1、Standard ECMA-277June 1998Standardizing Information and Communication SystemsPhone: +41 22 849.60.00 - Fax: +41 22 849.60.01 - URL: http:/www.ecma.ch - Internet: helpdeskecma.chPrivate Integrated Services Network(PISN) -Circuit Emulation Specification -Emulation of Basic Access by ATMNetworks.Standa
2、rd ECMA-277June 1998Standardizing Information and Communication SystemsPhone: +41 22 849.60.00 - Fax: +41 22 849.60.01 - URL: http:/www.ecma.ch - Internet: helpdeskecma.chIW Ecma-277.doc 09-07-98 11,38Private Integrated Services Network(PISN) -Circuit Emulation Specification -Emulation of Basic Acce
3、ss by ATMNetworks.Brief HistoryThis Standard is one of a series of ECMA Standards defining services and signalling protocols applicable to Private IntegratedServices Networks (PISNs). The series uses ISDN concepts as developed by ITU-T and the ATM Forum and is also within theframework of Internation
4、al Standards for Open Systems Interconnection as defined by ISO/IEC.This particular Standard specifies the circuit emulation functions for the emulation of a basic access over ATM. This Standardspecifies the static mapping of basic access information to ATM cells. Future enhancements may specify dyn
5、amic mappingfunctions.The need for circuit emulation within ATM reflects a user demand for carrying certain types of constant bit rate (CBR) or“circuit” traffic over ATM networks. For the support of such types of traffic, ATM networks shall emulate circuitcharacteristics in order to provide good sup
6、port for CBR traffic. A critical attribute of a circuit emulation service (CES) is thatthe performance realised over ATM should be comparable to that experienced with the current PDH/SDH technology.Initial work on circuit emulation has been carried out by the ATM Forum subworking group VTOA leading
7、to an approvedinteroperability specification, called CES-IS V2.0 (af-vtoa-0078.000). The CES-IS covers the following types of interfaces:1. Structure DS1/E1 Nx64 kbit/s (Fractional DS1/E1) Service2. Unstructured DS1/E1 (1.544 Mbit/s, 2.048 Mbit/s) Service3. Unstructured DS3/E3 (44.736 Mbit/s, 34.368
8、 Mbit/s) Service4. Structured J2 Nx64 kbit/s (Fractional J2) Service5. Unstructured J2 (6.312 Mbit/s) ServiceThe structured Nx64 and the unstructured DS1/E1/J2 services described in CES-IS V2.0 offer ways to connect DS1/E1/J2equipment across emulated circuits carried on an ATM network.Complementing
9、the work of the ATM Forum, this Standard provides for a circuit emulation service also for the N-ISDN basicaccess, allowing to connect such an access via an ATM connection to a PINX. This Standard therefore follows the basicprinciples and the structure of the CES-IS of the ATM Forum.In the same way
10、as the CES-IS, it specifies static mapping functions performed by a CES-interworking function (IWF) betweena basic access and an ATM connection, and the corresponding re-mapping between the ATM connection, and the link to thePINX.This Standard is based upon the practical experience of ECMA member co
11、mpanies and the results of their active andcontinuous participation in the work of ISO/IEC JTC1, ITU-T, ETSI and other international and national standardisationbodies. It is also closely related to the Circuit Emulation Service Specification, Version 2, of the ATM Forum (af-vtoa-0078.000). It repre
12、sents a pragmatic and widely based consensus.This Standard has been adopted by the ECMA General Assembly of June 1998.- i -Table of contents1 Scope 12 Conformance 13 References 14 Definitions 14.1 External definitions 14.2 Special definitions 25 List of acronyms 26 Reference configuration 27 Mapping
13、 functions 37.1 The mapping scheme 37.2 Functions of the CV1 channel 47.3 Mapping of a 4-octet-block structure into ATM cells 48 ATM virtual channel requirements for basic access emulation 48.1 ATM Peak Cell Rate (PCR) 48.2 Broadband Bearer Capability 48.3 ATM Adaptation Layer Parameters 58.4 ATM Si
14、gnalling / Call Establishment Procedures 5Annex A - Contents and functions of the CV1 channel 7Annex B - Protocol Implementation Conformance Statement (PICS) Proforma 9Annex C - The Monitor Channel Procedure 13- ii -.1ScopeThis Standard specifies the functions for the emulation of a basic access ove
15、r ATM, thus providing anefficient way to connect existing N-ISDN terminal equipment to a PINX over a digital ATM section. Such anATM connection can be either a (semi-)permanent connection, but might also be a switched virtualconnection as defined in related ATM Forum specifications.The objective of
16、this Standard therefore is to specify a mapping scheme for the three types of basic accessinformation (two B channels: the B1 and B2 channels, the D channel as well as maintenance/control/statusinformation) into ATM cells. Part of the maintenance/control/status information has to be terminated by an
17、IWU and has to be substituted by other information applicable at the ATM connection. A referenceconfiguration lays down that the point of emulation has to be placed at the network side of an extension line.This Standard specifies the static mapping of basic access information to ATM cells.This Stand
