PBX Interface Standards

By Jelani Harper
Updated: March 28, 2011

A number of interface standards for Private Branch Exchanges (PBXs)—the central component in Voice over Internet Protocol (VoIP) equipment, a computerized, call routing and messaging system with internet capability and more—have been developed in a relatively short amount of time. As needs for PBXs have changed, so have their interface standards, both of which reflect the universal need for modern, efficient communication. Presently, PBX standards have evolved towards unified communications (UC), a single system which connects wireless and wired phones, email, instant messaging and voicemail while granting users presence status.

With current VoIP equipment capable of handling upwards of over 100 calls concurrently, accessibility to PBX information is at a premium for many enterprises which lack the time to do so in individual applications. Interface standards for collecting data from PBX were created to meet these needs. Several interfaces (which were traditionally used to print every call via printer) are used to connect various applications which access data, while network ports such as TCP and UDP can stream information to applications as well.

Other PBX standards have evolved to meet a variety of needs, such as Internet Protocol (IP) standards H.323 and SIP. Originally used to connect IP phones to PBXs, these interfaces are not only employed to connect PBXs to each other (in addition to IAX protocols, which transmit voice and video calls) but also to interface PBXs to trunk lines. MGCP and Inter-Asterisk eXchange are examples of other protocols which operate via IP with network provider support. ISDN, which has become one of the most common digital standards for fixed telephony equipment, was also created to connect PBXs to trunk lines. This interface is able to supply 2 to 30 circuit capability and is commonly carried on T1 or E1 connectors.

The original use of PBX standards was to connect telephone extensions to the branch. While plain old telephone service (POTS), the common two wire interface found in most homes which can also connect PBXs to trunk lines--although here it’s limited in its effectiveness for performing basic functions such as detecting incoming calls while making outgoing ones--was certainly employed, manufacturers often utilized defined protocols that required their specific proprietary sets. Users benefited by obtaining function buttons specific to their branch features, while DECT became the standard for cordless phone connection.

Despite standards later created for more complex needs such as inter-branch connectivity and data collection, some of the latest VoIP technology specifically aimed towards providing UC access to users continues to support basic standards such as POTS, in addition to more versatile standards including ISDN, H.323, T.38 and SuperG3FAX in order to provide a truly unified platform—which is what PBX interface standards are evolving towards.
 

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