SAPI) 3 {{MTid origSetup},servld SERVid,destSAPISAPI) {{MTid setupAck}, bChannel Bid} 5 useOrd(servid, bChannel) 6 serviceCsCnf(TE-SAP) Network 7 serviceCnf(TE-SAP) Process Control 8 sendInfoOrder(SIU) TE-TPC System receivelnfoRepCnf(SIU) {{MTid data}, userData} ATN, SAPI 0 Request Confirm TE-UDT TE-UDT Order RepCnf ReportConfirm {64 kbps} SERVid teleservice identity address to the other terminal system the selected B-channel identity service information unit userData SIU fragment Fig. 3.30 An originating service establishment scenario for a circuit-switched teleservice 3 Logical Network Modelling The depicted terminal system initiates the procedure. The procedure is described as a numbered sequence of events. Note that this description is a simplified one, and that the actual implementation for different network concepts might vary somewhat. 1. The TEU requests a service from the TEC and refers a destination SAP. Note that, from the TE-CSP point of view, it does not matter if the TEU and TEC are integrated in a single unit, in which case we would not define events 1 and 2. The TEC requests the service from the terminal process controller (TE-TPC), providing the SAPI value and the service identifier. 3. The TCP sends an origSetup message to the operator network, in which it pro- vides the SAPI value and the SERVid value. The message type identifier (MTid) tells the network that this message is origSetup. 4. The operator network sets up the necessary resources (of the network resource system) across the whole network to the destination SAPI (destSAPI), and responds with a setupAck message when it is ready. This message also informs the TE-TPC which of the two B-channels (bChannel) must be used. 5. The TE-TPC orders the CNU to instantiate a TE--UDT that can handle the tele- service and to use it over the particular B-channel. 6. The TE-TPC responds to the TEC with some local identifier for the actual TE- 7. The TEC connects the TEU to the TE-SAP and informs the TEU that it can start using the teleservice. 8. The TE