Configuring SIP Provisional Message Reliability

To support interoperability with the PSTN such as hearing a ring back tone when you dial a number, the Vocera SIP Telephony Gateway needs to support SIP early media. This requires using the option tag "100rel", which enables reliable provisional responses. The Vocera SIP Telephony Gateway defaults to initially trying "100rel" from the following property:

VTGTry100Rel = true

If the SIP message returns a "420 Bad Extension" response, it will try the call again without requiring the "100rel" option tag.

To force calls to have early media (and a ring back tone) or otherwise fail, set the VTGRequire100Rel property to TRUE. If the SIP message returns a "420 Bad Extension" response, the call will fail.

Table 1. 100rel properties

Property

Description

VTGTry100Rel

Whether to support SIP early media by trying the "100rel" option tag with the SIP message. The default is TRUE, which means Vocera SIP Telephony Gateway intially tries "100rel". If the provisional response is not acknowledged, Vocera SIP Telephony Gateway will try the call again without requiring the "100rel" option tag.

VTGRequire100Rel

Whether to always require the "100rel" option tag to enable reliable provisional responses. The default is FALSE. When this property is set to TRUE and a provisional response is not acknowledged, the call will fail.