PBX Interface Standards for Business: A Complete Guide

PBX Interface Standards for Business: A Complete Guide

PBX Interface Standards for Business: A Complete Guide

Several 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 an 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, which reflect the universal need for modern, efficient communication. PBX standards have evolved towards unified communications (UC), a single system connecting wireless and wired phones, email, instant messaging, and voicemail while granting users presence status.

The interface standards most commonly used with PBXs are Digital Interface (DI), Analog Interface (AI), Integrated Services Digital Network Primary Rate Interface (ISDN-PRI), and Token Ring. DI is the interface standard for connecting a PBX to the Public Switched Telephone Network (PSTN). AI is the interface standard for connecting a PBX to the local loop of the PSTN. ISDN-PRI is the interface standard for connecting a PBX to an ISDN network. Token Ring is an interface standard for connecting a PBX to a Local Area Network (LAN).

Digital Interface (DI) is the interface standard for connecting a PBX to the Public Switched Telephone Network (PSTN). DI provides higher quality voice and data transmission than Analog Interface (AI), making it the interface standard of choice for most business applications. DI also supports caller ID, call waiting, and three-way calling. 

Analog Interface (AI) is the interface standard for connecting a PBX to the local loop of the PSTN. AI is typically used for connecting PBXs to telephone lines in residential or small business applications. 

Integrated Services Digital Network Primary Rate Interface (ISDN-PRI) is the interface standard for connecting a PBX to an ISDN network. ISDN-PRI supports voice and data transmission at speeds of up to 1.544 Mbps. ISDN-PRI interface standard also supports caller ID, call waiting, and three-way calling.

Token Ring is an interface standard for connecting a PBX to a Local Area Network (LAN). Token Ring supports data transmission at speeds of up to 4 Mbps. Token Ring also supports voice and video transmission.

PBX interface standards have evolved towards unified communications (UC), a single system that connects wireless and wired phones, email, instant messaging, and voicemail while granting users presence status. UC is the interface standard for connecting a PBX to a UC system. UC supports voice and data transmission at speeds of up to 1 Gbps. UC also supports caller ID, call waiting, three-way calling, and voicemail. 

PBX interface standards are constantly evolving to meet the ever-changing needs of businesses and individuals. The proper interface standards for your application will depend on several factors, including the type of PBX you are using, the type of network you are connecting to, and the types of features you require.

With current VoIP equipment capable of handling over 100 calls concurrently, accessibility to PBX information is at a premium for many enterprises that lack 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 a printer) are used to connect various applications which access data. At the same time, network ports such as TCP and UDP can also stream information to applications. 

Interface standards for PBX have been adapted to work with these network ports and allow for easy integration of VoIP call data into business processes. The interface standards most commonly used with PBXs are Digital Interface (DI), Analog Interface (AI), Integrated Services Digital Network Primary Rate Interface (ISDN-PRI), and Token Ring. 

Other PBX interface standards have evolved to meet various 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 (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, one of the most common digital interface standards for fixed telephony equipment, was also created to connect PBXs to trunk lines. This interface standard can supply 2 to 30-circuit capability and is commonly carried on T1 or E1 connectors.

With the ever-growing popularity of VoIP, many manufacturers have adopted Session Initiation Protocol (SIP) as the interface standard for connecting a PBX to the IP network. SIP supports voice and data transmission at speeds of up to 1.544 Mbps. SIP also supports caller ID, call waiting, and three-way calling.

The interface standard you choose for your PBX will depend on several factors, including the type of PBX you are using, the type of network you are connecting to, and the types of features you require. With the ever-growing popularity of VoIP, many manufacturers have adopted SIP as the interface standard for connecting a PBX to the IP network. SIP supports voice and data transmission at speeds of up to 1.544 Mbps. SIP also supports caller ID, call waiting, and three-way calling.

PBX interface standards were initially used to connect telephone extensions to the branch. While plain old telephone service (POTS), the standard 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 essential 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 interface standard for cordless phone connection.

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