User guide

bandwidth is highly limited and the costs for Internet access are at least 100 times higher than in
Europe and North America.
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To get a sense of how big the overhead can be when sending voice over
the Internet, consider the fact that a 5.6 kbit/s compressed audio will
require 18 kbit/s of bandwidth. The difference between the 5.6 kbit/s and
18 kbit/s is the packet headers
The packet headers are all the information that is necessary to carry the voice packets to the recipient.
IAX2 has done excellent work in reducing that overhead by limiting the amount of extra bits per packet.
It has also taken advantage of the concept of bundling conversations that are heading to the same
destination and wrapping them up inside the same packets.
Some of the tests performed during the writing of this primer (using a dial-up connection to the Internet)
have evidenced that an IP-based phone conversation using IAX2 is more feasible than a conversation
with SIP.
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3.2 Open Standards and Free and Open Source Software
We can not talk about the freedom of building our own telephone network without open standards and
free and open source software. Open standards allow everyone to implement interoperable
communication systems. With interoperability, we can build our private telephone network and later
plug it into the global network. With free software, we can learn from existing experiences, integrate
solutions and ultimately share our results with others.
One of the first questions that needs an answer is: Why should we build our
own VoIP infrastructure and not rely on free services like Skype?
The answer is simple: sustainability and flexibility. Free services might solve
our immediate problem, but do not guarantee technology ownership and
hence cannot guarantee our independence in the long run.
The question is not just about which technology is better, but rather which technology enables
communities to own their development process and adapt it to their own needs.
It is difficult to image sustainable development without knowledge transfer and technology ownership. A
solution based on open standards and free and open source software does not only provide a good
technical solution but also enables the possibility of adapting it to fit everyone's requirements.
8. 1 Mbps in East Africa costs more than 1000 USD/month while the same capacity in Sweden costs less than 10
USD/month.
9. A phone conversation using a voice compression algorithm like G.729 (8 Kbps) will require 30 Kbps using SIP and 24 Kbps
using IAX2. If we bundle five calls together the bit rate per call is 13 Kbps.
Page 7 TRICALCAR | www.wilac.net/tricalcar – Version: February 2008