Download

104 CHANNEL-ASSOCIATED INTEREXCHANGE SIGNALINGselected a R2 outgoing trunk. They indicate the next signal to be sent by the originatingISC.A-3 and A-6 indicate that the complete called number has been received. A-6ends the register signaling, and A-3 requests the calling party category, whichwill be acknowledged by a group B signal.A-4 and A-15 indicate that the call cannot be set up and are requests to the outgoingISC to release the connection.Group B Signals. These signals convey information on the nature and status ofthe called subscriber. These signals can be sent only by an ISC that receives thisinformation from a terminating local exchange in its national network.4.4.8 International R2 Interregister Signaling ExampleWe consider the international call shown in Fig. 4.4-6. The call is routed via transitcountry B. Trunks T 1 and T 2 have R2 signaling. Even if the national networks incountries A and C use R2 signaling, there are three signaling sections in the connection.This is necessary because local exchanges (e.g., X) are not equipped to handleinternational signaling procedures, and because some national R2 register signalsare not identical to the R2 register signals. If the networks of countries A and Cuse R2 signaling, end-to-end signaling is possible in signaling section 1 (betweenlocal exchange X and ISC-P), in section 2 (between ISC-P and ISC-R), and insection 3 (between ISC-R and the terminating local exchange Z).The signaling in the international network is shown in Fig. 4.4-7 (see Tables 4.4-4and 4.4-5). The called international number is 34-67-412-1093, where 34 is thecountry code of C, and 67-412-1093 is the national number of S 2 .Outgoing ISC-P seizes trunk T 1 to ISC-Q and starts by sending country code indicatorO-12, indicating a “transit” seizure (the call destination is not in country B).ISC-Q acknowledges with A-1, requesting the first digit of the called internationalnumber. We assume that ISC-R is the only ISC in country C. Therefore, ISC-Qcan make a route decision after receipt of the country code CC (34). In thisexample, it seizes a direct trunk T 2 to ISC-R. Since this ISC is in the destinationcountry, it should receive a terminal seizure signal, followed by the called nationalFigure 4.4-6. International connection. International R2 signaling on T 1 and T 2 .