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Talking Telecom


Figure 1: Telecom Architecture

Get up to speed on telecom terms with this handy glossary. If your organization has been considering converging your office desk phones with BlackBerry® smartphones with a solution such as BlackBerry® Mobile Voice System, you'll want to know what your colleagues in telecommunications are talking about.

Refer to Figure 1 to see these terms represented in a simplified telecom architecture diagram.

PBX (Private Branch eXchange)
A PBX is analogous to a router for the internal telecom network, and provides the basic foundation of an enterprise communication infrastructure. Common PBX manufacturers include Nortel, Avaya®, Siemens® and Cisco. A PBX provides the ability for users to dial within the enterprise using extension dialing, make external calls, and use central voice functions, such as call transfer, conferencing, and others.

The acronym PABX (Private Automatic Branch eXchange) is used interchangeably with PBX.

There are two main types of on-premise PBXs, TDM (Time Division Multiplexing) PBX and IP (Internet Protocol) PBX:

  • TDM PBX (Time Division Multiplexing PBX)
    TDM PBXs are the legacy system PBXs still use in many enterprises today.
  • IP PBX (Internet Protocol PBX)
    VoIP PBXs use Voice over Internet Protocol to transfer voice as data packets.

Many enterprises with a TDM PBX are in the process of switching to a VoIP PBX system. As a result, many companies operate hybrid environments running both TDM PBX and VoIP PBX systems.

PSTN(Public Switched Telephone Network)
A PSTN is the connection point for the PBX to the outside world. When users dial “9” to make an outside call, for example, they are in essence asking the PBX for permission to use the PSTN.

IP PBX (Internet Protocol Private Branch eXchange)
A PBX that is based on an IP architecture. Most new PBXs support both IP and TDM architecture. 

IP (Internet Protocol)
IP uses a packet switching technology instead of the point-to-point technology of TDM (Time Division Multiplexing). In a TDM scenario, callers have exclusive rights to use a physical path all the way from caller to receiver. In an IP scenario, however, data packets are disassembled, transmitted and reassembled when received.

A generic term describing any technology that allows voice traffic to be passed over an IP based network. Requires a higher quality of service than data only networks, in order to transmit voice packets from point A to point B in the correct order.

PBX Connection Methods:

ISDN (Integrated Services Digital Network)
ISDN is a basic type of telecommunications circuit. It’s the standard telecom circuit that allows for data traffic to be passed on a separate channel from the voice traffic. Data traffic here refers to a relatively small amount of call data like call setup data, caller ID, caller party name, etc.

PRI (Primary Rate Interface)
PRI is a type of ISDN circuit that allows for 23 voice channels plus one data path. (One data path can hold call data for 23 voice paths.) 

SIP (Session Initiation Protocol)
SIP is a standard VoIP circuit connection type. It creates a voice circuit inside the IP that carries data between the PBX and other connection point. In SIP environments, a TDM connection to the PSTN usually exists.

Find out how to mobilize your desk phone functionality. Learn how BlackBerry Mobile Voice System can work with your PBX system.
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