The following is a step-by-step description of a typical call.
An originating node user goes off hook and dials a terminating node user. The user can dial whatever number of digits are required to reach the terminating user. The originating call may be routed using Uniform Dial Plan (UDP), Automatic Route Selection (ARS), Automatic Alternate Routing (AAR), or a combination of these steering mechanisms.
Note:
The call might first route over a non-SBS trunk to an SBS Interworking Node that then routes the call to an SBS trunk. In this case, the SBS Interworking Node, not the originating Node, serves as the SBS Originating Node for this call.
Whichever routing mechanism is invoked (UDP/ARS/AAR), the call eventually routes to an H.323 IP trunk group. The call is translated to use QSIG signaling and specified in administration as an SBS trunk group with an SBS signaling group. The QSIG and SBS signaling group identification is the signaling portion of the call. This signaling portion is active for the duration of the call. A translation field identifies the SBS trunk group as reserved for SBS use. The signaling group associated with the SBS trunk group also has specific SBS translation. Apart from these fields, the SBS trunk group and signaling group are translated as a standard IP trunk group with standard QSIG signaling.
The SBS Terminating Node receives the signaling call. The SBS Terminating Node knows the call is an SBS call because it arrives on an SBS trunk group. The SBS Terminating Node determines that the called party in the signaling call SETUP message routes to a local extension or a non-SBS trunk. However, the Terminating Node temporarily refrains from terminating the call. Instead, the SBS Terminating Node allocates an SBS Extension to use for the duration of call setup. SBS Extension is a new type of Administered Without Hardware (AWOH) extension that is administered at all nodes that terminate SBS calls.
The SBS Terminating Node checks the isdn public/unknown numbering table. Upon finding a match for the SBS Extension, the SBS Terminating Node maps the number to a national (public network) Complete Number, including area/city code if applicable. The SBS Terminating Node also determines the local Country Code from the Feature Related System Parameters screen and adds it to the number created from the ISDN Numbering-Public/Unknown screen. The resulting number includes Country Code/Area/City/SBS Extension.
The SBS Terminating Node then sends the Complete Number to the SBS Originating Node on the SBS Signaling call. This is the number that the SBS Originating Node uses to route the bearer call.
The SBS Originating Node receives the Complete Number. The SBS Originating Node compares the Country Code received to the Country Code that the SBS Originating Node is located in. If the Country Codes are the same, the SBS Originating Node deletes the Country Code from the received number. If the Country Codes are different, the SBS Originating Node adds its SBS International Access Code (from the Feature Related System Parameters screen) to the received number.
The SBS Originating Node uses ARS to route on the Complete Number, which may have been modified. The Origination Node then initiates the SBS bearer call to the routed-to bearer trunk.
The SBS Originating Node associates the signaling and bearer calls internally.
The bearer call arrives at the SBS Terminating Node. The SBS Terminating Node determines that the call is for an SBS Extension and immediately answers the call.
The SBS Terminating Node then sends a message to the SBS Originating Node on the signaling call that contains a unique three digit ID. This ID is created by the SBS Terminating Node from the internal call identification. This unique ID is reserved for the duration of the call. The SBS Terminating Node uses this unique ID to determine which bearer call is associated with the SBS signaling call in the event of multiple simultaneous calls to the SBS extension at the SBS Terminating Node. Examples of multiple simultaneous calls to the SBS extension include misdirected PSTN calls, telemarketing calls, and so on
The SBS Originating Node then sends the unique ID through DTMF tones, on the bearer call, towards the SBS Terminating Node. The originating user does not hear the DTMF tones.
After receiving the unique ID, the SBS Terminating Node associates the proper bearer and signaling calls. The SBS Terminating Node completes the call to the original destination (local extension or non-SBS trunk).
The SBS Terminating Node releases the SBS Extension.
When the called party is ringing, the SBS Terminating Node sends an ALERTING message to the SBS Originating node on the SBS signaling call.
When the called party answers, the SBS Terminating Node sends a CONNECT message to the SBS Originating Node on the SBS signaling call.
When either the calling party at the originating node or the called party at the terminating node disconnects the call, both, the bearer and the signaling, calls become inactive.
