Chapter8. SIP Services
Example:If the Base retransmission timeout is 0.5 seconds and the Maximum number of retransmissions is 6,
theINVITE 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

Whenthe Telecommuting Module sends out a request which is not an INVITE request, it will wait for a reply until
theBase retransmission timeout and then start to retransmit the request. The time intervals between
retransmissionswill double for each new retransmission until the interval reaches 4 seconds. After that,
retransmissionswill be made with a 4-second interval.
Example:If the Base retransmission timeout is 0.5 seconds and the Maximum number of retransmissions is7,
therequests will be sent with intervals of 0.5 s, 1 s, 2 s, 4 s, 4 s, 4 s, and 4 s.
Save
Savesthe Sessions and Media configuration to the preliminary configuration.
Cancel
Revertsall of the above fields to their previous configuration.
Remote SIP Connectivity
Ifyou are at a hotel or somewhere else where you find yourself behind a NAT-ingdevice that does not understand
SIP,you will have use of the SIP Remote Connectivity of 3Com VCX IP Telecommuting Module. This will help
yourclient to traverse the NAT,even if the device doing the NAT does not understand SIP.The SIP Remote
Connectivityis only available if you have installed the Remote Connectivity module.
Ifyou have a STUN-capable SIP client, you need just turn on the STUN server of the Telecommuting Module to
makethe client work behind NAT. If you havea SIP client that does not do STUN (or if the STUN-capable client is
locatedbehind a Symmetric NAT device), you have to use the Remote NATTraversal feature. This is easier for the
client,but generates more network traffic for the Telecommuting Module.

STUN Server

Usethe STUN server if you have STUN-aware SIP clients. You will need at least two public IP addresses to make it
workwith all client implementations of STUN.
STUNwill not work properly if the NAT device uses Symmetric NAT(where the client’s private IP/port pair
translatesto different public IP/port pairs depending on destination, and where other computers than the destination
hostare not allowed to reply on that IP/port pair).
Theclient also needs extra configuring for this; it must know which IP addresses and ports the STUN server has.

STUN server function

Selectif the STUN server function should be switched On or Off.

STUN server IP addresses

Whenactivated, the STUN server requires two IP addresses, and a pair of ports on these two IP addresses, on the
TelecommutingModule. STUN clients will then send test packets to these ports.
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