PBX - Private Branch EXchange
PBX - Private Branch eXchange
Preface
A Private Branch eXchange (also called PBX, Private Business eXchange or PABX for Private Automatic Branch eXchange) is a telephone exchange that is owned by a private business, as opposed to one owned by a common carrier or by a telephone company. Historically a PBX was a company's manual switchboard, and was known as a PMBX (Private Manual Branch eXchange).
These were gradually replaced by automated electromechanical and then electronic switching systems, called PABXs (Private Automatic Branch eXchange). As PMBXs are almost unheard of these days, the terms PABX and PBX have become synonymous. When PABXs were built using solid state and digital components the term EPABX came into use but PBX is still more widely recognized. The PBX term was dominant for so long, that it is now being applied very liberally to systems providing complex services regarding telephony, even if they are not Private, Branches or eXchanging anything.
PBXs were distinguished from smaller "key systems" by the fact that external lines are not normally indicated or selectable at an individual extension. From a user's point of view calls on a key system are made by selecting a specific outgoing line and dialing the external number; calls on a PBX are made by dialing the escape code (usually 9, 0 in some systems) followed by the external number; an outgoing trunk line is automatically selected upon which to complete the call. This practice is becoming obsolete as number analysis systems have been changing with modern technology - you can use internal numbers or external numbers without any need for escape codes.
The Task
A small business on a tight budget with staff working from different offices, need:
- A single point of contact through the telephone network
- To be able to transfer calls internally to each office and to remote offices
- Any office to be able to answer the incoming calls
- Multiple incoming calls
- Interface with VOIP, (Voice Over IP), and PSTN, (Public Service Telephone Network) Trunks
- Auto Attendant
- Call accounting
- Call waiting
- Voicemail for each extension
- Direct Inward Dialing
- Music on Hold
- Dialing Rules based on extension/number called
Our Approach
Asterisk, a software implementation of a telephone private branch exchange (PBX). Like any PBX, it allows a number of attached telephones to make calls to one another, and to connect to other telephone services including the PSTN.
Its name comes from the asterisk symbol, *, which in Unix (including Linux) and DOS environments represents a wildcard, matching any sequence of characters in a filename.
Our Findings
The basic Asterisk software includes many features previously only available in expensive proprietary PBX systems -- voice mail, conference calling, interactive voice response (phone menus), and automatic call distribution. It's possible to create new functionality by writing dial plan scripts in Asterisk's own language, by adding custom modules written in C, or by writing Asterisk Gateway Interface scripts in Perl or other languages. Asterisk also supports a wide range of Voice over IP protocols, including SIP and H.323. Asterisk can interoperate with most SIP telephones, acting both as registrar and as a gateway between IP phones and the PSTN. Developers have also designed a new protocol, IAX, for efficient trunking of calls among Asterisk PBXes.
Our Results
Each of the requirements for our client were met, the system functions in the same way that a dedicated hardware PBX would function. The desk phones that were installed for this particular client were Cisco 7960's which are a very impressive phone. They lend themselves to Asterisk interoperability. Meaning the entire telephone system operates purely via VOIP for the office part of the network. Which in turn means it can use the same structured cabling as the rest of the office networks. We recommend having a dedicated switch and connection, or at least a sepperate VLAN, for the voice traffic. However it is possible to run the VOIP on the same LAN as the data. Depending on the hardware in place it's possible to do some QoS/Traffic Shaping for the connection so that voice takes priority.
PBX Conclusion
gdPBX supports a wide range of TDM protocols for the handling and transmission of voice over traditional telephony interfaces. gdPBX supports US and European standard signalling types used in standard business phone systems, allowing it to bridge between next generation voice-data integrated networks and existing infrastructure. gdPBX not only supports traditional phone equipment, it enhances them with additional capabilities.
gdPBX merges voice and data traffic seamlessly across disparate networks. While using Packet Voice, it is possible to send data such as URL information and images in-line with voice traffic, allowing advanced integration of information.
gdPBX provides a central switching core, hardware interfaces, file format handling, and codecs. It allows for transparent switching between all supported interfaces, allowing it to tie together a diverse mixture of telephony systems into a single switching network.
