Intruction to ISDN
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Abbreviation of integrated services digital network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second).
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Applications of ISDN
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Some applications of ISDN are..
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Internet Access
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ISDN is a fast, accurate, economical conduit for all kinds of Internet-based information, including global email, file transfer, news groups, bulletin boards and interactive applications. Emerging applications include electronic commerce and low-speed video and radio broadcasting. Net surfers can even cruise virtual malls to shop the world for goods and services in a convenient and secure sales environment.
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Telecommuting or Work-at-Home
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Both for full-time telecommuters and for those who work at home, ISDN supports fast, reliable LAN access, enhanced voice services, corporate email, file transfer, remote printing and all the other functions available to those that work in an office environment.
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Video Conferencing
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ISDN supports distance learning, business training, administrative conferencing and a wide range of other video-based applications with high fidelity audio and broadcast-quality, full color, full motion images. ISDN can be configured as set-top TV to PC, and PC to PC video conferencing at either 128 Kbps or 384 Kbps.
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Branch Office Communications
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ISDN provides high-performance, cost-effective connections for transferring information and linking your multiple business locations to create a fast, smooth-running Wide Area Network (WAN).
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Standby Inter-Networking
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ISDN can help you minimize the risks of outages or overflows by providing reliable, high-speed back up and extra bandwidth on a cost-effective, dial-up basis.
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Point-of-Sale Services
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ISDN delivers the speed and performance formerly associated only with costly private lines – at economical, public network prices. With ISDN, transaction times for processing credit card sales averages just four to six seconds. Compare that to analog telephone lines, which range from 30 to 60 seconds. That's especially important to queue-sensitive and high-volume retailers.
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Telemedia/Desktop Publishing
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ISDN offers the bandwidth and digital clarity to support such publishing-related functions as typesetting, processing color separations, creating printing plates, color scanning of photographs and page layout proofing. When turnaround speed is essential, ISDN is an ideal solution.
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Telemetry/Security
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With ISDN, a central surveillance site can visually observe numerous remote locations, while monitoring the status of alarms and access control devices.
The B channels provide connectivity for video and the D channel accommodates the other alarm inputs.
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channels of ISDN
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B Channel
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Operate at 64 Kbps. Carries information for user services including voice, audio,
video and digital data.
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D Channel
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Operate at 16 Kbps. Carries signals between the user and the network. This may also
carry user data packets.
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H Channel
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Operate at N X 64 Kbps. Carries information for user services including voice,
Audio, video and digital data.
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ISDN Services
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ISDN offers two services
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1- Basic Rate Interface (BRI)
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consists of two 64-Kbps B-channels and one D-channel for transmitting control information.
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2-Primary Rate Interface (PRI)
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consists of 23 B-channels and one D-channel (U.S.) or 30 B-channels and one D-channel (Europe).
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ISDN Advantages
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SPEED
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ISDN allows multiple digital channels to be operated simultaneously through the same regular phone wiring used for analog lines. The change comes about when the telephone company's switches can support digital connections. Therefore, the same physical wiring can be used, but a digital signal, instead of an analog signal, is transmitted across the line. This scheme permits a much higher data transfer rate than analog lines. BRI ISDN, using a channel aggregation protocol such as BONDING or Multilink-PPP, supports an uncompressed data transfer speed of 128 kb/s, plus bandwidth for overhead and signaling. In addition, the latency, or the amount of time it takes for a communication to begin, on an ISDN line is typically about half that of an analog line. This improves response for interactive applications, such as games.
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MULTIPLE DEVICES ON SINGLE LINK
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Previously, it was necessary to have a separate phone line for each device you wished to use simultaneously. For example, one line each was required for a telephone, fax, computer, bridge/router, and live video conference system. Transferring a file to someone while talking on the phone or seeing their live picture on a video screen would require several potentially expensive phone lines.
ISDN allows multiple devices to share a single line. It is possible to combine many different digital data sources and have the information routed to the proper destination. Since the line is digital, it is easier to keep the noise and interference out while combining these signals. ISDN technically refers to a specific set of digital services provided through a single, standard interface. Without ISDN, distinct interfaces are required instead.
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ISDN Disadvantages
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1-An external power supply is required. The telco's don't supply power for ISDN lines. If the power fails, the phones won't work.
2-Special digital phones are required or a Terminal Adapter to talk to the existing POTS devices.
3-It is very expensive to upgrade a central office switch ($500,000+) to ISDN
4-If the ISDN fails - the phone fails.