network protocols handbook.pdf

307Protocols GuideSS7 / C7 ProtocolProtocol NameDUP: Data User PartProtocol DescriptionData User Part (DUP), an application protocol in the SS7/C7protocol suite, defines the necessary call control and facility registrationand cancellation related elements for circuit-switcheddata transmission services. The data signalling messages aredivided into two categories:• Call and circuit related messages: used to set up andclear a call or control and supervise the circuit state.• Facility registration and cancellation related messages:used to exchange information between originating and destinationexchanges to register and cancel information related to userfacilities.While Data User Part (DUP) is still in use currently, but it is fallenout of favor except in certain parts of the world such as China.Protocol StructureThe pouting label of DUP contains the DPS, OPC, BIC and TSCfields. It is contained in a signalling message and used to identifyparticulars to which the message refers. This is also useby the message transfer part to route the message towards itsdestination point.The general format of the header of call and circuit related messagesis shown as follows:TSC - Time slot code (8 bits). If the data circuit is derived fromthe data multiplex carried by the bearer, identified by the beareridentification code:Heading code - The heading code (4 bits) contains the messagetype code which is mandatory for all messages. It uniquely definesthe function and format of each DAP message.Message specific parameters - Contains specific fields for eachmessage.Spare bits - Not used, should be set to “0000”.Related protocolsSS7, ASP, BICC, BISUP, ISUP, MTP, SCCP, TCAP, TUP, MAPSponsor SourceDUP is defined by ITU-T Q.741 (or X.61).Referencehttp://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-Q.741: SS7 Data User PartOPC DPSBICOPCTCSBICMessage specific parametersHeading CodeThe general format of the header of facility registration and cancellationmessages is shown as follows:OPC DPSSpare bitsOPCMessage specific parametersHeading codeOPC - The originating point code (14bits) is the code applicableto the data switching exchange from which the message issent.DPS - The destination point code (14bits) is the code applicableto the data switching exchange to which the message is to bedelivered.BIC - Bearer identification code (12 bits).