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 fromtwo 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). Note that there is a $10 licensing fee per session per server if you want to use G.729 (arguably the best CODEC for voice compression); and, of course, you do have to buy some telephony interface cards for your cheap commodity LINTEL (Linux on Intel) PC or Server, but it is still by far the cheapest hybrid telephony system that money can buy.
Althoughit's easy to think of Asterisk as just another VoIP server, that couldn't be further from the truth. Asterisk is an extremely flexible communications platform that can serve as a VoIP Signaling Server, a Media Gateway (allows IP telephony to interface with analog phones, fax machines, or PSTN lines), a traditional analog or TDM-based PBX phone system, voice mail, IVR, Unified Messaging, and too many other things to list! For example, you can build a phone system that can support 72 analog telephones or fax machines, 100 IP hard or soft phones on site or remote, a T1 line to the public telco for 23 simultaneous external PSTN connections, multiple IP-based IAX trunks to multiple remote offices for seamless toll-bypass 4-digit dialing, IVR, and almost unlimited voice mail for everyone -- for under $6,000 in a 1U chassis. Such a price point is easily 10 or more times cheaper than a commercial alternative. Here is a graphic illustration of such a system.
Of course, this all might sound too good to be true and you're probably wondering "what's the catch?" There is one catch (but diminishing), and it boils down to ease of use and having a person who is really good with Linux. However, you can always hire a consultant to implement the system for you on an hourly basisorgo to one of the manycompaniesselling turnkey systems that work out of the box like Xoasis or Coalescent. Coalescent for its part hascontributeda free Opensourcemanagement package calledAMP (Asterisk Management Portal). Asterisk itself also offers very reasonable support contractsto assist the do-it-yourselfers. Then there are companies like Xorcom, whichhasdone a fine job in simplifying the installation of Asterisk with a simple CD-ROM ISO that you can download and burn. This will allow you to install Debian Linux with Asterisk as a fully functional server. Xorcom is also working on implementing a GUI management tool into their Asterisk installer CD, and they may be looking at some of these GUI Management tools. With all these developments, Asterisk is on the verge of critical mass to explode on to the VoIP scene -- which will revolutionize the IP telephony market.>