PC sends a setup-request for a VC connection. This message is now sent on vc53 in vpi0. The request contains the destinationSAPI and some service parameters, primarily the capacity that is wanted on the VC connection. If the DNCP can accept the request, it responds with an accept message to the initiat- ing TPC on the same channel. 4. The access router then performs routing analysis and route management as usual. The result is, in this scenario, that the routing analyser suggests link L2, and the routing manager selects the idle vci13 on vpi6 in that link. The DNCP then requests from the other ATM router on L2 to setup the VC connection to the other ATMU. This request is sent on the dedicated channel vci1 in vpi0 on link L2. 5. Sooner or later, the initiating DNCP gets a response (setupAck) saying that the VC connection is set up to the other ATMU. The DNCP then orders its switch controller to connect L1/vpi2/vci124 to L2/vpi6/vci13. 6. Finally, the DNCP confirms the setup to the initiating TPC by telling it which VPI and VCI (here vci1124 on vpi2) to use for communication with the remote 3.4 Modelling Telecom Resource Systems ATMU. This response is the last thing that happens on vci53 on vpi0, i.e. the access router can then use this channel for new calls. Service ATM-DNCP Service Access (VC control) Distribution Protocol Protocol (ITU-T Q.2931) (B-ISUP) Switch Route Routing controll. Manager Analyser vpi0/vci5 Internal vpi0/vci53 vpi0/vci5 vpi0/vci1 vpi0{...} vpi0{vci5,vci53} vpi0/vci2 vpi2{vci124} vpi0/vci53 vpi0/vci2 vpi0{vci2} vpi2/vci124. vpi6{vci13} vpi6/vci13 vpi0/vci1 vpi0{vci1} ATM switch ATMU ATM-TPC ATM-DNCP ATM-DNCP ATM-TPC ATMU on link L2 Q.2931 B-ISUP Q.2931 service request (on vpi0/vci5) use vpi0/vci53 (on vpi0/vci5) setup(SAPI) (on vpi0/vci53) accept (on vpi0/vci53) setup (vpi6/vci13) (on vpi/vci1) setupAck (on vpi0/vci1) Switch Controller L1/vpi2/vc124 L2/vpi6/vci13 use (vpi2/vci124) (on vpi0/vci53) ATM switch ATM switch (on vpi2/vci124) (on vpi6/vci13) Fig. 3.70 A scenario for creating a VC con