Some Standards Used in IP PBX Software

-G.711: an international standard used for encoding (packetizing) telephone voice at either 56kbs or 64 kbps - this is uncompressed digitized voice.
-G.723: a protocol for compressing voice to 6.4 kbs or 5.3 kbs. The compression quality is very good with voice quality as good as normal telephone voice quality. It is supported by virtually all IP telephone equipment.
-H.323: Signaling & telephone services protocol for the transmission of IP packets representing any combination of voice, video and data. H.323 is designed for operation over existing IP networks. Includes facilities call setup signaling and media control. Allows VoIP equipment to interoperate.
-SIP (Session Initiation Protocol): A signaling & telephone services protocol similar to, but simpler than, H.323.

Where will an IP PBX be used?

IP PBXs are good candidates for being used particularly in

-new businesses which will avoid the costs of installing and maintaining two networks (its hard to replace equipment that works in existing offices)
-businesses that have many branches will reduce costs by
avoiding long distance charges incurred by calls between the branches and
using one centralized directory (which will be cheaper to maintain than many multiple directories)

What are the Advantages of an IP PBX?

Compared to a conventional PBX, an IP PBX
-handles both voice and data,
-is cheaper since it requires only one network to install and maintain instead of two,
-reduces equipment costs (only IP based products; no voice products needed),
-reduces long distance charges for inter-branch office calls (by using the data network),
-is easier to provision (just plug in from wherever),
supports services such as unified messaging,
-is more flexible,
-is more scalable,
-makes it easier to provide new services, such as data and video collaboration,
-allows remote configuration (over the Web), and
-supports modular software upgrades, new technologies (new CPUs, etc.) are easy to incorporate.