Sip Settings - Grandstream Networks GSC3510 Series User Manual

The option will decide which IP is going to be used in sending subsequent SIP packets (ex: Register refresh requests) after the list of
IPs for SIP server host is resolved with DNS SRV.
Default (prefer server with lowest SRV priority):
The device will always prefer to send SIP requests to the available server having the lowest priority, and in case it's down it contacts
the next one, but once the server having lowest priority is UP again, the device will switch over to this one.
DNS SRV Fail- Saved one until DNS TTL (Stay on responding IP until DNS timeout):
over Mode
On this mode, the device will resolve DNS SRV records and tries to send the request to the server having lowest priority and if it
doesn't respond, it will move on to the next IP until one of the servers responds, once this happen the device will keep contacting
this responding IP until DNS timeout (30 minutes) before starting over.
Saved one until no response (Stay on responding IP until its failure):
On this mode, the device will send SIP requests to the last responding IP, and it doesn't failover/switchover to the next one until this
responding server is down.
Register
When this feature is enabled (default), the device will register using the outbound proxy when the SIP server is failed to get the
Before DNS
registration.
SRV Fail-over
Specifies which NAT traversal mechanism will be enabled on the device. It can be selected from the dropdown list:
NAT NO
STUN
Keep-alive
UPnP
Auto
OpenVPN
NAT Traversal
If the outbound proxy is configured and used, it can be set to "NAT NO".
If set to "STUN" and STUN server is configured, the device will periodically send STUN message to the SUTN server to get the public
IP address of its NAT environment and keep the NAT port open. STUN will not work if the NAT is symmetric type.
If set to "Keep-alive", the device will send the STUN packets to maintain the connection that is first established during registration of
the device. The "Keep-alive" packets will fool the NAT device into keeping the connection open and this allows the host server to
send SIP requests directly to the registered phone.
If it needs to use OpenVPN to connect host server, it needs to set it to "VPN". If the firewall and the SIP device behind the firewall are
both able to use UPNP, it can be set to "UPNP". The both parties will negotiate to use which port to allow SIP through. The default
setting is "Keep-alive".
Adds the Proxy-Required header in the SIP message. It is used to indicate proxy-sensitive features that must be supported by the
Proxy-Require
proxy. Do not configure this parameter unless this feature is supported on the SIP server.

SIP Settings

SIP Basic
Settings
SIP Registration Allows the device to send SIP REGISTER messages to the proxy/server. The default setting is "Yes".