2. Intro
• It deals with the mechanical and electrical
specifications (Devices).
• Physical characteristics of interfaces and
medium.
• To move data in the form of electromagnetic
signals across a transmission medium
• The physical layer data consists of a stream of
bits (sequence of Os or 1s).
• Bits are encoded into signals
3.
4. • A signal is an electric current or
electromagnetic field used to convey data
from one place to another.
• A Transmitter encodes a message into a signal,
which is carried to a receiver by the
communications channel.
• Signals can be interpreted as either Analog or
Digital
5. Digital signals are non-continuous, discrete
Analog signals are continuous, non-discrete
6. common devices are used in
• Hub
• Switch
• Repeater
• Bridge
• Modem PC,
• Mobile phone, Telephone or Cables etc
are also devices use for data
communication.
8. • Primary duty of the physical layer is to carry
bits from one end to another.
• Data communication happens in some form of
electromagnetic wave transfer either wire or
wireless.
• Thus first duti of the physical layer is to
convert the bits into some EM waves at the
sender’s end and vice versa at the other end.
9. • Second important duty of physical layer is to see
that only the intended recipient receives the data
and nobody else particularly in cases where
there are multiple recipients in line.
• Physical layer have a addressing mechanism to
identify the actual recipient from different
candidate.
• There are three distinct problem that occur
during transmitting.
– First is the case where the sender is sending but the
receiver is not aware of it
10. Second is the case where there is a mismatch
between the sender and the receiver
11. Third case involves one sender and multiple
recipients.
Here there is a possibility of the sender and
receiver going out of sync. Which are shown as
below…
12. And the last important duty of the physical layer is
to multiplex and demultiplex the data
13. Machine port Level Addressing
• Every Machine that is networked contains a network
interface card.
• The card can be one or many depending on how many
networks a machine is connected to.
• The first task of the physical layer is to identify and
work with multiple network cards.
• Different card are attached to different ports of the
mother boards
• This ports are known as interfaces in networking.
• So when network has multiple interfaces and required
some mechanism to find out the actual interface to
pass the data out
14. Machine port Level Addressing
• Every Machine that is networked contains a network
interface card.
• The card can be one or many depending on how many
networks a machine is connected to.
• The first task of the physical layer is to identify and
work with multiple network cards.
• Different card are attached to different ports of the
mother boards
• This ports are known as interfaces in networking.
• So when network has multiple interfaces and required
some mechanism to find out the actual interface to
pass the data out
16. Transferring bits
• There are two different ways of transmitting bits
• Using analog waves and digital waves.
• The key here is the mechanism to find out a standard to
represent ones and zeros. They are popularly known as
coding mechanisms.
• For example the older 10MB Ethernet used to have a scheme
known as Manchester encoding.
• Modern ethernets use various coding schemes depending on
the type of wire they use to transmit data.
• Wire less transmission use CDMA which is 4th generation
mobile phones
• Another OFDM orthogonal Frequency division multiplexing
which is use 802.11(wifi networks) and 802.16(wimax).
17. Synchronizing the sender and receiver
• The sender and receiver not only must use the same bit
rate but also must be synchronized at the bit level.
• In other words, the sender and the receiver clocks must
be synchronized.
• If these two clocks are not synchronized the
transmission can o out of sync.
• Its difficult to avoid synchronization issues because
there is not central authority which confirms the time.
• Receiver might not have any clue of the speed of
sender it might need testing the input and set its clock
in sync with input.
18. Synchronizing the sender and receiver
• When the input does not provide proper clues then
the receiver might resort to trial and error to sort
out the problem
– For examples take the case of 100 mpb/sec of fast
etnernet is common in out networks
– Its sends 100 Mb data in a second which implies 100 bits
in one microsecond
– A difference of 1 microsecond is a big scale here
– so in one micro sec a 10 Gb Ethernet sends one
thousand bits it clock drifts few micro sec it loses an
entire file of a moderate size.
19. Synchronizing the sender and receiver
• One other way is to use the signal itself for self-
synchoronization.
• An excellent examples of this mechanism is
Manchester Encoding.
• Which is to used in classic Ethernet.
• Here two signals are sent to indicate one bits.
• Zeros are indicated by a positive voltage in the
beginning and a negative voltage after the middle
line
21. Multiplexing multiple data streams
• Multiplexing takes place at each layer.
