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The Internet Gate can enable SIP connectivity for remote users that use NAT devices without SIP support. It can adapt to characteristics of remote NAT devices.
Using FENT you can allow people behind non-SIP-capable NAT firewalls to register on your Internet Gate's SIP server.
You might need to purchase a license to be able to use FENT in your unit.
You configure FENT on the Advanced SIP Settings page.
FENT sends keep-alive packets to remote SIP clients behind non-SIP-capable firewalls to keep the SIP communications channel open to them. The keep-alive packets are SIP messages that are sent more often than the remote firewall's timeout.
There are two methods used for keep-alive:
You can enable both methods, then the REGISTER method is tried first and if it does not work properly the OPTIONS method is used.