TPO Hot backup can be  achieved through virtual IP addresses mechanism.

This approach has two majors limitations:

•Moving a virtual IP address from one TPO to another require to send ARP gratuitous request over the network.

•TPO cluster must remain in the same subnet. That means that the only possibility to have a geographically distributed TPO cluster is done by using VPLS configuration which is not in place in many cases.

With DNS Mode, client devices which connects to a TPO Group firstly resolves its name, then send messages to the obtained IP Address.

Redundancy use cases and requirements are identical to what is happening with Virtual IP mode, the turret should not figure out that a TPO has moved, neither the PBX should figure out that.

The time required for a TPO fail-over will be almost identical to what is possible in Virtual IP mode.