• A single cat-5 wire is capable of combining
approximately 250 telephonic conversations
together.
• A fiber optic cable can combine millions of
telephonic conversations.
• The actual number depends on the distance
covered and a few other factors. But it is always
possible to merge multiple conversations into a
single wire.
• So data communication also works in the same way
22. Multiplexing multiple data streams
• For example
– assume that our ISP provides us a 2Mb connection and
also assume that there are nine other users having the
same speed then the IPS ideally needs a single 20Mb
connection with the rest of the world.
– When traffic goes to the ISP it multiplexes our traffic
with the rest and sends it across
– And when response back its demultiplexes the
composite signal and distributes our share.
23. Inappropriateness of FDM and TDM
for Bursty Data
• a burst transmission or data burst is the broadcast
of a relatively high-bandwidth transmission over a
short period.
• TDM and FDM is very popular techniques used in
transmitting telephonic signals and also use for
broadcast television signals.
• But these multiplexing techniques are less attractive
to us for an important reason is that the computer
traffic is not constant like telephone or television
traffic
• So TDM and FDM is inefficient to handle bursty
data.
24. Inappropriateness of FDM and TDM
for Bursty Data
• For example
– Suppose we are load a website www.xyz.com.
– So entire page is downloaded in a few microseconds.
– The traffic is really high at that point of time.
– After that we screen the page for a while reading so at
that time traffic is 0
– Then we find new interesting link and click on it so again
traffic jumps up for a while
– So traffic is never remains constant it peaks for a few
microseconds and down again for few minutes and
peaks again.
25. Allocate slots to different senders during 1 cycle of 10
round
Only sender 2 has transmit others remain idle. Hence
amajor chunk of the bandwidth is wasted
26. The Electromagnetic Spectrum
• All forms of transmission , wired or wireless use some form
of electromagnetic waves
• These waves are nothing but electromagnetic energy
travelling from the sender to the receiver.
• The first is the frequency it is the number of times the wave
oscillates in unit time so more the oscillations, higher the
frequency.
27. The Electromagnetic Spectrum
• The second point is the wavelength.
• It is the distance between two aptitudes or the distance
between two consecutive cycles of the same wave.
• It is apparent that when the frequency increases the wave
is shortened and thus the wave length is reduced
28. The Electromagnetic Spectrum
• Third property of the wave is the power associated with it.
• It is calculated by the amplitude of the wave.
• Waves lose their power gradually in transit hence the
amplitudes reduce as they proceed further
29. The Electromagnetic Spectrum
• Radio Waves
• Microwaves
• Infrared and Millimeter Waves
• The ISM Bands
• The optical light and Free Space Optics
30.
31. Radio Waves
• Radio waves have the longest wavelengths of all the
electromagnetic waves.
• They range from around a foot long to several miles long. Radio
waves are often used to transmit data and have been used for
all sorts of applications including radio, satellites, radar, and
computer networks.
• The lowest part of the spectrum is known as radio waves
• Here the frequency is less and thus the waves are long
• 104 to 108 Hz
• Equation of waves is
ƛ f=c
– Where ƛ(Lambda) is the wavelength
– F is the frequency of the wave
– C is the speed of light in vacuum which is constant
• It clearly indicates that when f increases , ƛ must decrease to keep
the multiplication value constant.
32. Radio Waves
• The radio waves are poor candidates for data transmissions as
they have lower frequency and thus low capacity to encode
data.
• Also the data transmission has to complete with all radio station
and use only those frequencies which are not allocated to them.
• The radio wave range is sub divided into bands like
– VLF(very low frequency)
– LF(low frequency)
– MF(medium frequency)
– HF(high Frequency)
– VHF(very high Frequency)
• VLF,LF,MF waves are known as ground waves
• They follow the curvature of the earthy and are capable of
moving anywhere without reflection.
• And HF, VHF travel in straight line. This 2 waves are little use due
to the curvature of the earth
34. Microwaves
• Microwaves are a type of electromagnetic radiation, as are
radio waves, ultraviolet radiation, X-rays and gamma-rays.
Microwaves have a range of applications, including
communications, radar and, cooking.
• Electromagnetic radiation is transmitted in waves or
particles at different wavelengths and frequencies.
