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Integrated Services Digital Network
ISDN
is a completely digital telephone/telecommunications network which carries voice, data, and video over existing telephone network infrastructure. It is designed to provide a single interface for hooking up a phone, fax machine, PC, etc.

Why ISDN?

ISDN is an ideal solution for a wide range of applications. To help you determine whether or not ISDN is right for your organization, consider the following characteristics. If your application has one or more of these requirements, ISDN may be a perfect choice.

 

• High-speed dial-up connections to central LANs from numerous remote sites.
• Low-cost access to fast packet services.
• Increased interoperability based on well-defined international standards.
• Simultaneous use of data, voice, images, video, and other services.
• Intermittent connections rather than constant traffic.
• Rapid intracompany and intercompany communications.
• Cost-effective alternative to expensive leased lines.
• High-speed alternative to analog dial-up service.
• Redundant back-up for network integrity and disaster recovery.
• High-performance access to large, graphical files.

ISDN: A Definition

ISDN, Integrated Services Digital Network, is a service provided by local telephone companies which modifies regular telephone lines so that they can transmit data almost five times as fast as the fastest analog modems currently available. In addition to the significant increase in transmission speed, ISDN also allows the transmission of not only data, but a combination of data, voice, and video simultaneously on one line. This integration of voice, data and video on a single line means that one does not have to buy multiple services to meet data or voice communication needs. The economies of scale in an integrated network allow the carriers to offer these services at a lower cost than if provisioned separately. Additionally, a customer only needs to obtain a single access line to use these multiple services, saving dollars on initial installation and setup, as well as on long-term support.

This combination of services has numerous applications. For example, two users can engage in a face-to-face meeting and simultaneously edit a shared document. Seminars and lectures can be broadcast over networks so that employees can attend while seated at their desks. Known as desktop videoconferencing, this application has experienced significant growth over the past few years.

ISDN converts internet access from a painfully slow trial of patience to an enjoyable, productive, information gathering activity, especially on the graphic intensive pages of the world wide web. Pages previously accessed in minutes now appear in just seconds.

ISDN greatly increases the feasibility of telecommuting. Not long ago, corporations grasped telecommuting only as a laborious process which a few employees were forced to perform due to the need to work at multiple locations. Now, however, partly as a result of increasing rents and federal regulations which motivate corporations to reduce the number of commuters, and primarily due to the increased speeds provided by ISDN, corporate America embraces telecommuting via ISDN as the primary means to increased productivity. Employees can access all office files from their homes or remote locations, hold meetings, attend conferences, and edit shared documents in real time.

ISDN provides higher speeds than [POTS] by allowing data to be transferred digitally from end to end. In contrast POTS converts the digital data to analog within the local loop that extends into the home or office, significantly reducing transmission speed.

Converting to an ISDN compatible configuration for the consumer only requires an additional piece or two of relatively inexpensive hardware. Telecommuting to an office or base requires additional equipment at the base. While ISDN usage costs are slightly more expensive than analog telephone lines, users enjoy significant benefits which more than justify the costs. Most importantly, ISDN is available in most locations now

What Does ISDN DO ?

In the traditional analog network, the telephone company's central office is connected to the customer, through a two-wire loop. This connection supports either voice or data in a single transmission channel. With ISDN, the same twisted pair can support multiple channels, logically divided to support BOTH voice and data. When a regular telephone line is connected to ISDN, the ISDN-capable digital switch at the CO generates two new types of channels. The first of these, the 'B' or 'bearer' channel lines, transmits at 64 Kbps and is designed to carry the full range of voice, circuit switched data and packet switched data transmission- in other words, the information the subscriber wants to send over the network. There are two B channels established for each ISDN line.

The other type of channel, the D Channel, is used primarily for controlling the flow of information from the network, providing call-signaling and set-up information and other overhead functions, and transmitting lower speed packets. The advantage of the D Channel in ISDN is that it provides the signals, and the bearer channels are free to carry other information. In other signaling, such as POTS, signaling is combined with the same channel, a technique called in-band signaling.:

In the context of ISDN products, the term "BONDING" may appear periodically. This indicates that the device is capable of performing [inverse multiplexing] of many lower speed lines to provide Bandwidth ON Demand in order to aggregate traffic to the higher rates of 384 Kbps or 1,536 Kbps.

The B and D Channel types are grouped into data transmission structures that are offered to users as a package.

There are two kinds of service that can be provided, Basic Rate Interface and Primary Rate Interface.

Basic Rate Interface Basic Rate, or BRI Service, consists of two full duplex 64 [Kbps] [B Channels] and one 16 [D Channel]. BRI lines are typically deployed in small branch offices or in a home [telecommuting] office, and can be referred to as 2B+D.

Primary Rate Interface Primary Rate, or PRI Service, is deployed for users with much larger bandwidth requirements, such as large PBXs or high performance video desktop conferencing systems. In North America and Japan, the PRI interface runs at a data rate of 1,536 Kbps and is divided into 23 B Channels and one 64 Kbps D Channel. This can be referred to as 23B+D.

In Europe, a standard of 2,048 Kbps is used, which gives a Primary Rate consisting of 30 B Channels and 1 D Channel. In addition to the "standard" channels above, users can obtain equipment to form other data rates more specifically suited to a particular application. Through a process known as [inverse multiplexing], a user can create channels with bandwidths of 384 Kbps and, in turn, create a group of high bandwidth "pipes" within a primary rate interface.

ISDN Equipment and Interface Terminology