Questão 1
Questão
Layers four and five of the Internet protocol stack are implemented in the end systems but not in the routers in the network core.
Questão 2
Questão
With ADSL, each subscriber gets more downstream bandwidth than upstream bandwidth.
Questão 3
Questão
Twisted-pair cooper wire is no longer present in computer networks.
Questão 4
Questão
4. Two packets A and B are sent in that order through a connection-oriented communication network. They could arrive at the destination:
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a. in any order, after having traversed the same route.
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b. only in the order A-B, after possibly having traversed different routes.
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c. in any order, after possibly having traversed different routes.
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d. only in the order A-B, after having traversed the same route.
Questão 5
Questão
5. Two packets A and B are sent in that order through a connectionless communication network. They will arrive at the destination:
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a. in any order, after possibly having traversed different routes.
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b. in the order A-B, after having traversed the same route.
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c. in any order, after having traversed the same route.
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d. in the order A-B, after possibly having traversed different routes.
Questão 6
Questão
6. The Internet received its name in the 1980s because:
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a. it was an interim (temporary) design of what it later became, but the name stuck.
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b. it was meant to be a network internal to the United States Department of Defense.
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c. it consisted of many interconnected networks.
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d. it achieved international scope with the addition of the City University of London.
Questão 7
Questão
DNS lookups often involve a combination of recursive and iterative queries.
Questão 8
Questão
The Date: header in the HTTP response message indicates when the object in the response was last modified.
Questão 9
Questão
Skype relay nodes are typically peers under the control of Skype users.
Questão 10
Questão
The process that sends messages into, and receives messages from, the network through a software interface is called a socket.
Questão 11
Questão
In a P2P File Distribution architecture, the server must sequentially send (upload) file copies.
Questão 12
Questão
12. SMTP is used to:
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a. to transfer messages from one mail server to another.
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b. to transfer messages from mail server to a user agent.
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c. to define the format of message headers.
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d. all of the above.
Questão 13
Questão
13. Suppose a DNS resource record has Type=MX. Then:
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a. Value is the hostname of the DNS server that is authoritative for Name.
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Value is the IP address of the mail server that has the alias hostname Name.
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c. Value is the hostname of the mail server that has the alias hostname Name.
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d. none of the above.
Questão 14
Questão
14. Local DNS name servers:
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a. cache resource records, but discard them after a period of time that is on the order of a few days.
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b. cache resource records and never discard them.
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c. obtain resource records from Web caches.
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d. never cache resource records.
Questão 15
Questão
Consider an HTTP Web server using persistent connections. Suppose the server spawns a
separate process for each client that connects to the server. Then each of these spawned processes will have different server port numbers.
Questão 16
Questão
The size of the TCP RcvWindow never changes throughout the duration of the connection.
Questão 17
Questão
17. When a TCP segment arrives to a host, the socket to which the segment is directed depends on
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a. the source IP address of the datagram that encapsulated the segment.
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b. the destination port number.
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c. the source port number.
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d. all of the above.
Questão 18
Questão
18. UDP has which of the following characteristics:
Questão 19
Questão
19. When a UDP segment arrives to a host, in order to direct the segment to the appropriate socket, the OS uses:
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a. the source port number.
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b. the source IP address.
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c. the destination port number.
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d. all of the above.
Questão 20
Questão
20. Suppose a client sends an HTTP request message with the If-modified-since: header. Suppose the object in a server has not changed since the last time a client retrieved the object. Then the server will send a response message with the status code:
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a. 404 Not Found.
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b. 200 OK.
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c. 304 Not Modified.
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d. none of the above.
Questão 21
Questão
21. Streams are not needed in which of the following programs:
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a. TCPserver.
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b. UDPserver.
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c. TCPclient.
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d. UDPclient.
Questão 22
Questão
22. Consider the minimum time for P2P file distribution, as discussed in Section 2.6. Suppose the upload rate of the server is10 Mbps, the upload rates of all peers is 1 Mbps, and the download rates of all peers is 10 Mbps. Further suppose that there are 100 peers and the file is 100 million bits. The minimum distribution time is
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a. approximately 100 seconds.
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b. approximately 10 seconds.
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c. approximately 1 second.
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d. approximately 1000 seconds.
Questão 23
Questão
For BitTorrent, which of the following is true:
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a. Although a peer may have 50 concurrent TCP connections with other peers, at any given instant of time it sends data to less than 10 other peers.
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b. At a given instant of time, a peer A may upload to a peer B, even if peer B is not sending anything to A.
