User guide

The concept of trunking can be explained with the following metaphor:
Imagine that you need to send five letters to people living in another country.
You can use one envelope per letter, or include the five letters in a single
envelope and include the name of the final recipient in the first line of each
letter. Trunking operates in the same form and allows you to send multiple
letters (calls) in a single envelop (IP packet).
In summary, IAX2 is a friendly protocol for VoIP in developing regions for
three reasons:
1. Minimizes the use of bandwidth per single call
2. Provides native support for NATs (easier to use behind firewalls)
3. Minimizes the use of bandwidth for several calls (by means of
trunking)
4.5 VoIP Hardware
4.5.1 VoIP Phones
A VoIP phone is dedicated hardware that connects to a VoIP network. VoIP phones can run one or
several VoIP protocols.
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Some interesting features that you should consider when buying a VoIP
phone are:
• Low bandwidth: support for high compression codecs (e.g. G.729,
Speex)
• Good administration interface: Web interface
• Audio interface: An external audio output and hands-free headset
support (for teletraining)
Several models that can do more than you will ever need and work smoothly with Asterisk are
available in the price range of 100-120 USD.
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4.5.2 Soft Phones
An alternative to a hardware VoIP phone is to install software in a PC. A VoIP phone that runs in a
computer is known as a “software phone” or “softphone”. The only requirement is a working sound
card and to ensure that your personal firewall is not blocking the application.
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If you want to take advantage of bandwidth savings, consider using a softphone that supports IAX2.
18. As November 2007, several companies are manufacturing VoIP phones with IAX2
19. The following models have been evaluated as part of this primer: SwissVoice IP10S (150 USD), Thomson ST2030 (100
USD), Gulfstream Budgetome (75 USD), Cisco 7940 (300 USD).
20. The following softphones have been evaluated as part of this primer: IAXClient (IAX2), X-Lite (SIP)
Page 15 TRICALCAR | www.wilac.net/tricalcar – Version: February 2008