MODEL QUESTION AND ANSWERS UNITWISE AND MARKWISE
UNIT – 3 transmission media
(2 MARKS QUESTIONS)
1) State any two advantages of Co-axial Cable. (Any two Advantages- 1 Mark each)
- Lower attenuation than twisted pair.
- Low Cost due to less total footage of cable.
- Cheaper to design.
- Noise immunity due to low error rate
- Good Immunity to EMI/RFI.
- High Bandwidth
2) List any two advantages of optical fiber cable. (Any two advantages- 1 Mark each)
Advantages of optical fiber cable:
1) Higher bandwidth
2) Less signal attenuation
3) Immunity to electromagnetic interference
4) Resistance to corrosive materials
5) Light weight
6) Greater immunity to tapping
7) Easily available
3) Why the n/w cable is twisted? (2 marks for reason specified)
1) If wires are kept in parallel, signal may have crosstalk effect to avoid it wires are twisted.
2) It may results in greater level of noise.
4) Define Wi-Max. (definition 2 marks)
- Wi- Max is worldwide interoperability for Microwave Access.
- It is a wireless communication standard which can provide data rates up to 1 Gbps.
(5) Give any two disadvantages of unshielded twisted pair cable. (1 disadvantage- 1mark, any two disadvantages)
Disadvantages of unshielded twisted pair cable.
- Highly prone to crosstalk.
- Unable to provide secured transmission of data.
4 & 8 mark questions
1) Describe various factors to be considered while selecting transmission media. (Any 4 factors – 1 Mark each)
- Cost & Ease of installation: Costing is an important factor, when we select a media. Because absolute cost and ease of installation data are difficult to provide without referring to specific implementations, one can make relative judgments by comparing each medium to the others.
- Type of cable: Coaxial cable, Twisted Pair Cable, Fiber Optic Cable
- No of conductors/connectors: RJ-45, BNC, LC & ST
- Noise: It leads to distortion of a signal. Noise immunity of transmission media is considered at the time of selecting particular network.
- Bandwidth: Higher bandwidth transmission media support higher data rate.
- Radiation: It is leakage of signal from media caused by undesirable characteristics of media.
- Durability: Life span of media
- Interference: Interference occurs when undesirable electromagnetic waves affect the signal.
Interference can be caused by many factors, including
i.Electromagnetic Interference (EMI)
ii.Radio wave interference (RFI)
- Attenuation: Attenuation refers to the tendency of electromagnetic waves to weaken or become distorted during transmission. It is loss of energy as the signals propagates outwards. Attenuation increases with distance, as a wave passes through a medium, some of its energy is absorbed or scattered by the medium’s physical properties.
2) State the factors to be considered for selecting transmission media (Any 8 points, ½ marks each)
1.Type of medium.
2.No of conductors/connectors.
6.Reliability of connection
9.Ease of installation and maintenance access
10.Technical expertise required to install and utilize
11.Resistance to internal EMI , cross talk of parallel wires
12.Resistance to external EMI outside the cable.
3) Describe two application of i) twisted pair cable ii) co-axial cable (Any 2 applications of each – 1 Mark each)
i) Twisted pair cable ii) Co-axial cable
- Telephone lines. 1. Television Systems
- Local area Network 2. Connecting VCRs to television
- DSL Lines 3. Ethernet LANs
4) Compare guided and unguided media used in computer network. (Any 4 points – 1 Mark each)
|GUIDED MEDIA||UNGUIDED MEDIA|
|Also called as bounded or wired media||Also called as unbounded or wireless media|
|Point to point connection i.e. signal travelling is directed||Used for radio broadcasting in all directions i.e. signal travelling is undirected|
|Transport signal in electric current or light/ beam||Transport signal in the form of electromagnetic waves|
|Unidirection, not broadcast||Broadcast|
|Installation is costly and time consuming||Installation needs less time and money|
|Wired media leads to discrete network topologies||Wireless media leads to continuous network topologies|
|Attenuation depends exponentially on the distance||Attenuation is proportional to square of the distance|
|Example: Twisted Pair cable, Coaxial cable, Fiber optic cable||Example: Radio, Infrared light, Microwave|
5) State the transmission media applicable now a days for the following application:
i)) Cable TV ii) Cellular telephone iii) Wired LAN iv) Internet Backbone. (1 Mark each)
1) Cable TV: Coaxial cable (RG59)
2) Cellular telephone: microwave communication
3) Wired Lan: Twisted Pair and Fiber optic cable
4) Internet Backbone: Satellite Communication, fiber optic cable.
