Network Trasmmission Media

7/29/2019 Network Trasmmission Media

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McGraw-Hill The McGraw-Hill Companies, Inc., 2000

Sr.No.

OSI TCP/IP

1 7 Layers 4 Layers

2 Model was first defined beforeimplementation take place

Model defined after, protocolwere implemented.

3 OSI model does not support internetworking

TCP/IP support

4 Support connection less and connection oriented in the network layer

Support only connection oriented in the transport layer

5 OSI model gives guarantee of reliabledelivery of packet.

TCP/IP does not alwaysguarantee of reliable deliveryof packet.

6 The protocol are better hidden and can beeasily replaced as the technology changes.

It is not easy to replace theprotocols.

7 Separate session layer. No session layer, characteristicare provided transport layer.

8 Separate presentation layer. No presentation layer,characteristic are providedapplication layer.


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7.2

Figure 7.1 Transmission medium and physical layer


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7.3

Figure 7.2 Classes of transmission media


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7.4

Sr.No.

Guided Media Unguided Media

1 The signal energy is contained andguided within a solid medium. The signal energy propagates inthe form of unguidedelectromagnetic waves.

2 Twisted pair wires, coaxial cable, opticalfiber cable are the example of guidedmedia

Radio , Bluetooth, Infrared light arethe example of unguided media.

3 Used for point to point communication. Used for radio broadcasting in alldirections.

4 Wired media lead to discrete networktopologies.

Wireless media leads to continuousnetwork topology.

5 Additional transmission capacity can be

procured by adding more wires.

It is not possible procure additional

capacity.

6 Installation is costly, time consumingand complicated.

Installation needs less time andmoney,

7 Attenuation depends exponentially onthe distance.

Attenuation of proportional tosquare the distance.


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7.5

7-1 GUIDED MEDIA

Guided media, which are those that provide a conduitfrom one device to another, include twisted-pair cable,coaxial cable, and fiber-optic cable.

Twisted-Pair Cable

Coaxial Cable

Fiber-Optic Cable

Topics discussed in this section:


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7.6

Figure 7.3 Twisted-pair cable


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Figure 7.4 UTP and STP cables


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Unshielded Twisted Pair (UTP)

Physical Media


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Unshielded Twisted Pair (UTP)

Consists of 4 pairs (8 wires) ofinsulated copper wires typicallyabout 1 mm thick.

The wires are twisted together in ahelical form.

Twisting reduces the interferencebetween pairs of wires.

High bandwidth and Highattenuation channel.

Flexible and cheap cable.Category rating based on numberof twists per inch and the materialused

CAT 3, CAT 4, CAT 5, Enhanced CAT5 and now CAT 6.

Physical Media


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How to Crimping


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15/77McGraw-Hill The McGraw-Hill Companies, Inc., 2000


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Straight-Through Cable

7.16


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Crossover Cable

7.17


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Figure 7.5 UTP connector


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Figure 7.7 Coaxial cable


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7.20

A baseband coaxial cable transmits a single signal at a time at

very high speed, while a broadband coaxial cable can transmit

many simultaneous signals using different frequencies. A

baseband cable transmits a single stream of digital data at a very

high communication rate (million of bits per second) but must be

amplified by every 1000 feet or so. It is mainly used for local area

networks. A baseband coxial cable can carry only an analog

single, so it must be used in conjunction with a modem. It is more

complex to use in a network.

Baseband and Broadband coaxial cable


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7.21

Table 7.2 Categories of coaxial cables

RG for Radio Government


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7.22

Figure 7.8 BNC connectors

BNC stands for Bayone-Neill-concelman


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7.23

Figure 7.14 Fiber construction


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7.24

Figure 7.11 Optical fiber

An Optical transmission system has three key components:

1. The light source : A pulse of light indicates a 1 bit and the absence

of light indicate a 0 bit.

2. The transmission medium is an ultra-thin fiber glass.

3. The detector generates an electrical pulse when light falls on it


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7.25

Figure 7.11 Optical fiber


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7.26

Types of Fiber

Plastic core and cladding

Glass core with plastic cladding

Glass core and glass cladding


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7.27

Optical Fiber - Benefits

Greater capacity

Data rates of hundreds of Gbps

Smaller size & weight

Lower attenuation

Electromagnetic isolation

Long distance transmission

Safe and easy installation.

Long term

Security

Greater repeater spacing

10s of km at least


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7.28

Optical Fiber Disadvantage

High initial cost.

Maintenance and repairing cost.


