Pstn Fallback - AudioCodes Mediant 800B User Manual

device does not try to redirect the call to the next contact and drops the call.

The device tries each contact sequentially, listed in the Contact headers. If a SIP 6xx
Global Failure response is received during this process (e.g., 600 Busy Everywhere),
the device does not try to redirect the call to the next contact and drops the call.

The device redirects the call to the first contact listed in the Contact header. If the
contact responds with a SIP response that is configured in the Reasons for Tel-to-IP
Alternative Routing table (see 'Alternative Routing Based on SIP Responses' on page
544), the device tries to redirect the call to the next contact, and so on. If a contact
responds with a response that is not configured in the table, the device does not try to
redirect the call to the next contact and drops the call.

To configure handling of SIP 3xx responses with multiple contacts:
1. Open the Gateway Advanced Settings page (Setup menu > Signaling & Media tab >
Gateway folder > Gateway Advanced Settings).
2. From the '3xx Use Alt Route Reasons' drop-down list, select the required handling.
Figure 24-10: Enabling Alternative Routing for SIP 3xx with Multiple Contacts
3. Click Apply.
Note: If a SIP 401 or 407 response is received from a contact, the device does not
try to redirect the call to the next contact. Instead, the device continues with the
regular authentication process, as indicated by these response types.

24.4.5 PSTN Fallback

The PSTN Fallback feature enables the device to re-route a Tel-to-IP call to the legacy
PSTN using one of its trunks if the IP destination is unavailable. For example, if poor voice
quality is detected over the IP network, the device attempts to re-route the call to the
PSTN.
The following procedure describes how to configure alternative Tel-to-IP routing to the
PSTN.

To configure alternative Tel-to-IP routing to the PSTN:
1. In the Tel-to-IP Routing table (see 'Configuring Tel-to-IP Routing Rules' on page 525),
configure an alternative routing rule with the same call matching characteristics (e.g.,
phone number destination) as the "main" routing rule, but where the destination is the
IP address of the device itself.
2. In the IP-to-Tel Routing table (see 'Configuring IP-to-Tel Routing Rules' on page 534),
configure an IP-to-Tel routing rule to route calls received from the device (i.e., its IP
address) to a specific Trunk Group connected to the PSTN. This configuration is
necessary as the re-routed call is now considered an IP-to-Tel call.
Note: The PSTN Fallback feature is applicable only to digital interfaces.
User's Manual
Mediant 800B Gateway & E-SBC
548 Document #: LTRT-10632