6) Which is the most practice medium to use when connecting computer that are fewer than 100 meters apart but located at different building? Why?(Medium used for communication-2 Marks, Reasons-2 Marks)
In this situation fibre optic use for connecting computer that are fewer than 100 meters apart but located in different building.
Reasons: fiber optic cable had lot of advantages over other different transmission medium such as twisted pair, coaxial cable such as higher bandwidth, high data transfer rate, less signal attenuation, immunity to electromagnetic interference, resistance to corrosive materials, light weight..
7) If you have only two computers to connect to a network which type of cable is used? Name the type of the cable and state the pin assignment used at both the ends of cable connector. (Name of cable 1 mark, type of cable 1 mark, pin assignment 2 marks)
If only two computers are to be connected in a network then UTP cross over cable is used,
Pin assignment at both ends of cable connectors:
Twisted pair cable with send and receive pairs of wires crossed.
Cross over cable is used to establish a two station LAN.
Pin diagram of cross over connection:
Green white 1 ————————————- 3 Orange white
Green 2 ————————————- 6 Orange
Orange white 3 ————————————- 1 Green white
Blue 4 ————————————- 5 Blue white
Blue white 5 ————————————- 4 Blue
Orange 6 ————————————- 2 Green
Brown white 7 ———————————— 8 Brown
Brown 8 ————————————- 7 Brown white
8) Describe the construction of co-axial cable with neat and labled diagram.(Diagram-2 Marks, Explanation- 2 Marks)
8) Draw and explain Co-axial cable. (Diagram 2 marks, explanation 2 marks)
8) Draw and explain Co-axial cable. (Diagram 1 mark,explaination 1 mark,any 2 advantages & disadvantages 1 mark each)
8) Draw the sketch of co-axial cable (cross-sectional view) (Diagram-1 Mark, Labelling- 1 Mark)
- Co-axial cable as inner central conductor surrounded by an insulating sheath which in turn is enclosed in a outer conductor (Shield).
- This acts not only as a second conductor for completing the circuit but also acts as shield against noise.
- Outer conductor is covered by Plastic covering .
- Co-axial cable is also called as coax and is more expensive than UTP, STP , less flexible and more difficult to install in building where number of twists and turns on needed.
- It is reliable & can carry higher data rates.
- Various categories of Co-axial cable are available dependent on thickness & size of shield, insulator and outer coating.
- Co-axial cable standards are RG(radio government) 59,RG 58,RG11,etc.
Categories of coaxial cables:
|RG-59||75 Ω||Cable TV|
|RG-58||50 Ω||Thin Ethernet|
|RG-ll||50 Ω||Thick Ethernet|
Advantages of coaxial cable :-
- It carries signals of higher frequency ranges than twisted pair cable.
- Lower attenuation than twisted pair cable.
- Supports higher bandwidth.
Disadvantages of coaxial cable :-
- Cost of coaxial cable is more than twisted pair cable.
- Less flexible .
- More difficult to install in a building where a number of twists and turns are required.
- Limited to size of network.
9) Draw the neat sketch of fiber optic cable. Give the transmission characteristics of Fiber optic cable. State its applications (Diagram: 3 marks, transmission characteristics: 3 marks, application: 2 marks)
Structure of FIBER OPTIC CABLE:
- Low Attenuation: Carry signal to a longer a distance
- No EMI: No effect of External environmental condition
- High Band width up to 2 GBPS
- Noise resistance: Uses light signal rather than electricity
- Higher data transfer rate
- Widely used in network (WAN /MAN /Internet etc.)
- Telephone system
- Replacement of satellite for interconnecting countries together through sea media
10) Draw and explain fiber optic cable.(2 marks for diagram, 2 marks for explanation)
- As shown in the figure, at the center is the glass core through which the light propagates.
- In multimode fibers, the core is typically 50 microns in diameter.
- In single mode fibers, the core is 8 to 10 microns.
- The core is surrounded by a glass cladding with a lower index of refraction than the core, to keep all the light in the core.
- A thin plastic jacket is used to protect the cladding.
- Fibers are grouped in bundles, protected by an outer sheath.
- Fibers can be connected in three different ways.
- First they can terminate in connectors and be plugged into fiber sockets.
- Connectors lose about 10 to 20 percent of the light, but they make it easy to reconfigure systems.
- Second they can be spliced mechanically.
- Mechanical splices just lay the two carefully – cut ends next to each other in a special sleeve and clamp them in place.
- Alignment can be improved by passing light through the junction and then making small adjustments to maximize the signal.
- Third, two pieces of fiber can be fused to form a solid connection.
- A fusion splice is almost as good as a single drawn fiber.
11) Explain different modes of fibre optic cable.(For each mode 2 marks)
Current technology supports two modes for propagating light along optical channels.
- Single mode.
Multimode can be implemented in two form:
- Step index.
- Graded index.
- Multiple beams from a light source move through the core in different paths.
- How these beams move within the cable depends on the structure of the core as shown in the fig.
- In multimode step-index fiber, the density of the core remains constant from the center to the edges.
- A 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 due to a lower density, this alters the angle of the beam’s motion.
- The term step index refers to the suddenness of this change, which contributes to the distortion of the signal as it passes through the fiber.
- A multimode graded index fiber decreases this distortion of the signal through the cable.
- In this, density is highest at the center of the core and decreases gradually to its lowest at the edge.
- Following fig shows the impact of this variable density on the propagation of light beams.
- The single mode fiber is manufactured with a much smaller diameter than that of multimode fiber and with substantially lower density.
- The decrease in density results in a critical angle that is close enough to 900 to make the propagation of beams almost horizontal.
- In this case propagation is almost identical and delays are negligible.
- All the beams arrive at the destination together and can be recombined with little distortion to the signal.
12) Compare twisted pair cable and fiber optic cable with (eight point). (Any eight points- 1 Mark each)
|PARAMERTER||TWISTED PAIR CABLE||FIBER OPTIC CABLE|
|Ease of installation||Very Easy||Very Difficult need a proper training|
|Technical expertise required to install and utilize||No||Yes|
|Distance||Less in meters||Very high in kilometer|
|Speed||Moderate||Very high (may attain speed of light if silica material used)|
|Application||LAN (specifically for shorter distance)||LAN , MAN, WAN (specifically for longer distance)|
13) Describe 4 advantages and 4 disadvantages of optical fiber. (Any four advantages- ½ Mark each, Any four disadvantages- ½ Mark each)
1) Higher bandwidth:
Fiber-optic cable can support dramatically higher bandwidths (and hence data rates) than either twisted-pair or coaxial cable.
Currently, data rates and bandwidth utilization over fiber-optic cable are limited not by the medium but by the signal generation and reception technology available.
2) Less signal attenuation:
Fiber-optic transmission distance is significantly greater than that of other guided media.
A signal can run for 50 km without requiring regeneration.
We need repeaters every 5 km for coaxial or twisted-pair cable.
3) Immunity to electromagnetic interference:
Electromagnetic noise cannot affect fiber-optic cables.
4) Resistance to corrosive materials:
Glass is more resistant to corrosive materials than copper.
5) Light weight:
Fiber-optic cables are much lighter than copper cables.
6) Greater immunity to tapping:
Fiber-optic cables are more immune to tapping than copper cables.
Copper cables create antenna effects that can easily be tapped.
7) Easily available.
1) Installation/maintenance expertise:
Installation and maintains need expertise that is not yet available everywhere.
2) Unidirectional: propagation of light is unidirectional.
3) Cost: Fiber optic cable is more expensive
4) Fragility: Glass fiber is more easily broken than wire, making it less useful for applications where h/w portability is required.
5) Limited physical arc of the cable: Bend it too much and it will break.
14) Compare Broadband transmission and baseband transmission. (Any 4 points 1 mark each)
|Baseband Transmission||Broadband transmission|
|It uses digital signaling over single wire||It uses analog signals over multiple transmission frequencies.|
|It is bi directional communication i.e. it allows computer to send and receive data using single cable but sending and receiving can’t be done on same wire at same time.||Multiple channels or created in broadband by using frequency division multiplexing (FDM).|
|Multiple signals on single cable can be transmitted on single wire using multiplexing||Multiple channels or created in broadband by using frequency division multiplexing (FDM).|
|TDM(Time division Multiplexing) is used in Baseband||FDM is used in Broad band|
|TDM Divides single channel into multiple time slots||FDM allows baseband media to allow data to flow in different directions on single medium at same time|
|Digital signal used in base band transmission occupies entire band width of network medium to transmit a single signal||Transmission system is allocated apart of total bandwidth|
|E.g. 10 Base T,100 base T, 10 Base 5, 10 base2||E.g. 10 Broad 36|
- Satellite communication is similar to terrestrial microwave communication except that satellite acts as one of the station.
- Satellite performs the functions of an antenna and the repeater together.
