MSU Network

8/10/2019 MSU Network

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A

Sr Question

1 The first DATA network formed by ARPA was called

2 The research team chose to follow an approach known as _____ that became the basis for data netwo

3 The research team chose to follow an approach known as _____ that became the basis for data netwo

4What was major issue resulting into complexity with NW StandardMultiple organizations have created NW standards independently, which are not all compatible

5 What was the main motivation in early computer networks that were large and expensive?

6 Early computer networks were designed to permit sharing of expensive, _____ resources

7

Name three basic wiring types used to minimize interference in networksUnshielded Twisted Pair (UTP)

Coaxial Cable

Shielded Twisted Pair (STP)

8 A coaxial cable consists of a _____________ wire surrounded by a metal shield

9 A _______twisted pair cable consists of a pair of wires surrounded by a metal shield

10 Glass Fiber uses__________ to transport data

11

List 2 advantages of using Optical Fiber.1. Because they use light,neither cause electrical interference in other cables nor are they susceptible

2. Because glass fibers can be manufactured to reflect most of the light inward a fiber can carry a pul

3. Because light can encode more information than electrical signals an optical fiber can carry more i

4. Unlike electricity, which always requires a pair of wires connected into a complete circuit, light ca

12

List 2 disadvantages of using Optical Fiber.1. First, installing a fiber requires special equipment that polishes the ends to allow light to pass throu

2. Second, if a fiber breaks inside the plastic jacket: finding the location of the problem is difficult3. Third, repairing a broken fiber is difficult special equipment is needed to join two fibers
https://dl-web.dropbox.com/get/BCA_2013-2014/Sem%203/computer%20networks-i/computer%20networks/Full%20QnA%20Sem%203%202014%20final.xlsx?_subject_uid=265771387&w=AACkY3SVAf7VcGXKLBi-7_MZ6cf4xZ4fIpGAW_QMsZ1lJw&get_preview=1https://dl-web.dropbox.com/get/BCA_2013-2014/Sem%203/computer%20networks-i/computer%20networks/Full%20QnA%20Sem%203%202014%20final.xlsx?_subject_uid=265771387&w=AACkY3SVAf7VcGXKLBi-7_MZ6cf4xZ4fIpGAW_QMsZ1lJw&get_preview=1https://dl-web.dropbox.com/get/BCA_2013-2014/Sem%203/computer%20networks-i/computer%20networks/Full%20QnA%20Sem%203%202014%20final.xlsx?_subject_uid=265771387&w=AACkY3SVAf7VcGXKLBi-7_MZ6cf4xZ4fIpGAW_QMsZ1lJw&get_preview=1


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13 The satellite contains a _____________________ that consists of a receiver & transmitter

14

Define the function of the Transponder used in Satellite

transponder accepts an incoming radio transmission

amplifies itand transmits the signal back toward the ground at a slightly different angle than it arrived

15 Many long-distance telephone companies use ______________ to carry telephone conversations

16 Infrared is limited to _____________ area

17 In Lightwave light from a laser must travel in a _____________ line and must not be ____________

18

Why is the problem of interference is severe in copper wires?

because wires that comprise a NW often are placed in parallel with many other wires

19 RF technology can be combined with ______________ to provide communication across longer dist

20

In twisted Pair Cables how do twists change the electrical properties of the wire?

First, they limit the EM energy the wire emits: So they help prevent electric currents on the wire fromSecond, they make the pair of wires less susceptible to EM energy:They help prevent signals on othe

21 Most NWs do not send data as continuous streams of bits. But instead divides data into small blocks

22

List and Describe the use of Packet in NW

First, a sender and receiver need to coordinate transmission to ensure that data arrives correctly:

Dividing the data into small blocks helps a sender and receiver determine which blocks arrive intact aSecond, communication circuits and the associated modem hardware are expensive

multiple computers can share connections and HW to reduce costs

23 Conceptually, a NW that permits many sources to take turns accessing a shared resource is said to be

24How does dividing data into small packets ensures that all sources receive prompt servicebecause it prohibits one source from gaining exclusive access for an arbitrarily long time

25 Term _____ is used to denote a packet used with a specific NW Hardware


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26List the disadvantages and advantages of framing schemeThe chief disadvantage is overhead

The chief advantage is handling system failures and reboots

27 ________ on NW can permanentely damage NW equipment , changes the signal or completely des

28

What are the effects of Interference on NW1 cause permanent damage to NW equipment (lightening)

2 changes the signal

3 completely destroy a signal

4 create the opposite effect i.e although the sender does not transmit anything, a receiver might inter

29

Explain Parity Checking in NW

1 Parity checking requires the sender to compute an additional bit called a parity bit and to attach it2 The receiver removes the parity bit, performs the same computation as the sender and verifies that

3 The parity computation is chosen such that if one of the bits in the character is damaged in transit, t

that an error occurred.

30What are the two forms of parityOdd and Even

31

Two facts motivate the use of packets. List any one giving reason

First, a sender and receiver need to coordinate transmission to ensure that data arrives correctly:

Dividing the data into small blocks helps a sender and receiver determine which blocks arrive intact aSecond, communication circuits and the associated modem hardware are expensive

multiple computers can share connections and HW to reduce cost

32 All computers attached to an Ethernet participate in a distributed coordination scheme called ____

33 CSMA uses ____ activity on the cable to determine status

34 The interference/ mixture of two signals in CSMA is called ___

35 CSMA/CD will not suffice for Wireless LAN because of problem called ____

36 Wireless Used the modified version of CSMA/CD called ____

37 Early Communication systems had communication channel for connecting exactly two computers an

38 The best example of Bus Topology used today is ___

39 Localtalk uses ___ form of CSMA

40 Ring Toplogy uses ______ scheme for NW sharing


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41 _____ employed redundancy to overcome failures in Ring Topology

42

What are the three useful properties of point-to-point NW scheme ?

