about telephone network notes

1. SUBMITTED BY,
T. JANANI M.Sc.,
NSCAS

2.  The earliest electronic network is the telephone system.
 This telephone network commonly uses analog technology
that was quite different from digital technology used in the
computer-based networks.
 The advantages of digital technology over the analog
technology in terms of economics and services forced the
telephone industry to move rapidly to install fiber and digital
networks.

3.  The telephone network transmits analog signals and
hence a modem is required whenever a computer or
terminal is connected to the telephone line.
 The modem then converts digital data from a computer
to an analog signal that can be transmitted via a
telecommunication line and converts the analog signal
received to computer data.

4.  The telephone network consists of the subscriber's
line, switchboards, and trunk lines.
 Each subscriber line has an address, i.e. telephone
number. When a caller transmits a dial signal to the
switchboard, the switchboard connects the caller's
subscriber line to that of the receiver, enabling
communication
 The trunk line between the caller and the receiver is
occupied until either discontinues the communication.

5.  When the telephone system is to connect with a
network, it becomes necessary to dial the telephone
number to select the target device on the network.
 A device called Network Control Unit (NCU)
performs this, and most of the available modems,
include this NCU.

8.  A computer can be connected permanently to the
Internet using leased lines in addition to a modem
and router.
 These lines are based on speed of the connection,
installation cost, and recurring monthly charges.
 An example of usage of leased line is a system in
which only one terminal is connected to the host
computer.

9.  Though multiple computers /terminals using
multiplexing can be connected to one system via a single
leased line.
 It uses FDM for an analog leased line or TDM method
for digital leased line.
 DSU (Digital Service Unit) unit is used instead of
modem for digital line. Leased lines may also be used to
Connect LANs.

11.  Telephone networks are intended to transmit analog
signals. It uses layer 1 (physical layer) of . the OSI
model. It is the service to provide physical media.
 Therefore, telephone networks can carry any type
of protocol data.
 The data transmission speed depends on the
performance of the modem and quality of the line.

13. Advantages and Disadvantages of Telephone
Networks
Advantages :
• It is circuit-switching network, therefore, any receiver can
be selected and there is virtually no transmission delay.
• As it is widely spread therefore it is available at a low
price.

14. Disadvantages :
• It requires a long time for connection. A dial-up operation
is necessary before the line can be connected to the receiver.
This dial-up time is too long to use in data communication
systems.
• It has low transmission speed.
• The line quality is not sufficient for data transmission, and
is therefore, not appropriate for high speed data transmission
because telephone lines were originally developed for audio
communication

15. Example:
 The computer communication system is an example of
a system using the telephone network .
 The system is used to send and receive mail,
connection to Internet, if the account is TCP/IP, post
messages on a Bulletin Board system by accessing
the host computer system of an ISP through telephone
network.

17. Conclusion:
Telephone Network is not suitable are currently in
widespread use for voice and will soon be in widespread
use for data. For example, The system is used to send and
receive mail, connection to Internet. As it is widely
spread therefore it is available at a low price. Therefore,
telephone networks can carry any type of protocol data.