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7.29 Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, Pearson Education-Prentice Hall, 2011The electromagnetic spectrum and its uses for communication

The Electromagnetic Spectrum


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7.30 Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, Pearson Education-Prentice Hall, 2011

Radio Frequency Characteristics

Radio waves are easy to generate.

They can travel long distances.

They can enter building easily so they are widely used for communications

both indoors and outdoors.

Radio waves are omni directional , meaning that they travel in all directionsfrom the source, so that the transmitter and receiver do not have to be

carefully align physically.

The properties of radio waves are frequency dependent. At low frequencies

radio waves pass through obstacles well, but the power falls off sharply with

distance from the source.

Low frequency and medium frequency range cannot be used for data transferbecause of their very small bandwidth.


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7.31

Table 7.4 Bands


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Radio Transmission

In the VLF, LF, and MF bands, radio waves follow the curvature of the earth


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Radio Transmission

In the HF band, they bounce off the ionosphere.


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7.34

Figure 7.20 Omnidirectional antenna


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7.35

Microwaves are used for unicast

communication such as cellulartelephones, satellite networks,

and wireless LANs.

Higher frequency ranges cannotpenetrate walls.

Use directional antennas - point to point

line of sight communications.

Note

Microwave Transmission


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Above 100 MHz, the waves travel in nearly straight lines and can therefore be

narrowly focused. Concentrating all the energy into a small beam by means of

a parabolic antenna (like the familiar satellite TV dish) gives a much higher

signal-to-noise ratio, but the transmitting and receiving antennas must be

accurately aligned with each other.

Before the advent of fiber optics, these microwaves formed the heart of the

long distance telephone transmission system. In its simplest form the microwave link can be one hop, consisting of one pair

of antennas spaced as little as one or two kilometers apart, or can be a

backbone, including multiple hops, spanning several thousand kilometers.

A single hop is typically 30 to 60 km in relatively flat regions for frequencies in

the 2 to 8 GHz bands. When antennas are placed between mountain peaks, a

very long hop length can be achieved. Hop distances in excess of 200 km arein existence. The "line-of-sight" nature of microwaves has some very

attractive advantages over cable systems. Line of sight is a term which is only

partially correct when describing microwave paths.


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Atmospheric conditions and certain effects modify the propagation of

microwaves so that even if the designer can see from point A to point B (true

line of sight), it may not be possible to place antennas at those two points and

achieve a satisfactory communication performance.

In order to overcome the problems of line-of-sight and power amplification of

weak signals, microwave systems use repeaters at intervals of about 25 to 30

km in between the transmitting receiving stations The first repeater is placed in line-of-sight of the transmitting station and the

last repeater is placed in line-of-sight of the receiving station. Two

consecutive repeaters are also placed in line-of-sight of each other. The data

signals are received, amplified, and re-transmitted by each of these stations


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7.39

Infrared Light Wave Transmission

Unguided infrared light (waves) are widely used for short range

communication. The remote controls used on televisions, VCRs, and stereos

all use infrared communication. They are relatively directional, cheap, and

easy to build.

The fact that infrared waves do not pass through solid walls well is also a

plus. It means that an infrared system in one room of a building will not

interfere with a similar system in adjacent rooms or buildings: you cannotcontrol your neighbor's television with your remote control.

Security of infrared system against eavesdropping is better than that of radio

systems precisely for this reason, infrared light is suitable for indoor wireless

LAN.

For example connecting notebook computers and printers, but it is not a

major player in the communication game No government license is needed to operate an infrared system.


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7.40

Application of Infrared Light Wave Transmission

In remote control of home appliances : e.g. TV,DVD and VCD players.

Indoor wireless LANs.

Communication between in-house electronic gadgets such as keyboard,

mouse, printers, scanners and for controlling fan, air conditions.


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7.41

Bluetooth

The name "Bluetooth" is actually very old! It is from the 10th century Danish

King Harald Bltand - or Harold Bluetooth in English

Bluetooth is a specification for the use of low-power radio communications to

wirelessly link phones, computers and other network devices over short

distances.

Instead of creating a local-area network (LAN) or a wide-area network (WAN),

Bluetooth creates a personal-area network (PAN) just for you. Cell phones,for example, can be paired with wireless Bluetooth headsets.

In addition to being paired with cell phones, short-range Bluetooth technology

is also compatible with personal computers, laptops, printers, GPS receivers,

digital cameras, telephones, video game consoles and more.
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7.42

Bluetooth

Low cost as cables

Secure as cables must support authentication and encryption

Support both data and voice.

Connect to a variety of devices.

Data rates 721kbps , using the 2.45Ghz radio frequency band I.S.M

(Industrial, scientific and medical) Support many simultaneous and private

low power, compact and global.