1.Because each connection is installed independently, appropriate hardware can be used. For e.g. the do not need to be same on all connections

2.Because they have exclusive access the connected computers can decide exactly how to send data a

mechanism and a maximum frame size. Most importantly because the connection is independent of o

change.3.Because only 2 computer has access to the channel it is easy to enforce security and privacy . No ot

43Disadvantages of Point-to-Point NW if more than two hosts need to communicate with one another? the number of connections grows quickly as the size of the set increases

44

If shared communication reduces cost why is it not used for long distance communication as well? GBecause in sharing medium communication is required for Coordination and the time required depen

Shared NW with long delays are inefficient because they spend more time coordinating use of the shProviding a high BW channel over long distances is significantly more expensive than providing the

45

If shared communication reduces cost why is it not used for long distance communication as well?Because in sharing medium communication is required for Coordination and the time required depen

Shared NW with long delays are inefficient because they spend more time coordinating use of the shProviding a high BW channel over long distances is significantly more expensive than providing the


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46

What is Locality of Reference Principle in Data NW ?

Communication among a set of computers is not random, instead follows two patterns

First, if a pair of hostscommunicates once, it is likely to communicate again in the future and then pSecond, a computer tends to communicate most often with other computers that are nearby called

47 List the three topologies used most often with LANs

48

Explain Star Topology with supporting diagram

A NW uses a star topology if all computers attach to a central pointHubs (or switches) are used to connect computer together

A hub is an electronic device that accepts data from a sending computer and delivers it to all connectFigure 8.3 illustrates an idealized star NW:

In practice, star NW seldom have a symmetric shape in which the hub is located an equal distance froInstead, a hub often resides in a location separate from the computers attached to it

49

Explain Ring Topology with supporting diagram

A NW that uses a ring topology arranges for computers to be connected in a closed loopa cable connects the first computer to a second computer, another cable connects the second compute

Computers arranged in a circle as shown in Figure 8.4

Ring refers to logical connections among computers, not physical orientation

computers in a ring need not be arranged in a circle


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50

Explain Bus Topology with supporting diagram

A NW that uses a bus usually consists of a single, long cable to which computers attach

The ends of a bus NW must be terminated to prevent electrical signals from reflecting back along the

Any computer can send a signal down the cableand all computers receive the signal

Figure 8.5 illustrates the topologyAll computers attached to the cable can sense signalsany computer can send data to any other computer

The computers attached to a bus NW must coordinate

to ensure that only one computer sends a signal at any timeotherwise chaos results

51List advantages of a ring topologymakes it easy for computers to coordinate access and to detect whether the NW is operating correctly

52List advantages and disadvantages of a ring topologymakes it easy for computers to coordinate access and to detect whether the NW is operating correctlyHowever, an entire ring NW is disabled if one of the cables is cut

53

List advantages and disadvantages of star topology

helps protect the NW from damage to a single cable because each cable connects only one machinerequires more wires than a bus

54

List disadvantages of a bus topology

has the same disadvantage as a ring - a NW is disabled if someone accidentally cuts the main cable

55

How does sharing work on an Ehternet

Figure 8.7 illustrates how data flows across an Etherneta signal propagates from the sending computer to both ends of the shared cable.

Sharing in LAN does not mean that multiple frames are being sent at the same time

Instead, the sending computer has exclusive use of the entire cable during the transmission of a given

other computers must waitAfter one computer complete transmitting one framethe shared cable becomes available for another computer to use


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56

Explain how CSMA works

An Ethernet does not have a centralized controllerAll computers attached to an Ethernet participate in a distributed coordination scheme

It is called Carrier Sense Multiple Access (CSMA)

The scheme uses electrical activity on the cable to determine statusWhen no computer is sending a frame

the ether does not contain electrical signals

Determine whether the cable is currently being useda computer can check for a carrierIf no carrier is present,

the computer can transmit a frame

If a carrier is present,

the computer must wait for the sender to finish before proceedingChecking for a carrier wave is called carrier sense

57 In CSMA/CD, to guarantee that a collision has time to reach all stations before they stop transmitting

58

In CSMA/CD after a collision has occurred and if the computers begin to transmit as soon as the ethe

To avoid multiple collisions, each computer needs to delay after a collision before attempting to retr

A maximum delay d forces each computer to choose a random delay less than dWhen a computer chooses a delay at random it will select a value that differs from any of the values

The computer that chooses the smallest delay will proceed to send a frame and the NW will return to

59

Explain binary exponential backoffIf two or more computers happen to choose nearly the same amount of delay after a collision they w

To avoid a sequence of collisions

stations double the range after each collision

A random delay from 0 to d after 1st collisionA random delay between 0 and 2d after 2nd collision,

A random delay between 0 and 4d after 3rd , and so on

After a few collisions, the range from which a random value is chosen becomes largeThis technique is known as binary exponential backoff

It provides a quick recovery after a collision because each computer agrees to wait longer times betw


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60

Some wireless LANs characteristics:EM energy radiates in all directions

Wireless LAN transmitters use low power

Enough power to travel a short distanceMetallic obstructions can block the signalWireless units located far apart or behind obstructions will not receive each other's transmissions

61

How does CSMA/CA work

Instead of depending on all other computers to receive all transmissionsTrigger a brief transmission fromthe intended receiver before transmitting a packet

Before sending the frame, transmit a brief control messageReceiver responds by sending another control message to indicate that it is ready to receive a transm

Once a response from its intended recipient arrives sender begins transmitting the frame

62

What if Collision Occur in CSMA/CA for control message

Collisions of control messages can occur when using CSMA / CA, but they can be handled easilyWhen such collisions occur,

the sending stations apply random backoff before resending the control messagesBecause control messages are much shorter than data frames

the probability of a second collision is much lower than with conventional Ethernet

63

Advtantage & Disadvantage of Localtalk

The major disadvantage was lower throughput:

LocalTalk hardware transfers data at much lower speeds than EthernetThe major advantage was low cost:

because most of the HW needed to connect the computer to a LocalTalk was included with a comput

the NW was almost free (e.g, only a single cable was needed to connect two Macintosh computers ov

64

Hows doea a ring topology ensures that exactly one token exists on a token ring ?

