindigital networks which are based on the 2 048 kbit/s hierarchy".[5]ITU-T Recommendation I.113 (1993): "Vocabulary of terms for broadbandaspects of ISDN".[6]ITU-T Recommendation I.361 (1993): "B-ISDN ATM Layer specification".[7]ITU-T Recommendation I.413 (1993): "B-ISDN user-network interface".[8]ITU-T Recommendation I.432.1 (1995): "B-ISDN user-network interface -Physical Layer specification, General Characteristics".ITU-T Recommendation I.432.3 (1995): "B-ISDN user-network interface -Physical Layer specification for 2 048 kbit/s".[9]ITU-T Recommendation I.610 (1993): "B-ISDN operation and maintenanceprinciples and functions".[10]ITU-T Recommendation X.200: "Information technology - Open SystemsInterconnection - Basic reference model: The basic model".[11]IEC 950: "Safety of information technology equipment, including electricalbusiness equipment".[12]ITU-T Recommendation I.321 (1991): "B-ISDN protocol reference model and itsapplication".SIST ETS 300 742 E1:2003
Page 8ETS 300 742: April 1997[13]ETS 300 300 (1997): "Broadband Integrated Services Digital Network (B-ISDN);Synchronous Digital Hierarchy (SDH) based user network access; Physical layerUser Network Interfaces (UNI) for 155 520 kbit/s and 622 080 kbit/sAsynchronous Transfer Mode (ATM) B-ISDN applications".[14]ITU-T Recommendation I.604: "Application of maintenance principles to ISDNprimary rate access".[15]ITU-T Recommendation G.706: "Frame alignment and cyclic redundancy check(CRC) procedures relating to basic frame structures definedin Recommendation G.704".[16]ITU-T Recommendation G.704: "Synchronous frame structures at primary andsecondary hierarchical levels".[17]ITU-T Recommendation G.732: "Characteristics of primary PCM multiplexequipment operating at 2 048 kbit/s".[18]ITU-T Recommendation G.775: "Loss of signal (LOS) and alarm indicationsignal (AIS) defect detection and clearance criteria".3Definitions and abbreviations3.1DefinitionsFor the purposes of this ETS, the definitions given in ITU-T Recommendation I.113 [5] apply, specially foridle cell, valid cell and invalid cell.to be defined: These items or values are not yet specified.for further study: These items are required for further study.3.2AbbreviationsFor the purposes of this ETS, the following abbreviations apply:AISAlarm Indication SignalATMAsynchronous Transfer ModeB-ISDNBroadband Integrated Services Digital NetworkB-NTBroadband Network TerminationB-TABroadband Terminal AdapterB-TEBroadband Terminal EquipmentB–UNIBroadband–User Network InterfaceBERBit Error RateCATVCAble TeleVisionCLPCell Loss PriorityCMICoded Mark InversionCRCCyclic Redundancy CheckEMCElectro-Magnetic CompatibilityEMIElectro-Magnetic InterferenceFAWFrame Alignment WordHECHeader Error ControlISDNIntegrated Services Digital NetworkLANLocal Area NetworkLCDLoss of Cell DelineationLOFLoss Of FrameLOSLoss Of SignalLSBLeast Significant BitMAMedium AdapterMPHManagement Physical HeaderMSBMost Significant BitSIST ETS 300 742 E1:2003
Page 9ETS 300 742: April 1997NRZNon Return to ZeroOAMOperation Administration and MaintenanceOCDOut of Cell DelineationOSIOpen Systems InterconnectionPDHPlesiochronous Digital Hierarchyppmparts per millionPHPhysical HeaderPMPhysical MediumRAIRemote Alarm IndicationRDIRemote Defect IndicationREIRemote Error IndicationSDHSynchronous Digital HierarchySMFSub Multi FrameSTISurface Transfer ImpedanceTCTransmission ConvergenceTFVTerminal Failure VoltageTSTime SlotUNIUser Network InterfaceVCVirtual ContainerVPVirtual Path4Reference configuration at the user-network interface4.1Functional groups and reference pointsThe reference configurations defined for ISDN basic access and primary access are considered generalenough to be applicable to all aspects of the B-ISDN accesses.Figure 1 shows the B-ISDN reference configurations which contain the following:-functional groups: B-NT1; B-NT2; B-TE1; TE2; B-TE2; and B-TA;-reference points: TB; SB and R.B-TE1B-NT1B-TAReference pointSBRSBFunctional groupB-TA
Broadband Terminal AdaptorB-TE
Broadband Terminal EquipmentB-NT
