What is an IP PBX (Mixed PBX) and What is an IP Soft Switch:
To understand this, we need to see what is a PBX. A PBX or EPABX is a voice switch. Earlier, when there were only analog signals, the EPABX used to connect all the analog trunks, analog extensions and then switch the connection between analog trunks and analog extensions. The actual switch which does this switching is a TDM (Time Division Multiplexing) based hardware processor which resides at the heart of the PBX. If the number of trunks are equal to the number of extensions(phones), then you would probably not need this switch at all! But to save cost and still enable the services to all users (as every one is not going to access a trunk and speak, all the time), the number of trunk lines from the service providers is much lesser than the number of extensions. And the switch decides which user (phone) can access which trunk line from the service provider.
It was all fine till VOIP was introduced. Now, IP Trunks as well as IP Phones were introduced (For cost savings over longer distances, maintaining a single network and other advantages). But most of the companies had only analog PBX supporting analog trunks and analog phones. The existing investment on such PBX systems were quite high and people still wanted to use both analog trunks for local communications and analog phones as they were cheap. So, the PBX companies decided to add the IP Trunking facility and IP Extension handling facility to the existing analog PBX to handle VOIP in addition to analog lines and phones and called these systems Mixed PBX or IP PBX. But the processor used at the heart of such PBX is the same TDM based processor and IP Trunks and extensions are added much like adding analog trunks – by adding additional cards in a chassis based PBX system.
Then came IP Soft Switches. These were software based systems which controlled the whole switching environment of the PBX. They were down-loadable softwares which are loaded on to normal computer servers. So, a part of the switching is taken care by the inbuilt computer processor, RAM etc. and the rest of the switching is offloaded to the network switches which connected to the IP Phones. There were specialized PCI based Cards which can connect analog trunks, extensions to these IP Soft Switches.
This is catching on, as IP Soft Switches have following advantages over IP PBX (Mixed PBX) in VOIP Communication systems:
¤ Scalability: One thing that IP Soft Switches do very cleverly is to handle only the Control part (mostly) and a very limited amount of Switching part. So, the server does not actually act as a full fledged switch like how an IP PBX does. So, they are easily scalable to handle many more clients (even in thousands) as the processors are not burdened with the data packet switching.
¤ Hardware Independent platform: In other words, no single vendor lock in for the hardware components as they use the normal (any) Computer/Server to carry on the processes. So, there is no vendor lock-in for the hardware chassis type of systems used by IP PBX vendors – which are propreitary.
¤ Upgrade-ability: If there is a new version in the future, or if there is a new version of the PBX software with support for additional protocols, the software can be upgraded by downloading a new one. Even the IP PBX supports the core software upgrades, but it supports a very limited functionality.
¤ Expandability: If new trunks or extensions are required to be added (IP based), then it may just be required to purchase a license. This makes expansions (no of lines) very quick, flexible and easy. But for the IP PBX, an additional Card might need to be bought for higher expansions, which is generally proprietary and needs to be physically delivered and maintained by the same vendor.
¤ Analog Trunk/Extension Connectivity: In an IP PBX, the IP signals are converted in to analog for processing them inside in the TDM based platform. But in an IP Switch, there are PCI based Cards available for connecting analog trunks and extensions which can be fixed over any PC/Server that convert the analog signals in to IP signals for internal processing. Even these cards are most of the time open-source based and supplied by multiple vendors.
¤ Open Source/ Open Protocol Support: Some IP Soft Switch vendors make their whole code open-source – That gives a lot of flexibility for the application developers and even end users to write additional code for them and have complete control over them without having to rely on the vendors all the time (If they have the know-how). Some Soft Switches are based on native SIP based open protocols that they can get integrated with business processes (Like CRM/ERP softwares) much more easily than the IP PBX, which can utmost provide an API. But not all IP Soft Switches are open-source.
¤ Remote Installation/Management: All the users need to do is download the software and give the remote access to the engineers of the vendor company. They can access the server over internet and do the installation/ configuration completely over the internet. Even the maintenance and trouble shooting can be done this way, over the remote access that it makes the whole process faster and more reliable. For hardware failures, any local PC maintenance company can attend and replace.
¤ Software based Functionalities: Almost all the extra functionalities including voice mail, call handling, call billing, call recording, call centre features etc. are implemented via software. Compare this with the hardware based (but IP) separate systems of the IP PBX.
¤ Support for Carrier Networks: IP Soft Switches can also support Carrier based systems as they are hugely expandable to support thousands of users. The fact that the IP Soft Switch acts as a control for switching only and the access technology can be based on SIP/IP/GSM/CDMA/UMTS etc. is an added advantage. Some of them can also support converged communication services by integrating SS7 signalling with packet networks.
We have not touched the cost implications in all the above comparisons as they are dependant on the vendors. IP Soft Switches are not always cheaper than IP PBX. We ought to mention that IP Phones are much costlier than the normal analog phones, and investments need to be made for network infrastructure (Especially Network Switches) that support so many IP Phones and do the actual switching in the case of IP Soft Switches. Quality wise, all the PBX systems are good and Soft Switches may need to support additional components to suppress the echo generated during the conversion of analog signals to IP signals.