A token gives a host permission to send one frame.Before it can send a frame, the host must wait for the token to arrive

When a token arrives, temporarily removes from the ring and uses the ring to transmit

65

How does Token Ring scheme guarantees fair access:

as token passes around, each one will have an opportunity to useif a host does not have any data to send it the passes the token on without delay


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66 What is the example of Star Toplogy

67 What is the full form of ATM

68

When a frame is transmitted across a LAN, the electrical signals carrying the bits reach all stations. H

attached stations receive a copy of all signals?

Each station on the LAN is assigned a unique numeric value called a physical address, Hardware Ad

69 When a sender transmits a frame across the LAN, the sender includes ___ Address of the intended re

70 Each frame includes two addresses ?

71 Why is the sender address included in frame ?

72

List the tasks handled by the Network Interface Hardware1checks the length of an incoming frame

2 checks the CRC to ensure that the bits arrived intact and discards frames that contain errors3 compares the destination address to the station's HW Address, If it matches the station's HW Addr

discards

73 While comparing the incoming frame if the NIH find that it is not matching, what action does it take

74 standard for addressing has been created by _____

75 In IEEE addressing scheme, each address consists of ____ (Bits / Bytes ) MAC address.

76 MAC full form

77 NIH full form

78 Other names for MAC Address

79

How does IEEE deal with Hardware Address Assignment ?

Maintains that each address is unique and so IEEE allocates an address for each piece of network inteRather than assign individual addresses, IEEE assigns a block of addresses to each equipment vendor

Thus, a 48-bit address is divided into a 24 bit (first 24 bit) Organizationally Unique ID (OUI) that ide

Interface Controller (NIC)

80 The IEEE addressing scheme supports three types of addresses that correspond to three types of pack

81 Based on the Packet Delivery, Ethernet LAN addresses can be broken down into two subcategories. L


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82 What is a Unicast Address?

83 The ____ address on an ethernet frame will always be a unicast address.

84 When a packet is framed for transport and is being forwarded to a single destination, destination addr

85 ___ and Broadcast addresses are both classified as group addresses

86In case of multicasting, the tricky part of dealing with host groups and hardware addresses is performproblems

87

How is the transmission of multicast packets done?Transmission of multicast packets is a simple problem because they look exactly like any other packe

The interface transmits them over the communication medium without looking at the destination add

It's the kernel that has to assign a correct hardware destination address.The kernel handles the job of tracking which multicast addresses are of interest at any given time. T

running at any given time and the users' interest.

On the receiving end, it is the driver's job to accept the list of interesting multicast addresses and del

88 What is Broadcast address?

89 Broadcast addresses are always the same value, which is ____

90 Most LAN technologies define a frame to consist of two parts. List them

91 the ____ area of a frame does not have a fixed size

92 HW sometimes enforces a minimum as well as a maximum frame sizeIf the sender has less than the minimum, the data can be extended with ___


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93

An Ethernet frame begins with a header that contains three fields. List and Explain

The 64-bit preamble - alternating 1s and 0s that allow the receiver's hardware to synchronize with t

The first two fields of the header contain HW Address i.e. Destination Address and Source AddressThe third field of the header consists of a 16-bit Ethernet frame type

94 0800h in the Frame Type field specifies that data in the frame is for ___

95 To read packets, analyzer software places the computer's network interface hardware into ____ mode

96 What happens when analyser software is put into promicuous mode ?

97 A computer CPU does not process individual bits on the NW. Who Does that

98 Most NICs contain Direct Memory Access (DMA) circuit. How does it help?

99

How is NW packet handled in a computer?To receive a packet,

the CPU allocates buffer space in memory

and then instructs the NIC to read the next incoming packet into buffer

the NIC waitsfor a frame to cross the networkmakes a copy of the frame and process it

100The original Ethernet wiring scheme was informally called ___ or ___

101The ___ handles the digital aspects of the communication, e.g. address recognition and error detectio

converting bits into voltages, etc.

102Ethernet specifies a minimum distance separation between two transceivers, so when there are severa

between multiple connections

103if a carrier signal is present on the network, the multiplexor reports the carrier to ____

104A second generation of Ethernet wiring uses a thinner more flexible ___ cable than the original thick

105

Difference between Thinnet and Thicknet ?

Thinnet generally costs less than Thicknetto install and operate than ThicknetBecause HW that performs the transceiver function is built into the NIC no external transceivers are

Thinnet does not use an AUI cable to attach the NIC to the communication medium / it attaches dir

106A third generation of Ethernet (todays widely used technology) is


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107An electronic device serves as the center of the NW is known as ___ or ___

108The connection uses UTP wiring with ___ connectors

109A connection in a hub is called ___

110

As per the Topology Paradox, how does twisted pair Ethernet function physically & logically?

Physically, twisted pair Ethernet uses a star topologyLogically, twisted pair Ethernet functions like a bus

111

Is Ethernet a bus topology, or does the topology depend on the wiring? Explain the Topology Parado

A twisted pair Ethernet forms a classic star where each computer has a dedicated connection to the cePhysically, twisted pair Ethernet uses a star topology

Logically, twisted pair Ethernet functions like a bus

112Because physically, twisted pair Ethernet uses a star topology and Logically, twisted pair Ethernet fu

113What is Fast Ethernet?

