Configuring the 4300T
•Call processing server connectivity status indicators
•Support for multiple call processing servers using DNS
•Reporting of the currently active call processing server in environments using multiple call processing servers
•Local call switching between VoIP endpoints and premises based PSTN gateways during WAN link failures or other failures that prevent connectivity to network based call processing servers
•Calling features such as transfer, hold and conference are provided by V2IU Series appliances
•Simplified setup that creates a local dial plan in the V2IU appliance by monitoring traffic to network based call processing servers
How survivability works
The V2IU appliance automatically creates a local dialing plan by monitoring the registration requests sent by LAN based SIP user agents as they register with the network based call processing server. In creating this dial plan the V2IU appliance now has knowledge of all local SIP user agents installed on its LAN interface. This dial plan will be used during fallback mode of operation when the V2IU appliance provides local call switching between user agents and/or a LAN side PSTN gateway.
V2IU appliances continuously monitor the status of connectivity to network based call processing servers using application layer heartbeat messages. Configuration settings in V2IU appliances control how often messages are sent to the call processing server and how quickly the server will be declared unreachable in the event of a failure. The use of application layer messages provides the added benefit of detecting the failure condition where an V2IU appliance has IP connectivity to the call processing server but the call processing server software itself is not functioning properly.
Once a call processing server has been declared unreachable V2IU appliances enter fallback mode and perform call processing for local SIP user agents. A SIP PSTN gateway can also be installed at the branch office on the LAN side of the V2IU appliance and used for inbound and outbound calling during fallback mode. To maximize utilization of this gateway it can also be used when call switching is being performed by the network based call processing server.
Once connectivity to the network based call processing server is restored the V2IU appliance will automatically turn control of all subsequent call requests over to the softswitch. Calls in progress that were established while the V2IU appliance was in fallback mode will not be disrupted when connectivity is restored to the network based call processing server.
Redundant or multiple call processing servers can be used in conjunction with V2IU Series appliances to further enhance the availability of voice services. V2IU appliances will use DNS SRV records from a DNS server to obtain a
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