• This broad range of wavelengths is known as
the electromagnetic spectrum EM spectrum).
• The spectrum is generally divided into seven regions in
order of decreasing wavelength and increasing energy and
frequency.
• The common designations are radio waves, microwaves,
infrared (IR), visible light, ultraviolet (UV), X-rays and
gamma-rays.
35. Microwaves
• Microwaves are used mostly for point-to-point
communications systems to convey all types of information,
including voice, data and video in both analog and digital
formats, according to the Federal Communications
Commission (FCC).
• They are also used for supervisory control and data
acquisition (SCADA) for remote machinery, switches, valves
and signals.
• Microwaves have frequencies ranging from about 1 billion
cycles per second, or 1 gigahertz (GHz), up to about 300
gigahertz.
• his region is further divided into a number of bands, with
designations such as L, S, C, X and K, according to Ginger
Butcher's book "Tour of the Electromagnetic Spectrum.“
36. Microwaves
Letter Designation Frequency Range Wavelength Range
L band 1 to 2 GHz 15 cm to 30 cm
S band 2 to 4 GHz 7.5 cm to 15 cm
C band 4 to 8 GHz 3.75 cm to 7.5 cm
X band 8 to 12 GHz 25 mm to 37.5 cm
Ku band 12 to 18 GHz 16.7 mm to 25 mm
K band 18 to 26.5 GHz 11.3 mm to 16.7 mm
Ka band 26.5 to 40 GHz 5.0 mm to 11.3 mm
Q band 33 to 50 GHz 6.0 mm to 9.0 mm
U band 40 to 60 GHz 5.0 mm to 7.5 mm
V band 50 to 75 GHz 4.0 mm to 6.0 mm
W band 75 to 110 GHz 2.7 mm to 4.0 mm
F band 90 to 110 GHz 2.1 mm to 3.3 mm
D band 110 to 170 GHz 1.8 mm to 2.7 mm
37. INFRARED AND MILLIMETER WAVES
• The infrared waves are all around us and earth is full of infrared
waves.
• These waves are emitted by anything which is capable of
emitting heat.
• The Infrared Waves Frequency range lies in between 300 GHz -
405 THz and hence the Infrared Wavelength is in between 750
nm - 1 mm.
• Out Tv Remote controls use infrared waves to send signals.
• Lots of short range devices like VCR and stereos and electronic
toys use infrared waves.
• Problem with this waves is that they travel straight and cannot
pass through obstacles.
• If we use an infrared device outdoors the signals will collide
with the infrared signals present in the sunlight and result in
garbage.
38. Industrial, Scientific and Medical Radio
Band (ISM Band )
• GOV world over set aside some portion of the spectrum for
free unlicensed use.
• The ISM refers to a group of radio bands or parts of the
radio spectrum that are internationally reserved for the use
of radio frequency (RF) energy intended for scientific,
medical and industrial requirements rather than for
communications.
• ISM bands are generally open frequency bands, which vary
according to different regions and permits.
• The 2.54 GHz ISM band is a commonly accepted band for
worldwide operations.
• cordless phones, medical diathermy machines, military
radars and industrial heaters are just some of the
equipment that makes use of this ISM band.
39. Industrial, Scientific and Medical Radio
Band (ISM Band )
• The first band is between 902 to 928MHZ.
• This is the best band and can travel much longer and have
fewer chances for errors.
• There is another band 433.05-434.79 MHZ which are not
available for some countries of Europe.
• second band is between 2.4 to 2.48 GHZ, this is available
almost everywhere including India.
• Third band is between 5.736 to 5.860 GHZ this is a wider
range and less crowded
40. The optical light and free space optics
• FSO (free space optics) is an optical communication
technology in which data is transmitted by propagation of
light in free space allowing optical connectivity.
• This communication is wire less
• In FSO signal goes to much faster speed then in the manual
case.
• FSO can transfer data at 1 Gbps speed up to a distance of 2
KM.
• For examples
– Its usefulness in aircrafts that communicate with satellites.