Broadband Network TerminationB-NT2TBTE2orB-TE2Figure 1: B-ISDN reference configurationsIn order to clearly illustrate the broadband aspects, the notation for reference points and for functionalgroups with broadband capabilities are appended with the letter B (e.g. B-NT1, TB). The broadbandfunctional groups are equivalent to the functional groups defined in ISDN. Interfaces at the R referencepoint may or may not have broadband capabilities.Interfaces at reference points SB and TB will be standardized. These interfaces will support all ISDNservices.SIST ETS 300 742 E1:2003
Page 10ETS 300 742: April 19974.2Examples of physical realizationsFigure 2 gives examples of physical configurations illustrating combinations of physical interfaces atvarious reference points. The examples cover configurations that could be supported by standardizedinterfaces at reference points SB and TB. Other configurations may also exist. For example, physicalconfigurations of B-NT2 may be distributed or use shared medium to support Local Area Network (LAN)emulation and other applications.Figure 3 illustrates possible physical configurations, but does not preclude alternative configurations.Whether a single interface at the SB reference point can cover different configurations, as illustrated infigure 3, is for further study.Figures 2a and 2b show separate interfaces at the SB and TB reference points; figures 2c) and 2d) showan interface at SB but not at TB; figures 2e and 2f show an interface at TB but not at SB; figures 2g and 2hshow separate interfaces at S, SB and TB; figures 2i and 2j show interfaces at SB and TB which arecoincident.SIST ETS 300 742 E1:2003
Page 11ETS 300 742: April 1997Additionally, figures 2b), 2d), 2f), 2h) and 2j) show an interface at reference point R.B-NT2TSB-NT1BBa)B-TE1B-NT2TSB-NT1BBB-TARb) TE2
orB-TE2 Configurations where B-ISDN physical interfaces occur at reference points SB and TBSBc)B-NT1B-NT2+B-TE1SBB-TARd)B-NT1B-NT2+TE2
orB-TE2 NOTE Configurations where B-ISDN physical interfaces occur at reference point SB onlyB-NT2B-NT1+e)B-TETBTB-NT1BB-TARB-NT2+f)TE2
orB-TE2 Configurations where B-ISDN physical interfaces occur at reference point TB onlyB-NT2TSB-NT1BSBRh)TATE2B-TE1B-NT2TSB-NT1BTE1g)B-TE1SBConfigurations where B-ISDN and ISDN physical interfaces occur at reference points S, SB and TBB-NT1RB-TAj)TE2
orB-TE2 S
and T
coincidentBBB-NT1B-TE1i)S
and T
coincidentBBConfigurations where a single B-ISDN physical interface occurs at a location where both referencepoints SB and TB coincideEquipment implementingfunctional groupsPhysical interface at thedesignated reference pointNOTE:The need for an access to a TB-Reference point (between B-NT1 and B-NT2) is for furtherstudy.Figure 2: Examples of physical configurations for broadband user applicationsSIST ETS 300 742 E1:2003
Page 12ETS 300 742: April 1997a) centralized B-NT2 configurationB - TE1B - TE1B - TE1B - NT2B - NT1TBSBSBSBb) distributed B-NT2 configurationsb1)generic configurationWWMAMAWMA(note 1)SBSBRTE2orB - TE2B - TAB - NT1B - NT2MAB - TARTE2orB - TE2B - TE1(note 2)TBb2)physical configurationsMAB - TE1B - NT1WWTBTBMAMAB - TE1SBSBB - NT1B - TE1SBWWWWB - TE1B - TE1SBSB(note 1)MAMAMAMASIST ETS 300 742 E1:2003
Page 13ETS 300 742: April 1997c) multi-access B-TE configurationsc1)generic configurations (note 7)TBB - NT1B - NT2SBB - TE*B - TE*B - TE*SSBSSB(note 3)c2)physical configurations(note 5)(note 4)(note 6)B - NT2B - NT1SSBSSBSBTBB - TE*B - TE*B - TE*SBB - NT2B - NT1SSBSSBSBTBB - TE*B - TE*B - TE*(note 5)(note 4)SSBSSBSSBSSBSSBSSBSBSBSBB - NT2B - NT1TBB - TE*B - TE*B - TE*B - TE*B - TE*B - TE*B - TE*B - TE*B - TE*NOTE 1:MA: Medium Adapter; accommodates the specific topology of the distributed B-NT2. Theinterface at W may include topology dependant elements; it may be a non-standardizedinterface.NOTE 2:There will be a physical link between these two Medium Adapters in the case of ringconfigurations.NOTE 3:There will be a physical link between B-TE* and B-NT2 in the case of ring configurations.NOTE 4:B-TE* includes shared medium access functions.NOTE 5:The measurable physical characteristics of the SSB interface are identical to those of the SBinterface. The functional characteristics of the interface, however, may be a superset of thoseat the SB interface.NOTE 6:The B-NT2 may be null in the case of commonalty between SB and TB.NOTE 7:Additional termination functions (e.g. for loopback in bus configuration) and OAM functions maybe necessary for multi-access B-TE* configurations. Requirements and implementations ofthese functions are for further study.Figure 3: Examples of physical configurations for multipoint applicationsSIST ETS 300 742 E1:2003