Connecting a computing device to a communicating device.

Allows any device with a Bluetooth chip to connect to the internet while

located within the range of the access point.

Example- a notebook could link to the internet using a mobile phone as anaccess point.


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7.43


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7.44

Communication Satellite

A satellite is a physical object which revolves around earth at known at

known height (orbit).

Artificial satellites are launched into orbits for various purpose like

communications.

Satellite communication system offer more flexibility than submarine cables,

underground cables, fiber-optics systems.

With the satellite to satellite communication, it is possible to communication

with any point on the globe.

A satellite system basically consists of a satellite in space and many earth

stations on the ground which are linked with each other through the satellite.

A ground based station controls the overall operations of satellite.

A satellite receives the signal transmitted from the earth station, it then

processes or amplifies the signal and then it retransmits the signal back to

earth in the desired form. This processing is done by a radio repeater which is

also called as transponder.

A communication satellite is a microwave repeater station that permit two or

more users to deliver or exchange information simultaneously.


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7.45

Geostationary Earth Orbit

GEO is also called as geosynchronous orbits.

It has 24 hour period of revolution but are inclined with respect to equator.

Orbits that are below a mean altitude of about 36,000 km periods of revolution

shorter than 24 hours and hence are termed as non GEO.

GEO satellite has the ability to provide coverage of an entire hemisphere at

one time.

Satellite are designed to last only about 15 yeas in orbit, because of service of

satellite, fuel, battery cells and failed components.


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7.46

Advantage of Geostationary Satellite

Keeping track of geostationary satellite is relatively easy as the satellite

remains almost stationary with respect to a given earth station.

The relative positions of satellite and earth station are fixed hence continuous

communication is possible by one satellite only.

There is no break in communication as only one satellite is to track.

The coverage area on earth is very large because the height of satellite is

more.

Very small energy storage is required as at very high height of satellite, it is

coming under high intensity solar radiations most of time.

The effect of Doppler shift frequency is negligible.


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7.47

Disadvantage of Geostationary Satellite

Because of higher height of satellite the propagation time for signal is muchlonger.

Signal has to travel longer distance, greater path loss and attenuation takes

place. Therefore highly sensitive are required.

Satellite are designed to last only about 15 yeas in orbit, because of service of

satellite, fuel, battery cells and failed components.

Satellite launching mechanism must be powerful and most accurate.


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7.48

Application of Geostationary Satellite

Television broadcasting

Regional, national and international global communications.

Telephone and data circuits.

Mobile telephone services.

Private networks for corporations, government agencies.

Military application.


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7.49

Medium Earth Orbit (MEO)

The altitude of MEO system is around, 1500 km to 36000 km.

Satellite orbit period is about 6 hours.

Transmission distance and propagation delay are greater than for LEO but

still significantly less than GEO.

Advantage of MEO MEO satellite can provide true global coverage.

MEO satellite system offers lower path loss than GEO.

Transmission delay is moderate.

The satellite architecture is distributed, therefore it gives strength.


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7.50

Disadvantage of MEO

To cover entire global large number of satellite are required typically 10 to 12

Received signal strength is variable because of range and distance angle .

Doppler effect can be observed significantly.

Technology is yet to mature.

It increase orbital debris due to large number of satellites per system.

Application of MEO

Surveillance of earth surface.

Global Positioning System (GPS).

Data gathering for military.


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7.51

LOW Earth Orbit (LEO)

The LEO in which satellites are at an height of approximately 1000 km andeach passes a given user in only a few minutes.

The advantage of using a LEO satellite network is that the range to the user is

shorter, hence less power is required.

The propagation delay is reduced as well.

Satellite orbit period is between 1.6 and 1.8 hours.

LEO satellite at height below about 1500 km are subject to atmospheric drag

and a harsh radiation environment and are likely to required replacement after

5 to 8 years of operation.


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7.52

Advantage of LEO

LEO satellite can provide true global coverage.

LEO satellite system offers lowest path loss compared to MEO and GEO.

broadcast delay is lowest.

Disadvantage of LEO

To cover entries global large number of satellite are required .

Architecture and space segment is most complex.

Satellite replacement rate is more than GEO and MEO

Application of LEO

In mobile satellite communication.

Earth resource applications.

Geological surveys.


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Transmission Impairments

In any communication system, the received signal is never matching to sometransmission impairments.

The most important impairments are as follows.

Impairment

DistortionAttenuation Noise


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Attenuation

The strength of a signal decrease with increase in distance travelled over amedium.

Attenuation means loss of energy. When signal travels over a medium or

channel.

To remove the attenuation better use to the amplification.

Distortion Distortion means that the signal changes its form or shape.