114Of the fast Ethernet standards ____ is by far the most common and is supported by the vast majority

115100BASE-TX - 100 Mbit/s used Cateory ___ UTP cable and is most popular LAN cabling this days

116100BASE-FX is a version of Fast Ethernet over _____

117100Base-FX uses a 1300 nm near-infrared (NIR) light wavelength transmitted via two strands of opti

118List 2 connectors options for 100BaseFX

1191000BASE-T (also known as IEEE 802.3ab) is a standard for gigabit Ethernet over copper wiring mu

120_____ is a fiber optic gigabit Ethernet for distance capability between 220 metres and 550 metres usi

121____ is a fiber optic gigabit Ethernet standard specified in IEEE 802.3 Clause 38 which uses a long w

over single-mode fiber.

122IEEE Standard _____ deals with Wireless LANs

123802.11a uses ___ frequency

124802.11b and 802.11g uses ___ frequency

125802.11g gave speed Up to ___ in 2.4 GHz band

126802.11b gave speed Up to ___ in 2.4 GHz band


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127802.11a used ___ channels in which ___ are used for data ___ for synchronisation

128802.11a gave speed upto ____

129____ is used to tackle the 2 main issues hiden terminal and expose station in wireless

130Distribute Coordination Function (DCF) used ___ or ___ method to tackle the problem of hiden term

131Virtual carrier sensing uses additional ACKs, Carrier Sense, and Binary Exponential Backoff (BEB)

132Wireless communication quality between two nodes can be unequal due to ___

133IEEE ___ deals with bluetooth standard

134In Bluetooth, Slave nodes need to be within __ meters of the master node.

135In Bluetooth, Piconet uses centralized ____ division Multiplexing.

136What was the cause for rise in demand for Wireless LAN?

137List four most popular wireless standards

138

Name 3 Network Terms Associated with Wireless and Explain them

1. Base Station - all communication through an Access Point (AP) or Wireless Hub2. Infrastructure Wireless : AP is connected to the wired Internet.

3. Ad Hoc Wireless : wireless nodes communicate directly with one another without the need of AP

139

2 main issues in 802.11a

Complex Encoding

More difficulty in penetrating walls

140What was the problem with frequency used by 802.11b

141In wired Ethernet (802.3) you could seize the channel i.e. take the full control of the medium. But it i


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142

Explain Hidden Terminal Problem with diagramWireless stations have transmission ranges and not all stations are within radio range of each other.

Simple CSMA will not work!C is transmitting to B.

If A senses the channel, it will not hear Cs transmission and falsely conclude that A can begin a tr

143

Explain Exposed Station Problem with diagram

B wants to send to C and listens to the channel.When B hears As transmission, B falsely assumes that it cannot send to C.

144

Explain in brief how virtual carrier sensing works

Sender broadcasts a Request-to-Send (RTS) and the intended receiver sends a Clear-to-Send (CTS).

Upon receipt of a CTS, the sender begins transmission of the frame.

RTS, CTS helps determine who else is in range or busy (Collision Avoidance).

145what is NAV with reference to virtual carrier sensing

146

Explain Persistent Physical Carrier Sensing

The station senses the channel when it wants to send.If idle, the station transmits

If the channel is busy, the station defers until idle and then transmits (1-persistent).

Upon collision, wait a random time using binary exponential backoff (BEB)

147

List 3 types of nodes in bluetooth and their numbers as specified in architecture

1 Master node1 to 7 active slave nodes

0 to 255 parked nodes


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148

List 2 types of nodes in bluetooth as specified in architecture

1 Master node1 to 7 active slave nodes

0 to 255 parked nodes

149

List the 13 profiles and exlpain them1. Generic access profile

provides secure channels between the master and slave.

2. Service discovery profileallows devices to discover what services are available from other devices.

3. Serial port profile

for applications that need a serial port communication4. Generic object exchange profile

provide support for the client/server model.

note that a slave can be a client or a server.

5. LAN access profile

is a direct competitor of 802.11.allows a Bluetooth device to connect to a fixed network.

6. Dialup access profileEricssons original motivation

allows a notebook computer to communicate to a mobile phone without wires

7. Fax profileallows fax machines to connect to mobile phones wirelessly to send and receive faxes

8. Cordless Telephony Profile

connect a cordless telephone handset to a base station without wires.

9, Intercom profileallows two telephones to connect like walkie-talkies

10, Headset Profilegood for hands free telephony I.E. while driving a car

The last three profiles are for wireless devices to exchange a wide variety of data11. Object Push profilefor simple objects

12. File transfer profile - general file transfer

13. Synchronization profile - was designed to facilitate the exchange of data in both directions betwe

150

Infrared technology used in local networks exists in three different forms. List with speed at each forIrDA-SIR (slow speed) infrared supporting data rates up to 115 Kbps

IrDA-MIR (medium speed) infrared supporting data rates up to 1.15 Mbps

IrDA-FIR (fast speed) infrared supporting data rates up to 4 Mbps

151Which profile is used if you want to synchronise phonebook in your smartphone with your computer

152While original V 1.0 of bluetooth is a complete specification from application layer to physical layer

153Communication in bluetooth is only possible between ____ and ____nodes


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154The Bluetooth 802.15 specification not only creates competition for other wireless technologies, nam

other.

155

What are parked nodes in bluetooth

a slave device in a low power state to conserve the drain on the devices batteriesIn this state the device can onlyrespond to the signal from the master node

156Each LAN technology is designed for a specific combination of ____, distance and cost

157To overcome distance limitations, some LAN technologies allow two LANs to be joined together wit

158_____ Limitation is the fundamental part of LAN designs.

159When designing a NW technology, we choose a combination of ____, _____ and _____achieved at

160To help save expense, LAN technologies usually use a ______ communication medium such as a sha

161As a consequence of using a shared medium, a LAN design must include a mechanism that guarantee

162The two most popular access mechanisms, CSMA / CD and ______, each take time proportional to th

163To ensure that delays do not become significant a LAN technology works with a fixed maximum __

164_____ has low delay and high bandwidth

165Repeaters are part of the Ethernet standard, which specifies that the network will not operate correctl

166Like a Repeater, ____ is an electronic device that connects 2 LAN segments.

167Two LAN segments connected by a ____ behave like a single LAN

168The most valuable function a bridge performs is ____

169

How is the interconnections among switches and the capacity of each connection chosen?

to accommodate the expected trafficto provide redundancy in case of failure

170To ensure that all stations attached to a LAN receive a sufficiently ____signal, we should calculate th

171A repeater is usually an analog ____ device that continuously monitors electrical signals on each LA

172When a frame arrives on a segment, the bridge extracts and checks ____ address and takes one of th

173Most bridges are called ____ OR ____ bridge - Because they learn the locations of computers autom


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174To learn the locations of computers automatically the bridges uses ___ address information in the fra

175In bridging between multiple locations, Filtering at both sites is performed because of ___ constraint

176Bridges HW used with long-distance connections must perform ____i .e. saving a copy of each fram

177The bridges perform a computation known as the _____ algorithm to decide which bridges will not

178DST allows a bridge to determine whether forwarding will introduce a ____

179

Fiber modems contains HW to perform two chores. List them

1. electronic circuitry in fiber modem converts between AUI signals and digital representation

2. and optical driver translates between the digital representation and pulses of light which travel alon

180

Can an arbitrarily long Ethernet be constructed by using repeaters? Why?1. The answer is NO

2. Although such an arrangement does guarantee sufficient signal strength, each repeater and segmen3. If the delay becomes too large, the scheme fails.4. Repeaters are part of the Ethernet standard, which specifies that the network will not operate corre

181

Repeaters have several drawbacks. List them

1. repeaters do not understand complete frames - a repeater does not distinguish between a valid fram2. When a collision/interference occurs on one segment - a repeater recreates the signals on the other3. Similarly when interference generates unwanted electrical noise on a segment, repeaters transmit

182

Why are Bridges more popular than repeaters ?

because they help isolate problems like

1. bridge will not forward a collision from one segment to another2. if interference occurs on one of the 2 segments connected by a bridge, it will simply discard the sa

3. bridge keeps problems on one segment from affecting the other


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183

When a frame arrives on a segment, the bridge extracts and checks destination address and takes one

1. If the bridge knows that the destination computer is attached to the same segment over which the f

the bridge can discard the frame2. If the destination does not lie on the segment over which the frame arrived the bridge must send a

184

Most bridges are called adaptive or learning bridge - Because they learn the locations of computers

1. a bridge uses source address information in the frames that arrives

2. When a frame arrives, the bridge extracts the physical source address from the frame header and a

185

If a computer did not send any frames a bridge could not detect its location. So how will bridge learn

Computers do not usually remain silent

1. A host usually emits at least one frame when the system first boots2. Furthermore, computer communication is usually bidirectional, a computer that receives a frame u

186

What are the three advantages of using bridges between Buildings?First, because it requires only a single fiber connection, the bridge solution is less expensive than usin

Second, because the connection between buildings attaches to the bridge, individual computers can b

between buildingsThird, because a bridge allows simultaneous communication on the two segments, using a bridge inst

impact communication among computers in the other building

187

Two methods are popular for a bridged NW to span long distances and each involves a long-distance

First uses a leased serial line to connect the sites - more common because it is less expensiveSecond uses a leased satellite channel - because it permits communication across an arbitrary distanc

188List operational differnce between a hub and a switch.a hub simulates a single shared medium

while a switch simulates a bridged LAN with one computer per segment

189The table used to store next-hop information is commonly called a __________

190The Software used to compute the entries for a Routing Table for shortest path computation is know


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191A switch usually has multiple I/O connectors, making it possible to connect multiple computers

192As per the routing in WAN, the relationship between graph theory and NW is strong. A machine atta

193

What are the key issue that separates WAN technologies from LAN technologies?1. Scalability - a WAN must be able to grow as needed to connect many sites

2. it can deliver reasonable performance for large size NW

3. provides sufficient capacity to permit the computers to communicate simultaneously

194

How can a WAN scale to handle many computers?

1. Instead of using a point-to-point (PTP) leased data circuit that connects one computer directly to an

connect2. The initial size of a WAN is determined by the number of sites and the number of computers conn

3. Additional switches can be added as needed to connect additional sites or additional computers

195The basic electronic switch used in a WAN is called a ____ switch in general

196Each PS is a small computer with special HW has a ___, ____ and ____to send and receive

197

What forms of PTP (Point to Point) are used to build a WAN?

Almost every form of PTP communication has been used to build a WAN i.e.

Copper cables, optical fibers, microwaves, and satellite channels

198

On what basis the interconnections among switches and the capacity of each connection is chosen?

1. to accommodate the expected traffic2. to provide redundancy in case of failure

199The fundamental paradigm used with wide area PS systems is ___ and ____ switching

200

Explain how Store and Forward works in a PS

1. To perform store and forward, a PS must buffer packets in memory2. the store operation occurs when a packet arrives the forward operation occurs next

3. the processor examines the packet, determines over which interface it should be sent and starts the

4. if multiple packets must be sent to the same output device,

the PS can hold packets in memory, until the output device is ready

201In WAN addressing, the simplest hierarchical scheme partitions an address into two parts. List them.

the first part identifies a PS and the second part identifies a computer attached to that PS

202In WAN, an address is represented as a single ___ value


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203In WAN, if the packet is destined for a computer attached to another PS

the packet must be forwarded further that leads to the switch and a PS uses the ____ address

204A PS does not keep complete information about how to reach all possible destinations. A switch simp

205In next hop forwarding, a PS usually assigns each interface a small integer, ____

206What is source independence in Next-hop forwarding?Next-hop forwarding depends only on the destination known as source independence

207

What are the advantages of Source independence in next hop forwarding?Source independence in next hop forwarding.allows the forwarding mechanism to be compact and e

1. Because all packets follow the same path only one table is required

2. Because forwarding does not use source information only the destination address needs to be extra3. Furthermore, a single mechanism handles forwarding uniformly - packets that originate on directlymechanism

208The process of forwarding a packet to its next hop is known as ____

209

What are the advantages of two-part hierarchical addressing?1. The advantages of two-part hierarchical addressing is that more than one entry contains the same n

2. all destination addresses that have an identical first part will be forwarded to the same PS

3. Thus, a PS only needs to examine the first part of a hierarchical address

210

What are benifits of using only one part of a two-part hierarchical address?

