Main Tech Page

© 2017 DIGIFON

About ISDN for Live Audio Networking        by Dave Immer

ISDN stands for "Integrated Services Digital Network" and is so named because with it one can dial phone calls that handle combinations of voice, video, audio, data and control signals on a single digital subscriber loop connected to the local central office of the telephone company. ISDN is a worldwide standard accepted in over 100 nations where availability varies. ISDN service is typically delivered over a single ‘twisted pair’ of copper wires, identical to Plain Old Telephone Service (POTS) lines. ISDN service can also be delivered via fiber and converted to copper at the user premises.

These days you can’t really discuss ISDN without including the internet, or IP. Both are digital networks and both can deliver the same data. The difference is ISDN connections are circuit-switched 64kbs channels and IP connections are packet-switched  with optional average bit-rates. ISDN connections are a fixed, guaranteed speed, private and exclusive. Broadband IP connections have fluctuating conditions and share a common public network.

The ISDN specification guarantees a rock-solid bit-rate making it perfectly suited for live production audio. The internet is always presenting jitter, dropped packets and fluctuating bit-rates, particularly problematic for marginal-speed connections. But the disadvantages of IP are being overcome by improved up/download speeds and new audio coding algorithms.

For those of us involved in creating, producing and delivering audio for broadcast, entertainment, advertising and other uses, ISDN remains the standard network of choice. But ISDN is a mature technology and faces increasing pressure from IP: While ISDN has reliability and stability, broadband internet has the advantage of being practically ubiquitous and steadily getting faster.  This is significant because ISDN is sometimes not available or too expensive.

From 1995-2000, ISDN saw wide deployment throughout the US with many uses like internet access, file transfer, video conferencing, financial networking and broadcast audio. But with the ascendance of broadband internet, the community of users has shrunk and is now a niche collection of production audio facilities, agencies and voiceover talent. In it's heyday many of those involved in telecommunications believed that ISDN was destined to become the "Plain Old Telephone Service" of the near future. The great convenience of the public internet swept aside that prediction.

ISDN persists as a known quantity to many users who are comfortable with the technology and the popular hardware. And it is ISDN’s steady, reliable 64kbs channels that are it’s great strength. There are audio production studios who, as a matter of policy, will only accept ISDN connections and not IP. But one should avail themselves of the right tool for the job and have the ability to use IP when appropriate. ISDN (when available) remains the best choice for live audio networking.