- Ground station A sends information to ground station B via the satellite Problem arises that if the earth along with its ground stations is revolving and the satellite is stationary the sending and the receiving earth stations and the satellite will be out of sync as time passes by.
- So normally geo stationary satellites are used which move at the same revolutions per minute as the earth in the same direction exactly like the earth.
- So both earth and satellite complete one revolution in exactly same time.
- Relative position of ground station with respect to satellite will never change.
- Movement of earth doesn’t matter to communicating nodes on earth.
- Using satellite we can communicate between any two parts of the world.
- However 3 satellites are needed to cover earth’s surface entirely Two frequency bands are used for signals from earth to satellite (uplink 6GHz) and from satellite to earth (down link 4GHz)
There are 3 methods for satellite communication system:
1) FDMA (frequency division multiple access)
2) TDMA (time division multiple access)
3) CDMA (code division multiple access)
FDMA puts transmission on separate frequency .
TDMA assigns each transmission a certain portion of time On the designated frequency .
CDMA gives unique code to each transmission and spreads on available set of frequencies
Multiple access indicates that many users can use.
1) Satellite communication has low delay because signals travel faster in air than solid.
2) Satellite communication is broad cast media
16) With the help of diagram explain satellite communication. (Diagram: 2 marks, explanation: 4 marks, frequency band: 1 mark, application: 1 mark )
SATELLITE COMMUNICATION :
- In satellite communication, signal transferring between the sender and receiver is done with the help of satellite.
- In this process, the signal which is basically a beam of modulated microwaves is sent towards the satellite called UPLINK (6 Ghz).
- Then the satellite amplifies the signal and sent it back to the receiver’s antenna present on the earth’s surface called as DOWNLINK (4Ghz), as shown in the diagram given below.
- As the entire signal transferring is happening in space.
- Thus this type of communication is known as space communication.
- In the diagram given below has uplink frequency of about 6 Ghz & downlink frequency fo 4 Ghz.
- That is satellite receive microwave signal at 6 Ghz frequency amplifies & down convert it to 4 Ghz 7 transmit it back to earth station to avoid collision.
- Two satellites which are commonly used in satellite communication are Active and passive satellites.
- It is just a plastic balloon having a metal coated over it.
- This sphere reflects the coming microwave signals coming from one part of the earth to other part.
- This is also known as passive sphere. Our earth also has a passive satellite i.e. moon.
- It basically does the work of amplifying the microwave signals coming.
- In active satellites an antenna system, transmitter, power supply and a receiver is used.
- These satellites are also called as transponders.
- The transmitters fitted on the earth generate the microwaves.
- These rays are received by the transponders attached to the satellite.
- Then after amplifying, these signals are transmitted back to earth.
- This sending can be done at the same time or after some delay.
- These amplified signals are stored in the memory of the satellites, when
- earth properly faces the satellite.
- Then the satellite starts sending the signals to earth.
Geostationary or Geosynchronous satellite :
- It is specifically used for low cost Communication, which is placed at an altitude of 36,000 KM from the earth
Frequency band used in satellite communication :
|C||3.7 to 4.2 Ghz||5.925 to 6.425Ghz|
|Ku||11.7 to 12.2 Ghz||14 to 14.5 Ghz|
|Ka||17.7 to 21 Ghz||27.5 to 31 Ghz|
Application of satellite:
1) Satellite television
4)satellite internet access
17) Explain infrared communication. List any two disadvantages of infrared
communication.(explanation -2 marks, Two disadvantages -2 marks)
- Infrared communication (IR) is an example of wireless communication.
- However, it is limited to very simple applications & suffers from several disadvantages, mainly very small bandwidth & distances that it can support.
- Infrared communication works in the micrometer range, which is 1 to 430 THZ.
- The term infrared comes from the fact that red color has the longest wavelength amongst the colors in visible light.
- However, the wavelength of infrared is longer than that of red color, and hence the frequency of infrared communications is smaller than that of red color.
- Hence, we have the term below red color or Infrared.
- Infrared communication is used by military for surveillance, for vision in the darkness at night, tracking objects, etc.
- We use infrared communication whenever we use our remote controls to operate television sets, DVD players, etc. Weather forecasting & astronomy also make use of infrared communication.
i.The major disadvantage is that the sun generates radiation in the infrared band.This can cause a lot of interference with IR communication.
ii.Infrared signals cannot penetrate walls
iii. Large areas require multiple emitter panels, which will increase the cost of the system.
18) Explain following wireless technologies used in computer communication:i) Wi-Fi ii) Bluetooth(WiFi diagram – 1 Mark, Explanation- 3 Marks, Bluetooth diagram – 2 Marks, Explanation 2 Marks)
- Wi-Fi stands for wireless fidelity.