• The drawback of FSO is that the communication is heavily
dependent on atmospheric conditions
42. Wired Physical Layer
• The UTP cable
• Fiber Optic Cables
• Design of fiber cables
• Sending and receiving devices
• Comparison between UTP and Fiber Optics
• Other cables
• Total Internal Reflection principle
43. The UTP cable
• Unshielded twisted pair (UTP) cables are widely used in the
computer and telecommunications industry as Ethernet
cables and telephone wires.
• Unshielded means no additional shielding like meshes or
aluminum foil.
• Twists are introduced to make the media immune to
crosstalk
44. Advantage
• Twists help cancel out crosstalk
• Inexpensive
• Possible to bend the UTP
• Technology behind UTP is fairly matured
• There is less attenuation in UTP cables
• The technology is evolving
46. fiber-optic
• A fiber-optic system is similar to the copper wire system
that fiber-optics is replacing.
• The difference is that fiber-optics use light pulses to
transmit information down fiber lines instead of using
electronic pulses to transmit information down copper
lines.
• Looking at the components in a fiber-optic chain will give a
better understanding of how the system works in
conjunction with wire based systems.
• At one end of the system is a transmitter.
• This is the place of origin for information coming on to
fiber-optic lines.
• The transmitter accepts coded electronic pulse information
coming from copper wire.
47. fiber-optic
• It then processes and translates that information into
equivalently coded light pulses.
• A light-emitting diode (LED) or an injection-laser diode (ILD)
can be used for generating the light pulses.
• There are three types of fiber optic cable commonly used:
– single mode,
– multimode
– plastic optical fiber (POF).
• Transparent glass or plastic fibers which allow light to be
guided from one end to the other with minimal loss.
48.
49. fiber-optic
• Single Modem fiber is used in many applications where
data is sent at multi-frequency (WDM Wave-Division-
Multiplexing) so only one cable is needed - (single-mode on
one single fiber)
• Single-mode fiber gives you a higher transmission rate and
up to 50 times more distance than multimode, but it also
costs more.
• Single-mode fiber has a much smaller core than
multimode.
• The small core and single light-wave virtually eliminate any
distortion that could result from overlapping light pulses,
providing the least signal attenuation and the highest
transmission speeds of any fiber cable type.
50. fiber-optic
• Multimode fiber gives you high bandwidth at high speeds
(10 to 100MBS - Gigabit to 275m to 2km) over medium
distances.
• Light waves are dispersed into numerous paths, or modes,
as they travel through the cable's core typically 850 or
1300nm.
51. Design of fiber-optic
• It has three different layers
– Innermost layer is called the core which is made up of pure glass
– And this core carries the light rays within
– The layer out side the core is known as the cladding.
– it is also made of glass or plastic with lower refractive index then
the core
52. Design of fiber-optic
• Fiber optic cables are designed in three different ways.the
first two types are multimode(thicker) and third type is
single mode(thin)
53.
54. Design of fiber-optic
• First one is known as single step multimode where
the cladding has less refractive index than the core
but the core has a consistent index throughout its
width so its generate reflection like mirror.
• In second type of fiber the graded index multimode
fiber the core has a higher refractive and its reduce
the consistently.
• The ray is traveling in the inner half of the cable
move slowly in a straight line due to the higher
refractive index of the material. This is mostly use in
Lans
55. Design of fiber-optic
• The single step multimode fiber rays travel straight
in a zigzag path.
• It is used for short distance communications
57. Design of fiber-optic
• The sending computer passes electric pluses to a
device which converts these into light pulses
• The light pulses are carried by the fiber optic cable
to the receiver.
• There is a device at the receiving end which
converts the light pulses back to electric pulses
58. Design of fiber-optic
• The sender device uses LED or Laser to convert
electric pulses into light pulses
• The receiving device uses photodiodes to generate
electric current from the light pulses to signal.
• Speed of communication in fiber optic cables
depends on the rate of conversion from electric
pulse to light pulses and vise versa.
• Cable can carry data in Gbps for long distance and
Tbps for sort distance
59. Differences
• The sender device uses LED or Laser to convert
electric pulses into light pulses
• The receiving device uses photodiodes to generate
electric current from the light pulses to signal.
• Speed of communication in fiber optic cables
depends on the rate of conversion from electric
pulse to light pulses and vise versa.
• Cable can carry data in Gbps for long distance and
Tbps for sort distance
61. Intro
• Wireless means network create without wire.
• Here NIC card that we need to have for
connecting to a communication is that the
wireless communication is inherently broadcast.
• The main difference is that wire communication
create P2P network and wireless communication
is inherently broadcast.
• Wireless has all the advantages and limitations of
broadcasting.
• Its own advantages and limitations.
62. advantages
• Its does not require explicit addressing to read
the recipient.
• The receiver can be anywhere in the vicinity and
the message would reach it.
• The receiver can even be mobile.
63. Dis-advantages
• Wireless networks share the bandwidth available.
• Many products conform to
the 802.11a, 802.11b/g/n,
and/or 802.11ac wireless standards collectively
known as Wi-Fi technologies
• The 802.11 or wifi LAN were started off with 11
MB to all user. 802.11 also known as 802.11b.
• Later on version increase the speed of Wi-Fi
technologies like 802.11g provides 54 Mb.
• Latest version is 802.11n which is provide 100mb.
64. • There is a altogether a new standard for wireless
networks originally designed for static broadband
called 802.16 or wiMax.
• Its use for mobile now a day.
• The other type of wireless network is called the
satellite network.
• A satellite network is wireless but has more
bandwidth and also works in the range where the
signal travels a long distance
66. • Using wire the broadcast will eventually reach
everyone because node join with wire.
• But in wireless sender usually has a limited range
and all machines beyond that range do not receive
the broadcast.
• The limit of range is also a boon when we want
multiple transmissions between multiple senders
and receivers.
• As below figure show
67. Where A is sending to B
E is sending to F
Dotted curves indicate the range of A and E
So we say that both are in range
68. • As above figure show that if the ranges overlap it will receive
one transmission of many.
• So here D is receiving both the signals and gets the
summation of both signals.
• When receiver receive summation of signal like this it cannot
understand anything and generate the garbage.
• So its need to filter ones own signal out of the summation.
• This technique is used in CDMA which is a popular wireless
technology
69. • This problem also known as Exposed station problem.
• As above figure show that B sending to and D in
interested to send to E.
• When D senses the channel it finds the channel busy
and defers to send
• E does not receive the signal from B and it is safe If D
sends the data to E in fact the signal will not be garbled
if send now but d has no way to know that
70. • It is also possible to have a case where the sender
start transmitting completely unaware of the fact
that the receiver is busy at that point of time in that
case the transmission results in garbage.
• Below figure show that
B has already started sending to D and E want to send
to D.
72. • As above both problem are due to a single reason
when ever sender senses the cannel it senses its
surrounding.
• As above figure show the solution of it lets see
– Suppose B is interested in sending something to D
– Before starting to send B send a small frame called
RTS(request to send) to D
– In response D replies with CTS(clear to send)
73. • The RTS and CTS additionally contain the length of
the frame to be transmitted so E also will came to
know how long he should keep quiet.
• When more then one sender sends RTS signals they
collide and the receiver does not respond
• When the sender does not receive the
acknowledgement it tries again after some random
time.
75. • Antennas is a device to send and receive wireless
signals
• Cable tv, mobile, dth used parabolic antenna which are
hidden inside.
• Dth and other used just for receiving the television or
radio broadcasting.
– Two type of antennas
• Omni directional
• focused
• Computer are no exception to this rule.
• Antennas are required for sending and receiving
wireless transmission.
• In short antenna is a device which either radiates or
collects electromagnetic energy (data)
• They have almost the same work as do as LED and
photodiodes
76. • The sending antenna converts the electric pulse
into an electromagnetic wave which is received by
the receiving antenna and is converted back to
electric pulse again.
• Antennas used in radios are omnidirectional its
range of 30MHz to 1Ghz
• While focused antennas are required for higher
frequencies then radio which is more then 1Gbps.
• The focused antenna derives from the
electromagnetic waves with
– Higher frequencies tend to travel in straight lines
– Lower frequencies tend to travel in all direction.
78. • Access point important function
is to connect to other wireless of
wired network access point and
controls incoming and outgoing
transmissions.
• Its allocates time and bandwidth
to be used to all the nodes and
controls.
• The node take turn in
transmission according to the
instructions from the access
point.
• Access point allocate different
frequency bands and time bands
for sending and receiving thus its
avoid the possibility of collision.
79. • When tow or more laptops communicating with
each other using ad-hoc mode in presence of access
point.
