There seems to be a constant debate about the value of moving to an open source PBX. Asterisk is the first one that comes to mind, but it is not the only one available. There are pros and cons relating to the open source debate; these were covered in the previous tip, "Open Source PBX: Risk or Value?"
Asterisk is the best-known of the open source PBX offerings. Continuous development of the Asterisk code is provided by more than 400 community developers. The latest releases are 1.2.18 and 1.4.4. It is anticipated that the forthcoming release, 1.6, will add new features and capabilities and solve some problems. What many do not know is that there is a business edition of Asterisk, B.1, that is not free but licensed. B.1 may be of interest to more enterprises because it will be certified and supported as a product. Asterisk can also be connected to Microsoft's Exchange 2007 to provide a start to the migration to unified communications.
Some of the limitations that Asterisk release 1.6 will address are:
- Issues with firewalls
- Security problems that are not well publicised
- V-mail must be resident on the same server as the call
- Call Detail Records (CDR) that have limited tracking for events
- Poor cluster support
- Failover support
- Limited call bridging
- Limited call capacity and performance
- Although I have cited Asterisk in relation to these problems, they also exist on other open source PBX platforms.
Many open source platforms are available. This tip is not attempting to be exhaustive but to provide five other sources for open PBX software. The five implementations are not all Asterisk derivatives. They represent, in some cases, a completely different approach.
OpenPBX is a legal variation of Asterisk. It has a similar set of features and functions to Asterisk. Developers are of the opinion that OpenPBX is a more open system for development than Asterisk is.
Sipfoundry has created a number of programs around the SIP protocol. Sipfoundry has produced a SIP protocol stack, independent of the PBX code. The SIP protocol is the focus of these developments. sipXpbx is part of a family of open source projects for SIP implementations. reSIProcate www.resiprocate.org, the SIP protocol stack and related applications, is part of this family. Because of the design of sipXpbx, developers believe it can scale to much larger implementations than Asterisk can. sipXpbx is written in C++. The latest release, 3.6, is now stable for use. The family of SIP-related functions includes sipXvxml, suitable for implementation of auto attendant and voicemail functions.
This is a lesser-known open source PBX functional similar to Asterisk. It has added SIP proxying and session border control functions. It can be used for functions other than a PBX: a trunk gateway, IVR engine or SIP router. It is also written in C++ and is considered to be more modular in its code base (cleaner), providing a better message-passing architecture.
This is an industrial-strength SIP proxy. It is the SIP Express Media Server - SEMS. It is interoperable with other SIP implementations. It is written in C. The latest release of SEMS is 0.10.0 rc2. SEMS is known for its good performance.
The OpenSER code base is inherited from SER. It is also written in C. The latest release of OpenSER is v1.2.0. It can be used to support a variety of server functions, including a proxy, register, location, application and dispatcher servers.
Looking at these five open source PBX alternatives demonstrates that there will continue to be other entrants into this space. Although these solutions compete with one another, they are not carbon copies of Asterisk. Some of them are completely different approaches and should also be evaluated if the enterprise is considering an open source PBX solution.
About the author: Gary Audin has more than 40 years of computer, communications and security experience. He has planned, designed, specified, implemented and operated data, LAN and telephone networks. These have included local area, national and international networks as well as VoIP and IP convergent networks in the U.S., Canada, Europe, Australia and Asia.
This was first published in July 2007