Integrated Services Digital Network 1. Introduction Integrated Services Digital Network The Integrated Services Digital Network (ISDN) is a development of the plain ordinary telephone system (POTS) that enables it to carry data and other traffic as well as voice calls. Instead of using a continuously changing analogue voltage on the line between the network and your house, it uses pulses having one of a few discrete voltage levels to encode a series of digits. This is known as "pulse code modulation" (PCM). It is the original "digital subscriber loop" (DSL) technology. It is more complicated than the POTS way, but has some big advantages: Two simultaneous phone calls can be made (or more on primary rate), using the same pair of wires that your POTS telephone used to connect to. This is achieved by interleaving the data for each call, a technique called "time division multiplexing" (TDM). The phone company doesn't have to dig up the road to change to ISDN and effectively give you a second line. Calls can be connected much more quickly - typically within one second over ISDN, compared with 20 1
52
Embed
Integrated Service Digital Network Final,Final Report
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Integrated Services Digital Network
1. Introduction
Integrated Services Digital Network
The Integrated Services Digital Network (ISDN) is a development of the plain
ordinary telephone system (POTS) that enables it to carry data and other traffic as
well as voice calls. Instead of using a continuously changing analogue voltage on the
line between the network and your house, it uses pulses having one of a few discrete
voltage levels to encode a series of digits. This is known as "pulse code modulation"
(PCM). It is the original "digital subscriber loop" (DSL) technology. It is more
complicated than the POTS way, but has some big advantages:
Two simultaneous phone calls can be made (or more on primary rate), using
the same pair of wires that your POTS telephone used to connect to. This is
achieved by interleaving the data for each call, a technique called "time
division multiplexing" (TDM). The phone company doesn't have to dig up the
road to change to ISDN and effectively give you a second line.
Calls can be connected much more quickly - typically within one second over
ISDN, compared with 20 seconds or more over POTS. This is especially
important when connecting a home computer to an office network ("wide area
networking") or validating credit card transactions, for example.
Data can be sent faster (64,000 bits per second in each direction) and more
reliably, so data calls can be shorter and therefore cheaper. You don't need a
modem to exchange data between computers, although you will probably need
a cheaper "terminal adapter" (TA) or ISDN card instead. There is no modem
"training" time to wait for (and perhaps pay for) after the call connects.
1
Integrated Services Digital Network
Noise, distortion, echoes and crosstalk become inaudible, because the
telephone no longer has to measure an exact analogue value, it only has to
decide which of a few discrete voltages is present at any particular instant.
In most countries, the "trunk" network between telephone exchanges has
already been converted to digital technology, for this reason. ISDN just
extends it the "last mile" to your home.
The digits can represent any data, including faxes, files, web pages, sound,
pictures and ordinary voice calls. This is the meaning of "integrated
services".
(Figure Of ISDN)
2
Integrated Services Digital Network
So why isn't everyone using ISDN:-
ISDN may not be available in your area, because it is expensive to upgrade a
telephone exchange to support it. A "network termination unit" (NTU) may
also have to be installed at the user end (not necessary in North America),
and any "loading coils" removed from the line. Also, it won't work if you
live more than about 5 km from your local telephone exchange, which
affects around 10% of users, depending on location.
In order to make fast data calls, both ends must have digital connections.
Most internet service providers (ISPs) already support this. Voice calls can
be made from ISDN terminals to ordinary POTS phones without problems.
Long-distance ISDN data calls may be considerably more expensive than
voice calls because they can't be compressed. ISDN data calls may also be
charged by time in places where POTS calls are not normally timed. Voice
calls over ISDN typically cost the same as over POTS, however.
Supplementary services such as "caller display", "ring back when free" and
"charge advice" work differently (usually better) than on POTS lines, but are
not always available and may cost extra.
ISDN terminals often need a local power supply, which can be a problem in
emergencies. POTS phones normally take their power from the line.
3
Integrated Services Digital Network
Telephone companies developed ISDN (Integrated Services Digital
Network) as part of an effort to standardize subscriber services.
This included the User-Network Interface (UNI), better known as the local
loop.
The ISDN standards define the hardware and call setup schemes for end-to-
end digital connectivity.
These standards help achieve the goal of worldwide connectivity by ensuring
that ISDN networks easily communicate with one another.
In an ISDN network, the digitizing function is done at the user site rather than
the telephone company.
4
Integrated Services Digital Network
(Figure of ISDN Working)
Unlike POTS, ISDN is digital from end to end.
With asynchronous connections (POTS) the local loop is analog and requires
PCM (Pulse Code Modulation) - explained later.
Benefits of ISDN include:
Carries a variety of user traffic signals, including data, voice, and video
Offers much faster call setup than modem connections
B channels provide a faster data transfer rate than modems
B channels are suitable for negotiated Point-to-Point Protocol (PPP)
links
ISDN also provides more bandwidth than a traditional 56 kbps dialup
connection.
ISDN uses bearer channels, also called B channels, as clear data paths.
Each B channel provides 64 kbps of bandwidth.
An ISDN connection with two B channels would provide a total usable
bandwidth of 128 kbps.
Each ISDN B channel can make a separate serial connection to any other site
in the ISDN network.
ISDN lines can be used in conjunction with PPP encapsulation.
2.ISDN DEVICES
Terminal Equipment 1 (TE1)
This is any device that understands isdn signaling standards.
ISDN compatible device (Router with ISDN Interface)
TE1s connect to the ISDN network through a four-wire, twisted-pair
digital link
Example: Telephones, personal computers, fax machine or
Video conferencing machine.
5
Integrated Services Digital Network
Terminal Equipment 2 (TE2)
This is any device that does not understand the isdn signaling standard.