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c. Among the chunks that a peer does not have, the peer will request chunks that appear to be relatively rare in the torrent.
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d. All of the above.
Questão 24
Questão
24. Consider the latency model for dynamic congestion windows. Which of the following components contribute to latency?
Questão 25
Questão
25. TCP applies fast retransmit to a segment when:
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a. it estimates unusually large RTTs.
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b. it receives three ACKs for an earlier segment.
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c. the segment's timer expires.
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d. none of the above.
Questão 26
Questão
26. Nmap is often used to:
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a. do port scans over a range of ports at a target host.
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b. measure throughput between hosts.
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c. measure round-trip times between hosts.
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d. decipher encrypted traffic.
Questão 27
Questão
27. With SYN cookies, when a server receives a SYN segment, it returns a SYNACK with:
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a. an initial sequence number that is a hash of the IP addresses and port numbers in the SYN segment (as well as of other things).
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b. initial sequence number 1.
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c. a randomly chosen initial sequence number.
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d. none of the above.
Questão 28
Questão
Before sending a packet into a datagram network, the source must determine all of the links that packet will traverse between source and destination.
Questão 29
Questão
The primary role of a router is to forward datagrams from input links to output links.
Questão 30
Questão
Forwarding involves transferring a packet from the router’s input link to the appropriate output link.
Questão 31
Questão
All link layer protocols that support IP have the same frame structure (i.e., length of frame,
number and length of header fields).
Questão 32
Questão
CRC error detection, as used in Ethernet, is always able to detect whether there is an error in a frame.
Questão 33
Questão
The even parity bit scheme can correct single bit errors.
Questão 34
Questão
With CDMA, each sender uses the same code, cm, m=1,...,M.
Questão 35
Questão
Each LAN adapter has a unique LAN address.
Questão 36
Questão
41. A channel partitioning protocol has which of the following characteristics forwarding table is:
Questão 37
Questão
42. In slotted ALOHA with N active nodes, the probability that no node transmits in a given slot is
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a. (1-p)N
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b. (1-p)N
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c. pN
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d. 1-p
Questão 38
Questão
43. An ARP query packet is encapsulated in
Questão 39
Questão
Ethernet provides which of the following services to the network layer
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a. error detection.
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flow control.
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reliable data transfer.
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all of the above.
Questão 40
Questão
45. For Ethernet, if an adapter determines that a frame it has just received is addressed to a different adapter
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a. it discards the frame without sending an error message to the network layer.
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it discards the frame and sends an error message to the network layer.
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it sends a NACK (not acknowledged frame) to the sending host.
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it delivers the frame to the network layer, and lets the network layer decide what to do.
Questão 41
Questão
A typical "infrastructure network" wireless network includes base stations.
Questão 42
Questão
In CDMA, the chipping rate is typically the same as the original data rate.
Questão 43
Questão
The 11 channels in the 802.11 are non-overlapping.
Questão 44
Questão
If you enter an Internet café and more than one AP is present, then the packets your host
Questão 45
Questão
During the 802.11 association handshake protocol, the wireless host gets assigned an IP address.
Questão 46
Questão
51. In CDMA, let Ym be the received value in the mth mini-slot for some slot i. Let cm, m=1,...,M, be the sender's M code values. To determine the bit value the sender sent, the receiver:
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a. multiples Ym with the sum of the M code values.
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b. multiplies each Ym with the corresponding cm, sums the resulting values and divides by M.
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simply declares Ym as the sent value.
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d. none of the above.
Questão 47
Questão
52. A beacon frame sent by an AP includes
Questão 48
Questão
53. The 802.11 protocol does not implement collision detection because (Click all that apply)
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a. collision detection was found to be useless in wired Ethernet.
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b. the adapter would still not be able to detect all collisions due to hidden terminals.
c. it is costly to build wireless hardware that detects collisions.
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c. it is costly to build wireless hardware that detects collisions.
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d. all of the above.
Questão 49
Questão
54. Packets sent by two stations in 802.11 can collide because
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a. at a given time, the random backoff values of the two stations are the same.
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b. the packets are sent to different APs but on the same channel.
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c. the two stations could be hidden from each other.
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d. all of the above.
Questão 50
Questão
An 802.11 frame includes:
Questão 51
Questão
In IP spoofing, the attacker interchanges the source and destination addresses in the sender's IP datagram.
Questão 52
Questão
Nonce's are often used to combat the playback attack.
Questão 53
Questão
65. Filtering in a firewall can be based on: