152118005 COMPUTER NETWORKS Answers to - E. Seke

Last edited : 18.06.2014

152118005 COMPUTER NETWORKS

Answers to Selected Exam Questions

by

Erol Seke

Eskişehir Osmangazi University

Faculty of Engineering and Architecture

Department of Electrical & Electronics Engineering

Department of Computer Engineering

152118005 COMPUTER NETWORKS 2

1. 23.01.2001 final exam

An extension (N4) to the following local net will be made using the IP range

220.2.1.128/25 as shown using dashed lines in the following figure. The existing routing

table entries are partially given below. Complete the routing tables according to your

assignments to the new network. Try to cause minimum disturbance to the existing

network.

G1 G2

For Destination Route To For Destination Route To

220.2.2.0/24 220.2.2.1 220.2.3.0/24 220.2.3.1

default discard 220.2.1.0/25 220.2.1.2

default

Solution

G1 G2

For Destination Route To For Destination Route To

220.2.2.0/24 220.2.2.1 220.2.3.0/24 220.2.3.1

default discard 220.2.1.0/25 220.2.1.2

220.2.1.0/25 220.2.1.1 default 220.2.1.1

220.2.3.0/24 220.2.1.2

220.2.1.128 220.2.1.129


2. 23.01.2002 final exam

Given the following network and IP-divisions, assign IP addresses to the selected

interfaces and write down the explicit routing entries for each router/gateway. Ignore

CDIR rule of “allowed network IP addresses”.

a.b.c.0/24

Solution

64 A

64 B

32 C

32 D

64 E

router Which net/IP To where

IP address mask

A1

B1 B2

C1

D1

D2

E1

router Which net/IP To where

R1 a.b.c.0/25 a.b.c.130

R1 default X

R2 a.b.c.0/26 a.b.c.66

R2 default a.b.c.129

R3 default a.b.c.65

IP address mask

A1 a.b.c.193 26

B1 a.b.c.129 26 B2 a.b.c.130 26

C1 a.b.c.97 27

D1 a.b.c.65 27

D2 a.b.c.66 27

E1 a.b.c.1 26

255

0


3. 16.01.2003 final exam

For the network whose general topology is given below, mark networks on the horizontal

scale, assign IP numbers to networks, and interfaces from a given Class-C IP range

(a.b.c.0) and write down the routing table entries for each gateway. Assume that each

network has 20 hosts maximum.

Solution

e1 x.y.z.m e4 .2/27 e7 P2.2/24

e2 .1/27 e5 P2.1/24 e8 .128/27

e3 P1.1/24 e6 .64/27 e9 P1.2/24

P1 : 10.100.1.0/24 P2 : 10.100.2.0/24 (private networks)

GW1 GW2 GW3

N2 -> e4 N3 -> e7 N2 -> e5

N3 -> e9 def. -> e2 def. -> e3

def. -> x.y.z.r

Just a straight

connection

(No other host)

GW1

GW3

GW2

a connection to x.y.z.r

e1

e2

e3 e4

e5

e6

e7

N3

N1

N2

e8

e9

0

255

N1 N2 N3

0/27 64/2

7

128/27



4. 16.01.2003 final exam

Draw the signal encodings of the given bit-stream : 1101011010

Solution


5. 15.01.2004 final exam

5-routers are connected to construct an intranet as shown. Assign subnet and interface IP

addresses from a single class-C range. Let this range be aaa.bbb.ccc.xxx where xxx

represents your freedom. Also determine routing table entries for each router. Try to

make the routing tables as simple as possible. Use the IP-ruler given below and mark

your networks on it.

Solution

Interface IP-Address Netmask A1 .1 /26

A5 .225 /28

A6 .233 /28

B2 .65 /26

B6 .234 /28

B7 .241 /28

C2 .66 /26

C5 .226 /28

D3 .129 /26

D7 .242 /28

D8 .249 /28

E4 .193 /27

E8 .250 /28

Routing Table Entries

A B C D E

.64/26->.226 .128/26->.242 Default->.225 .192/27->.250 Default->.249

.128/26->.234 .192/27->.242 Default->.241

.192/27->.234 Default->.233

Default->ISP


6. 15.01.2004 final exam

Draw the waveforms according to encoding schemes for the given bit-stream : 101110001

Solution


7. 06.11.2002 1st midterm

Draw the RZ, NRZ-I, Manchester, Differential Manchester and AMI signals for the bit-

stream 0110010111.

Solution


8. 06.11.2003 1st midterm

Describe internetworking connecting devices in clear sentences

(layers, operation, use etc.)

Solution

Connecting devices are divided into two categories

Networking devices

Internetworking devices

We have two types of internetworking devices

Routers

Gateways

Routers : Having Physical, Data Link and Network Layers, routers may route packets to

any connected network or network which is known to be accessible there off. If the

destination is on a connected network then router sends the data to the destination host.

Otherwise it tries to determine, using its routing tables, the best route to the destination,

possibly via another neighboring router and hands the data over to that router which does

the same analysis. Internet which is the network of networks works this way and the data

reaches its destination passing over several routers.

Gateways : These have all seven layers like any computer, which allows them to do

anything doable to a received packet. Usually they operate as a router. Additionally

installed software makes them capable of relaying data between different types of

networks which are otherwise incompatible and with different standards. For example a

gateway may receive data packets from a TCP/IP network and convert them to be

transferred to an AppleTalk (a Macintosh proprietary protocol) network. Gateways do

this by converting the headers and trailers (possibly adding some headers and discarding

some) to make them compatible to the destination standard.


9. 14.11.2000 2nd

midterm

Fill out the following table according to the features of the named connecting devices.

Repeater Bridge Router Gateway Switch

Operating Layer

Creates separate

segments

Connect different

protocol networks

Connect same

protocol networks

Maximum number

of ports

Solution

Repeater Bridge Router Gateway Switch

Operating Layer

Physical

Layer

Data Link

Layer

Network

Layer

Lives in

all Layers

*

DataLink/

Network

Layer *

Creates separate

segments

No Yes Yes Yes Yes

Connect different

protocol networks

No No No Yes No

Connect same

protocol networks

Single

Network

Yes Yes Yes Yes

Maximum number

of ports

2 2 * 2 more 2 or more 2 or more

* Usually operating on the Data Link layer, some Switches have routing capability which

forces them to also work on Network Layer.

* A gateway is a computer, so it might have the capability to do anything doable to

network bits/pieces.

Some bridges are designed to serve more than 2 segments, essentially doing the same

thing i.e. they can be called multiport bridges.


10. 18.12.2002 2nd

midterm Complete the routing tables for routers A, B and C for the following network

Solution

Router-A Router-B Router-C Default -> Ii Default -> .65 Default -> .129

.96/27 -> .66

.192/26 -> .130

e1 a.b.c.1 / 26 N1 a.b.c.0 / 26

e2 a.b.c.65 / 27 N2 a.b.c.64 / 27

e3 a.b.c.66 / 27 N3 a.b.c.96 / 27

e4 a.b.c.97 / 27 N4 a.b.c.128 / 26

e5 a.b.c.129 / 26 N5 a.b.c.192 / 27

e6 a.b.c.130 / 26 N6 a.b.c.224 / 27

e7 a.b.c.193 / 27

e8 a.b.c.225 / 27


11. 17.12.2003 2nd

midterm

A simple message exchange protocol (MEP) is designed to be connection oriented. In MEP a host with a

message to transfer to another simply establishes a connection and delivers the message if the connection is

successful. Otherwise it drops the message to a publicly known messaging center to be picked up by the

destination host when it gets on the line. Assume that sockets are created and bind successfully. Using the

methods Connect, Accept, Listen, GetData, SendData, Close and the events

Connect, Close, ConnectionRequest, DataArrival, Timeout draw timings of the

exchanges for three cases below.

a) Host A successfully delivers a message to host B.

b) A tries B. B does not answer. A drops the message to the message center (Host MC).

c) B gets on line and connects to MC to pick up messages (if any) waiting for itself.

Solution


12. 08.04.2005 1st midterm

Using a C class IP-range a.a.a.x assign IP numbers to interfaces and fill in the routing tables. Estimated

number of hosts in each network is shown.

N1 .128/26 N3 .0/26 N5 .224/27

N2 .192/27 N4 .64/26

e11 .129 e15 .225

e22 .193 e25 .226

e33 .1 e35 .227 e34 .65

R1 R2 R3

N2 -> e25 N1 -> e15 N1 -> e15

default -> e35 default -> e35 N2 -> e25

default -> Id


13. General ‘Fill in the Blanks’ Questions (may have some duplicates)

1. The connection points between the Network Layer and the Transport Layer is the IP number(s)

whereas the connection points between the Transport Layer and the upper layers are called Ports

which are represented by 16 bits in the TCP segment header.

2. Unlike TCP the Transport Layer Protocol UDP is a connectionless protocol.

3. The programmatic connection between the Network Layer and the upper (application) layers is

usually established by small software running in Transport Layer. These are usually called Sockets.

4. In a 802.3 LAN, IP to ethernet address translation is performed by/with ARP which stands for

Address Resolution Protocol.

5. In an IP address with CIDR standard a quad can range from 0 to 255.

6. Bluetooth uses Time Division Multiplexing.

7. A Bluetooth network with 7 active slaves is called a Piconet.

8. Bluetooth standard specifies 13 applications which are called profiles.

9. As modulation technology, Bluetooth employs FSK with 1M bps.

10. The number of necessary OSI layers in a bridge is two

11. Routers and Gateways are internetworking-connecting devices

12. A networked computer must minimally have a host-IP, a netmask and default gateway-IP numbers

set up in order to do IP-networking properly.

13. An IP-address with all host bits set to 1 is called Broadcast address.

14. A Class-B IP-range may have about 65000 hosts in it.

15. IEEE-802.3 defines broadcast networks standards.

16. The word ‘Base’ in 10BaseT identifies the media as baseband.

17. The letter ‘T’ in 10BaseT indicates that it is a twisted-pair cable.

18. An ethernet address with all bits set to 1 is called ethernet broadcast address.

19. CIDR addressing scheme allows us to create subnets for efficient IP use.

20. ARP is a process of obtaining ethernet addresses from IP-addresses.

21. Performance of a network is usually measured by the amount of data transferred per unit time.

22. Reliability of a network is usually measured by the frequency of failure (inverse of it).

23. Logical to physical addressing conversion is done in the Network Layer.

24. In stop and wait flow control method receiver ACKs each data frame received. The alternative to

this is called sliding window.

25. CSMA stands for "Carrier Sense Multiple Access" which is standardized in IEEE 802.3.

26. The 10 Mbps twisted pair ethernet is usually designated by 10BaseT.

27. Ethernet or NIC addresses are 48 bit unique numbers used to identify physical devices in CSMA/CD

networks.

28. Bridges divide the networks into smaller segments in order to reduce traffic.

29. Repeaters and Bridges are networking connecting devices.

30. In class-B IP-addresses 16 and 16 bits are reserved for host and network identification respectively.

31. Topologically fully connected networks have the highest performance and the highest cost among

the possible .

32. In full-duplex transmission mode devices can transmit and receive simultaneously.

33. For bit-rate to be three times the baud rate we need at least 8 constellations.

34. Physical Layer deals with the physical and electrical specifications.

35. The term point-to-point indicates the dedicated links between two nodes.

36. Bus topology is the simplest and cheapest topology to implement in small networks.

37. Full-Duplex transmission mode can be characterized simply as "two way simultaneous

transmission/reception".

38. Performance of a network is usually measured by bits per second

39. Switching/Routing is the job of Network Layer.

40. Sliding Window line discipline where only some of the enquiries are acknowledged is more efficient

then Stop-and-Wait.

41. 10BaseT can have a maximum segment length of 100 meters.

42. All NICs are manufactured having unique Hardware Address.

43. Physical addressing, error control and access (to media) control are managed by the Data Link layer.

44. An advantage of 10BaseT over 10Base2 is that 10Base2 is maintained easier than 10Base2.

45. ‘Preamble’ field at the beginning of an ethernet frame is used for synchronization.

46. Bridges must have the following layers;

1. Physical Layer 2 Data Link Layer.


47. ‘Time To Live’ field in an IP packet determines the number of hops (routers) it passes through

before it is discarded.

48. A host running in an IP-network on the ethernet must be assigned these three numbers properly in

order for the networking software to operate correctly;

1. IP address, 2. Netmask, 3. Gateway address. 49. ARP is used on IEEE-802.3 networks in order to obtain ethernet addresses using the IP addresses.

50. The field named as ‘Window Size’ in a TCP segment header indicates the sliding window size.

51. Standard TCP services use some standard TSAP numbers known as well known ports numbers.

52. TCP is a connection oriented protocol while UDP is not.

53. The three problems which limit a communication line are attenuation, distortion and noise.

54. In order for a 2400 baud modem to achieve 9.6 kbps the constellation diagram must have at least 16

distinct points.

55. The filter with a bandwidth of 300-3400 Hz at the end office for an ordinary voice phone line is

removed for DSL operation.

56. An ADSL modem and a splitter are the required equipment residing at the customer’s premises for

the ADSL system.

57. Three of the BlueTooth profiles are Service Discovery, Serial Port, Cordless Telephony.

58. In piconets of BlueTooth, Frequency Hopping Spread Spectrum technique is used with 1600

hops/sec and hop sequence is dictated by the master.

59. Pseudoternary encoding technique is used on T and S interfaces of ISDN system in order to maintain

synchronization during the long sequences of zeros.

60. PRI ISDN service carries 23 bearer and 1 data channels with a total of 1544 kbps.

61. Bus topology usually requires terminators at both ends of the cable.

62. In half-duplex transmission mode both station can transmit and receive but not at the same time.

63. Logical addressing and routing is the function of network layer.

64. Mail services are being made available by application layer.

65. Manchester coding is one of the polar encoding techniques which effectively eliminate DC

component of the signal.

66. In Diff. Manchester, the transition in the middle is used for synchronization.

67. The number of signal units per second is called baud-rate.

68. In QAM both amplitude and phase of the carrier signal are varied.

69. In stop-and-wait flow control technique, every frame is acknowledged.

70. Physical Layer deals with the physical and electrical specifications.

71. Full-duplex transmission mode can be characterized simply as "two way simultaneous

transmission/reception".

72. All NICs are manufactured having unique ethernet address/MAC number.

73. 10BaseT can have a maximum segment length of 100 meters.

74. The words and numbers '10', ‘Base’ and 'T' in 10BaseT respectively indicate 10 Mbps baseband and

twisted pair.

75. Carrier extension and Frame bursting are features added to 802.3 by the gigabit ethernet standards.

76. 1000Base-T uses 4 pairs of Cat-5 UTP.

77. Flooding is a packet routing method in which incoming packet is sent to every neighbor except

where it came from.

78. In Distance Vector Routing a router receives routing information from all of its neighbors and by

using the knowledge about its distance to its neighbors it constructs its own routing table which in

turn used by the router and distributed to the neighbors.

79. Hierarchical Routing reduces the memory requirements at some penalty on the path optimality in

large networks with large number of routers.

80. If packets from a live audio/video source are to be distributed to multiple destinations we need to talk

about Broadcast Routing.

81. The 802.11 configuration in which no central coordination is used for is called Distributed

Coordination Function 82. Multipath Reception is a problem in wireless systems, which deteriorates the received signal at the

receiver.

83. When there is no central coordination is employed in 802.11, channel access privileges (who

transmits when) are determined by a protocol called Carrier Sense Multiple Access / Collision

Avoidance.

84. In wireless ethernet, when stations directly talk to each other, a station wanting to transmit data when

the channel is idle transmits Request To Send (RTS) frame first.

85. The small clusters of stations communicating using Bluetooth are called Piconets.


86. There can be only seven active slaves in a Bluetooth station cluster.

87. The master station in a Bluetooth cluster employs Time Division Multiplexing in order to

communicate with slaves and send commands to them.

88. The destination address field in a Bluetooth frame is three bits

89. Bluetooth operates on 2.4 GHz ISM band and its range is about 10 meters.

90. The PSTN term Local Loop refers to the wiring between the customer and end office of the telecom

company.

91. In PSTN, in order for a modem customer to achieve 56 kbps transmission rate, the connection to ISP

must be digital.

92. QAM stands for Quadrature Amplitude Modulation which means changing both Amplitude and

Phase of the carrier.

93. In 128-QAM, one change in carrier transmits seven bits including parity.

94. In DMT which is employed in DSL, of 256 frequency channels 5 are not used to prevent interference

between voice and data signals.

95. Original antialiasing filter is removed in DSL, but a pair of Low Pass Filter is still used to split voice

and data channels in end office and in customer premises.

96. ISDN stands for Integrated Services Digital Network.

97. In ISDN two standard services are provided; BRI and PRI.

98. A B channel in ISDN service has the data rate of 64 kbps whereas a D channel carries 16 kbps.

99. 23B+D configuration in ISDN is capable of carrying 1544 kbps.

100. Two features brought by gigabit ethernet, Carrier Extension, Frame Bursting are required to

achieve 200 m in hub based networks.

101. Fast ethernet on Cat-5 cable runs at most 100 meters.

102. Hubs/Repeaters just repeat the incoming data and send it through all other connected lines. 103. Different modes of light travel different total distances resulting in dispersion which causes distortion

in multimode fibers at long distances.

104. Multistation Access Unit is a term which refers to devices used to form a star topology in Token

Ring.

105. FDDI stands for Fiber Distributed Data Interface.

106. In Token Ring there is at least one frame traveling around the ring, and it is called the Token.

107. The communication speed in FDDI is 100 Mbps.

108. Two common transmission rates in ATM are 155.52 Mbps and 622 Mbps.

109. In ATM systems delivery is not guaranteed but the order is.

110. Since the ATM cell size is 53 bytes ATM routers can be designed to be entirely hardware (no

software).

111. In ATM, after the connection establishment between the source and destination, data always follow

the same route which is called Virtual Circuit.

112. Fiber, among other common transmission media, has the best performance thanks to its high

bandwidth and low EMI.

113. OSI stands for Open Systems Interface.

114. Service-point addressing (different number for each program) is the task of transport layer in OSI 7-

layer model.

115. Signaling standards is in the interest of physical layer.

116. Ethernet bridges consist of physical and data-link layer(s).

117. In an ethernet network the interfaces are identified/addressed by their ethernet address/hardware

address/MAC address.

118. The number of pins on a RJ-45 connector at the end of a cat-5 cable is 8.

119. In Differential Manchester represents the binary stream 001011.

120. In an ethernet frame specified by IEEE 802.3, preamble is used for synchronization.

121. In Manchester encoding represents the binary stream 001101.

122. The destination address in an ethernet frame is 48 bits.

123. The ‘Time-To-Live’ field in IP-datagram determines the number of hops.

124. Netmask is used to separate the network address from the IP address.

125. The service that converts hostnames into host IP numbers is called Name Service.

126. The interface IP-numbers of a router between IP networks shall be selected from the ranges of the

connected networks.

127. Routing table defines where to deliver the IP-packets when the destination is not in the same

network.

128. Exponential Back-off algorithm is used to determine the time to wait for another transmission

attempt in CSMA-CD networks.


129. Fast ethernet on twisted pair cable is referred as 100Base-TX.

130. Fast ethernet on fiber runs at most 2000 meters.

131. Bit rate is bits per second whereas the baud rate is symbols/changes per second.

132. ADSL stands for Asymmetric Digital Subscriber Line.

133. Channel 0 in DMT of DSL is used for basic telephony service.

134. In DSL, a filter called splitter must be used in both customers’ and Telco’s premises.

135. 23B+D configuration in ISDN is capable of carrying 1544 kbps.

136. CSMA/CD is not used in wireless ethernet because most radio devices can not listen and transmit

simultaneously.

137. The RF communication technique in wireless ethernet, in which the communication frequency is

periodically switched within a set of predetermined sequence, is called Frequency Hopping Spread

Spectrum.

138. A Bluetooth device is expected to support the applications Generic Access and Service Discovery and

the other profiles are optional.

139. A collection of Bluetooth piconets is called scatternet.

140. In Differential Manchester encoding technique, the transition in the middle helps synchronization but

reduces the transmission rate.

141. In Link State Routing routing, a router obtains the distances of its neighbors and shares this

information with all other routers it knows using specially designed packets.

142. ARP is used on IEEE-802.3 networks in order to obtain ethernet address from IP address

143. In class-A IP-addresses 24 bits are reserved for host identification.


14. 30.03.2006 1st midterm

A local network with 3 routers and

3 subnets is connected as shown in

the figure. Assume that a Class-C

IP (MyNet/24) range has been

divided into four 64-IP sub-ranges

and assigned to subnets NA, NB and

NC. One sub-range has been left

unused as spare. Connections

between routers are done using

10.x.x.x IP numbers. Answer the

following accordingly.

1. Which of the following is most likely incorrect?

a) in B : default -> IAB b) in C : default -> IBC c) in A : default -> ICA

d) in C : default -> IAC e) in A : NB/26 -> IBA

(this setting will cause packets circling around and going nowhere. The default gateway

for router A shall be IISP)


a) IA = an IP from NA range. b) a host setting in NC : GW=IISP, NM=26 bits

c) a host setting in NB : GW=IB, NM=26 bits d) ID = IBC e) NM of IAB is 16 bits.

(Gateway IP must be in the same network, otherwise it won’t work. Another suspicious

setting is to have ID = IBC which actually poses no problem since these small two device

networks need not see each other.)


a) in ISP : MyNet/24 -> IA b) in B : NC/27 -> ICB c) in A : GW=IISP

d) IAB=10.0.0.1 and IBA=10.10.10.10 e) a host setting in NC : nameserver=IA

(ISP does not see IA. The correct setting should be MyNet/24 -> ID. Since nameserver

IP can be any IP which reside on the host who runs the name-service, e is an OK setting.

We may decide to route some packets to NC through IBC-ICB network and the rest through

A which probably is a default GW for B. So, b is also OK.)

4. In ethernet networks every host needs at least one …………

a) transport layer b) ethernet adapter c) IP address d) modem e) gateway

5. UTP ethernet networks are usually connected using ………….

a) software b) friendship c) RJ-45 d) RJ-13 e) fiber cables

6. ARP in TCP/IP-on-ethernet networks stands for ……………………

a) Address Restriction Protocol b) Address Resolve Problem

c) Acknowledgement Return Protocol d) All Return Policy

e) Address Resolution Protocol

7. It is ARP’s job to find out ….................

a) destination’s ethernet address b) destinations IP address

c) acknowledgement number d) ethernet’s location e) where the gateway is


8. The binary stream which NRZ-I waveform corresponds to is ……..

a) 01101111 b) 11010000 c) 10010111 d) 01011100 e) 01101000

9. The diff. Manchester waveform corresponding to the binary stream 01101000 is

………

a) b) c)

d) e)

10. Repeaters operate similar to ……… which also just create electronic nodes to extend

the cable length.

a) Ethernet hubs b) Bridges c) Ethernet switches d) Connectors e) Hoppers

11. Fast ethernet ……..

a) uses only optical-fiber so it is really fast

b) is not backward compatible with old ethernet.

c) runs 2000 meters with twisted pair cable d) switches are full-duplex

e) hubs are 10 Mbps

12. Which one of the following is incorrect?

a) Full-duplex means simultaneous transmission and reception.

b) Simplex device cannot talk back.

c) One of the reliability measures of networks is the robustness in catastrophe.

d) On a dedicated link there can only be two devices.

e) Half-duplex means only half of the cable is duplex.

13. ………. layer handles the physical addressing of communicating devices.

a) Physical b) Logical c) Data link d) Network e) Transport

14. Gateways are similar to routers …………………………..

a) in the way they route incoming packets.

b) that they both use the same OSI layers.

c) requiring ethernet addresses on all ports.

d) except when working with IP packets.

e) which can be thought of advanced switches.

15. Class of an IP address can be determined from ………. and determines the ……….

a) the first 3 quads -- network part.

b) the number of netmask bits -- network address.

c) the routing table -- destination IP address.

d) the first 4 bits -- number of hosts in the network.

e) the host bits -- netmask.


15. 27.04.2007 2nd

midterm

1. What is the name of the algorithm used in CSMA/CD networks in order to avoid

repeated collisions?

a) collision avoidance b) crash prevent c) exponential back-off

d) exponential collisions e) collision detection

2. In which of the following, are the received cells guaranteed to be in order?

a) ATM b) Wireless ethernet c) TCP/IP d) ISDN e) ADSL

3. Multimode fibers have more …......... than single mode fibers at the receiving end.

a) light b) dispersion c) speed d) wavelength e) cable length

4. What is the signal that travels around the token-ring and carries data called?

a) Packet b) cell c) frame d) token e) bus

5. What is the name of the fixed route established at the time of initial connection setup

in ATM networks?

a) connection network b) data route c) virtual circuit d) ring e)

VPN

6. What is the maximum length of Cat-5 cable in a fast ethernet network?

a) 180 m b) 200 m c) 1000 m d) 1200 m e) 100 m

7. Which one of the following is the lowest bit rate in ATM networks?

a) 155 Mbps b) 622 Mbps c) 1544 kbps d) 1000 Mbps e) 10 Mbps

8. QAM uses different ……… in order to transmit multiple bits in one signal change.

a) frequencies b) pulses c) bit-rates d) amplitude-phase e) bits

9. Higher capacity channel in BRI service of ISDN is called ……. channel?

a) DSL b) B c) PRI d) NT1 e) D

10. What is the lowest discrete channel in discrete multitone signaling of DSL used for?

a) control b) voice c) data d) channel allocation e) unused

11. What does A in ADSL stand for?

a) Alternative b) Asynchronous c) Attenuated d) Asymmetric e) Additive

12. What is the type of operation in wireless ethernet when a management/arbitration

device exists?

a) point coordination b) distributed coordination c) managed arbitration

d) management point e) access point

13. What does FHSS stand for in wireless communication?

a) Fairly Harmonic Signal Sink b) Frequency Halving Signal Spectrum


c) Frequency Hopping Spread Spectrum d) Fast High Simple Solution

e) Full Harmonic Signal Spectrum

14. Concatenation of multiple frames for a single transmission in gigabit ethernet is

called ….

a) carrier extension b) combination c) flow control d) full frame

e) frame bursting

15. How many bits are used for addressing in gigabit ethernet?

a) 64 bits b) 48 bits c) 32 bits d) variable e) 128 bits

16. What is the maximum length of 100Base-FX segment?

a) 2000 m b) 100 m c) 185 m d) 5000 m e) 200 m

17. What is the netmask of the gateway interface in a sub-C network where only 14

hosts may exist and IP address of one of the hosts is 193.145.122.76?

a) 255.255.255.224 b) 193.145.122.15 c) 255.255.255.0

d) 255.255.255.240 e) 193.145.122.240

18. What is the name of routing type in which every incoming packet is sent to every

neighbor router except the one from which the packet came?

a) distribution b) multicast c) link-state d) shortest-path e) flooding

19. The shortest routes from a router to all other routers make up a …….. because of the

optimality principle.

a) short-node b) cut-tree c) sink-tree d) binary-tree e) tentative-route

20. What is the main difference of dynamic routing compared to static one?

a) real-time connection establishment b) dynamic routing table-updates

c) dynamic behavior against flooding d) multiple output routes

e) dynamic change of hardware position


16. 18.03.2008 1st Midterm

1. Which of the following does not have a Data-Link Layer?

a) Router b) Gateway c) Switch d) Bridge e) Repeater

2. How many network bits does125.140.128.16 have?

a) 8 b) 16 c) 24 d) 32 e) 1

3. How many cable segments does a fully connected network of 10 hosts have?

a) 100 b) 45 c) 90 d) 10 e) 81

4. Which specifications the Physical Layer deals with?

a) Physical-Electrical b) Logical-Electrical c) Capacity-Load

d) Routing-Switching e) Delivery-CSMA/CD

5. How many bytes are ethernet addresses in CSMA/CD networks?

a) 16 b) 5 c) 6 d) 48 e) 4

6. IP address of a host is found using its name by the service named ………………

a) Routing service b) Encription service c) Network Layer

d) Name service e) ARP service

7. How many pins of RJ-45 connectors are required when used in 10Base-T networks?

a) 8 b) 4 c) 2 d) 6 e) 3

8. Which binary stream is represented by in NRZ-I?

a) 110100 b) 010110100110 c) 111101110101 d) 001011 e) 010110100110

9. What is a broadcast IP address?

a) IP address of a broadcasting host b) IP address with all hosts bits set to zero

c) IP address with all network bits set to 1 d) IP address with all host bits set to 1

e) IP address with last byte set to 255

10. Which OSI layer deals with physical addressing of the device?

a) Ethernet L. b) IP L. c) Address L. d) Physical L. e) Data Link L.

11. Which of the following can be a measure for the reliability of a computer network?

a) Mean time between failures b) Implemented protocol

c) Type of hosts d) Connections per unit time e) Protection software used on hosts

12. A dedicated physical link between two hosts is said to be?

a) Mesh Lin b) Shared link c) Simplex d) Point-to-point e) Duplex

13. Which of the following is a disadvantage for networks with bus topology?

a) Less cabling than ring b) Needs a central device c) Cheaper connectors

d) It is collision-free e) Cable faults down entire network


14. Which of the following is not an advantage of fiber-optic media for communication?

a) Has high bandwidth b) Has low EMI c) Has high security

d) Has low attenuation e) Requires high-tech equipment

15. In a router, what is the name of the structure that tells where to deliver IP-packets?

a) Router address b) Routing table c) Delivery table

d) Status table e) Default entry table

16. Which of the following is not one of the seven OSI layers?

a) Adaptation b) Session c) Network d) Transport e) Presentation

17. What is the purpose of preamble bits in an ethernet frame?

a) Initialization of ARP b) Pre-bit counting c) Synchronization

d) Error checking e) Destination address

Answer the following according to the network given

18. What are the routing table entries in B, other than a possible default?

a) NB ->I5, NC -> I6, NA -> I4 b) A -> I2, C -> I7

c) NA -> I2, NC -> I7, ND -> I7 d) ND -> I3, NA -> I1, NC -> I8

e) ND -> I7, NC -> I8, NA -> I2, NB -> I5

19. Which one of the following is probably incorrect?

a).GW of a host in ND is I3 b) GW of a host in ND is I9 c) GW of a host in NB is I5

d) I3 and I6 are same e) Netmasks of I2-I4 and I6-I7 are same

20. NA is a sub class-C network. Which of the following is possible?

a) I1=10.1.1.1 b) I1=220.140.141.x c) Netmask of NA = 255.255.255.254

d) A host IP in NA=72.16.141.19 e) A host in NA has GW = 190.16.128.1


17. 28.04.2008 2nd

Midterm

1. The use of "Spread Spectrum" techniques is pointless in ………?

a) baseband systems b) 802.11x c) wireless systems

d) satellite communications e) between two radio stations f) bluetooth

2. What is the name of the fixed route established at the time of initial connection setup

in ATM networks?

a) VPN b) virtual circuit c) connection network

d) passage e) data route f) cell network

3. In ethernet networks, physical addressing is dealt with ……….

a) ethernet connector b) logical layer c) network layer

d) data-link layer e) physical layer f) physical address layer

4. What is the netmask of the gateway interface in a sub-network where only 14 hosts

may exist and IP address of one of the hosts is 193.145.122.76?

a) 255.255.255.224 b) 193.145.122.15 c) 255.255.255.0

d) 193.145.122.240 e) 255.255.255.240 f) 255.255.0.0

5. What was the bit rate of IEEE 802.5 (token-ring) when it was first standardized?

a) 4.16 Mbps b) 10.2 Mbps c) 100 Mbps d) 12 Mbps e) 144.5 Mbps f) 512 kbps

6. What are small bluetooth networks called?

a) chirpnets b) minibus c) BLAN d) smalltalk e) scatternet f) piconet

7. What is the algorithm to handle collisions in ethernet networks?

a) Collision Pooling b) Time Division Mux c) exponential-backoff

d) ARP e) CSMA-CD f) CSMA-CA

8. The number of allowed hops for an IP packet is kept in the ……… field.

a) AHF b) IHL c) Frag. Off. d) TTL e) ToS f) PID

9. A fully connected network of 6 hosts requires a total of ………….. interfaces.

a) 30 b) 36 c) 35 d) 15 e) 18 f) 25

10. Which of the following is most important disadvantage of bus networks?

a) have many collisions b) expensive cables used c) one fault downs entire net.

d) less cabling required e) lower international standard f) higher traffic

11. How many channels are reserved for voice in DMT technique used in ADSL?

a) 1 b) 5 c) 251 d) 256 e) 4 f) 0

12. What are the router settings for N3 in R1 and default route in R2?


a) N3->d, def->p b) N3->w, def->d c) N3->p, def->u

d) N3->p, def->d e) N3->N2, def->ISP f) N3->d, def->d

13. Problems encountered in IP networks are usually reported with this protocol.

a) TCP b) SNMP c) SMTP d) HTTP e) ARP f) ICMP

14. What are VLAN tags?

a) Error indicator attached to IP packets b) Routing information on ethernet adapters.

c) A number in ethernet frame used to group switched hosts. d) Special MAC

numbers

e) A special number on ethernet switches f) A special group number on networked

hosts

15. Which of the following does represent 10001000 in Manchester coding?

a) b) c)

d) e) f)

16. What does C in DHCP stand for?

a) Connection b) Contention c) Collision d) Count e) Configuration f) Control

17. Which of the following is name of a digital channel used in ISDN?

a) 2B1Q b) TE1 c) BRI d) PBX e) B8ZS f) OFDM

18. What are the splitters used for in DSL?

a) Use two telephony device b) separate voice and data signals

c) use multiple telco lines d) use multiple computers

e) reject low frequency components for data f) for splitting power

19. Distance Vector Routing uses …….. to determine distances to its own neighbors.

a) incoming vectors b) outgoing packets c) leaky bucket

d) shortest path e) flooding f) ping

20. Class of an IP address can be determined from ………….

a) first 8 bits b) first 3 bytes c) last 8 bits d) first 3 bits e) first 4 bits f) netmask


18. 27.04.2010 2nd

Midterm

1. A sequence of events in a TCP session between two hosts (H1,H2) is given below.

Determine what is wrong with it.

1) H2: Connect, 2) H1: ConnectionRequest, 3) H1: Accept, 4) H1: SendData,

5) H2: DataArrival, 6) H2: Accept, 7) H1: Close

a) Host-1 cannot send data in step-4 b) Host-1 should not close yet in step-7

c) Accept is incorrect in step-6 d) Accept is incorrect in step-3

e) DataArrival is not called in step-5

2. In ----- packets/frames/cells guaranteed to be in order?

a) ATM b) Wireless ethernet c) TCP/IP d) ISDN e) ADSL

3. Multimode fibers have more ----- than single mode fibers at the receiving end.

a) light b) dispersion c) speed d) wavelength e) cable length

4. Higher capacity channel in BRI service of ISDN is called ----- channel?

a) DSL b) B c) PRI d) NT1 e) D

5. A in ADSL stands for ----- ?

a) Alternative b) Asynchronous c) Attenuated d) Asymmetric e) Additive

6. When a management/arbitration device exists in wireless ethernet networks, the type

of operation is called ----- ?

a) access point b) distributed coordination c) managed arbitration

d) management point e) point coordination

7. VLAN tags are ---- ?

a) Error indicators attached to IP packets b) Routing information on ethernet

adapters.

c) Numbers in ethernet frame used to group switched hosts.

d) Special numbers on ethernet switches

e) Special group numbers on networked hosts

8. Splitters used on telephony wires connected to DSL modems are used to ----- ?

a) Use two telephony device b) reject high frequency data signals

c) use multiple telco lines d) use multiple computers

e) reject low frequency components for data f) for splitting power

9. In ISDN 23B+D configuration is capable of carrying ----- kbps.

a) 10000 b) 100000 c) 52000 d) 1544 e) 622


10. Distance Vector Routing uses ----- to determine elements of its own distance vector.

a) incoming vectors b) outgoing packets c) flooding

d) shortest path e) echo packets

11. Manchester coding is one of the encoding techniques used to eliminate ----- ?

a) DC component of the signal b) High frequency components

c) common mode signals d) redundancy e) echo signals

12. ATM routers can be entirely hardware as ATM frame/packet/cell size is ----- bytes.

a) 64 b) 72 c) 53 d) 1544 e) 46

13. ----- is a collection of Bluetooth piconets.

a) nanonets b) micronets c) picosubnets d) bluenets e) scatternet

14. Transmitting a packet on every route except the one where it came from is called -----.

a) flooding b) broadcast c) multicast d) replicast e) routing

15. The filters used in telephony end offices limit high frequency components on

telephone lines. What is its cut-off frequency when ADSL modems are used on

customer lines?

