Which of the following are ISDN interfaces?

A. Asymmetric DSL Interface (ADSLI)

B. Basic Rate Interface (BRI)

C. Ultra-Advanced Rate Interface (UARI)

D. Primary Rate Interface (PRI)

E. Broadband-ISDN (B-ISDN) & ATM

Choose the most appropriate answer from the options given below:

The correct answer is B, D, and E only.

Key Points

• ISDN (Integrated Services Digital Network) is a circuit-switched telephone network system that also provides access to packet-switched networks for digital transmission of voice and data, offering better quality than analog systems.
• ISDN supports data transmission in increments of 64 kilobits per second (kbit/s) and can provide up to 128 kbit/s bandwidth in both upstream and downstream directions, achieved through channel bonding.

​Types of ISDN Interfaces:

• Basic Rate Interface (BRI): Includes two 64 Kbps B channels for data and one 16 Kbps D channel for signaling. BRI provides a total bandwidth of 144 Kbps (with overhead).
• Primary Rate Interface (PRI): Offers 23 or 30 B channels (depending on the country), each 64 Kbps, and one D channel at 64 Kbps. PRI provides a bandwidth of 1.536 Mbps, with some overhead.
• Broadband ISDN (B-ISDN): Relies on fiber optics and is designed to provide higher speeds than narrowband ISDN, using advanced technology for wider bandwidth services.

ISDN Services:

• Bearer Services:
  • These services transfer information (voice, data, video) between users without altering the content.
  • The network simply transmits the data without processing it, falling within the first three layers of the OSI model.
  • Bearer services are defined in the ISDN standard and can operate using circuit-switched, packet-switched, frame-switched, or cell-switched networks.
• Teleservices:
  • ​These services involve the network processing or changing the content of the data.
  • They correspond to OSI layers 4-7 and rely on bearer services.
  • Teleservices cater to complex user needs without requiring users to understand the details.
  • Examples include telephony, telefax, teletex, telex, videotex, and teleconferencing. However, these services are not yet standardized in ISDN.
• Supplementary Services:
  • These services add extra functionality to bearer and teleservices, such as reverse charging, call waiting, and message handling—common in modern telephone services.