Pstn Fallback As A Special Case Of Alternative Routing; Relevant Parameters; Mapping Pstn Release Cause To Sip Response - AudioCodes Mediant 1000 User Manual

SIP User's Manual
7.7.3

PSTN Fallback as a Special Case of Alternative Routing

The PSTN Fallback feature enables the gateway to redirect PSTN originated calls back to
the legacy PSTN network if a destination IP route is unsuitable (disallowed) for voice traffic
at a specific time.
To enable PSTN fallback, assign the IP address of the gateway as an alternative route to
the desired prefixes. Note that calls (now referred to as IP-to-Tel calls) can be re-routed to
a specific trunk group using the Routing parameters (refer to 'IP to Trunk Group Routing'
on page 138).
7.7.4

Relevant Parameters

The following parameters (described in 'General Parameters' on page 132) are used to
configure the Alternative Routing mechanism:
AltRoutingTel2IPEnable
AltRoutingTel2IPMode
IPConnQoSMaxAllowedPL
IPConnQoSMaxAllowedDelay
7.8

Mapping PSTN Release Cause to SIP Response

The Mediant 1000 FXO module is used to interoperate between the SIP network and the
PSTN/PBX. This interoperability includes the mapping of PSTN/PBX Call Progress Tones
to SIP 4xx or 5xx responses for IP Tel calls. The converse is also true: For Tel IP calls,
the SIP 4xx or 5xx responses are mapped to tones played to the PSTN/PBX.
When establishing an IP Tel call, the following rules are applied:
If the remote party (PSTN/PBX) is busy and the FXO gateway detects a Busy tone, it
sends 486 Busy to IP. If it detects a Reorder tone, it sends 404 Not Found (no route to
destination) to IP. In both cases the call is released. Note that if
DisconnectOnBusyTone is set to 0, the FXO gateway ignores the detection of
Busy/Reorder tones and doesn't release the call.
For all other FXS/FXO release types (caused when there are no free channels in the
specific trunk group, or when an appropriate rule for routing the call to a trunk group
doesn't exist, or if the phone number isn't found), the gateway sends a SIP response
(to IP) according to the parameter DefaultReleaseCause. This parameter defines
Q.931 release causes. Its default value is '3', which is mapped to the SIP 404
response. By changing its value to '34', the SIP 503 response is sent. Other causes
can be used as well.
Version 5.2 399
7. Telephony Capabilities
September 2007