TAILIEUCHUNG - Signaling System No.7 Protocol Architecture And Sevices part 23

Detailed Call Walk-Through Earlier in this chapter, we presented an ISUP message flow in order to illustrate the exchange of messages to establish and release an ISUP call. Now that we have discussed more of the ISUP details, we will build on that illustration. | Detailed Call Walk-Through Earlier in this chapter we presented an ISUP message flow in order to illustrate the exchange of messages to establish and release an ISUP call. Now that we have discussed more of the ISUP details we will build on that illustration. This section provides more detail about the call processing that was driven by the ISUP message events used in the earlier example. Although this chapter s primary focus is the ISUP protocol it is important to understand how ISUP is applied in its normal domain of trunk call processing. Call Setup Refer back to Figure 8-3 where a call originates from a line at SSP A and terminates to a line at SSP B over an interexchange ISUP trunk. When call processing has completed translations of the called number at SSP A the translations results indicates that the call requires routing to an interexchange trunk group. The provisioned signaling type for the selected trunk group determines whether ISUP signaling or some other signaling such as Multifrequency MF is used. When the signaling type is determined to be ISUP the trunk circuit to be used for the outgoing call is reserved for use. The SSP populates the IAM with information about the call setup such as the CIC CdPN Call Type CgPN and PCM Encoding scheme. The IAM information is placed in the User Data field of the MTP3 SIF. The MTP3 information is populated based on the SS7 network information that is associated with the selected trunk group. As previously noted each switching exchange contains a provisioned association usually static between routesets and trunkgroups. The IAM is then transmitted onto a signaling link toward the destination identified in the message by the DPC. If quasi-associated signaling is used the message s nexthop node is an STP that will route the message to the intended SSP. If associated signaling is used the IAM is transmitted directly to the SSP that is associated with the trunk being set up. SSP A starts timer T7 which is known as the .

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