18、ard complements the work of the ATM Forum on circuit emulation services for higher bandwidth.This Standard applies for private networks, however, it is also suitable for public networks.2 ConformanceIn order to conform to this Standard, a circuit emulation functional unit shall satisfy the requireme
19、ntsidentified in the Protocol Implementation Conformance Statement (PICS) proforma in annex A.3 ReferencesThe following publications contain provisions which, through reference in this text, constitute provisions ofthis Standard. All publications are subject to revision, and parties to agreements ba
20、sed on this Standard areencouraged to investigate the possibility of applying the most recent editions of the publications indicatedbelow.AF UNI 4.0 ATM User-Network Interface (UNI) - Signalling specification (version 4.0)AF CES-IS V2.0 ATM Forum circuit emulation service interoperability specificat
21、ion, vs. 2.0 (af-vtoa-0078)ISO/IEC 11579-1 Information technology - Telecommunications and information exchange between systems- Private Integrated Services Network - Part 1: Reference configuration for PISNExchanges (PINX) (1994)ISO/IEC 11579-3 Information technology - Telecommunications and inform
22、ation exchange between systems- Private Integrated Services Network - Part 3: Reference configuration for extensionlinesITU-T G.960 Access digital section for ISDN basic rate access (1993)ITU-T I.363.1 B-ISDN ATM Adaptation Layer specification: Type 1 AAL (1996)ITU-T I.412 ISDN user-network interfac
23、es Interface structures and access capabilities (1988)ITU-T I.430 Basic user-network interface Layer 1 specification (1995)ITU-T Q.512 Digital exchange interfaces for subscriber access (1995)4 DefinitionsFor the purpose of this Standard the following definitions apply.4.1 External definitionsThis St
24、andard uses the following terms defined in other documents:G01 Integrated Services Digital Network CCITT Rec. I.112G01 Private Integrated Services Network (PISN) ISO/IEC 11579-1- 2 -G01 Private Integrated Services Network Exchange (PINX) ISO/IEC 11579-1G01 Extension line ISO/IEC 11579-34.2 Special d
25、efinitionsG01 Data Upstream (DU): Transmission of data from the CES-IWF to the PINX.G01 Data Downstream (DD): Transmission of data from the PINX to the CES-IWF.5 List of acronymsAAL ATM Adaptation LayerAI Activation IndicationAR Activation RequestARL Activation Request with local loopATM Asynchronou
26、s Transfer ModeCBR Constant Bit RateCES Circuit Emulation ServiceCLP Cell Loss PriorityDC Deactivate ConfirmationDD Data DownstreamDI Deactivation IndicationDR Deactivate RequestDU Data UpstreamISDN Integrated Services Digital NetworkIWF Interworking FunctionIWU Interworking UnitPCR Peak Cell RatePE
27、T Private network Exchange TerminationPICS Protocol Implementation Conformance StatementPINX Private Integrated Services Network ExchangePISN Private Integrated Services NetworkPTS Private Termination System functional groupingRES RESetRSY ReSYnchronisationSDT Structured Data TransferSW SWitching fu
28、nctional groupingTE Terminal equipmentTIM Timing requiredTM Test ModeUAI U only Activation IndicationUAR U Activation RequestVTOA Voice and telephony over ATM6 Reference configurationFigure 1 shows how a basic access circuit emulation by means of an ATM digital section corresponds to thereference co
29、nfiguration for PINX extension lines. As part of the PTS, the circuit emulation function residesat the PINX side of the extension line. A private exchange termination (PET) connects to an ATMinterworking function 1 (ATM IWF 1) which performs the mapping of the basic access circuit mode channelsto an
30、 ATM CBR channel. At the other end of the ATM digital section, a further ATM interworking function(ATM IWF 2) re-maps the ATM CBR to a PINX basic access. The two ATM IWFs insert the CBR linkbetween the TE and the PINX. Signalling and user information sent by either the TE or the PINX aretransported
31、transparently through the intermediate ATM network. The circuit emulation function cares for bitintegrity of both types of information.- 3 -TE SWSPTSTESWSTESWSIWF2IWF1P1ATMP1PETDigital SectionTcvr 2Tcvr 5TCF 1P2TCF 2TCF 5Tcvr 3TCF 3PNTTcvr 1Tcvr 4TCF 4PLTP3P4P5Figure1 - Basic Access Circuit Emulatio
32、n as part of the PTSFigure 2 shows an example how basic access in case of multiple N-TEs is supported by two virtual ATMchannels.N-TEN-TE IWF2IWF2IWF1IWF1Basic access / S0ATM linksTwo virtual ATM channels,carrying 256 kbit/s eachexample of two instances of an IWF(each providing the counterpart toa b
33、asic access IWF)PINXFigure 2 - Basic Access over ATM in case of multiple N-TEs7 Mapping functionsIn order to transfer signalling and user information to / from a basic access, this information and the relatedOAM information shall be mapped into ATM cells. This shall be carried out in two steps. In t
