physical layer ppt networks frouzan networks layers

physical layer network

1. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Physical LayerPhysical Layer
PART IIPART II

2. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Position of the physical layer

3. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Services

4. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Chapters
Chapter 3 Signals
Chapter 4 Digital Transmission
Chapter 5 Analog Transmission
Chapter 6 Multiplexing
Chapter 7 Transmission Media
Chapter 8 Circuit Switching and Telephone Network
Chapter 9 High Speed Digital Access

5. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Chapter 7
Transmission
Media

6. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Transmission medium and physical layer

Transmission media are actually located below the
physical layer and directly controlled by the physical layer.

Computer and other telecommunication devices use
signals to represent data. These signals are transmitted
from one device to another in the form of electromagnetic
energy, which is propagated through transmission media.

7. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Classes of Transmission Media

Guided media, which are those that provide a
conduit from one device to another. Signal
travelling along any of these media is directed and
contained by the physical limits of the medium.

8. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Twisted-Pair Cable

One of the wires is used to carry signals to the receiver, and
the other is used only as a ground reference. The receiver
uses the difference between the two levels.

In addition to the signal sent by the sender on one of the
wires, interference (noise) and crosstalk may affect both wires
and create unwanted signals. The receiver at the end,
however, operates only on the difference between these
unwanted signals. This means that if the two wires are
affected by noise or crosstalk equally, the receiver is immune
(the difference is zero).

The number of twists per unit of length (e.g., inch) determines
the quality of the cable; more twists mean better quality.

9. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
UTP and STP

STP cable has a metal foil or braided-mesh covering
that encases each pair of insulated conductors.

Although metal casing improves the quality of cable
by preventing the penetration of noise or crosstalk, it
is bulkier and more expensive.

10. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Table 7.1 Categories of unshielded twisted-pair cablesTable 7.1 Categories of unshielded twisted-pair cables
CategoryBandwidth Data Rate Digital/Analog Use
1 very low < 100 kbps Analog Telephone
2 < 2 MHz 2 Mbps Analog/digital T-1 lines
3 16 MHz 10 Mbps Digital LANs
4 20 MHz 20 Mbps Digital LANs
5 100 MHz 100 Mbps Digital LANs
6 (draft) 200 MHz 200 Mbps Digital LANs
7 (draft) 600 MHz 600 Mbps Digital LANs

11. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
UTP connector

RJ45 (Registered Jack) is the most common UTP
connector.

RJ45 is a keyed connector, meaning the connector
can be inserted in only one way.

12. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Coaxial cable

Coaxial cable (or coax) carries signals of higher frequency
ranges than twisted-pair cable, in part because the two media
are constructed quite differently.

Coax has a central core conductor of solid or stranded wire
(usually copper) enclosed in an insulating sheath, which is, in
turn, encased in an outer conductor of metal foil, braid, or a
combination of the two.

The outer metallic wrapping serves both as a shield against
noise and as a second conductor, which completes the circuit.

This outer conductor is also enclosed in an insulating sheath,
and the whole cable is protected by a plastic cover.

13. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Table 7.2 Categories of coaxial cablesTable 7.2 Categories of coaxial cables
CategoryImpedance Use
RG-59RG-59 75  Cable TV
RG-58RG-58 50  Thin Ethernet
RG-11RG-11 50  Thick Ethernet

Each Radio Government (RG) number denotes a
unique set of physical specifications, including the
wire gauge of the inner conductor, the thickness
and type of the inner insulator, the construction of
the shield, and the size and type of the outer casing.

14. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
BNC connectors

Bayone-Neill-Concelman Connectors

Three popular types are BNC connector, BNC T
connector, BNC Terminator.

BNC Connector is used to connect the end of the
cable to a device, such as a TV set. The BNC T
connector is used in Ethernet networks to branch
out a cable for connection to a computer or other
devices.

15. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Bending of light ray

Fiber-optic cable is made of glass or plastic and
transmits signals in the form of light.

A glass or plastic core is surrounded by a cladding
of less dense glass or plastic. The difference in
density of the two materials must be such that a
beam of light moving through the core is
reflected off the cladding instead of being
refracted into it.

16. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Propagation modes
Multimode is so named because multiple beams from a
light source move through the core in different paths.
Multimode step-index fiber

Density of the core remains constant from the center to the
edges

Beam of light moves through this constant density in a straight
line until it reaches the interface of the core and the cladding.

At the interface, there is an abrupt change to a lower density
that alters the angle of the beam’s motion. The term step index
refers to the suddenness of this change.

17. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Modes

Multimode graded-index Fiber

The word index here refers to the index of refraction
that is related to density.

Single mode Fiber

Single mode uses step-index fiber and a highly
focused source of light that limits beams to a small
range of angles, all close to the horizontal.

18. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Modes

19. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Table 7.3 Fiber typesTable 7.3 Fiber types
Type
Core
µm
Cladding
µm
Mode
50/12550/125 50 125 Multimode, graded-index
62.5/12562.5/125 62.5 125 Multimode, graded-index
100/125100/125 100 125 Multimode, graded-index
7/1257/125 7 125 Single-mode

20. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Fiber construction

Outer jacket is made of either PVC or Teflon.

Inside the jacket are Kevlar strands to strengthen the cable.
Kevlar is a strong material used in the fabrication of
bulletproof vests.

Below the Kevlar is another plastic coating to cushion the
fiber. The fiber is at the center of the cable, and it consists of
cladding and core.

21. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Fiber-optic cable connectors

Three different types of connectors

Subscriber channel (SC) connector is used in cable TV. It uses a
push/pull locking system.

Straight-tip (ST) connector is used for connecting cable to
networking devices. It uses a bayonet locking system and is
more reliable than SC.

MT-RJ is a new connector with the same size as RJ-45

Fiber optic has several advantages over metallic cable

Higher bandwidth, less signal attenuation, immunity to
electromagnetic interference, resistance to corrosive materials,
light weight, more immune to tapping.

Disadvantages: Installation/maintenance [need expertise],
Unidirectional [propagation of light is unidirectional], Cost.

22. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Electromagnetic spectrum for wireless
communication

Unguided Media: Wireless

Signals can travel via ground propagation, sky
propagation, line-of-sight propagation.

23. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Table 7.4 BandsTable 7.4 Bands
BandBand RangeRange PropagationPropagation ApplicationApplication
VLFVLF 3–30 KHz Ground Long-range radio navigation
LFLF 30–300 KHz Ground
Radio beacons and
navigational locators
MFMF 300 KHz–3 MHz Sky AM radio
HF HF 3–30 MHz Sky
Citizens band (CB),
ship/aircraft communication
VHF VHF 30–300 MHz
Sky and
line-of-sight
VHF TV,
FM radio
UHF UHF 300 MHz–3 GHz Line-of-sight
UHF TV, cellular phones,
paging, satellite
SHF SHF 3–30 GHz Line-of-sight Satellite communication
EHFEHF 30–300 GHz Line-of-sightLong-range radio navigation

24. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Wireless transmission waves

25. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Omnidirectional antennas

Radio waves are electromagnetic waves ranging in frequencies
between 3 KHz and 1 GHz and those between 1 and 300 GHz
are called Microwaves.

Radio waves

Omnidirectional; Propagate to long distances

Can penetrate walls and so no boundary.

Radio waves are used for multicast communications, such as
radio and television, and paging systems

26. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Unidirectional antennas
Microwaves are unidirectional.
Very high frequency microwave cannot penetrate walls.
Parabolic dish antenna

Every line parallel to the line of symmetry (line of sight) reflects off the curve at
angles such that all the lines intersect in a common point called the focus.
Horn antenna
Outgoing transmissions are broadcast up a stem (resembling a handle) and
deflected outward in a series of narrow parallel beams by the curved head.

Received transmissions are collected by the scooped shape of the horn, in a
manner similar to the parabolic dish, and are deflected down into the stem.
Microwaves are used for unicast communication such as cellular telephones,
satellite networks, and wireless LANs

27. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Infrared Signals

300 GHz to 400 THz.

Infrared signals can be used for short-range communication
in a closed area using line-of-sight propagation

Cannot penetrate walls.

Some manufacturers provide a special port called the IrDA
port that allows a wireless keyboard to communicate with a
PC.