Each signal component has its own propagation speed through a medium

and, therefore own delay in arriving at the final destination


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Noise

When the data travels over a transmission medium, noise gets added to it. Noise is a major limiting factors in communication system performance.

Noise can be categorized into four types as follows:

1. Thermal noise

2. Intermodulation noise

3. Crosstalk

4. Impulse noise


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Thermal noise

It is the random motion of electrons in wire which creates an extra signal notoriginally sent by the transmitter.

Crosstalk noise

Intermodulation noise or induced noise

Impulse noise

Impulse noise gets generated due to many reasons such as external

electromagnetic disturbances, lighting etc.

It does not affect the quality of analog signal to a great extent but it affect thedigital data.

If signals at different frequencies are transmitted simultaneously on a

common transmission medium then it results in intermodulation nosie.

Crosstalk basically means interface between the adjacent telephone channels.

Sometimes when talking on the telephone, you can hear another conversation in

the background. That is crosstalk


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Bandwidth

The range of frequencies that contain the information is called bandwidth. Butthe term channel bandwidth is used to describe the range of frequencies

required to transmit the desired information.

For example the amplitude modulation (AM) systems needs a channel

bandwidth of 10 kHz to transmit a signal of 5 kHz bandwidth.


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Frequency

The number of cycle per second of waves is called frequency. The data is generally in the form of pulses and pulses is a composite signal

which contains many frequency.


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Wavelength

The distance a simple signal can travel in one wave.


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Line Configuration

Line configuration means the way two or more communication devices attachto a link.

A Link is the physical communication pathway that transfers data from one

device to another.

There are two possible line configurations.

1. Point-to-Point.

2. Multipoint.


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Point-to-Point

A point-to-point line configuration provides a dedicated link between twodevices.

The entire capacity of the channel is reserved for transmission between those

two devices.

Most point-to-point line configurations use an actual length of wire or cable to

connect the two ends, but other options, such as microwave or satellite links,

are also possible as shown in Fig.

When you change television channels by infrared remote control, you

are establishing a point-to-point line configuration between the remote

control and the televisions control system.

A B


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Multipoint

A multipoint (also called multidrop) line configuration is one in which morethan two specific devices share a single link as shown in Fig.

A

BC

D


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Network Interface Card

Each station on an Ethernet network (such as a PC, workstation, or printer)has own NIC.

NIC is the interface between the PC and the physical network connection.

This card physically connects to the cable that links your network.

The NIC fits inside the station and provided the station with a 6-byte physical

address, normally written in hexadecimal format, with colon between thebytes.

Example

06: 01 :02 : 01 : 2C : 4B


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Network Interface Card

Prepare data

NIC prepare data so that it can transmit through the cable. The cardtranslates data bit back and forth as they go from the computer to the

cable and back again.

Address data

Each NIC has its own unique address that it imparts to the data stream.

The card provides the data with an identifier. When it goes out on to the

net and enables data seeking a particular computer to known where toexit the cable.

Control data flow

The card has RAM on it to help it, place the data so that it doesnt

overwhelm the receiving computer on the cable.

Make (and agree on) the connection to another computer

Before it actually sends data, the NIC an electronic dialog with the

other PC on the network that wants to communicate. They agree on

thing like the maximum size of data groups to be sent. The total

maximum size of data (amount), the time interval between data checks

the amount of time that will elapse before confirmation that the data has

arrived successfully and how much data each card hold before it

overflows.


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Repeater

Repeater is an electronic device. It operates only in the physical layer. The basic purpose of a repeater is to extend the distance of LAN.

A repeater receives signal and before it becomes too weak or corrupted,

regenerates the original bit pattern. The repeater then sends the refreshed

signal.

A repeater does not actually connect two LANs; it connects two segments of

the same LAN. A repeater is not a device that can connect two LANs of

different protocols.

A repeater does not amplify the signal; it regenerate the signal. When it

receives a weakened or corrupted signal, it creates a copy, bit for bit, at the

original strength.

Repeater operates at physical layer of OSI model.


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Hub

All network required a central location to bring media segment together.These central locations are called hub.

In hub data packet coming from one port is sent to all other ports

Since every packet is sent out to every computer on the network, there is a lot

of wasted transmission. This means that the network can easily become

bogged down.

Hubs are typically used on small networks where the amount of data goingacross the network is never very high.

There is two type is hub

Passive Hubs

Active Hubs


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Hub

A passive hub is just a connector. A passive hub simply combines the signals

of network segment. There is no signal regeneration. This type of hub is a

part of the transmission media.

