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Managing Calls Using IP Telephony
November 2009 219
Understanding SIP Functionality
The following section provides information about SIP functionality
and processes. For a detailed introduction to the SIP protocol, see
Introduction to the SIP Protocol on page 244.
Using a SIP Proxy Server
To make an outgoing connection using the IP, your application must
know the IP address of a local proxy server which is responsible for
forwarding the SIP call towards its final destination. In a typical
environment, the proxy server is the local IP to PSTN gateway. For
more information about using proxy servers, see Understanding the
SIP Protocol on page 244.
To receive incoming calls using the internet, you must register your
location so that proxy servers can locate you.
For more information about configuring proxy servers, see the
installation and configuration guide that came with your software
and the Bfv API Reference Manual, Volume 6, Appendix A.
Verifying Dialed Strings
If your application either does syntax verification/modification of the
dialed string or it is desirable to do number translation or lookup
without modifying the application, then the application needs to
perform number translation.
Channel numbers enable your application to differentiate between
types of call in the context of the Call Control Bfv API. SIP and other
IP protocols use a Uniform Resource Identifier (URI). The software
detects and recognizes the format of the dial string and sends the
call to the appropriate channel. In Brooktrout SDK 4.0 and beyond,
the dial strings follow the URI syntax, so tel: and fax formats are not
supported and must be reformatted by your application.
Prefixes to dial strings are provided as a means for your application
to behave intelligently by supporting channel selection in hybrid
systems. Prefixes are optional.
Using prefixes, dial strings can also be pre-qualified by your
application as in the following example:
SIP/T38://xxxxx@brooktrout.com