• Its controlling the nodes which are registered with
it.
• If laptops are not registered then also communicate
then its use DCF(distributed coordinated function )
or ad-hoc mode.
• Wireless network use priority bases transmission.
• The RTS and CTS (Request to Send / Clear to
Send)have the highest priority, then access point
then ad-hoc
81. • A wireless LAN can operate in two different ways.
• First way is to work with a central channel arbitrator
known as the access point. Here no node transmits
anything unless explicitly granted permission by the
access point.
• And second way is to talk to each other directly
without any intervention.
• First mode is known as the infrastructure mode and
the second mode is known as the ad-hoc mode.
• AD-hoc is also referred to as DCF(Distributed
coordinated function) because control is distributed
among the nodes which communicate as well as
control the network.
82. • And the infrastructure mode is referred to as
PCF(point coordinated function) because the nodes
are coordinated by the access point.
84. 802.11 b
• Its Spread spectrum technique called HR-DSSS(high
rate direct sequence spread spectrum)
• Its free do not require licensing
• 2.4 GHz ISM band
• Direct Sequence Spread Spectrum(seq 0 and 1)
• 11 Mb
• Ad-hoc mode uses CSMA/CA
• Available bandwidth depends on distance
• Covers more distance than 802.11a
85. OFDMA and 802.11 a
• 802.11 using OFDM(orthogonal frequency
division multiplexing) instead of HR-DSSS in
802.11 b
• 52 narrow frequencies
• Transmission is distributed to all these freq
• Better immunity to interference
• Different schemes for different ranges
• Maximum bandwidth of 54 Mb
• 802.11a came a little later than 802.11b.
86. 802.11g
• Uses the same OFDM
• Operating in the 2.4 GHz ISM band
• Network deployed with 802.11b can be
upgraded to 11g without much hassle
• Its fully backwards compatible with the
802.11b hardware.
• b/g cards make the up gradation process
much easier
• In India, the 802.11g is more significant
87. 802.16
• Second most popular wireless network is 802.16 or
wimax(worldwide interoperabilitiy for microwave
access).
• WiMax in Slang
• Achieve a data rate of 30–75 Mb
• Distance of coverage between 3 to 10 km
• WiMax forum takes care of interoperability issues of
802.16 devices
• 802.16d, the standard for Fixed Wireless Broadband
• OFDMA and 802.16e
• 10–66 GHz originally but now much lower
• 802.16d for fixed, later version 802.16e provides both,
fixed and mobile wireless
88. 802.16
• 10–66 GHz originally but now much lower
• 802.16d for fixed, later version 802.16e
provides both, fixed and mobile wireless
89. 802.16d
• This is a standard for fixed wireless and also
referred to as fixed wimax
• OFDMA (multi-user version of OFDM) with 256
sub-carriers (DMT)
• It is connection oriented
• Each user has a specific slot allocated to it for
sending as well as receiving. The receiving slot is
bigger than the sending slot.
• Initial part of frame contains the sending part
from the base station and then the receiving part
by the base station
90. 802.16d
• The second part is smaller than the first one,
as uploading is usually less than downloading
• Two different frequencies are used.
• Hamming code for forward error correction.
• Frames are sent like a continuous bit stream
which improves the bandwidth utilization.
• Different quality of service (QoS) is provided
93. Intro
• Television programs relayed up to the satellite which
redirects the signals back to out television sets.
• Same satellite use for data transmit.
• Each communication satellite contains a few
transponders
• Each one is capable of sending and receiving a
specific part of the spectrum.
• Both sending and receiving frequencies are kept
different to eliminate interference.
• Its transponder out data in narrow or a wider region.
• Distance from the earth 35800 km in orbit.
• This orbit known as geosynchronous.
• Its move same speed of earth speed
94. Intro
• Three type of orbits
– UEO(upper earth orbit)
– MEO(medium Earth Orbit)
– LEO(lower earth orbit)
• MEO use for global positioning satellite system
• LEO is the preferred choice for data
communication
95. Wireless communication using
Satellite
• Three different orbits
• GEO is almost full.
• The LEO is near to earth
• satellite phones with few miliwatts of power.
• 1 to 7 msec esponse time
• LEO satellites are less expensive to launch
• Teledesic and GlobalStar