Page 14ETS 300 742: April 19974.3Basic characteristics of the interfaces at TB and SB reference points for 2 048 kbit/s4.3.1Interface at TB reference pointThere is only one interface per B-NT1 at the TB reference point. The operation of the physical medium ispoint-to-point in the sense that there is only one sink (receiver) in front of one source (transmitter).Point-to-multipoint configurations at TB at the ATM and higher layers are for further study.4.3.2Interface at the SB reference pointOne or more SB interfaces per B-NT2 are present. The interface at the SB reference point is point-to-pointat the physical layer in the sense that there is only one sink (receiver) in front of one source (transmitter)and may be point to multipoint at the other layers.4.3.3Relationship between interfaces at SB and TBConfigurations described in figures 2i and 2j require that the interface specifications at TB and SB shouldhave a high degree of commonalty, in order to ensure that a simple broadband terminal may beconnected directly to the TB interface.4.4Relationship between ISDN interfacesFigures 2g and 2h show configurations where B-ISDN and ISDN interfaces may occur at SB and Srespectively. In this case B-NT2 functionalities have to ensure the interface capabilities for both S and SB.Other configurations for supporting terminals at the interface at the S reference point may exist.4.5Functional groups characteristicsLists of functions for each functional group are given below. Each particular function is not necessarilyrestricted to a single functional group. For example, "interface termination" functions are included in thefunction lists of B-NT1, B-NT2 and B-TE. The function lists for B-NT1, B-NT2, B-TE and B-TA are notexhaustive. Not all specific functions in a functional group need to be present in all implementations.4.5.1Network termination 1 for B-ISDN (B-NT1)This functional group includes functions broadly equivalent to layer 1 of the OSI reference model.Examples of B-NT1 functions are:-line transmission termination;-transmission interface handling;-OAM functions.4.5.2Network termination 2 for B-ISDN (B-NT2)This functional group includes functions broadly equivalent to layer 1 and higher layers of the ITU-TRecommendation X.200 [10] reference model. B-NT2 can be null in the case of commonalty between TBand SB.Examples of B-NT2 functions are:-adaptation functions for different media and topologies (MA functions);-functions of a distributed B-NT2;-cell delineation;-concentration;-buffering;-multiplexing/demultiplexing;-resource allocation;-usage parameter control;-adaptation layer functions for signalling (for internal traffic);-interface handling (for the TB and SB interfaces);SIST ETS 300 742 E1:2003
Page 15ETS 300 742: April 1997-OAM functions;-signalling protocol handling;-switching of internal connections.B-NT2 implementations may be concentrated or distributed. In a specific access arrangement, the B-NT2may consist only of physical connections. When present, implementations of the B-NT2 are locallypowered.4.5.3Terminal equipment for B-ISDN (B-TE)This functional group includes functions broadly belonging to layer 1 and higher layers of the ITU-TRecommendation X.200 [10] reference model.Examples of B-TE functions are:-user/user and user/machine dialogue and protocol;-interface termination and other layer 1 functions;-protocol handling for signalling;-connection handling to other equipment;-OAM functions.The possibility of powering the B-TE via the SB interface is for further study.4.5.3.1Terminal equipment type 1 for B-ISDN (B-TE1)This functional group includes functions belonging to the B-TE functional group with an interface thatcomplies with the B-ISDN SB and/or TB interface recommendations.4.5.3.2Terminal equipment type 2 for B-ISDN (B-TE2)This functional group includes functions belonging to the functional group B-TE but with a broadbandinterface that complies with interface ITU-T Recommendations other than the B-ISDN interface ITU-TRecommendations or interfaces not included in ITU-T Recommendations.4.5.4Terminal adapter for B-ISDN (B-TA)This functional group includes functions broadly belonging to layer 1 and higher layers of the ITU-TRecommendation X.200 [10] reference model that