Integrated Services Digital Network (ISDN) is a technology that was created in the 1980s. This technology grew in popularity because it can deliver high speed voice, video, images, data, etc. This article will explore ISDN, the related technology for ISDN communication and how to record calls using this communications standard.
What is ISDN?
ISDN is a set of communications standards that uses digital communication to transmit voice, data and signaling over a Public Switched Telephone Network (PSTN). The purpose of ISDN was to replace outdated landlines to digital lines and improve communication by providing higher speed and better quality.
The problem ISDN solves.
ISDN was designed to create an end-to-end digital communication.
In the image above, the user wants to dial their Internet Service Provider (ISP) from their computer and they want to connect to the internet. The ISP provides the user a connection to the internet. The language the computer uses for communication is in digital. The telephone lines are analog phone lines. In order to communicate from the digital computer to the analog phone line there was a device that would modulate the signal and demodulate the signal at both ends. This device was called a modulator demodulator (MODEM). When the signal reaches the Public Switched Telephone Network (PSTN) the signaling is digital within the network. The signal is analog between the PSTN and the ISP and there is a modem connecting to the ISP server where that device is digital. In this scenario, the signal goes from digital to analog to digital to analog to digital.
ISDN solves this by keeping the signal as digital end to end. ISDN is an interface that provides digital end-to-end communication over regular phone lines. In terms of telephony benefits, ISDN allows users to transmit multiple phone calls as digital audio over regular analog PSTN lines.
ISDN includes three protocol standards E, I and Q series.
The E series refers to telephone equipment such as E.163 or E.164. This refers to the existing telephone network. The E.163 refers to the international telephone numbering plan and E.164 is the international addressing plan. This ensures that each device has a unique number where texts and calls are routed correctly to individual devices in every country. The E.163 was the old standard and replaced by E.164.
The I series refers to concepts, aspects and interfaces. These include the series:
- I.100 – Concepts, structures and terminology.
- I.200 – Service capabilities to be provided to users.
- I.300 – Network aspect such as protocol reference model, channel signaling, addressing and numbering.
- I.400 – User network interfaces, functional grouping and reference points, transmissions rates and Open Systems Interconnection (OSI) layer protocol specifications.
- I.500 – Inter-network interfaces for working between ISDN, Public Switched Telephone Network (PSTN), Packet Switched Public Data Network (PSPDN), Public Data Network (PDN), etc.
- I.600 – These are maintenance principles to test for failures, verification, etc.
The Q series refers to switching and signaling.
What is BRI?
Basic Rate Interface (BRI) provides two bearer channels (B channels) and one delta channel (D channel). The two B channels are 64k. The D channel is 16k and used for signaling, or to setup or tear down the link of communication. The B channels are used to transmit or “bear” the data. In terms of telephony benefits, BRI line can replace two analog phone lines.
What is PRI?
ISDN lines are often used as telecom trunk lines. A common call recording scenario is a passive recording from the trunk lines setup (Scenario 3). This configuration utilizes special PRI Line recording boards. Call traffic and signaling is passively collected and recorded by call recording software.
What is the common method to record ISDN BRI and PRI lines?
In general, companies should pursue Active Recording based on CSTA protocols whenever possible. This configuration provides the ability to record digital and VoIP phones, remote sites to a centralized recorder and there is no need for individual phone wiring to the recorder. In essence, this configuration provides the most flexible method of recording.
Analog and TDM lines are recorded lines tapped (connected in parallel) to recording boards. For more information about setting up this scenario or any other call recording configuration, please contact us.
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Last Updated on June 28, 2022