Editing ISDN (section)

== Uses ==

=== Telephone industry ===

ISDN is a core technology in the telephone industry. A [[telephone network]] can be thought of as a collection of wires strung between switching systems. The common electrical specification for the signals on these wires is [[Digital Signal 1|T1]] or [[E-carrier|E1]]. Between telephone company switches, the signaling is performed via [[Signaling System No 7|SS7]]. Normally, a PBX is connected via a T1 with [[robbed bit signaling]] to indicate on-hook or off-hook conditions and [[Multi-frequency|MF]] and [[Dual-tone multi-frequency|DTMF]] tones to encode the destination number. ISDN is much better because messages can be sent much more quickly than by trying to encode numbers as long (100 [[Millisecond|ms]] per digit) tone sequences. This results in faster call setup times. Also, a greater number of features are available and fraud is reduced.

In common use, ISDN is often limited to usage to [[Q.931]] and related protocols, which are a set of [[Signaling (telecommunications)|signaling protocol]]s establishing and breaking circuit-switched connections, and for advanced [[calling feature]]s for the user.<ref>{{cite journal |last1 =Aaron |first1 =R | last2 = Wyndrum | first2 = R |title= Future trends |journal= IEEE Communications Magazine |date=March 1986 | volume = 24 | issue = 3 | pages = 38–43 | publisher = [[AT&T Bell Laboratories]] |doi= 10.1109/MCOM.1986.1093028}}</ref> Another usage was the deployment of [[videoconference]] systems, where a direct end-to-end connection is desirable. ISDN uses the [[H.320]] standard for [[audio coding]] and [[video coding]].

ISDN is also used as a smart-network technology intended to add new services to the [[public switched telephone network]] (PSTN) by giving users direct access to end-to-end circuit-switched digital services and as a backup or failsafe circuit solution for critical use data circuits.

=== Video conferencing ===

One of ISDNs successful use-cases was in the [[videoconference]] field, where even small improvements in data rates are useful, but more importantly, its direct end-to-end connection offers lower latency and better reliability than packet-switched networks of the 1990s. The [[H.320]] standard for [[audio coding]] and [[video coding]] was designed with ISDN in mind, and more specifically its {{nowrap|64 kbit/s}} basic data rate. including [[audio codecs]] such as [[G.711]] ([[Pulse-code modulation|PCM]]) and [[G.728]] ([[CELP]]), and [[discrete cosine transform]] (DCT) [[video codecs]] such as [[H.261]] and [[H.263]].<ref>{{cite news |last1=Davis |first1=Andrew |title=The H.320 Recommendation Overview |url=https://www.eetimes.com/document.asp?doc_id=1275886 |access-date=7 November 2019 |work=[[EE Times]] |date=13 June 1997 |archive-date=2 January 2016 |archive-url=https://web.archive.org/web/20160102055138/http://www.eetimes.com/document.asp?doc_id=1275886 |url-status=live }}</ref><ref>{{cite book |title=IEEE WESCANEX 97: communications, power, and computing : conference proceedings |date=May 22–23, 1997 |publisher=[[Institute of Electrical and Electronics Engineers]] |location=University of Manitoba, Winnipeg, Manitoba, Canada |isbn=9780780341470 |page=30 |url=https://books.google.com/books?id=8vhEAQAAIAAJ |quote=H.263 is similar to, but more complex than H.261. It is currently the most widely used international video compression standard for video telephony on ISDN (Integrated Services Digital Network) telephone lines.}}</ref>

=== Broadcast industry ===

ISDN is used heavily by the broadcast industry as a reliable way of switching low-latency, high-quality, long-distance audio circuits. In conjunction with an appropriate [[codec]] using MPEG or various manufacturers' proprietary algorithms, an ISDN BRI can be used to send stereo bi-directional audio coded at {{nowrap|128 kbit/s}} with 20&nbsp;Hz&nbsp;– 20&nbsp;kHz audio bandwidth, although commonly the [[G.722]] algorithm is used with a single {{nowrap|64 kbit/s}} B channel to send much lower latency mono audio at the expense of audio quality. Where very high quality audio is required multiple ISDN BRIs can be used in parallel to provide a higher bandwidth circuit switched connection. [[BBC Radio 3]] commonly makes use of three ISDN BRIs to carry {{nowrap|320 kbit/s}} audio stream for live outside broadcasts. ISDN BRI services are used to link remote studios, sports grounds and [[Remote broadcast|outside broadcasts]] into the main [[Recording studio|broadcast studio]]. ISDN via satellite is used by field reporters around the world. It is also common to use ISDN for the return audio links to remote satellite broadcast vehicles.

In many countries, such as the UK and Australia, ISDN has displaced the older technology of equalised analogue landlines, with these circuits being phased out by telecommunications providers. Use of IP-based streaming codecs such as [[Comrex]] ACCESS and [[ipDTL]] is becoming more widespread in the broadcast sector, using broadband internet to connect remote studios.<ref>{{cite web|last1=McCoy|first1=Jason|title=IPDTL, Source-Connect vs Skype for voice over talent|url=http://mccoyproductions.net/live-directed-voice-over-sessions-via-ipdtl-source-connect-and-skype/|publisher=McCoy Productions|access-date=16 March 2015|date=2014-02-05|archive-date=2015-02-28|archive-url=https://web.archive.org/web/20150228184624/http://mccoyproductions.net/live-directed-voice-over-sessions-via-ipdtl-source-connect-and-skype/|url-status=dead}}</ref>

=== Backup lines ===

Providing a backup line for business's inter-office and internet connectivity was a popular use of the technology.<ref>{{Cite web|url=https://www.cisco.com/c/en/us/support/docs/dial-access/dial-on-demand-routing-ddr/11047-backup-11047.html|title=BRI ISDN Backup With Backup Interface|website=Cisco|language=en|access-date=2020-03-04|archive-date=2020-03-04|archive-url=https://web.archive.org/web/20200304102125/https://www.cisco.com/c/en/us/support/docs/dial-access/dial-on-demand-routing-ddr/11047-backup-11047.html|url-status=live}}</ref>