Calls Dropping after 20 seconds
If you find that calls on your local SIP phones drop after approximately 20 seconds, TELNET into the router and issue the following command:

sys sip_alg 0 [ENTER] (-- that's a zero on the end)

This ADSL router has two Analogue (FXS) phone ports on the back. To have them successfully connect they need to have different network ports assigned to them, and - very importantly - if you also have a SIP server (eg: Asterisk) on the LAN, the FXS ports must not use network port 5060 otherwise external SIP phones will not be able to register with the local server. Here's a sample configuration with one FXS port connected to the local server and one connected to voip.co.uk:

• Note that the FXS ports have been assigned local (to the router) ports 5061 and 5062, but they register to their hosts on port 5060 because this has been added to the end of the Domain and Proxy addresses (a bit obscured on the right side) - adding ':5060' to these addresses is important; if not done, things won't register.

Firmware version 2.5UK had a bug which caused an outgoing INVITE to get the top via header address translated, but an outgoing CANCEL not to. This meant (2) in 17.2.3 of RFC 3261 did not match, and as a result a call does not get cancelled.

Upgrading to 2.5.9UK has been reported as fixed.