a) 3000 Hz b) 3400 Hz c) 4500 Hz d) no filter e) 9600 Hz

16. Which of the following is name of a digital channel used in ISDN?

a) 2B1Q b) TE1 c) BRI d) PBX e) OFDM

17. FDDI stands for -----.

a) Fiber Distributed Data Interface b) Fully Distributed Device Interface

c) Frequency Data Digital Interface d) Fiber Data Device Interconnection

e) Faulty Data Dynamic Interface

18. Gigabit ethernet uses ----- bit hardware address.

a) 53 b) 48 c) 16 d) 32 e) 128

19. In IP networking, network and host addresses are separated using ----- ?

a) ARP b) TCP c) gateway d) netmask e) separator

20. In TCP sockets, DataArrival and ConnectionRequest are -----.

a) Messages b) Signals c) Properties d) Methods e) Events


19. 22.03.2011 1st Midterm

1. Which of the following does not need data link layer?

I) Gateway II) IP-Router III) Repeater IV) Ethernet Hub

V) Ethernet Switch VI) Ethernet Bridge

a) all b) I,II,III c) IV, V d) III, IV e) V, VI

2. Eight hosts making up a fully connected network has a total of ………….. dedicated lines.

a) 8 b) 28 c) 64 d) 56 e) 49

3. DMT divides freq. band into 256 channels in ADSL, of which …. are used for voice.

a) 1 b) 5 c) 251 d) 255 e) 4

4. What are the default route entries for R1 and R2 respectively?

a) ISP, ISP b) p, d c) ISP, d

d) u, p e) u, u

5. What is the netmask of the gateway interface in a sub-network where maximum of 25

hosts exist and IP address of one of the hosts is 192.168.1.1?

a) 192.168.1.0 b) 192.168.1.224 c) 192.168.1.27

d) 255.255.255.0 e) 255.255.255.224

6. In OSI systems, IP-routing is dealt with ……….

a) application layer b) data-link layer c) logical layer

d) network layer e) physical layer


a) Network b) Session c) Routing d) Transport e) Presentation

8. What is a broadcast IP address for 193.140.141.128 / 26 ?

a) 193.140.141.128 b) 193.140.141.127 c) 255.255.255.63

d) 255.255.255.191 e) 193.140.141.191

9. The diff. NRZ-I waveform corresponding to the binary stream 01101000 is ………

a) b) c)

d) e)

10. Which one of the following is a job of the Physical Layer?

a) Switching, routing b) Signaling standards c) Segmentation-

reassembly

d) Encryption, Compression e) Physical addressing

11. Gigabit ethernet uses ….. bit physical addresses.

a) 16 b) 32 c) 24 d) 48 e) 64

12. How many differential pairs do 10BaseT UTP interfaces need?

a) 6 b) 1 c) 2 d) 4 e) 8

13. ADSL stands for ….?

a) Asymmetric Digital Subscriber Line b) Asynchronous Digital Subscriber Line


c) Asynchronous Digital Serial Line d) Advanced Digital Serial Line

e) Asynchronous Delivery Serial Line

14. ARP finds out ….. from ……

a) IP, Hostname b) Hostname, IP c) Ethernet Addr, name

d) Gateway-IP, IP e) Ethernet Addr, IP

15. The word “splitter” usually refers to …. in networking?

a) A high-pass filter that extracts data signals in ADSL lines

b) A low-pass filter that extracts voice signal in ADSL lines

c) A multiport device that duplicates packets towards all connected lines

d) A connector box that splits customers’ premises from Telco’s

e) A BNC T connector for splitting coaxial lines.

16. What does the initial part of Ethernet frame that is designed for synchronization called?

a) Preample b) Syncpulses c) Header d) Synchronizer e) Preloader

17. Repeaters operate similar to … that extend the cable length.

a) Bridges b) Ethernet hubs c) Ethernet switches d) Connectors e) Routers


18. No default route entry is used in routers. What are the routing table entries in B?

a) NB ->I5, NC -> I6, NA -> I4 b) NA -> I1, NC -> I8

c) NA -> I2, NC -> I7 d) NB ->I5, NC -> I8, NA -> I1

e) NA -> I2, NC -> I9, NB -> I5


a).GW of a host in NA is I3 b) Hosts in NA can reach hosts in NC

c) GW of a host in NB is I5 d) Netmasks of I2-I4 and I6-I7 are same

e) I6 and I3 are same

20. NA is a class-B network. Which of the following is possible?

a) I1=192.168.1.1 b) I1=193.140.141.255

c) Netmask of NA = 255.255.255.0 d) A host IP in NA=72.16.141.19

e) I2 and I4 are from the same network


20. 22.03.2011 2nd

Midterm

1. The router and distances columns in the following table completely describe a network of

routers. The columns 2-4 indicates the distance of connected router from the router on the

leftmost column. As shown on the table, source A is marked as permanent and B and C are

marked as tentative nodes. Since destination node is F, determine the next state/values after

evaluating the current working node that is to be selected. Fill your answer (next state) into

the empty column provided (using the shortest path routing algorithm approach).

(p:termanent, t:tentative, c:current working node) (hint: drawing the network schema may help)

router distances state

A B,2 C,3 E,1 p,A,0 p,A,0

B A,2 D,1 G,3 t,A,2 t,A,2

C A,3 D,2 F,4 t,A,3 t,A,3

D B,1 C,2 F,2 , ,∞ , ,∞

E A,1 G,4 t,A,1 p,A,1

F C,4 D,2 G,1 , ,∞ , ,∞

G E,4 B,3 F,1 , ,∞ t,E,5

2. A LAN is constructed by dividing a /24 block (n.n.n.x) into 4 equal subnets (named as N1,

N2, N3 and N4) and connecting these subnets using dedicated router-to-router connections.

Router-to-router interfaces are named as Ixy to indicate the interface of Rx connecting it to

Ry. The interface at the other end of the connection is Iyx. Determine subnet addresses for

minimum number of router entries. Determine router entries afterwards. Omit n.n.n parts

while filling in the tables.

Net Network

address R1 R2 R3

N1 .0/26 .64/26 -> I31 default -> I12 default -> I13

N2 .128/26 .128/25 -> I21

N3 .64/26 default -> Isp

N4 .192/26

3. An ethernet frame carrying a short IPv4 packet is sent to host=74.125.39.105

(eth=00:10:30:BA:4C:21) on the internet from local host=193.140.128.34

(eth=1A:2B:3C:4D:5E:6F) through a gateway=193.140.128.1 (eth=DE:AD:BE:EF:00:11).

Fill in the components of the frame below.

Dest addr DE:AD:BE:EF:00:11

R1 R3

2

R2

N3 N1 N2

N4

Isp (service provider)


Src addr 1A:2B:3C:4D:5E:6F

Source IP 193.140.128.34

Dest IP 74.125.39.105

4. Server software for a simple connectionless (UDP) messaging protocol is to be prepared.

Protocol has a total of 7 possible messages. These are; Clients to server Meaning and action to do

M0:username:password username is online. Reply with M3. Send M4 to

everyone.

M1:username:password username is offline. Send M5 to everyone.

M2:username:password:username2:message Send M6 to username2

Server to clients Meaning

M3:key:connected_client_list Ok. Here are the other clients and your key.

M4:key:username username is online.

M5:key:username username is offline.

M6:key:username:message message is sent by username to you

Server keeps a fixed size table of clients (TOC) as follows.

User Name Password IP key

ahmet falanfilan 192.168.1.15 Ax2w1q ahmet is online

ayse vesaire this one is offline

Existence of IP number in the table indicates that the user is online. “key” is the signature

of the server (a special long string) uniquely generated for the client, proving that the

messages from server is genuine.

Complete the following software flow for DataReceived event of the server.

1. Data is received as given in the Client-to-Server column.

2. Split data into D0, D1, D2, D3, D4 (Mx goes to D0, username goes to D1 etc.)

a. If(D1:D2 pair is found in TOC(index) where index=1 to N)

i. If(D0=M0)

1. Generate key, save in TOC(index)

2. Save client IP in TOC(index)

3. Send M3:key(index):client_list to IP

4. Send M4:key(i):D1 to everyone in the TOC (data sent to clients carries their own unique key from the table; i=1 to N)

5. goto END

ii. If(D0=M1)

1. Delete IP in TOC(index)

2. Send M5:key(i):D1 to everyone in the TOC (i=1 to N)

3. goto END

4.

iii. If(D0=M2)

1. If(IP of TOC(index) ≠ client IP) goto END

2. Find index ix of D3 in TOC

3. Send M6:key(ix):D1:D4 to IP of TOC(ix)

4. goto END

3. END


21. 02.06.2011 Final Exam

1. An Ethernet frame carrying an ICMP packet is sent from host H to router R2 through

router R1. What is the frame+packet’s destination Ethernet address and destination IP

address?

a) ER2+IR2 d) E1+I2

b) E1+I1 e) EH1+IR2

c) E2+I1 f) E2+I2

2. A typical socket-server application responds user requests using TCP over a specified port?

What is the typical sequence in terms of socket functions on server side?

a) Listen, DataArrival, Accept, SendData, Close

b) Listen, ConnectionRequest, Accept, DataArrival, GetData, SendData, Close

c) Open, Connect, Accept, SendData, DetData, Close

d) ConnectionRequest, DataArrival, GetData, Accept, SendData, Close, Listen

e) Open, SendData, Listen, GetData, DataArrival, RetrieveData, Close

f) Listen, Open, GetData, SendData, Close

3. What are the DHCP pool types?

a) Automatic, Backed-up b) Configured, Free c) Large-pool, Limited

d) Dynamic, Recursive e) Static, Dynamic f) Switched, Bridged

4. What are the minimal OSI layers of a switching router?

a) Physical, DataLink, Network b) Transport, Network, DataLink

c) Application, VLAN, Switching d) Switching, Routing

e) Bridging, Routing, Physical f) DataLink, Physical

5. Connection between VLANs can be provided by …..?

a) VLAN-tags b) fiber cable c) router d) bridge e) switch f) VLAN-server

6. IEEE 8092.3 covers mostly …..?

a) CSMA/CD on Ethernet b) Token-Ring c) Token-Bus

d) ATM e) Network Layer f) DoD Layers

7. Four routers are connected as a ring. Including broadcast and network addresses, what is

the minimum number of IP addresses needed/wasted for inter-router connections?