34、he first step amapping scheme shall provide for the mapping of the basic access structured bit stream into a fixed structureof 4 octets/32 Bits. In a second step shall provide for the mapping of such 4 octet / 32 Bit strings into ATMcells.The OAM and physical layer related information and the relate
35、d functions are outlined in annex A. They arereferred to as “CV1”.7.1 The mapping schemeThe mapping scheme for the basic access bit stream consisting of two B channels, a D channel and controldata into a 4-octet block structure shall be as outlined in figure 3. The bit stream from a terminal ismappe
36、d into such a block by IWF2, and is remapped by the remote IWF1 before being transferred to thePINX, and vice versa.- 4 -8 . . . . . . . . . . 1 8 . . . . . . . . . .1 8 . . . . . . . . .1 8 . . . . . . . . . 1 (bit)DCV1 Spare B1 B21 2 3 4 (octet)Figure 3 - The mapping scheme for basic access inform
37、ationOctets 1 through 4 shall carry the following bit streams:Octet 1: Bits 8,7: D-channel informationOctet 1, Bits 6-1: CV1 information (see ITU-T G.960, and clause 7.3)Octet 2: the content and use are outside the scope of this Standard (Note);Octet 3: B1 channelOctet 4: B2 channelNOTEOctet 2 can b
38、e used as a monitoring channel, as in public network applications.7.2 Functions of the CV1 channelThe functions of the CV1 channel includeG03 transfer of commands, status report information and defect conditions for each direction oftransmission, as specified in annex A;G03 controlling the initializ
39、ation and transfer of data in octet 2, which can optionally be used as amonitoring channel. The procedures for this are specified in annex C.7.3 Mapping of a 4-octet-block structure into ATM cellsThe 4-octet block structure shall be mapped onto ATM cells using AAL type 1 (AAL-1) as specified inITU-T
40、 Rec. I.363.1. Within AAL-1, the SDT (structured data transfer) pointer, as specified in ITU-T Rec.I.363.1, shall be used.AAL-1 with the SDT pointer leaves either 46 or 47 octets for it payload which is filled with the 4 octetblocks beginning with octet 1. All octets of the AAL-1 payload shall be fi
41、lled completely, thus allowing a4-octet-block to be spread across two consecutive ATM cells, e.g. the two first octets at can appear at theend of one ATM cell, whereas the two last octets (B1, B2) will then appear in the following ATM cell,immediately starting after the AAL 1 / SDT header octet(s).8
42、 ATM virtual channel requirements for basic access emulationTo support basic access emulation, ATM virtual channels shall be configured as specified in the followingsubclauses.NOTEIf PVCs are used, the corresponding information will be set by management means.8.1 ATM Peak Cell Rate (PCR)The PCR on C
43、LP=0+1 required for AAL-1 transport of 256 kbit/s user data is 683 cells per second.If the OAM traffic is to be included in the PCR per UNI 4.0, the OAM traffic parameter cells needs to beadded to the above or specified separately.8.2 Broadband Bearer CapabilityTable 1 specifies the values for the f
44、ields in this information element.- 5 -Table 1 - Broadband Bearer Capability IE Field Values for CES SVCsField ValueBearer Class 1000 0 BCOB-XTraffic Type 001 Constant bit rateTiming Requirements 01 End-to-end timing requiredSusceptibility to clipping 00 Not susceptible to clippingUser Plane Connect
45、ion Configuration 00 Point-to-point8.3 ATM Adaptation Layer ParametersTable 2 specifies the field values for the Nx64 structured circuit emulation service, If the called party doesnot accept these parameters, it shall release the call in accordance with UNI 4.0.Table 2 - AAL Parameters IE Field Valu
46、es for Nx64 structured Circuit Emulation Service SVCsField ValueAAL Type 0000 0001 AAL Type 1Subtype 0000 0010 Circuit TransportCBR rate 0100 0000 Nx64 kbit/s, N1Multiplier 4Structured Data Transfer Blocksize 4Partially filled cells method Partially filled cells method is not used8.4 ATM Signalling
47、/ Call Establishment ProceduresThe procedures for establishing the ATM connection between CES-IWF1 and CES-IWF2 are independentof the circuit emulation functions specified in this Standard and are out of its scope.- 6 - 7 -Annex A(normative)Contents and functions of the CV1 channelThe CV1 control ch
48、annel facilitates the transfer of commands, status report information and defect conditions foreach direction of transmission.A.1 Bit structure of the CV1 channelThe CV1 information is contained in octet 1, Bits 6 to 1 of the 4-octet structure defined in subclause 7.1above. Its content is coded as i
49、ndicated in figure A.1:Figure A.1 - Bit structure of the CV1 channelTable A.1 shows the A Bit (Bit 2) and E Bit (Bit 1).If the option to use octet 2 as a monitoring channel is not supported, the A and E bits shall be permanentlyset to binary ONE (Inactive state).If the option is supported, the transitions of the A and E bit from active to inactive states as well as thepersistence in a particular state shall be used as specified in annex C.Table A.1 - Bit A and Bit B valuesBit 2 Bit A Bit 1 Bit E0 Active (A) 0 Active (E)1 Inactive (A )1 Inactive (E )A.
