As the commoditization and open sourcing of operating systems and applications continue to disrupt the software companies, telephony vendors have so far enjoyed a relative calm in the closed and proprietary phone systems market with substantial profit margins. That could now all be turned on its head with the proliferation of open source VoIP and PBX software. There are now a handful of these open source telephony platforms such as OpenPBX and Pingtel, but one of the most interesting is Asterisk, which even has its own communication protocol IAX in place of SIP for unified signaling and data transport.
Asterisk’s IAX has all the attractive characteristics of SIP yet it plays nice with NAT and firewalls due to the fact that it uses a single UDP port for signaling and voice transmission. SIP, on the other hand, uses one port for signaling and another for voice, which makes it difficult to handle in NAT and firewall devices. Another benefit of IAX is its trunking capability. Think of it as the commuter lane for VoIP traffic, since multiple voice channels can share a single IP datagram (think of this as the enclosure for voice packets). This is no small feat, since the overhead of an IP datagram can be anywhere from two to five times bigger than the actual voice data itself while traversing Frame Relay or VPN tunnels! If the IP header can be shared, it can mean the difference between supporting 19 simultaneous G.729 voice channels using SIP or 55 simultaneous G.729 channels when using IAX where 512 kbps of a Frame Relay link is allocated for voice traffic. To make Asterisk universally appealing, it supports nearly all communication protocols, including SIP, H.323, MGCP, and even some limited proprietary Cisco SCCP (Skinny) support. With such a robust feature set, it’s hard to believe Asterisk is free (GPL license).................
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Kiggundu Mukasa # Computer Network Consultancy###
KYM-NET LTD. # Intranets & Internet Solutions#
Plot 80 Kanjokya Street
P.O. Box 24284 Kampala, Uganda
Tel: +256 77 972255
+256 71 221141
Fax: +256 31 262122
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