Isdn - Integrated Services Digital Network

ISDN

INTEGRATED SERVICES DIGITAL NETWORK

Shaikh Sameer & Aparna Arora

II Year Engineering In Information Technology

SHAH & ANCHOR KUTCHHI ENGG. COLLEGE,

Mahavir Education Trust's Chowk,

W.T. Patil Marg, Chembur.

Mumbai - 400088.

Email : luv2sam786@yahoo.co.in , heartthrob_aps_86@yahoo.co.in

Figure 12-1 Sample ISDN Configuration Illustrates Relationships Between Devices and Reference Points

ISDN applications

TABLE OF CONTENTS

1. INTRODUCTION

2. HISTORY OF ISDN

3. INTERFACES

4. ISDN LAYERS

5. ISDN INFORMATION ELEMENTS

6. ISDN REFERENCE POINTS

7. APPLICATIONS OF ISDN

8. ADVANTAGES

9. DISADVANTAGES

10. CONCLUSION

11. REFERENCES

ABSTRACT

This paper presents a brief overview of ISDN. The modem, a breakthrough in computer communications, allowed computers to communicate by converting their digital information into an analog signal to travel through the PSTN. There is an upper limit to the amount of information that an analog telephone line can hold. Currently, it is about 56 kb/s bidirectionally, but are limited by the quality of the analog connection and go only about 45-50 kb/s. Some phone lines do not support 56 kb/s connections at all.

ISDN which stands for INTEGRATED SERVICE DIGITAL NETWORK allows multiple digital channels to be operated simultaneously through the same regular phone wiring used for analog lines, 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.

1. INTRODUCTION

ISDN, which stands for Integrated Services Digital Network, is a system of digital phone connections which has been available for over a decade. This system allows voice, video, data and graphics to be transmitted simultaneously across the world at very high speeds using end-to-end digital connectivity over standard communication lines.

There are two basic types of ISDN service: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). BRI consists of two 64 kb/s B channels and one 16 kb/s D channel for a total of 144 kb/s.

The ISDN Basic Rate Interface (or BRI) is a standard connection you would have in any home or small business, offering two simultaneous connections (any mix of fax, voice and data). When used as a data connection, ISDN BRI can offer two independent data channels of 64kbps each, or 128kbps when combined into one connection. The ISDN Primary Rate Interface (or PRI) offers 30 channels (of 64kbps each), giving a total of 1920kbps. These channels, known as "bearer" or "B" channels, are at the heart of the flexibility of ISDN.

PRI is intended for users with greater capacity requirements. Typically the channel structure is 23 B channels plus one 64 kb/s D channel for a total of 1536 kb/s. In Europe, PRI consists of 30 B channels plus one 64 kb/s D channel for a total of 1984 kb/s.

2. HISTORY OF ISDN

The early phone network consisted of a pure analog system that connected telephone users directly by a mechanical interconnection of wires. This system was very inefficient, was very prone to breakdown and noise, and did not lend itself easily to long-distance connections. Beginning in the 1960s, the telephone system gradually began converting its internal connections to a packet-based, digital switching system. A standards movement was started by the International Telephone and Telegraph Consultative Committee (CCITT), now known as the International Telecommunications Union (ITU). The ITU is a United Nations organization that coordinates and standardizes international telecommunications.

In the early 1990s, an industry-wide effort began to establish a specific implementation for ISDN in the U.S. Members of the industry agreed to create the National ISDN 1 (NI-1) standard so that end users would not have to know the brand of switch they are connected to in order to buy equipment and software compatible with it. However, there were problems agreeing on this standard. In fact, many western states would not implement NI-1. Both Southwestern Bell and U.S. West (now Qwest) said that they did not plan to deploy NI-1 software in their central office switches due to incompatibilities with their existing ISDN networks.

Ultimately, all the Regional Bell Operating Companies (RBOCs) did support NI-1. A more comprehensive standardization initiative, National ISDN 2 (NI-2), was later adopted. Some manufacturers of ISDN communications equipment, such as Motorola and U S Robotics (now owned by 3Com), worked with the RBOCs to develop configuration standards for their equipment. These kinds of actions, along with more competitive pricing, inexpensive ISDN connection equipment, and the desire for people to have relatively low-cost high-bandwidth Internet access have made ISDN more popular in recent years.

3. INTERFACES

The U interface is a two-wire (single pair) interface from the phone switch, the same physical interface provided for POTS lines. It supports full-duplex data transfer over a single pair of wires, therefore only a single device can be connected to a U interface. This device is called an Network Termination 1 (NT-1). The NT-1 is a relatively simple device that converts the 2-wire U interface into the 4-wire S/T interface. The S/T interface supports multiple devices (up to 7 devices can be placed