2. 9.2
TELEPHONE NETWORKTELEPHONE NETWORK
Telephone networks use circuit switching. TheTelephone networks use circuit switching. The
telephone network had its beginnings in the latetelephone network had its beginnings in the late
1800s. The entire network, which is referred to as the1800s. The entire network, which is referred to as the
plain old telephone systemplain old telephone system ((POTSPOTS), was originally an), was originally an
analog system using analog signals to transmit voice.analog system using analog signals to transmit voice.
3. 9.3
DIAL-UP MODEMSDIAL-UP MODEMS
Traditional telephone lines can carry frequenciesTraditional telephone lines can carry frequencies
between 300 and 3300 Hz, giving them a bandwidth ofbetween 300 and 3300 Hz, giving them a bandwidth of
3000 Hz. All this range is used for transmitting voice,3000 Hz. All this range is used for transmitting voice,
where a great deal of interference and distortion canwhere a great deal of interference and distortion can
be accepted without loss of intelligibility.be accepted without loss of intelligibility.
4. • Bit rate is the number of bits or data elements sent per
second. Baud rate is the number of signal elements per
second. Each signal element sends one piece of
information ie. Symbol, thus Symbol rate and Baud rate
is the same.
• In the analog transmission of digital data, the bit rate is
equal to the baud rate times the number of bits or data
elements /symbol .
9.4
9. 9.10
DIGITAL SUBSCRIBER LINEDIGITAL SUBSCRIBER LINE
After traditional modems reached their peakAfter traditional modems reached their peak
data rate, telephone companies developed anotherdata rate, telephone companies developed another
technology, DSL, to provide higher-speed access to thetechnology, DSL, to provide higher-speed access to the
Internet.Internet. Digital subscriber lineDigital subscriber line ((DSLDSL) technology is) technology is
one of the most promising for supporting high-speedone of the most promising for supporting high-speed
digital communication over the existing local loops.digital communication over the existing local loops.
The set of technologies is often referred asThe set of technologies is often referred as
xDSL.xDSL.
11. 9.12
ADSL
• ADSL is an asymmetric communication
technology designed for residential users; it is
not suitable for businesses.
• It uses the existing local loops that can
handle bandwidths up to 1.1 MHz.
• It uses an adaptive technology. The
system uses a data rate based on the
condition of the local loop line.
13. 9.14
Discrete multitone technique
Contrary to its name, while a DSL circuit provides digital service, it is actually not a digital
signal. The underlying technology of transport across DSL facilities uses high-frequency
sinusoidal carrier wave modulation, which is an analog signal transmission.
19. 9.20
CABLE TV NETWORKSCABLE TV NETWORKS
TheThe cable TV networkcable TV network started as a video servicestarted as a video service
provider, but it has moved to the business of Internetprovider, but it has moved to the business of Internet
access. We discuss how this network can be used toaccess. We discuss how this network can be used to
provide high-speed access to the Internet.provide high-speed access to the Internet.
20. 9.21
Traditional cable TV network
Due to a large No. of Amps, communication in the
traditional cable TV network is unidirectional.
What is CATV?
23. 9.24
CABLE TV FOR DATA TRANSFERCABLE TV FOR DATA TRANSFER
Cable companies are now competing with telephoneCable companies are now competing with telephone
companies for the residential customer who wantscompanies for the residential customer who wants
high-speed data transfer.high-speed data transfer.
24. 9.25
Bandwidth
• Downstream Video _ 54 – 550 MHz ie more than 80
TV channels at 6 MHz/ch.
• Downstream Data Band _ 550 – 750 MHz also at 6
MHz/ch. Uses the 64-QAM modulation technique. The
theoretical downstream data rate is 30 Mbps.
• Upstream Data Band _ 5 – 42 MHz also at 6 MHz/ch.
Uses the QPSK modulation technique, as lower
frequencies more susceptible to noise. The theoretical
upstream data rate is 12 Mbps.
Division of coaxial cable band by CATV
