Integrated Services Digital Network is ...

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<h2>Integrated Services Digital Network</h2><div class="wp-caption alignright" style="width: 310px"><a href="http://content.answcdn.com/main/content/img/CDE/ISDN1.GIF" target="_blank"><img title="Integrated Services Digital Network" alt="Integrated Services Digital Network" src="http://content.answcdn.com/main/content/img/CDE/ISDN1.GIF" width="300" height="270" /></a> </div><div class="wp-caption alignright" style="width: 310px"><a href="http://www.windowsnetworking.com/img/upl/image003_b1123756471079.gif" target="_blank"><img title="Integrated Services Digital Network" alt="Integrated Services Digital Network" src="http://www.windowsnetworking.com/img/upl/image003_b1123756471079.gif" width="150" height="135" /></a> </div><div class="wp-caption alignright" style="width: 310px"><a href="http://www.althos.com/sample_diagrams/ag_ISDN_System_low_res.jpg" target="_blank"><img title="Integrated Services Digital Network" alt="Integrated Services Digital Network" src="http://www.althos.com/sample_diagrams/ag_ISDN_System_low_res.jpg" width="150" height="135" /></a> </div>
Integrated Services for Digital Network is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network. It was 1st defined in 1988 in the CCITT red book. Prior to ISDN, the telephone system was viewed as a way to transport voice, with some special services available for data. The key feature of ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system. There are several kinds of access interfaces to ISDN defined as Basic Rate Interface (BRI), Primary Rate Interface (PRI), Narrowband ISDN (N-ISDN), and Broadband ISDN (B-ISDN).
ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in potentially better voice quality than an analog phone can provide. It offers circuit-switched connections, and packet-switched connections (for data), in increments of 64 kilobit/s. A major market application for ISDN in some countries is Internet access, where ISDN typically provides a maximum of 128 kbit/s in both upstream and downstream directions. Channel bonding can achieve a greater data rate; typically the ISDN B-channels of three or four BRIs (six to eight 64 kbit/s channels) are bonded.
ISDN should not be mistaken for its use with a specific protocol, such as Q.931 whereby ISDN is employed as the network, data-link and physical layers in the context of the OSI model. In a broad sense ISDN can be considered a suite of digital services existing on layers 1, 2, and 3 of the OSI model. ISDN is designed to provide access to voice and data services simultaneously.
However, common use reduced ISDN to be limited to Q.931 and related protocols, which are a set of protocols for establishing and breaking circuit switched connections, and for advanced calling features for the user. They were introduced in 1986.
In a videoconference, ISDN provides simultaneous voice, video, and text transmission between individual desktop videoconferencing systems and group videoconferencing systems.
Integrated services refers to ISDN's ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of most people's complete communications needs at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. It also refers to integrated switching and transmission in that telephone switching and carrier wave transmission are integrated rather than separate as in earlier technology.
The entry level interface to ISDN is the Basic(s) Rate Interface (BRI), a 128 kbit/s service delivered over a pair of standard telephone copper wires. The 128 kbit/s payload rate is broken down into two 64 kbit/s bearer channels ('B' channels) and one 16 kbit/s signaling channel ('D' channel or data channel). This is sometimes referred to as 2B+D.
BRI-ISDN is very popular in Europe but is much less common in North America. It is also common in Japan â€" where it is known as INS64.
The other ISDN access available is the Primary Rate Interface, which is carried over an E1 (2048 kbit/s) in most parts of the world. An E1 is 30 'B' channels of 64 kbit/s, one 'D' channel of 64 kbit/s and a timing and alarm channel of 64 kbit/s.
In North America PRI service is delivered on one or more T1 carriers of 1544 kbit/s (24 channels). A PRI has 23 'B' channels and 1 'D' channel for signalling (Japan uses a circuit called a J1, which is similar to a T1). Inter-changeably but incorrectly, a PRI is referred to as T1 because it uses the T1 carrier format. A true T1 (commonly called "Analog T1" to avoid confusion) uses 24 channels of 64 kbit/s of in-band signaling. Each channel uses 56 kb for data and voice and 8 kb for signaling and messaging. PRI uses out of band signaling which provides the 23 B channels with clear 64 kb for voice and data and one 64 kb 'D' channel for signaling and messaging. In North America, Non-Facility Associated Signalling allows two or more PRIs to be controlled by a single D channel, and is sometimes called "23B+D + n*24B". D-channel backup allows for a 2nd D channel in case the primary fails. NFAS is commonly used on a T3.
PRI-ISDN is popular throughout the world, especially for connecting PBXs to PSTN.
While the North American PSTN can use PRI or Analog T1 format from PBX to PBX, the POTS or BRI can be delivered to a business or residence. North American PSTN can connect from PBX to PBX via Analog T1, T3, PRI, OC3, etc...