Using only one part of a two-part hierarchical address has two practical consequences1. First, the computation time required to forward a packet can be reduced

2. Second, the entire RT can be shortened to contain one entry per destination PS instead of one entry

211

Explain in brief the next-hop forwarding algorithm.

the next-hop forwarding algorithm can be summarized as below:To forward a packet when using two-part hierarchical addresses

begin by extracting the part of the packet's destination address that corresponds to a PS called pIf p matches the number assigned to the local PS thenuse the second part of the address to locate an attached computer

Otherwise use p to select a next hop from the RT

212PS having computers attached can be classified as ____ switches

213PS not having computers attached can be classified as ___ switches


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214

What the values in the RT must guarantee?

1. Universal routing - The RT in a switch must contain a next-hop route for each possible destination

2. Optimal routes - In a switch, the next-hop value in the RT for a given destination must point to th

215A serial data circuit connecting two machines is often called a ____

216In routing in WAN, a ___ can be used to compute and understand next-hop routes

217

Explain the use of Default Route in WAN.

1. Although hierarchical addressing reduces the size of the RT by removing duplicate routes for indi

2. Abbreviated RT still contains many entries with the same next hop

3. Most WAN systems include a mechanism that can be used to eliminate the common case of duplic

4. the mechanism allows a single entry in a RT to replace a long list of entries that have the same nex5. Only one default entry is allowed in any RT, and the entry has lower priority than other entries

6. If the forwarding mechanism does not find an explicit entry it uses the default entry, if exist (optio

218

What is the difference between Static routing and Dynamic routing

Static routing - A program computes and installs routes when a PS boots;

the routes do not changeDynamic routing - A program builds an initial RT when a PS boots;

the program then alters the RT as conditions in the NW change

219List at least one advantages and disadvantages of Static RoutingThe chief advantages of static routing are simplicity and low NW overheadThe chief disadvantage is inflexibility -- static routes cannot be changed easily

220

Wht does most NWs use dynamic routing?

1. because it allows the NW to handle problems automatically. For example, programs can monitor

2. The programs can then modify routes to accommodate failure - Because large NWs are designed w

221The SW to compute the entries for a RT represents the NW as a graph, known as ______ Algorithm

the other nodes in the graph.


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222

Why is Dijkstra's Algorithm popular?

DA is popular because it can be used with various definitions of shortest pathit does not require edges to represent geographic distance

it allows each edge to be assigned a value, called a weight

and defines the distance between two nodes to be the sum of the weights along a path between the no

223Dijkstra's Algorithm computes shortest paths in a graph by using ____ on edges as a measure of dista

224

Dijkstra's Algorithm needs three data structures to store. List them

1. The current distance to each node,2. the next hop for the shortest path,

3. and information about the remaining set of nodes

225Dijkstra's Algorithm uses weight (i, j) as a function that returns the weight of the edge from node i

exists from node i to node j

226

Explain in brief the distributed route computation.1. Each PS computes its RT locally,

2. Then sends messages across the NW to neighboring PS to inform them of the result3. Each PS to send its routing information to neighbors periodically (e.g., seconds)4. After an initial startup period, each PS learns the shortest paths to all destinations

227One of the best-known algorithms for distributed route computation is ____ algorithm

228In Distance Vector Algorith, when will a PS change its Routing Table?When a message arrives at a PS from neighbor N, the PS examines each item in the message and chPS has been using

229An alternative form of distributed route computation existscalled ____ routing

230

Like a Distance Vector Algorith, an Shortest Path First algorithm can adapt to HW failures. What is t

SPF has the advantage that all computations can be carried out simultaneously1. After the status of a link changes, all PS receive a status message, and each switch begins computi

2. In contrast, a DVA it requires a PS to update its RT before sending a message to another PS

231What is a network protocol?A set of rules that specify the format of messages and the appropriate act


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232A set of rules that specify the format of messages and the appropriate actions required for each messa

233What is the advantage of dividing a protocol in to sub-pieces?Makes easier to design, analyze, implement, and test

increases flexibility because it allows subsets of protocols

234

What needs to be considered when dividing a protocol design into sub-pieces?The division must be chosen carefully to

To ensure the resulting system is efficient and effective

To avoid duplication of effort, they can share data structures and information

To handle all possible HW failures or other exceptional condition

235How to guarantee that protocols will work well together?instead of developing each protocol in isolation, protocols are designed and developed in complete,

236One of the most important tools in a plan for Protocol Design is called a ____ model

237Layering model describes one way the communication problem can be divided into sub-pieces called

238

List all the 7 layers of OSI model and functionality defined at each layer

Layer 1 Physical:

Basic NW HW, specification of LAN HWLayer 2 Data Link

How to organize data into frames and how to transmit frames

Layer 3 NW

How addresses are assigned and how packets are forwardedLayer 4 Transport

How to handle details of reliable transfer

Layer 5 SessionHow to establish a communication session with a remote system

Layer 6 Presentation

How to represent/match dataLayer 7 Application

How particular application uses a NW

239Layering models provide a simple explanation of the ____ among the complex HW and protocol com

240

What were the issues in protocol stacks created by several vendors and had to be replaced with TCP/

They had few common issues

1. mostly incompatible - protocols from a given stack cannot interact with protocols from another


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241

List the protocol stack and their developer which are now replaced by TCP / IPNovell - Netware

Banyan - VINES

Apple - AppletalkDigital - DECNETIBM - SNA

242Usually, each layer places additional information in a ____ before sending data to a lower layer

243

What must happen as per the Scientific Basis For Layering?1. Layer N SW on the destination computer must receive the exact message sent by layer N SW on

2. Whatever transformation a protocol applies before sending a framemust be completely reversed when the frame is received

244

List techniques being used to tackle different issues in protocol design

1. Sequencing For Out-Of-Order Delivery2. Sequencing To Eliminate Duplicate Packets

3. Retransmitting Lost Packets

4. Avoiding Replay Caused By Excessive Delay

5. Flow Control To Prevent Data Overrun6. Mechanisms To Avoid NW Congestion

245

Explain Sequencing For Out-Of-Order Delivery1. One of the problem is out-of-order delivery.