a) 4 b) 8 c) 6 d) 64 e) 32 f) 16

8. Which of the following is not a part of the IP datagram?

a) Fragment offset b) Packet identifier c) Type of service

d) TTL e) Dest. ethernet address f) Header length

9. FDDI stands for?

a) Fiber Digital Data Interconnect b) Full Duplex Data Integration

c) Fiber Data Domain Internet d) Fiber Distributed Data Interface

e) Fast Digital Data Internetwork f) Fully Distributed Domain Interface

10. How does source host know if a destination host is on the same IP network?

a) Looks up from a hosts list b) DHCP server tells it c) Via ARP

d) From network part of IP addr. e) If it responds then it is local f) it doesn’t

R1 H

2 R2 IH1

EH1 I1

E1

I12

E12

I2

E2

frame

IH2 EH2 IR2 ER2


11. Name server is a ….?

a) host with full of names b) short of an HTTP-server c) routing application

d) program for administrators. e) network protocol f) program answering name queries

12. Which of the following is a well-known routing method?

a) multilink routing b) selective routing c) multicast routing

d) link stared routing. e) short-test routing f) vector-metric routing

13. In DMT of ADSL how many channels are used for analog voice communication?

a) 5 b) 1 c) 6 d) 2 e) 8 f) 256

14. ATM cells are ….. bytes?

a) 53 b) 64K c) 1524 d) 2048 e) 48 f) 64

15. Which of the following is a common wireless communication technique?

a) Direct Synchronous Serial Shift b) Frequency Hopping Spread Spectrum

c) Fully Hierarchical Shifted Spectrum d) Orthogonal Fast Direct Maintenance

e) Spectrum Balanced Orthogonal Shift f) Frequency Adaptive Discrete Multiplexing

16. Wireless ethernet and BlueTooth interfere as their operating frequencies coincide at ….. ?

a) 900MHz b) 5.GHz c) 1.9GHz d) 2.11GHz e) 4.9GHz f) 2.4GHz

17. Bridges do not separate logical networks since …. ..

a) they are used to connect logical nets. b) this is done by network administrators.

c) what seems logical may not really be. d) CompNet students do not know how to.

e) they work on physical addresses. f) logical addressing is costly

18. In a network with several switches bridges and routers, usually the routers are the

bottlenecks as ………..

a) fiber cables do not work with routers.

b) they are fast and reliable.

c) they have software layers to do the job and software is slow.

d) they require additional money to operate adequately.

e) they are the most disliked by the administrators.

f) bottles usually have narrow necks for TCP/IP packets.

19. What is ‘default route’ refers to for routers?

a) They usually end up in poorer departments and later in dusty shelves.

b) Branches and leaves of the network tree.

c) The most reliable route among all connected interfaces when the network is congested.

d) The interface to send through when the destination is not known for an IP packet.

e) It is the administrators’ traffic monitoring software.

f) All traffic is routed to ‘default route’.

20. What is the nominal bit rate of ‘fast ethernet’?

a) 1000 MB/s b) 10 GB/s c) 10 MB/s d) 200 MB/s e) 1 Gb/s f) 100 MB/s


22. 19.03.2013 1st Midterm Exam

1. An IP(v4) packet is sent from host Ha in network A to host Hb in network B. The route

between R1 and R2 is an ethernet network. What is the frame+packet’s destination

Ethernet address and destination IP address in R1-R2 route?

a) ER0+IR0 d) E2+Ib

b) Eb+Ib e) E1+I2

c) E1+I1 f) ER2+Ib

2. Which of the following needs a physical layer?

I) Gateway II) IP-Router III) Repeater

IV) Ethernet Hub V) Ethernet Switch VI) Ethernet Bridge

a) I, II, V b) IV, V c) III, IV d) V, VI e) III, IV, V f) all

3. How many electrical lines does a 100BaseT interface minimally have?

a) 2 b) 4 c) 6 d) 8 e) 16 f) 1

4. DMT divides freq. band into 256 channels in ADSL, of which …. are used for voice.

a) 1 b) 5 c) 251 d) 255 e) 4 f) 6

5. What are the default route entries for R1 and R2 respectively?

a) p, d b) ISP, ISP c) ISP, d

d) u, p e) u, u f) ISP, p

6. What is the optimal netmask of the gateway interface in a sub-network where maximum

of 10 hosts exist and gateway IP address is 192.168.1.1?

a) 192.168.1.0 b) 192.168.1.224 c) 192.168.1.28

d) 255.255.255.0 e) 255.255.255.240 f) 192.168.1.240

7. In OSI systems, IP-routing is dealt with ……….

a) switching layer b) data-link layer c) logical layer

d) network layer e) physical layer f) security layer


a) Network b) Session c) Switching

d) Transport e) Application f) Physical

9. What does ADSL stand for ?

a) Asynchronous Direct Serial Line b) Asymmetric Digital Subscriber Line

c) Advanced Digital Serial Line d) Alternative Digital Serial Load

e) Asynchronously Delivery Sub Line f) Advanced Data Serial Link

10. Gigabit ethernet uses ….. bit physical addresses.

a) 80 b) 32 c) 24 d) 128 e) 64 f) 48

11. ARP is used to find out ethernet address from IP address and stands for ….

a) Adaptive Repeat Protocol b) Adaptive Replication Protocol

R1 R0

2 R2 IH1

EH1 I1 E1

I12

E12

I2

E2

frame IR0 ER0

A Ha

Ia Ea

B Hb

Ib Eb

ER2 IR2


c) Asymmetric Rate Polling d) Address Resolution Protocol

e) Advanced Resolution Perimeter f) Address Recovery Program

12. The word “splitter” usually refers to …. in ADSL networking?

d) A high-pass filter that extracts data signals in ADSL lines

b) A multiport device that duplicates packets towards all connected lines

c) A connector box that splits customers’ premises from Telco’s

d) A BNC T connector for splitting coaxial lines.

e) A splice box that converts fiber signals to electrical signals on copper wires.

f) A low-pass filter that extracts voice signal in ADSL lines

13. Initial part of Ethernet frame is designed for synchronization. What is it called?

a) Preample b) Syncpulses c) Header d) Synchronizer e) Preloader f) TTL

14. Which of the following is a disadvantage for networks with bus topology?

a) Needs a central device b) More cabling than TP c) Cheaper connectors

d) Has no collision e) Cable faults down entire network f) none

15. Repeaters operate similar to … that extend the cable length.

a) Bridges b) Ethernet hubs c) Ethernet switches

d) Connectors e) Routers f) Gateways



a) ND ->I14, NC -> I10, NA -> I1 b) ND ->I5, NC -> I10, NB -> I5, NA -> I1

c) NA -> I2, NC -> I8, ND -> I13 d) NA ->I4, NC -> I6, ND -> I7

e) NA -> I3, NC -> I10, ND -> I13 f) NA -> I3, NC -> I10, ND -> I13


a) GW of a host in NA is I1 b) Networks I2-I4 and I11-I12 can be the same

c) GW of a host in NB is I5 d) Netmasks of I2-I4 and I6-I8 can be the same

e) Networks I2-I4 and I6-I8 can be the same f) Hosts in NA can reach hosts in NC


a) I1=192.168.1.1 b) I1=193.140.141.255


e) I1 and I2 can be the same. f) I2 and I4 are from the same network


23. 07.05.2013 2nd

Midterm Exam

1. Which one of the following methods is more likely to be called in ConnectionRequest

event function?

a) SendData b) GetData c) Accept d) Connect e) Listen f) Close

2. What does the transmission data blocks called in ATM?

a) cell b) frame c) packet d) dataframe e) log f) payload

3. Single-mode fibers are thinner than multimode fibers. That’s why they have less …. .

a) light b) dispersion c) speed d) wavelength e) cable length f) strength

4. In ADSL, speech signals are separated from data signals using … in customer's premises?

a) multiplexer b) MSAU c) HPF d) ADC e) amplifier f) splitter

5. According to the link-state table given, what is the first hop of the shortest path from H to

A?

a) E b) G c) D d) F e) C f) B

6. What is the total cost of the shortest path

between A and H?

a) 2 b) 3 c) 4 d) 7 e) 6 f) 5

7. Distance Vector Routing uses …. to determine elements of its own distance vector.

a) incoming vectors b) outgoing packets c) flooding

d) shortest path e) echo packets f) routing

8. What is the name of the routing technique where incoming packets are sent through every

available connection?

a) flooding b) broadcasting c) multicasting d) hierarchical e) spanning f) copying

9. ATM routers can be entirely hardware since ATM data-block size (intentionally used a

general name here) is …. bytes.

a) 64 b) 72 c) 53 d) 1544 e) 46 f) 83

10. … is a connectionless protocol whereas … is connection oriented protocol.