Even though many network professionals use the term "ISDN" to refer to the lower-bandwidth BRI circuit, in North America BRI is relatively uncommon whilst PRI circuits serving PBXs are commonplace.
Each one of these channels is known as a DS0.
Most B channels can carry a 64 kbit/s signal, but some were limited to 56K because they traveled over RBS lines. This was commonplace in the 20th century, but has since become less so.
The signaling channel (D) uses Q.931 for signaling with the other side of the link.
In theory, Frame Relay can operate over the D channel of BRIs and PRIs, but it is seldom, if ever, used.
There are two points of view into the ISDN world. The most common is that of the end-user, who wants a digital connection into the telephone network from home, whose performance would be better than a 20th-century analog 56K modem connection. Discussion on the merits of various ISDN modems, carriers' offerings and tariffs are from this perspective. Since the principal consumer application is for Internet access, ISDN was mostly superseded by DSL in the early 21st century. Inexpensive ADSL service offers speeds up to 5 Mbit/s, while more expensive versions are improving in speed all the time. By 2010, ADSL speeds of several millions of bits per 2nd had become commonplace, thus making ISDN obsolete before it fairly started.
There is a 2nd viewpoint: that of the telephone industry, where ISDN is a core technology. 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 T1 or E1. Between telephone company switches, the signaling is performed via SS7. Normally, a PBX is connected via a T1 with robbed bit signaling to indicate on-hook or off-hook conditions and MF and 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 tone sequences. This results in faster call setup times. Also, a greater number of features are available and fraud is reduced.
ISDN is also used as a smart-network technology intended to add new services to the public switched telephone network 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.
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. IP based streaming codecs are starting to gain a foothold in the broadcast sector, using broadband internet to connect remote studios. However reliability and latency is crucially important for broadcasters and the quality of service offered by ISDN has not yet been matched by packet switched alternatives.
ISDN-BRI never gained popularity as a general use telephone access technology in Canada and the US, and remains a niche product. The service was seen as a solution in search of a problem, and the extensive array of options and features were difficult for customers to understand and use. ISDN has long been known by derogatory backronyms highlighting these issues, such as It Still Does Nothing, Innovations Subscribers Don't Need, and I Still Don't kNow.
Once the concept of broadband Internet access came to be associated with data rates incoming to the customer at 256 kbit/s or more,[a] and alternatives like ADSL grew in popularity, the consumer market for BRI didn't develop. Its only remaining advantage is that while ADSL has a functional distance limitation and can use ADSL loop extenders, BRI has a greater limit and can use repeaters. As such, BRI may be acceptable for customers who are too remote for ADSL. Widespread use of BRI is further stymied by some small North American CLECs such as CenturyTel having given up on it and not providing Internet access using it. However, AT&T in most states will still install an ISDN BRI line anywhere a normal analog line can be placed and the monthly charge is roughly $55.
ISDN-BRI is currently primarily used in industries with specialized and very specific needs. High-end videoconferencing hardware made by companies such as Sony, Polycom, Tandberg, and LifeSize via the LifeSize Networker can bond up to 8 B-channels together to provide digital, circuit-switched video connections to almost anywhere in the world. This is very expensive, and is being replaced by IP-based conferencing, but where cost concern is less of an issue than predictable quality and where a QoS-enabled IP does not exist, BRI is the preferred choice.
<h3>Related Sites for Integrated Services Digital Network</h3>
<ul><li>Integrated Services Digital Network - DocWiki - Cisco Systems, Inc <a href="http://docwiki.cisco.com/wiki/Integrated_Services_Digital_Network" target="_blank">read Integrated Services Digital Network</a></li>
<li>Integrated Services Digital Network â€"â€¦ <a href="http://de.wikipedia.org/wiki/Integrated_Services_Digital_Network" target="_blank">read Integrated Services Digital Network</a></li>
<li>History of Integrated Services Digital Network (ISDN) <a href="http://ezinearticles.com/?History-of-Integrated-Services-Digital-Network-(ISDN)&id=3312583" target="_blank">read Integrated Services Digital Network</a></li>
<li>The Benefits of Integrated Services Digital Network (ISDN) <a href="http://ezinearticles.com/?The-Benefits-of-Integrated-Services-Digital-Network-(ISDN)&id=3319819" target="_blank">read Integrated Services Digital Network</a></li></ul>

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tags: Integrated, Services, Digital, Network, Integrated Services Digital Network, isdn, telephone, channel, kbit/s

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