Advanced - SIP/RTP (Tab) - SIP(Section): Use Outbound
This setting can be used to toggle the support for draft-ietf-sip-outbound-20. Enable this to force the re-usage of connections, what snom phones already do. However, if you use this setting the phone will stick to the network flow created during line registration. Additionally you have to specify a value for Keep Alive.
In some cases such as NAPTR/SRV entries with the same priority, customers need the phone to use the same network path created during line registration for all subsequent requests sent for this identity (otherwise the phone might try to resolve an FQDN and end up sending SIP requests to a different server than the one used for the SIP registration. In order for the phone to use the same network path created during line registration for all subsequent requests sent for this identity, the following settings must be used:
1. Setting offer_outbound (this setting described here) must be enabled
2. Setting keepalive_interval must be set or alternatively the phone must send REGISTER requests very often (for example every 30 seconds) - see user_expiry
Setting offer_gruu may be enabled, but it is no longer required.