a) TCP,UDP b) FTP,HTTP c) ATM,ADSL d) UDP,TCP e) LDP,UP f) ATP,TP

11. Transmitting a packet on every route except the one where it came from is called ….

a) flooding b) broadcast c) multicast d) replicast e) routing f) overloading

A B C D E F G H

A 2 1 2

B 2 1 3

C 1 3 2

D 1 3 4

E 2 3

F 4 3 1

G 3 3 3 1

H 2 1 1


12. A class C IP range is to be divided into 4 unequal subnets with number of addresses: 128,

64, 32 and 32. What are the numbers of netmask bits that are '1', in this order?

a) 24,25,26,26 b) 25,26,27,27 c) 26,27,28,28

d) 24,23,22,21 e) 27,26,25,25 f) 28,27,26,26

13. What is the meaning of MA in CSMA/CD?

a) Managed Addressing b) Monitored Access c) Multiplexed Address

d) Multiple Access e) Multiple Avoidance f) Manual Application

14. Which service is expected to be implemented in Bluetooth?

a) Fax service b) Serial port c) LAN access

d) Cordless telephony e) intercom f) Service discovery

15. The A in ADSL stands for …..

a) Analog b) Assimilated c) Asymmetric d) Advanced e) Adapted f) Addressed

16. The number of allowed hops for an IP packet is kept in the ……… field.

a) AHF b) IHL c) Frag. Off. d) ToS e) TTL f) PID

17. In an IP router, network address is extracted from destination address using …. ?

a) ARP b) TCP c) gateway d) netmask e) extractor f) separator

18. In TCP sockets, Listen and Accept are ….?

a) Methods b) Signals c) Properties d) Messages e) Events f) Variables

19. What is the algorithm to handle collisions in UTP ethernet networks?

a) Collision Pooling b) Time Division Mux c) exponential-backoff

d) ARP e) CSMA-CD f) CSMA-CA

20. When an IP router could not find an entry in the routing table for a destination IP address,

where is the packed sent to?

a) Admin desktop b) default route c) nearest neighbor

d) Packet manager e) next router f) held forever

21. What is the maximum length of Cat-5 cable in a fast ethernet network?

a) 180 m b) 200 m c) 1000 m d) 1200 m e) 100 m f) 50 m


24. 19.03.2014 1st Midterm Exam

1. Bir ağ, içinde en fazla 10 bilgisayar olacak şekilde tasarlanmıştır. Ağ geçidinin IP-adresi

192.168.1.1’dir. Optimal ağ maskesi aşağıdakilerden hangisidir?

a) 255.255.255.240 b) 255.255.255.0 c) 192.168.1.240

d) 192.168.1.0 e) 192.168.1.224 f) 255.255.255.128

2. Aşağıdakilerden hangisi yedi OSI katmanından birisi değildir?

a) Network b) Session c) Switching

d) Transport e) Application f) Physical

3. Donanımsal adresten IP adresini bulmakta kullanılan ARP aşağıdakilerden hangisinin

kısaltılmışıdır?

a) Advanced Resolution Perimeter b) Adaptive Replication Protocol

c) Asymmetric Rate Polling d) Address Range Protocol

e) Address Resolution Protocol f) Address Recovery Program

4. Aşağidekilerden hangisi bus topolojiye sahip ağların bir dezavantajıdır?

a) Merkezi control birimi gereklidir b) Ağ hataları tüm ağı çalışmaz hale getirir

c) Bağlantı elemanları daha ucuzdur d) Çerçeve çarpışması yoktur

e) TP’ye gore daha çok kablo kullanılır f) Hiçbiri

5. Yönlendiriciler “Distance Vector Routing” yaparken aşağıdakilerden hangisini

diğerleriyle paylaşmak üzere kendi “distance vector” tablosunu doldurmak için kullanır?

a) komşulardan alınan tablolar b) dışarı giden paketler c) taşkın

d) en kısa yol e) alternative yollar f) eko paketleri

6. A bilgisayarından yola çıkan bir IP paketi R1-R2 arasındaki ethernet ağını geçiyor. IP

paketini taşıyan ethernet çerçevesinin kaynak ethernet adresi ve taşıdığı IP paketinin

kaynak IP-adresi aşağıdakilerden hangileridir?

a) E2 Ib b) Ea Ia c) EH1 IH1

d) E12 Ia e) E2 I2 f) Ea Ib

7. Aşağıdakilerden hangisi kullanılan yönlendirme yöntemlerinden birisidir?

a) multicast routing b) selective routing c) short-test routing

d) link stared routing. e) multilink routing f) vector-metric routing

8. Ethernet köprüleri IP ağlarını birbirinden ayıramazlar, çünkü …

a) bu iş ağ sorumluları tarafından yapılır b) ethernet adresleri ile çalışırlar

c) IP ağları daha pahalıdır d) konnektörleri uymaz

e) IP ağları zaten ayrıdır f) güvenlik katmanları yoktur

9. “Fast ethernet”in veri iletim hızı hangisidir??

a) 1000 MB/s b) 10 GB/s c) 10 MB/s d) 200 MB/s e) 1 Gb/s f) 100 MB/s

10. Bir bilgisayar IP paketi göndereceği alıcı bilgisayar ile aynı ağda olduğunu nasıl bilir?

R1 R0

2 R2 IH1

EH1 I1 E1

I12

E12

I2

E2

çerçeve IR0 ER0

A Ha

Ia Ea

B Hb

Ib Eb ER2 IR2


a) bir tablodan b) DHCP sunucusundan c) ağ adresinden

d) ARP ile e) cevap gelirse öğrenmiş olur f) öğrenemez

11. CSMA/CD kısaltması içindeki CD aşağıdakilerden hangisidir?

a) Carrier Detection b) Carrier Device c) Cat Direction

d) Collision Detection e) Channel Division f) Channel Distribution

Aşağıdaki ağ için bir C sınıfı IP adres aralığı veriliyor. 0-255 aralığı 4 eşit parçaya

bölünüyor ve 0’dan başlayarak sırasıyla N1, N2, N3 ve N4 ağlarına atanıyor. Aşağıdaki 3

soruyu buna göre cevaplayınız?

12. Aşağıdakilerden hangisi R1 yönlendiricisinin yönlendirme tablosunda vardır?

a) .128/26 -> I32 b) .128/26 -> I42 c) .192/25 -> I22

d) .0/27 -> I21 e) .128/25 -> I22 f) .64/25 -> I22

13. Aşağıdakilerden hangisi R2 yönlendiricisinin varsayılan ağ geçididir?

a) I1 b) I21 c) I22

d) Isp e) I32 f) .129

14. Aşağıdakilerden hangisi N1 ağındaki bir bilgisayardan N3 ağındaki bir bilgisayara

gönderilen IP paketini N1 içinde taşıyan ethernet çerçevesindeki varış ethernet adresidir?

a) N3 ağındaki bilgisayarın eth. adresi b) N3’ün broadcast eth. adresi

c) N1’in broadcast eth. adresi d) I21 bağlantısının eth. adresi

e) I11 f) I11 bağlantısının eth. adresi

15. Tekrarlayıcıların (repeaters) IP yada ethernet adresleri için ayarlanması gerekmez, çünkü

a) sadece sinyalleri güçlendirir b) otomatik olarak algılar

c) bağlı yönlendiriciden kendisi alır d) fabrika çıkışında adresler girilir

e) ayar tutmaz f) aslında gerekir

16. 193.140.141.71 / 27 IP adresi ve ağ maskesine sahip bilgisayarın bulunduğu IP ağında

broadcast adresi nedir?

a) 193.140.141.128 b) 193.140.141.127 c) 255.255.255.32

d) 255.255.255.127 e) 193.140.141.95 f) 255.255.255.71

R1 R2

N1 N4

N3 Isp (servis sağlayıcı)

N2

I21 I11

I22 I42

I32 I1


25. 07.05.2014 2nd

Midterm Exam

1. İki TCP/IP soketi TCP ile bağlıdır. Sunucu tarafından yapılan SendData çağırması istemci

üzerinde hangi olayı tetikler?

a) GetData b) Connect c) ConnectionRequest

d) Accept e) DataArrival f) Listen

2. Aşağıdakilerden hangileri TCP sunucu soketin bağlantı öncesi ilgilenmesi/ayarlaması

gerekenlerden değildir?