2. A connectionless NW system that can change routes may deliver packets out of order

3. To handle out-of-order deliveries, transport protocols attaches a sequence number to each packet4. Receiver stores the sequence number of the last packet received in orderas well as a list of additional packets that arrived out-of-order

5. If the packet is the next one expected, delivers the packet to the next highest layer and checks its li

6. If the packet has arrived out of order adds the packet to the list and wait

246

Explain Sequencing To Eliminate Duplicate Packets

1. Malfunctioning HW can cause packets to be duplicated

2. Duplication often arises in WANs, but can also occur in LAN Ex. a transceiver malfunction in a Lthe sender senses a collision3. Sequencing solves the problem of duplication;

4. The receiving SW checks for duplicates when it examines the sequence number of an arriving pack

5. If the packet has already been delivered or the sequence number matches one of the packets waitin


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247

Explain in breif the Retransmitting Lost Packets

1. For reliable transfer (i e , transfer without loss), protocols use a small message, called acknowledg

2. Sender starts a timer when sending a frame;

3. Receiver sends an ACK if frame received correctly

4. If an ACK arrives before the timer expires, sender cancel the timer5. If the timer expires before an ACK arrives, send another copy of the packet (retransmission) and s

248In what situation the Retransmission cannot succeed?

Retransmission cannot succeed if a HW failure has permanently disconnected the NW or if the receiv

249There should be a bound on the ___ number of retransmissions of lost packets

250

How can Retransmission introduce duplicate packets

1. Because a sender cannot distinguish between a packet that has been lost and a packet that experien2. Both copies of the packet may be delivered

251

What adverse effect can a Replay cause with control packets?

1. Protocols often send a special control packet to terminate a conversation2. If a copy of a termination request arrives from a previous conversation, it can cause protocol SW t

252What precautions does a protocol take to prevent replay?

Protocols mark each session with a unique ID (e g time session was established), and require ID be

253____ occurs when a computer sends faster than the destination can absorb it, so data is lost

254Several techniques are available to handle data overrun and collectively, the techniques are known as

255

How does a stop-and-go system work in flow control.

A sender waits after transmitting each packet for an ACKWhen the receiver is ready for another packet, the receiver sends a control message, usually a form o

256To obtain high throughput rates with flow control, we can use _____


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257

How does sliding window works in flow control?

1. The sender and receiver use a fixed window size i.e. maximum amount of data that can be sent bef

2. Sender and receiver might agree on a window size3. The sender extracts data to fill packets that correspond to the first window

and transmits a copy of each packet4. If reliability is needed, the sender retains a copy in case retransmission is needed5. The receiver must have buffer space to receive the entire window

6. When a packet arrives in sequence, receiver passes the packet to the application and transmits an A

7. When an ACK arrives, the sender discards its copy of the acknowledged packet and transmits the n

258If congestion in network persists, a PS will run out of memory and begin discarding packets. Furtherm

259

List the two approaches for dealing with congetion

1. Arrange for PS to inform senders when congestion occurs2. Use packet loss as an estimate of congestion

260

In protocol design, why details must be chosen carefully? Explaing with supporting example.

small design errors can result in incorrect operation, unnecessary packets, or delays

Ex: sequence # should be chosen so that they are not reused frequently, but small enough to avoid wa

Similarly, a higher-level protocol can cause excessive overhead if the protocol chooses a non-optima

261____ technologies are designed to provide high-speed communication across short distances

262___ technologies are designed to provide communication across large areas

263

What is universal service?

Most modern computer communication systems allow communication between any two computers a

telephones, known as universal service

264With ____ , a user on any computer in any organization can send messages or data to any other user

265

Why cannot extension techniques such as bridging be used with heterogeneous network technologie

1. each technology uses its own packet format and addressing scheme

2. a frame created for one network technology cannot be transmitted on a network that uses a differen


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266Despite the incompatibilities among network technologies, researchers have devised a scheme that pr

267The basic component used to connect heterogeneous networks is a _____

268

What can a router connect?

two LANsa LAN and a WANor two WANs

269

Why would an organisation need multiple connections? Explain both reasons.

1. Load-balancing and speed - the processor in a given router is insufficient to handle the traffic pass

2. Redundancy improves internet reliability - To avoid a single point of failure

The protocol software continuously monitors internet connections and It instructs routers to send traf

270

What does the exact details of internet topology chosen be dependent on?

The exact details of internet topology to be chosen often depend on the following

1. bandwidth of the physical networks

2. expected traffic3. organization's reliability requirements

4. cost

5. performance of available router hardware

271

What details are hidden by the Internet software in general

1. physical network connections

2. physical addresses3. routing information

272We say that an internet is a ____ network system because Users/application programs are not suppo

273Several protocols have been proposed for use with internets but ____ Internet Protocol suite is the mo

274

List 5 Layers of TCP / IP reference model from top to bottom.1. Application

2. Transport

3. Internet4. Network Interface5. Physical

275____ computer to refer to a computer that connects to the Internet and runs applications

276The addressing scheme IP version 4 is also known as ____


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277

Why would MAC addresses do not suffice for internet addressing

becausethe Internet can include multiple network technologies

and each technology defines its own MAC addresses

278In IPv4, each host is assigned a unique ___-bit number known as the host's IP address or Internet add

279When sending a packet across the Internet, what should senders protocol software must specify at thits own 32-bit IP address (the source address)and the address of the intended recipient (the destination address)

280

List and explain the 2 parts of IP address.

