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Chapter 8. SIP Services
Example: If the Base retransmission timeout is 0.5 seconds and the Maximum number of retransmissions is 6,
the INVITE requests will be sent with intervals of 0.5 s, 1 s, 2 s, 4 s, 8 s, and 16 s.
Maximum number of retransmissions for non-INVITE requests
When the Telecommuting Module sends out a request which is not an INVITE request, it will wait for a reply until
the Base retransmission timeout and then start to retransmit the request. The time intervals between
retransmissions will double for each new retransmission until the interval reaches 4 seconds. After that,
retransmissions will be made with a 4-second interval.
Example: If the Base retransmission timeout is 0.5 seconds and the Maximum number of retransmissions is7,
the requests will be sent with intervals of 0.5 s, 1 s, 2 s, 4 s, 4 s, 4 s, and 4 s.
Save
Saves the Sessions and Media configuration to the preliminary configuration.
Cancel
Reverts all of the above fields to their previous configuration.
Remote SIP Connectivity
If you are at a hotel or somewhere else where you find yourself behind a NAT-ing device that does not understand
SIP, you will have use of the SIP Remote Connectivity of 3Com VCX IP Telecommuting Module. This will help
your client to traverse the NAT, even if the device doing the NAT does not understand SIP. The SIP Remote
Connectivity is only available if you have installed the Remote Connectivity module.
If you have a STUN-capable SIP client, you need just turn on the STUN server of the Telecommuting Module to
make the client work behind NAT. If you have a SIP client that does not do STUN (or if the STUN-capable client is
located behind a Symmetric NAT device), you have to use the Remote NAT Traversal feature. This is easier for the
client, but generates more network traffic for the Telecommuting Module.
STUN Server
Use the STUN server if you have STUN-aware SIP clients. You will need at least two public IP addresses to make it
work with all client implementations of STUN.
STUN will not work properly if the NAT device uses Symmetric NAT (where the client’s private IP/port pair
translates to different public IP/port pairs depending on destination, and where other computers than the destination
host are not allowed to reply on that IP/port pair).
The client also needs extra configuring for this; it must know which IP addresses and ports the STUN server has.
STUN server function
Select if the STUN server function should be switched On or Off.
STUN server IP addresses
When activated, the STUN server requires two IP addresses, and a pair of ports on these two IP addresses, on the
Telecommuting Module. STUN clients will then send test packets to these ports.
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