ISDN Non-compatible devices.
Will require a terminal adapter.
Example: Analog phone or modem, requires a TA (TE2 connects to TA).
Network Terminator Type 1 (NT1)
When you connect a te1 device to the isdn network, you use an nt1. An NT1
will connect any 2-wire te1 device to the isdn network.
Network Terminator Type 2 (NT2)
Devices using 4 wire cables must use an NT2 to convert the 4 wire connector
to a 2 wire connector that can be physically connected to the isdn network
through an NT1.
Terminal Adaptor (TA)
A terminal adaptor allows a non isdn device (a device that is a te2) to
communicate with the isdn network via an nt1. This is typically needed where
the device uses a non-polar electrical signaling system. Isdn’s electrical
signaling is bipolar, thus a converter is needed.
6
Integrated Services Digital Network
Local Termination (LT)
This is an nt1 at the ISP’s side of the connection.
Exchange Termination (ET)
This is the connection between the customer's last mile (local loop) connection
and the service provider's isdn network. Usually, this is the line card in the
isdn switch at the provider's local exchange office.
3.ISDN REFERENCE POINTS
R :-
This is the connection reference point designating the connection interface
between an isdn terminal adaptor and a non-isdn device. There really aren't
any standards for this reference point as this reference point was designated
for devices that allow non-isdn devices to communicate with the isdn devices.
Clearly there are many proprietary ways to do this, none of which are part of
any standard.
S/T :-
This is the connection reference point designating the connection interface
between an isdn capable device and a network terminator 1. Reference point’s’
is for user terminals that connect to the isdn network. Reference point’s’
defines connections between nt1 and nt2 devices. An s/t reference point
combines the functions of the s and the t reference points. S/t is governed by
the itu i.430 specification.
U:-
7
Integrated Services Digital Network
This is the connection reference point designating the connection interface
between an isdn nt1 and the isdn services presented by the isdn switch.
V:-
This is the connection reference point between the line termination equipment
and the exchange termination equipment.
Following Figure illustrates a sample ISDN configuration and shows three devices
attached to an ISDN switch at the central office. Two of these devices are ISDN-
compatible, so they can be attached through an S reference point to NT2 devices. The
third device (a standard, non-ISDN telephone) attaches through the reference point to
a TA. Any of these devices also could attach to an NT1/2 device, which would
replace both the NT1 and the NT2. In addition, although they are not shown, similar
user stations are attached to the far-right ISDN switch.
Figure Sample ISDN Configuration Illustrates Relationships Between
Devices and Reference Points:-
8
Integrated Services Digital Network
(FIGURE OF ISDN REFERANCE POINTS)
(FIGURE OF ISDN REFERANCE POINTS)
9
Integrated Services Digital Network
4. ISDN Services
There are two types of services associated with ISDN: • BRI • PRI
(FIGURE OF ISDN SERVICES)
10
Integrated Services Digital Network
4.1 ISDN BRI Service
The ISDN Basic Rate Interface (BRI) service offers two B channels
and one D channel (2B+D). BRI B-channel service operates at 64 kbps
and is meant to carry user data; BRI D-channel service operates at 16
kbps and is meant to carry control and signaling information, although
it can support user data transmission under certain circumstances.
The D channel signaling protocol comprises Layers 1 through 3 of
the OSI reference model. BRI also provides for framing control
and other overhead, bringing its total bit rate to 192 kbps.
The BRI physical layer specification is International
Can transport many types of Network traffic (Voice, Data, Video, Text, Graphics etc)
Faster Data transfer rate than modem
Faster Call setup than Modems
Carries a variety of user traffic, such as digital video, data, and telephone network services, using the normal phone circuit-switched network
Offers much faster call setup than modems by using out-of-band signaling (D channel)
Provides a faster data transfer rate than modems by using the 64-kbps bearer channel (B channel)
Can combine multiple B channels to bandwidth of 128 kbps Can negotiate PPP links Carries a variety of user traffic, such as digital video, data, and telephone
network services, using the normal phone circuit-switched network Offers much faster call setup than modems by using out-of-band signaling (D
channel) Often less than one second
Provides a faster data transfer rate than modems by using the 64-kbps bearer channel (B channel)
Can combine multiple B channels to bandwidth of 128 kbps Can negotiate PPP links
13.ISDN ADVANTAGES
36
Integrated Services Digital Network
The basic advantage of ISDN is to facilitate the user with multiple digital
channels. These channels can operate concurrently through the same one
copper wire pair.
The digital signals broadcasting transversely the telephone lines.
ISDN provides high data rate because of digital scheme which is 56kbps.
ISDN network lines are able to switch manifold devices on the single line
such as faxes, computers, cash registers credit cards readers, and many
other devices. These all devices can work together and directly be
connected to a single line.
ISDN takes only 2 seconds to launch a connection while other modems take
30 to 60 second for establishment.
14.ISDN DISADVANTAGEES
The disadvantage of ISDN lines is that it is very costly than the other
typical telephone system.
ISDN requires specialized digital devices just like Telephone Company.
15. CONCLUSION
ISDN is replacing our old analog phones and offers a lot of new services.
37
Integrated Services Digital Network
Easy way to transmit voice and data simultaneously at the same time using
advantages of a digital communication.
Due to its easy accessibility it is widely used.
16. REFERENCES
38
Integrated Services Digital Network
Thiagarajan Viswanathan, Telecommunication Switching Systems and
Networks by, PHI Learning Pvt. Ltd., New Delhi.
Communication Networks, A Leon-Garcia and Indra Widiaja, TMH,
New Delhi
Data and Computer Communications by W Stallings, Pearson Education