A passive hub reduce by half the maximum cabling distance permitted. With

passive hub, each computer receives the signal sent from all the other

computers connected the hub.

Passive Hub

Active Hub

An active hub is actually a multiport repeater. An active hub is that regenerate

or amplifies the signals.

By using active hubs the distance between devices can be increased.

One disadvantage of an active hub is that they amplify noise along with thesignal.


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Hub

A passive hub is just a connector. A passive hub simply combines the signals

of network segment. There is no signal regeneration. This type of hub is a

part of the transmission media.

A passive hub reduce by half the maximum cabling distance permitted. With

passive hub, each computer receives the signal sent from all the other

computers connected the hub.

Passive Hub

Active Hub

An active hub is actually a multiport repeater. An active hub is that regenerate

or amplifies the signals.

By using active hubs the distance between devices can be increased.

One disadvantage of an active hub is that they amplify noise along with thesignal.


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Bridge

A bridge goes one step up on a hub in that it looks at the destination of the

packet before sending.

If the destination address is not on the other side of the bridge it will not

transmit the data.

Bridges provides interconnecting two or more LANs.

Purposes of bridges

1. Isolate network by MAC addresses.

2. Manage network traffic by filtering packet.


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Isolate network by MAC addresses

Let us consider that you have one segment called segment 100 with 50 users

in several departments using this network segment.

Here one bridge is used to isolate the account departments and another

bridge is used to isolate the engineering department.

The bridge will only allow to pass through that are not on the local segment.

The bridge will first check its routing table to see if the packet is on the localsegment, if it is it will ignore the packet and not forward it to the remote

segment


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Manage network traffic by filtering packets.

Bridge can make a decision whether to forward the packet across the bridge,

if the destination address is not on the same port or it can decide to not

forward the packet if the destination is on the same ports.

This process of deciding whatever or not to forward a packet is termed

filtering packets network traffic is managed by dividing which packets can

pass through the bridge. The bridge filters packets.


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Type of bridge

These bridges examine the MAC address of the frames to determine whether

the packet is on the local segment or on the distant segment. Each bridge

required to manually build the routing table. This manually building a routing

table is called fixed/static routing.

Transparent Bridge

Source Routing Bridges

The main idea of source routing is that each station should determine the route

to the destination when it wants to send a frame and therefore include the route

information in the header of the frame.

In general when a station wants to transmit a frame to another station on thedifferent LAN, the station consult its routing table.

If the route to destination is found, then the station simply inserts the routing

information into the frame.


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Source Routing Bridges

How Discover a route ?

The station who wants to discover a route first broadcasts a special frame

called route broadcasts frame.

This frame will visit every LAN exactly once and eventually reaches the

destination.

Then the destination station responds with another special frame called the all

route special frame which generate all possible routes back to source station

After collecting all routes the source chooses the best possible route and save

it.


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Router

Routers are internetwork connectivity devices. An internetwork may consists of

two or more physical connected independent network. These networks can be

of different type.

Delivering packets according to logical network address is called routing.

Routers performs routing. Routing is the process of finding a path from a

source to every destination in the network.

Routers are intelligent. They can use algorithms to determine most efficient

path for sending a packet to any given network.

Router are also working to connect LAN to wide area network (WAN).

Routers are of two types.

1. Static routers: Static routers do notdetermine paths, but you need to specify

them.

2. Dynamic routers: Dynamic routers havecapacity to determine routes.


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Gateway

The term Gateway is used in networking to describe the Gate to the Internet

The Gateway controls traffic that travels from the inside network to the Internet

and provides security from traffic that wants to enter the inside network from

the Internet.

Gateway connects two independent networks. A gateway is protocol converter.

A gateway can accept a packet formatted for one protocol (e.g. TCP/IP) and

convert it to a packet formatted for another protocol (e.g. Apple Talk) before

forwarding it.

The gateway must adjust the data rate, size and data format. Gateway is

generally software installed within a router.


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Modem

Modem means modulator-demodulator.

At the sending end, a modem modulates a carrierwith the data to prepare it for

transmission.

At the receiving end, the modulated carrier is demodulated and the data is

extracted.

A modem also performs other functions, such as digital-to-analog/analog-to-

digital conversion, compression/decompression, error correction, and

encryption/decryption.

Phone lines are designed for analog, voice signals. Data communication using

phone line requires a special communication device, which convert the data

signals to those more compatible with the phone line capabilities. Special

communication device modem is used with telephone line for data transfer
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Features Modem

Speed

Self Testing

Auto Answer

Auto Dial/Redial

Voice over Data

Types Modem

Half Duplex and Full Duplex

Four Wire

Documents

Network Trasmmission Media