IP-PBX systems and softswitches are in some ways apples and oranges. While in most cases softswitches are IP-PBX systems, the reverse is not always true.
When a system is referred to as an IP-PBX, that typically indicates only that the system supports VOIP communication to the handset and/or the PSTN (via something like SIP trunks). Avaya and Nortel have IP-PBX systems, along with a host of other established and new manufacturers in the telecom space.
A “softswitch” in the truest sense is a PBX that derives its feature functionality primarily from software. Voicemail, call handling, call center functionality, etc., are all implemented via software and use hardware only for basic connectivity to the PSTN or the handset. Asterisk is an example of a softswitch.
Softswitches are almost always IP-PBX systems, as this is the easiest way to avoid a reliance on specific hardware. Asterisk, for example, can operate as a pure IP-PBX softswitch on standard PC server hardware. Communication with both the PSTN and the handsets is accomplished via a software-based VOIP stack.
IP-PBX systems, on the other hand, are not always softswitches. Almost all IP-PBX systems offered by the hardware giants like Nortel and Avaya achieve their features via hardware — expansion boards that fit into the main chassis. In my opinion, while these systems can derive some capabilities from firmware, it isn’t proper to call such a system a softswitch.
There are also some hybrid systems like those from Vertical Communications and AltiGen. These systems are software-based in the sense that the majority of their features come from software running on a Windows Server PC, but with the exception of Vertical’s HMP system they do require specific hardware to operate.
There aren’t any capacity or capability limitations intrinsic to IP-PBX systems or softswitches given that we’re talking about architecture, but the real-world implementations of softswitches can grow larger simply because they are sometimes used for carrier-level switching. Any capacity differences you see in the market are likely not the result of the technology but rather the marketing focus of the manufacturer (the SMB market is very attractive, but don’t assume that just because IP-PBX systems are usually focused on the 25-250 seat size that you can’t get them larger).
Connectivity to a third-party application server isn’t something that would necessarily be impacted by the IP-PBX / softswitch distinction, as even most purely hardware-based systems these days support gateways that allow for integration with external application servers. That said, a softswitch will generally make the job far easier. Most softswitches include programming APIs that allow gateways to be programmed in a common programming language like VB or a .NET language. Asterisk is programmable if you don’t mind getting your hands dirty, and both AltiGen and Vertical’s TeleVantage include COM object-based SDKs that allow extensive control of the switches for the creation of IVRs and custom PC-based call management.
Contrast this with some of the proprietary script-based gateways of some hardware-based systems (including some hardware-based IP-PBX systems) where it’s not a standard programming interface and the end-user is not able to modify the gateway without assistance (read: cost) from the provider.
The major difference between Softswitch and IP-PBX is that they are analogous to Switch/MSC and PBX respectively in TDM networks.
Where as IP-PBX purpose is to ….
a. convert the IP Phone calls to TDM calls to interface with PSTN Switches or other switches.
b. Switch calls within the phones of IP-PBX
A broad definition based difference is below.
A programmable network switch that can process the signaling for all types of packet protocols. Also known as a “media gateway controller,” “call agent” or “call server,” such devices are used by carriers that support converged communications services by integrating SS7 telephone signaling with packet networks. Using network processors at its core, softswitches can support IP, DSL, ATM and frame relay in the same unit.
According to the International Softswitch Consortium, a softswitch should be able to …..
(1) control connection services for a media gateway and/or native IP endpoints,
(2) select processes that can be applied to a call,
(3) provide routing for a call within the network based on signaling and customer database information,
(4) transfer control of the call to another network element, and
(5) interface to and support management functions such as provisioning, fault, billing, etc.
Software Makes It Flexible …..
The switching technology in a softswitch is in software (hence its name) rather than in the hardware as with traditional switching center technology. This software programmability allows it to support existing and future IP telephony protocols (H.323, SIP, MEGACO, etc.).
IP PBX ….
(Internet Protocol Private Branch eXchange) A telephone switch that supports voice over IP (VoIP). IP PBXs convert IP phone calls into traditional circuit-switched TDM connections for the PSTN. They also support traditional analog and digital telephones, allowing enterprises to migrate slowly to an all-IP telephony environment.
That’s it. Looks complicated and confusing. Can be….but doesn’t have to be.