I) Bind II) LocalPort III) RemoteHost

IV) Listen V) RemotePort VI) Protocol

a) I, VI b) III, V c) II, VI

d) IV, II e) I, II f) I, VI

3. Single-mode fiber kablolar multi-mode kablolara göre daha uzak mesafelere veriyi daha

verimli taşıyabilirler. Bunun nedeni aşağıdakilerden hangisidir?

a) Daha az dispersion/yayılma olur b) İnce olduğundan dış etkilerden korunaklıdır

c) Nerde çokluk orda yokluk d) Kalın olduğundan sağlam olur

e) Camdan yapılırlar f) Bu bilgi yanlış

4. ATM gerçek-zamanlı veri taşıma uygulamaları için IP tabanlı sistemlere göre daha

uygundur. Neden?

a) ATM Acele Transfer Mode demektir b) Fiber üzerinden yapılır

c) IP çok basittir d) Küçük paket & virtual-circuit

e) Asynchronous olduğundan f) ATM yönlendiricileri daha hızlıdır

5. Tek DSL kablosu üzerinden hem analog ses sinyali hem de digital veri nasıl iletilir?

a) Tek değil iki hat kullanılır b) Ses de digital gönderilir

c) ATM kullanılır d) Time Division Multiplexing yapılır

e) Modemler öyle çalışır f) Frekans bandı süzgeçler ile kanallara ayrılır

6. Aşağıdakilerden hangisi TCP/IP soket event/olayı (callback function) değildir?

a) ConnectionRequest b) DataArrival

c) SendData d) Close

e) Connect f) Error

7. Switching-Router denilen cihaz Hangi OSI katmanlarına sahip olmak zorundadır?

a) DataLink, Network, Physical b) Application, Physical, Transport

c) Transport, DataLink, Physical d) Physical, Network

e) Session, Transport, Network f) Switching, Routing, Bridging

8. Varsayılan Ağ Geçidi ne demektir?

a) Ağların geçtiği IP adresi b) Sahibi bulunamazsa paketin bırakılacağı IP

c) Ağın en uçtaki kablosu d) DNS'in çalıştığı makinanın IP adresi

e) Kayıtların tutulduğu veritabanı f) Ağın merkezindeki dağıtım cihazı

9. Exponential-backoff algoritmasının bazı networklerde çalışma sebebi nedir?

a) Traffic management b) Routing c) Multiplexing

d) Collisions e) Fragmentation f) CSMA/CA


10. Aşağıdakilerden hangisi Biphase (Manchester/Differential Manchester) kodlamanın

sebeplerindendir?

a) Error correction b) Error detection c) Voltage stability

d) Cable capability e) Synchronization f) Frame data containment

11. ICMP paketleri neden kısadır?

a) Yönlendiriciler bölerek kısaltır b) Çarpışma olmasın diye

c) Sadece kısa mesajlar taşır d) Kısa olursa daha hızlı gider

e) Daha ucuz olması için f) RFC792'ye gore kısa değildir

12. VLAN anahtarları diğer VLAN gruplarını tanımak için hangi ethernet alanını kullanır?

a) padding b) VTag c) taşkın

d) preamble e) dest-address f) type/len

13. DHCP içindeki C'nin açılımı nedir?

a) Configuration b) Control c) Central

d) Correction e) Correspondence f) Connection

14. Kablosuz haberleşmede neden "Collision Detection" yerine "Collision Avoidance"

kullanılır?

a) Ucuza getirmişler

b) Çarpışmanın tespit edilemeyeceği durumlar olabilir

c) IP numaraları ortak olabilir

d) Kablosuzda zaten çarpışma olmaz

e) Uzak mesafelere yayın yapabilmek için

f) Elektromanyetik dalga her yöne yayılır

15. “Fast ethernet”in hızı nedir?

a) 1 Gbps b) 10 Mbps c) 100 Mbps

d) 10 Gbps e) 150 Mbps f) 250 Mbps

16. Yönlendiriciler diğer yönlendiricilerle olan uzaklıklarını nasıl paylaşırlar?

a) ping göndererek b) en kısa yoldan c) her pakete ekleyerek

d) distance-vectors ile e) dönüşümlü olarak f) flooding/taşkın ile

26. 29.05.2014 Final Exam

1. FDDI stands for ….?

a) Full Duplex Data Integration b) Fiber Data Domain Internet

c) Fast Digital Data Internetwork d) Fiber Distributed Data Interface

e) Fiber Digital Data Interconnect f) Fully Distributed Domain Interface

2. A sequence of events in a TCP session between two hosts (H1,H2) is given below.

Determine what is wrong with it.

1) H2: Connect, 2) H1: ConnectionRequest, 3) H1: Accept,

4) H1: SendData, 5) H2: DataArrival, 6) H2: Accept, 7) H1: Close

a) Host-1 cannot send data in step-4 b) Host-1 should not close yet in step-7

c) Accept is incorrect in step-6 d) Accept is incorrect in step-3

e) DataArrival is not called in step-5 f) H2 cannot initiate connection


3. In ATM, packets/frames/cells guaranteed to be received in correct order, thanks to…?

a) virtual circuits b) packet size c) ordering algorithm

d) network management e) leased lines f) cell congestion

4. Dispersion, seen in multimode fibers than single mode fibers, eventually results in ….

a) faster transmission b) higher reliability c) more reflections

d) harder cable splice e) shorter segments f) shorter packets/frames

5. What is asymmetric in ADSL?

a) telco line lengths b) monthly bills c) signal attenuation

d) customer premises e) splitter frequency f) upstream/downstream channels

6. Virtual LAN tags are ---- ?

a) Error indicators attached to IP packets b) Routing information on ethernet adapters.

c) Numbers in ethernet frame used to group switched hosts.

d) Special numbers on ethernet switches e) Special group numbers on networked hosts

f) Numbers indicating the length of the frame

7. Low-Pass Filter outputs of the splitters used on DSL lines is connected to ----- ?

a) DSL lines b) telephony devices c) service provider lines

d) DSL modems e) computers f) nowhere

8. IP-Routing Algorithms looks for the …. of the IP-packets.

a) ethernet address b) destination IP address c) source IP address

d) encoding e) payload f) CRC-field

9. Manchester coding and 8B10B coding are two of the encoding techniques that help ease --

----- while eliminating the DC level of the signal?

a) synchronization b) decoding c) reducing the power

d) faster transmission e) data compression f) collision problems

10. Multicasting is -----.

a) a routing method that serves multiple networks b) a kind of a flood routing

c) one host pretending like several hosts d) receiving packets from multiple hosts

e) Multiple routers serving a single network

f) transmitting a packet to multiple destinations

11. Gigabit ethernet uses ----- bit hardware address.

a) 53 b) 48 c) 16 d) 32 e) 128 f)64

12. In IP networking, network address is determined by using IP address and the -----

a) ARP b) TCP c) gateway d) netmask e) separator f) UDP

13. In TCP sockets, ConnectionRequest is a callback function called -----.

a) by DataLink layer b) by a remote procedure

c) when the socket is ready for connection d) by a user request

e) when a remote host requests a connection f) by the physical layer

14. What are the router settings for N3 in R1 and default route in R2?


a) N3->d, def->p b) N3->w, def->d c) N3->p, def->u

d) N3->d, def->d e) N3->N2, def->ISP f) N3->p, def->d



a) NB ->I5, NC -> I6, NA -> I4 b) NA -> I1, NC -> I8

c) NA -> I2, NC -> I7 d) NB ->I5, NC -> I8, NA -> I1

e) NA -> I2, NC -> I9, NB -> I5 f) A -> I3, C -> I9


a).GW of a host in NA is I3 b) Hosts in NA can reach hosts in NC

c) GW of a host in NB is I5 d) Netmasks of I2-I4 and I6-I7 are same

e) I6 and I3 are same f) I2, I4 are non-unique private IPs


a) I1=192.168.1.1 b) I1=193.140.141.255


e) I2 and I4 are from the NA network f) I2 and I4 are from the NB network

27. 29.05.2014 Final-MakeUp Exam

1. Aşağıdaki yerel ağ ve ağdaki bilgisayarlarda kullanılmak üzere 193.140.128.0/27 IP-

numaraları ve ağ maskesi veriliyor. Buna göre alt-ağların ve ağ-geçitlerinin IP-

numaralarını/ağ-maskelerini belirleyiniz. (üzerine yazınız)

R1, R2 ve R3 yönlendiricilerinin yönlendirme tabloları içeriklerini belirleyiniz.

Rx R1 R2 R3

N2

N3 N1

192.168.1.1/24


Çözüm :

Abu atamalarla, N1, N2 ve N3 sırasıyla 4, 13 and 5 bilgisayar içerebilir.

Yönlendirme tabloları da aşağıdaki şekilde olabilir.

R1 R2 R3 N3->192.168.2.2 N3->192.168.3.2 Default->192.168.3.1

N2->193.140.128.26 Default->193.140.128.25

Default->192.168.1.1

2. UDP ve gerçek-IP ile çalışan sunucu tabanlı bir mesajlaşma protokolü tasarlanacaktır. Her

kullanıcı bir kısa-isim (nickname)'e sahip olacaktır. İstemci programları ilk açılışta sunucuya

varlıklarını, kapanışta da kapandıklarını bildireceklerdir. İstedikleri zaman kimlerin aktif

olduğunu sunucudan sorgulayabilecek, sunucu kendilerine sorduğu zaman da, açık iseler,

cevap vereceklerdir. İstemciler birbirlerine sunucu üzerinden mesaj gönderecekler, sunucu

herşeyin tablosunu zaman etiketli tutacaktır. Buna gore;

a) Olası mesajları ve formatlarını tasarlayınız, örnek veriniz

b) Sunucudaki olası tabloları tasarlayınız.

Çözüm :

ID message format comment

M1 uname|online sent to indicate uname is now online (IP is cached in table)

M2 offline sent to indicate user is going offline (found by its IP)

M3 onlinelist ask the users that are online (sender is found by IP)

M4 online_user_list online_user_list is sent by server

M5 areyoualive server asks if the user (at the last known IP) is online

M6 touser|message message is sent from user to touser (sender is found by IP)

Örnek : majortom|we have arrived! (sent by groundcontrol to majortom)

Örnek : Apollo;Hercules;groundcontrol;majortom;pokerface

We need at least two tables with headers

username IP onlineflag timestamp

fromuser touser timestamp message

Rx R1 R2 R3

N2

N3 N1

192.168.1.1/24

..1.2/2

..2.1/24 ..2.2/24 ..3.2/24 ..3.1/24

..128.24/29

..128.0/28

..128.1/28 ..128.16/29

..128.17/29 ..128.25/29

..128.26/29

Documents

152118005 COMPUTER NETWORKS Answers to - E. Seke