- Wi-Fi provide data rate of 54 Mbps.
- Wi-Fi based on IEEE 802.11 standard.
1) Easy to use.
2) Easy and simple to expandability.
3) Easy to install and setup.
4) No requirement of wires
1) The range of Wi-Fi is limited
2) Security is less in Wi-Fi connections as compared with others.
3) Wi-Fi connections are highly suspect able interruption by other devices which are operating in close proximity.
- Bluetooth is short range wireless technology.
- Range of Bluetooth is 10 meters.
- Bluetooth Architecture define 2 types of networks.
- It consist of 1 master node and 7 slave nodes.
- Piconet have 8 active nodes(7+1) in the range of 10 meters.
- There can be only 1 master station in each piconet.
- Communication is between master and slave
- Slave-slave communication is not possible.
- Piconet can have 255 parked nodes, that can not take part in communication
- There will be 7 slaves in active state and 255 nodes in parked state.
- It is formed by combining various piconets.
- Slave in one piconet can act as master in other piconet.
- Such a node can receive message from the master in the first piconet and deliver the message in second piconet.
- Station can be member of two piconets.
- Staion can not be master of two piconet.
19) Describe of the following terms w.r.t. the cellular telephony. (1 mark each point)
1) Soft hand off: Is a process of transferring an ongoing call from one channel to another without the loss of service.
Soft hand off refers to a feature used by the CDMA and W-CDMA standards, where a cell phone is simultaneously connected to two or more cells during a call.
2) Roaming: Roaming is a general term referring to the extension of connectivity service in a location that is different from the home location where the service was registered.
Roaming ensures that the wireless device is kept connected to the network, without losing the connection.
The term “roaming” originates from the GSM Global System for Mobile Communications as the ability for a cellular customer to automatically make and receive voice calls, send and receive data, or access other services, including home data services, when travelling outside the geographical coverage area of the home network.
In roaming vlr visitors location register is utilized.
3) AMPS: Advanced Mobile Phone Service (AMPS) is a standard system for analog signal cellular telephone service in the United States and is also used in other countries.
It is based on the initial electromagnetic radiation spectrum allocation for cellular service by the Federal Communications Commission AMPS allocates frequency ranges within the 800 and 900 Megahertz (MHz) spectrum to cellular telephone.
Each service provider can use half of the 824-849 MHz range for receiving signals from cellular phones and half the 869-894 MHz range for transmitting to cellular phones.
The analog service of AMPS has been updated with digital cellular service
4) GSM: Global System for Mobile Communications, is a standard set developed by the European Telecommunications Standards Institute to describe protocols for second generation (2G) digital cellular networks used by mobile phones.
It became the de facto global standard for mobile communications e. The GSM standard was developed as a replacement for first generation (1G) analog cellular networks, and originally described a digital, circuit switched network optimized for full duplex voice telephony.
This was expanded over time to include data communications, first by circuit switched transport, then packet data transport via GPRS (General Packet Radio Services) and EDGE (Enhanced Data rates for GSM Evolution or EGPRS).
“GSM” is a trademark owned by the GSM Association
20) Explain handoff procedure of cellular mobile phone. (Handoff Procedure -2 Marks, Types of Handoff – 2 Marks)
- Assume that there is a call going on between two parties over a voice channel.
- When the mobile unit moves out of coverage area of a particular cell site the reception becomes weak.
- Then the cell site will request a hand off.
- The system will switch the call to a new cell site without interrupting the call or changing the user.
- This procedure is called as the hand off procedure or handover procedure.
Following are various types of handoffs. Supported by a Mobile Station (MS):
- Hard Hand Off
- Soft Hand off
- Queued hand off
- Delayed hand off
- Forced hand off
- Hard hand off:A hard handoff is a handoff technique used with cellular networks that requires the user’s connection to be entirely broken with an existing base station before being switched to another base station.
- Soft hand off:The hand off is known as soft handoff if the MS starts communication with a new base station without stopping the communication with the older base station.
- Delayed Hand off:In many situations, instead of one level, a two level handoff procedure is used, in order to provide a high opportunity for a successful handoff. A hand off can be delayed if on available cell take the call.
- Forced handoff :A forced handoff is defined as the off which would normally occur but prevented from happening or a handoff that should not occur but is forced to happen.
- Queued handoff:In the queued handoff process, the MTSO arranges the handoff requests in a queue instead of rejecting them, if the new cell sites are busy.