Appendix A. More About SIP

8.The Telecommuting Module checks if there is a matching row in the Dial Plan table.

9.The Telecommuting Module checks if the SIP packet Request-URI contains one of its Local SIP Domains. If so, and no match was found in the above list, the Telecommuting Module returns a SIP packet with error code 404 (Not Found) to the sender.

After finding something to guide it in routing the packet, the Telecommuting Module proceeds to the next list, which tells it where to send the packet (if it hasn’t already sent a 404 reply). This list is also searched until a match is found.

1.The Telecommuting Module sends the SIP packet to the Outbound Proxy if one has been entered.

2.The Telecommuting Module checks for the SIP domain of the Request-URI in the DNS Override For SIP Requests table.

3.If there are still unresolved domain names, the Telecommuting Module makes an ordi- nary DNS lookup.

SIP Packet Headers

This is a list of the more common SIP packet headers, and advice on how to modify them using different settings in the Telecommuting Module.

Request-URI

The Request-URI (RURI) of the SIP packet can be found in the first line, right after the name of the SIP method used. The RURI tells the destination of the packet.

When the Telecommuting Module acts as registrar for the domain of the RURI, it rewrites the RURI from user@domain into whatever the user gave as its Contact when it registered.

When the incoming RURI is one that the Telecommuting Module has previously substituted in a Contact header, the RURI is also rewritten.

When an XF account is used, the domain part of the incoming RURI will be changed into the domain of the XF account.

From

The From header contains the SIP user who sent the SIP request.

The Telecommuting Module only changes the From header when the built-in b2bua is used, like when an XF account is used.

To

The To header contains the SIP user who should receive the SIP request.

The Telecommuting Module only changes the To header when an XF account is used.

Contact

The Contact header tells on which address the SIP client wants to be contacted.

326