allow a TE2 or a B-TE2 terminal to be served by aB-ISDN UNI.5UNI specifications5.1Interface location with respect to reference configurationAn interface point Ia is adjacent to the B-TE or the B-NT2 on their network side; interface point Ib isadjacent to the B-NT2 and to the B-NT1 on their user sides (see figure 4).B-TEB-NT2B-NT1BSTBIabIIabIFigure 4: Reference configuration at reference points SB and TB5.2Interface location with respect to the wiring configurationThe interface points are located between the socket and the plug of the connector attached to the B-TE,B-NT2 or B-NT1. The location of the interface point is shown in figure 5.SIST ETS 300 742 E1:2003
Page 16ETS 300 742: April 1997In this ETS, the term "B-NT" is used to indicate network terminating layer 1 aspects of B-NT1 and B-NT2functional groups, and the term "TE" is used to indicate terminal terminating layer 1 aspects of B-TE1,B-TA and B-NT2 functional groups, unless otherwise indicated.connecting cordWiring at thecustomer premisesB - TEB - NTIabI(note)NOTE:The length of the connecting cord can be zero.Figure 5: Wiring configuration6Service and layering aspects of the physical layer6.1Services provided to the ATM-layerThe physical layer provides for the transparent transmission of ATM-PDUs between physical layer ServiceAccess Points (Ph-SAP). The ATM-PDU is called ATM cell. The ATM cell is defined in ITU-TRecommendation I.361 [6]. As no addressing is implemented in the physical layer only a single Ph-SAPcan exists at the boundary between physical layer and ATM layer. The inter-arrival time between cellspassed to the ATM layer is not defined (asynchronous transmission). The physical layer provides the ATMlayer with timing information.6.2Service primitives exchanged with the ATM layerThe service primitives between physical layer and ATM-layer are defined in ITU-TRecommendation I.361, section 3.2 [6].6.3Sublayering of the physical layerThe physical layer is subdivided into two sublayers:-the physical medium (PM) sublayer;-the transmission convergence (TC) sublayer.No service access point and service primitives are defined between the PM and the TC sublayers. Thefunctions of the individual sublayer are defined in ITU-T Recommendation I.321 [12].7Physical medium characteristics at the TB and SB reference point of the UNIfor 2 048 kbit/s7.1Bit rate and interface symmetryThe bit rate of the interface is 2 048 kbit/s. The interface is symmetric, i.e. it has the same bit rate in bothtransmission directions.The nominal bit rate in free running clock mode shall be 2 048 kbit/s with a tolerance of 50 parts permillion (ppm).SIST ETS 300 742 E1:2003
Page 17ETS 300 742: April 19977.2Physical characteristicsOnly electrical interfaces are recommended. The implementation selected depends on the distance to becovered and user requirements arising from the details of the installation.7.2.1Electrical interface7.2.1.1Interface rangeThe maximum range of the interface depends on the specific attenuation of the transmission mediumused (e.g. twisted pair, coaxial cable) and is for further study.7.2.1.2Transmission mediumTwo coaxial cables or two twisted pairs, one for each direction, shall be used. The wiring configurationshall be point-to-point.The impedance shall be respectively 75 W and 120 W. Further details (e.g. attenuation of the electricalpath between the interface points Ia and Ib) shall match the definitions according to ETS 300 166 [2].7.2.1.3Electrical parameters at interface points Ia and IbThe digital signal presented at the output port and the port impedance should conform to ETS 300 166 [2]for the interface at 2 048 Mbit/s.The digital signal presented at the input port and the port impedance should conform to ETS 300 166 [2]for the interface at 2 048 Mbit/s modified by the characteristics of the interconnecting coaxial pair ortwisted pair.7.2.1.4Electrical connectorsThe presentation of interface point Ib at B-NT1 or B-NT2 shall be via a socket.The presentation of interface point Ia at B-TE or B-NT2 shall be using either:a)a socket, i.e. the connection shall be made to the equipment toward the network with a cable withplugs on both ends; orb)an integral connecting cord with plug on the free end (see figure 6: Connector types).socketsocketplugPre
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