Chapter 43 VoIP trunk gateways 373Networking Configuration Guide4 System B recognizes the code as its own, and uses a local target line to route the call to thecorrect telephone.Fallback to PSTN from VoIP trunksFallback is a feature that allows a call to progress when a VoIP trunk is unavailable or is notproviding adequate quality of service (QoS).Refer to the information under “Describing a fallback network” on page 374 for details aboutsetting up fallback for VoIP trunks.By enabling Fallback to circuit-switched, also known as PSTN fallback, on the H323 Settings orSIP Settings panels, you allow the system to check the availability of a VoIP trunk, then switch thecall to a PSTN line, if the VoIP trunk is not available. For the PSTN fallback to work on a suitablebandwidth, QoS monitor must be enabled and a transmit threshold must be set. For QoS andtransmit threshold settings refer to Table 81.You use scheduling and destination codes to allow the call to switch from H.323 or SIP to a PSTNline without requiring intervention by the user.Use the dialing plan worksheet in the Programming Records to plan your dialing requirements soyou can pinpoint any dialing issues before you start programming. If you are programming anexisting system, you can look at what numbers the users are familiar with dialing, and you canattempt to accommodate this familiarity into your destination codes plan.OttawaDialout:2244Gateway: 3dedicated VoIP trunk private networkDN 2244Target line XXX recognizes 2244DN 2244 assigned with target line XXX
