Where this is distinguished, it is not directly at the level that user's experience the end result. In the case of what is called a "softswitch", one answer is found in organizations like the ISC (International Softswitch Consortium) and vendors who built products around their architecture recommendations. These systems tend to be very complex and componetized, where basic functionality operates in self-contained components that then interact with the whole through defined open standards and network protocols, such as SIP. The primary reason for ISC-style architectures is a result of proprietary development, where code and internal operations cannot be shared or modified. Hence, by breaking up functionality into subcomponents, it is possible to replace a component subsystem as a whole while retaining the interfaces. A perfect example is call forwarding. In a "traditional" proprietary (ISC-model) softswitch, call forwarding would be an entirely separate self-contained proprietary "feature" server interacting over SIP. If someone wants to create a different call forwarding behavior, one slips in an alternate server. By contrast, it is far easier in an open source/free software PBX to simply modify the feature code that implements call forwarding directly to create new and specialized versions of that feature. Hence, you do not find or have need for micro-services for tiny features in pbx software that originated as open source and free software or that did not follow the path of proprietary architectures, such as Bayonne, Asterisk, or FreeSwitch. A perfect example of a traditional "softswitch" architecture is SipX, which originated as a proprietary VoIP pbx codebase. However, even at this point, such distinctions I think are still somewhat artificial, as Brian suggests. What does distinguish architectures that may be relevant to end users is whether a IP-PBX solution operates as a B2BUA (back-to-back user agent) or not. A pure B2BUA solution is one where all media as well as signalling goes directly through the central PBX switch. A perfect example of this is how Asterisk traditionally works. This makes it very easy to adapt and connect multi-protocol endpoints, to convert media formats for endpoints who do not have common codecs, etc, since all media endpoints talk to the switch rather than each other. However, since all media goes through a central point, the scalability of such systems can often become "compute-bound", and extra latency is induced. A "pure" network solution by contrast has all media connect directly peer to peer by the user agent endpoints, and the "pbx" really only handles and coordinate independently operating endpoints through signalling. This often requires separate servers for gateways to the PSTN or other protocols. But it does offer better latency and scalability, and the ability to provide end-to-end media security, such as when using ZRTP. This difference, between B2BUA and non-B2BUA, is I think far more relevant today than traditional classifications such as IP-PBX, softswitch, "SIP Server", etc. Brian West wrote:
It depends on how you look at it... most will say there is no difference... but last I checked you usually don't run heavy apps on a softswitch.
FreeSWITCH can be everything from softphone to softswitch and everything in between including PBX. The default config comes configured as a PBX.
/b
On Feb 28, 2009, at 9:47 AM, Fred wrote:
Hello
Even though I successfully set up an Asterisk voice server, I'm no telecom expert, and would like some clarification about the following things: - What is an SIP server as opposed to a IP PBX? - What is the different between a PBX like Asterisk and a softswitch?
Thank you.
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