Computer Networks – Exam
1 Short questions
For each question, please circle a single best answer.
1.In the CSMA/CD protocol, what condition on the transmission delay T trans and the
propagation delay T prop has to be satisfied to guarantee that a node always detects a collision?
A. T trans > T prop
B. T trans > 2T prop CORRECT
C. T trans < T prop
D. 2T trans < T prop
2.Alice and Bob communicate in an alphabet that has L letters. They use a monoalphabetic
substitution cipher with key K. Assume that Trudy obtains a plaintext m and the
corresponding ciphertext c. Under what conditions can Trudy recover the key K completely?
A. m contains at least 1-
L unique letters. CORRECT
B. L
m≥.
C. K
m≥.
D. m is not empty.
3.The WiMaX protocol:
A. provides the maximum available data rate over a wireless channel.
B. uses unlicensed spectrum, such as WiFi.
C. provides a mechanism for scheduling. CORRECT
D. All of the above options are correct.
4.Two hosts simultaneously send data through a link of capacity 1Mbps. Host A generates data
with a rate of 1Mbps and uses TCP. Host B uses UDP and transmits a 100bytes packet every 1ms. Which host will obtain higher throughput?
A. Host A.
B. Host B. CORRECT
C. They obtain roughly the same throughput.
D. They experience congestion collapse and negligible throughput.
5.What is the theoretical upper-bound on the number of simultaneous TCP/IPv4 connections
that a host with a single IP address can handle? (Ignore memory limitations.)
A. 216
B. 232
C. 264CORRECT
D. unlimited
6.Host A sends a TCP segment (Seq = 43, ACK = 103), to which host B replies with a TCP segment (Seq = 103, ACK = 57). The payload of the first TCP segment is
A. 14 bytes long. CORRECT
B. 43 bytes long.
C. 46 bytes long.
计算机学院排名D. 57 bytes long.
E. 60 bytes long.
7.The Distance-Vector algorithm is not:
A. iterative.
B. asynchronous.
C. distributed.
D. used in RIP.
E. None of the above. CORRECT
8.Longest prefix matching is used:
A. in routers to know on which link interface to forward packets. CORRECT
B. in classless addressing to use the address space more efficiently than in classful addressing.
C. by NAT to increase the available address space in home networks.
D. to assign subnet masks.
E. None of the above.
9.An authoritative DNS server knows a top-level domain server via:
A. hostname.
B. IP address. CORRECT
C. canonical hostname.
D. alias.
E. domain.
10.A user requests aWeb page that consists of some text and 3 images. The browser’s cache is empty. For this page, the client’s browser:
A. sends 1 http request message and receives 1 http response messages.
B. sends 1 http request message and receives 3 http response messages.
C. sends 1 http request message and receives 4 http response messages.
D. sends 3 http request messages and receives 3 http response messages.
E. sends 4 http request messages and receives 4 http response messages. CORRECT
11.What is the advantage of using a layered model of networking?
A. Simplified the network
B. For the purpose of standardization
C. Divides the complexity of internetworking into discrete, more easily learned operation subsets
D. All of the above CORRECT
12.What is the name of protocol data unit(PDU)at the network layer of the OSI reference model?
A. Transport
B. Frame
C. Packet CORRECT
D. Segment
13.Which is true when a broadcast is sent out in an Ethernet 802.3 LAN?
A. The broadcast is sent only to the default gateway.
B. The broadcast is sent only to the destination hardware address in the broadcast.
C. The broadcast is sent to all devices in the collision domain. CORRECT
D. The broadcast is sent to all devices in the broadcast domain.
14.Segmentation of a data stream happens at which layer of the OSI model?
A.Physical
B.Data Link
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D.Transport CORRECT
15.Which of following international standard defines for Fast Ethernet?
A.IEEE 802.3
B.IEEE 802.3z
C.IEEE 802.3u CORRECT
D.IEEE 802.3ae
16.What does the Data Link layer use to find hosts on a local network?
A.Logical network addresses
B.Port numbers
C.Hardware addresses CORRECT
D.Default gateways
17.What were the key reasons the ISO released the OSI model?
A.To allow companies to charge more for their equipment
B.To help vendors create interoperable network devices CORRECT
C.To help vendors create and sell specialized software and hardware
D.So the IBM mainframe would be replaced with the PC
18.What is used at the Transport layer to stop a receiving host’s buffer from overflowing?
A.Segmentation
B.Packets
C.Acknowledgments
D.Flow control CORRECT
19.When data is encapsulated, which is the correct order?
A.Data,frame,packet,segment,bit
B.Segment,data,packet,frame,bit
C.Data,segment,packet,frame,bit CORRECT
D.Data,segment,frame,packet,bit
20.What does the term“Base”indicate in 100Base-TX?
A.The maximum distance
B.The type of wiring used
C.A LAN switch method using half duplex
D.A signaling method for communication on the network CORRECT
21.What is the maximum distance of 100Base-T?
A.100 feet
B.1000 feet
C.100 meters CORRECT
D.1000 meters
22.Which of the following would describe a transport layer connection that would ensure reliable delivery?
A.Routing
B.Acknowledgments CORRECT
C.Switching
D.System authentication
23.Which of the following is not considered a reason for LAN congestion?
A.Low bandwidth
B.Too many users in a broadcast domain
C.Broadcast storms
D.Routers CORRECT
24.Which of the following are two basic types of dynamic routing?
A.Static and default
B.TCP and UDP exchange
C.Distance-vector and link-state CORRECT
D.None of the above
25.If your LAN network is currently congested and you are using only hubs in your network,what would be the BEST solution to decrease congestion on your network?
A.Cascade your hubs.
B.Replace your hubs with switches. CORRECT
C.Replace your hubs with routers.
D.Add faster hubs.
26.What technology is a used by most switches to resolve topology loops and ensure that data flows properly through a single network path?
A.RIP
B.STP CORRECT
C.IGRP
D.Store-and-forward
27.Which of the following is one of the characteristics of IP?
B.unreliable and connectionless CORRECT
D.unreliable and connection-oriented
28.What is the valid host range for subnet 172.16.10.16(Mask 255.255.255.240)?
A.172.16.10.20 through 172.16.10.22
B.172.16.10.16 through 172.16.10.23
C.172.16.10.17 through 172.16.10.31
D.172.16.10.17 through 172.16.10.30 CORRECT
29.What range of addresses can be used in the first octet of a Class B network address?
A.1–126
B.128–190
C.128–191 CORRECT
D.129–192
30.Which of the following is not true?
A.IP is connectionless and provides routing.
B.ARP is used to find an IP address of a host. CORRECT
C.UDP is connectionless.
D.TCP is connection oriented.
31.Which class of IP address provides a maximum of only 254 host addresses per network ID?
A.Class A
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