User guide

In the Training Centre we decide that all calls coming from any Telecentre are forwarded using SIP to
the support desk.
[incoming_telecentres_calls]
exten => _X.,1,Dial(SIP/support-desk) ; Calls from any Telecentre
; are forwarded to Support Desk
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9.2.3 The register command
When the IP address of the peer is unknown, we have no way to place a call. Imagine the situation
when one of the PBX's has a static IP address but the PBX at the other end does not. To compensate
for this, the PBX that has a dynamic address needs to actively register with the other unit. In our
previous example we are using two register commands, although in the strict sense the register
command is only needed when one of the PBX's has a dynamic IP address. When the IP address of
the other peer is known we can replace the host=dynamic statement in the configuration file with
host=<ip_address or domain>
10. Learning more
• One of the best books about Asterisk is: Asterisk, The Future of Telephony, Jim Van
Meggelen, Jared Smith, Leif Madsen. O'Really 2005. Under Creative Commons.
http://www.oreilly.com/catalog/asterisk/
• Free download: http://www.asteriskdocs.org/modules/tinycontent/index.php?id=11
• To keep an eye of what is going on in emerging telephony. http://www.oreillynet.com/etel/
• The VoIP info website is a huge wiki with lots of tips and tricks. Finding what you exactly need
can require some dedicated browsing though. http://www.voip-info.org/wiki-
Asterisk+tips+and+tricks
• VoIP4D, VoIP for development resources http://voip4d.it46.se
11. Conclusions
This primer is an attempt to introduce some of the essentials of IP telephony. By giving a few concrete
scenarios, we hope to have created awareness about the endless opportunities that VoIP brings in
developing regions. VoIP in conjunction with low cost wireless technologies can bring voice and data
42. The Dial() to the SIP support-desk needs to configured in the sip.conf of the Training Center.
Page 44 TRICALCAR | www.wilac.net/tricalcar – Version: February 2008