IP addressis divided into two parts:

A prefixidentifies the physical network to which the host is attached

Each network in the Internet is assigned a unique network number

A suffixidentifies a specific computer (host/node) on the networkEach computer on a given network is assigned a unique suffix

281IP addressis divided into two parts: A ___ which identifies the physical network to which the host is

network

282The original classful IP addressing divided the IP address space into___primary classes, each class h

283The first ___ bits of an IP address determined the class to which the address belonged. It specifies ho

284List the binary values for first 4 bits for class A and B0000,1000

285List the binary values for first 4 bits for class A B and C0000,1000,1100

286Notation that has been accepted is to express each 8-bit section of a 32-bit number as a decimal value

287dotted decimal addresses range is from ___ to ____

288Equivalent Dotted Decimal / Binary Representation for

289

a. 10000001 00110100 00000110 00000000 - 129.52.6.0b. 11000000 00000101 00110000 00000011 - 192.5.48.3c. 00001010 00000010 00000000 00100101 - 10.2.0.37

d. 11000000 10101000 00000001 00001010 - 192.168.1.10

e. 00001110 10001011 01111001 01101101 - 14.139.121.109

290How many bits are used in suffix i.e. for hosts in class A, B and C?

24, 16, and 8


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291What is the maximum no of host per network in class C?

256 i.e. 2 raise to 8

292To obtain a network prefix, a corporation usually contacts an ___

293

As the Internet grew, the original classful addressing scheme became a limitation. Two mechanisms

What are they?Subnet addressingClassless addressing

294What did the two mechanisms do to overcome the limitation of classful addressing scheme.

1. instead of having three distinct address classes, it allowed the division between prefix/suffix on an

295

How can an IP address be divided at an arbitrary boundary?

The classless and subnet addressing schemes require hosts and routers to store an additional piece of

and the host suffixTo mark the boundary, IP uses a 32-bit value known as an address mask, also called a subnet mask

296The classless and subnet addressing schemes mark the boundary, using a 32-bit value known as an ad

297

Consider the mask needed for the example. It has 26 bits of 1s followed by 6 bits of 0s. In dotted de

192.5.42.59?192.5.42.59/26

298Assume an ISP has the following block 192.162.121.0/24Suppose the ISP has 2 customers where one customer needs 12 IP addresses and the other needs 9. T

299What are the possible host address in 128.211.0.16/28 block?

128.211.0.17 through 128.211.0.30

300

List five special IP addresses

Network AddressDirected Broadcast Address

Limited Broadcast Address

This Computer Address

Loopback Address


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301

Explain Special Address - Network Address1. It is convenient to have an address that can be used to denote the prefix assigned to a given networ

2. IP reserves host address zero and uses it to denote a network3.Thus, the address 128.211.0.16/28 denotes a network because the bits beyond the 28 are zero

4. A network address should never appear as the destination address in a packet

302

Directed Broadcast Address

1. To simplify broadcasting (send to all), IP defines a directed broadcast address for each physical ne

2. When a packet is sent to a network's directed broadcast, a single copy of the packet travels across t3. the packet is then delivered to all hosts on the network

4. The directed broadcast address for a network is formed by adding a suffix that consists of all 1 bits

303Suppose you have a network 192.168.1.0/24. Network ID is 192.168.1.0 (All 0s in Suffix) Hosts = 19

304

Limited broadcast1. Limited broadcast refers to a broadcast on a directly-connected network:

informally, we say that the broadcast is limited to a single wire

2. Limited broadcast is used during system startup by a computer that does not yet know the network3. IP reserves the address consisting of 32-bits of 1s refer to limited broadcast

4. Thus, IP will broadcast any packet sent to the all-1s address across the local network

305

This Computer Address

1. A computer needs to know its IP address before it can send or receive Internet packets

2. TCP/IP contains protocols a computer can use to obtain its IP address automatically when the com

3. The startup protocols also use an IP to communicate4. When using such startup protocols, a computer cannot supply a correct IP source address

5. To handle such cases, IP reserves the address that consists of all 0s to mean this computer


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306

Loopback address

1. Loopback address used to test network applications2. It is used for preliminary debugging after a network application has been created

3. A programmer must have two application programs that are intended to communicate across a netw4. Each application includes the code needed to interact with TCP/IP

5. Instead of executing each program on a separate computer, the programmer runs both programs on

communicating6. When one application sends data to another data travels down the protocol stack to the IP software

7. A programmer can test the program logic quickly without needing two computers and without sen8. IP reserves the network prefix 127/8 for use with loopback

9.

10. During loopback testing no packets ever leave a computer

the IP software forwards packets from one application to another11. The loopback address never appears in a packet traveling across a network

307____ the most popular loopback address

308

Purpose of each Special Address

Network Address - identifies a network

Directed Broadcast Address - broadcast on specific net

Limited Broadcast Address - broadcast on local netThis Computer Address - Used during bootstrap

Loopback Address - testing

309

Why each router is assigned two or more IP addresses?one address for each network to which the router attaches

A router has connections to multiple physical networks

Each IP address contains a prefix that specifies a physical network

310

Why does a single IP address does not suffice for a router?

because each router connects to multiple networks

and each network has a unique prefix

311A host computer with multiple network connections is said to be ____

312Multi-homing is sometimes used to increase reliability. How is it done?

if one network fails, the host can still reach the Internet through the second connection

313

What are the two primary purposes of Multi-homing?

1. increase reliability

2. increase performance


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314How can multihoming improve performance?

connections to multiple networks can make it possible to send traffic directly and avoid routers, whic

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