IP PBX architecture

There are three different types of IP PBX architectures: IP, hybrid IP, and Legacy Time Division Multipler (TDM)

IP

An IP architecture does all of its switching in the IP world which means no transcoding between the TDM bus and IP bus. Typically customers benefit from this type of architecture because it is scalable and additional hardware is not required to do the digital signal processing (DSP) to convert the media. Examples of this type of architecture are 3Com NBX, 3Com VCX, Asterisk, and Cisco Call Manager.

Hybrid IP

A hybrid IP architecture must convert its media between the IP and TDM world. This means more resources are required to do the transcoding. Typically these types of systems have certain limitations of how many IP phones can be used. Examples of this type of architecture are Avaya Communications Manager, Avaya IP Office, Nortel BCM, and Nortel Succession.

Legacy TDM switch

There is no worry about converting media between IP and the TDM bus as this is a TDM only solution. These are typically older type systems. Examples of this type of architecture are Avaya Definity, Avaya Partner, Nortel Meridian, and Nortel Norstar.

Another important part of IP PBX architecture is the Operating System used. There are really three OS choices:

Linux

Linux provides a strong platform for IP PBX platforms. While these systems are typically quite reliable training and installation costs are often significantly higher than other operating systems. Examples using Linux include 3Com VCX, Asterisk, and Alcatel Omni.

Windows

Windows allows products to more easily integrate with other applications. These types of platforms are typically less reliable and security patch maintenance is frequently a big issue. Examples using Windows include Cisco Call Manager, Nortel BCM, Siemens HiCom, Siemens HiPath, Toshiba Strata CS, Vertical Communications InstantOffice, and Vertical Communications TeleVantage.

Real-time

Real-time operating systems are extremely reliable in terms of call completions. Oftentimes separate application servers are required to run other solutions. Since the applications are not on the PBX, there is less opportunity for an errant program to disrupt the call processing. Examples using this type of OS include VxWorks - 3Com NBX, Nortel Succession, proprietary OS - Avaya Definity, Nortel Meridian, and Nortel Norstar.

Sip Architecture - found in many different type of sources as Asterix