Optimized Call Routing and PSTN Backup

There are two ways to save costs for PSTN calls in a multisite deployment:

• Toll bypass: Calls between sites within an organization that use the IP WAN
instead of the PSTN. The PSTN is used for intersite calls only if calls over the IP WAN are not possible—either because of a WAN failure or because the call is not admitted by Call Admission Control (CAC).

• Tail-end hop-off (TEHO): Extends the concept of toll bypass by also using the IP WAN for calls to the remote destinations in the PSTN. With TEHO, the IP WAN is used as much as possible, and PSTN breakout occurs at the gateway that is located closest to the dialed PSTN destination. Local PSTN breakout is used as a backup in case of IP WAN or CAC.