Integrated Services Digital Network Explained
Integrated Services Digital Network (ISDN) is a set of communication standards for digital transmission of voice, video, data, and other network services over traditional circuits of the public switched telephone network (PSTN). Unlike the analog phone system, ISDN is all-digital, which enables faster and more reliable transmission.
Technical Specifications
ISDN supports data transmission speeds of up to 128 Kbps. The standard ISDN setup includes:
- Network Termination (NT): This device connects the physical phone lines to your ISDN equipment.
- ISDN Adapter (or Digital Modem): This adapter interfaces with your computer or other digital devices.
Types of ISDN
Basic Rate Interface (BRI)
BRI consists of two 64 Kbps bearer (B) channels and one 16 Kbps delta (D) channel, often written as 2B+D. This configuration is typically used for residential and small enterprise applications.
Primary Rate Interface (PRI)
PRI is more suited for larger organizations and can differ by region. In North America, PRI includes 23 B channels and one 64 Kbps D channel, often noted as 23B+D. In Europe, PRI usually consists of 30 B channels and one 64 Kbps D channel, or 30B+D.
Special Considerations
Equipment Requirements
Although ISDN uses existing telephone lines, it requires specific hardware:
- Network Terminator (NT1/NT2): Converts the ISDN line into something usable by ISDN devices.
- ISDN Adapters: Facilitate the connection of digital devices to the ISDN line. These are sometimes called digital modems.
Compatibility
ISDN lines need compatible devices on both ends. For example, to make an ISDN call, the receiving end must also have an ISDN setup.
Historical Context
ISDN emerged in the 1980s as an improvement over analog systems, initially seen as a revolutionary step in digital communications. However, its adoption faced challenges due to the need for specialized equipment and the emergence of more cost-effective broadband technologies. Despite this, ISDN played a crucial role in transitioning from analog to digital communication, setting the stage for contemporary digital networks.
Applicability
Voice and Video Communication
ISDN is well-suited for video conferencing and digital voice transmission because of its high data integrity and low latency.
Internet Access
In some regions, ISDN was used for early internet connections before broadband became widely available.
Comparisons
ISDN vs. DSL
- Speed: DSL generally offers higher speeds than ISDN.
- Hardware: DSL requires different modems and does not need separate network termination devices.
- Usage: While ISDN can handle a combination of voice and data on the same lines, DSL is primarily for data and requires a splitter for voice calls.
Related Terms
- PSTN: Public Switched Telephone Network, the analog system for voice communication that ISDN improved upon.
- Broadband: High-speed internet access that has largely replaced ISDN in many scenarios.
FAQs
What is the maximum data transfer speed of ISDN?
Do I need special equipment for ISDN?
Is ISDN still in use today?
References
- John C. Bellamy, “Digital Telephony,” Wiley, 2000.
- “ISDN and Broadband ISDN: With Frame Relay and ATM,” William Stallings, 2002.
Summary
ISDN marked a significant leap from analog to digital communications, utilizing traditional phone lines to deliver high-speed, reliable digital transmission for voice, video, and data. Although supplanted by more advanced broadband technologies, ISDN’s development paved the way for modern digital communication systems. Understanding ISDN’s components, types, and historical impact provides valuable insight into the evolution of telecommunications technology.
