1: MCQs

Question 1

How many connections are necessary to make a connected packet-switched network with n nodes?

Answer 1

n−1, but a sufficient number will be much larger.

Question 2

What are the factors that should be taken into account when designing a recommender system?

Answer 2

accuracy,
diversity,
privacy,
persistence (repetitions), demographics,
robustness (to frauds), serendipity (elements of surprise),
trust,
labelling.

Question 3

Which of the following best describes Groupon’s business model?

• Subscription
• Merchant model
• Affiliate model
• Infomediary model
• Utility model

Answer 3

• Affiliate model.

Question 4

What is not true about the TCP?

• There is a handshake between sender, receiver
• It is a connectionless protocol
• It is reliable
• The data sent is ordered

Answer 4

• TCP isn’t connectionless.

The Internet Protocol Stack 5-layer model has 4 logical layers (application, transport, network, link) and 1 physical layer.

• TCP provides a reliable connection, heavy.
• UDP is connectionless and quick, light.

Question 5

Which of the following can be an IP address?

• 143.33.208.45
• 128.3.25.124.87
• 126.25.43.21.35.64
• none of the above

Answer 5

143.33.208.45 (first), as address consists of 4 integers.

IPv6 addresses have colon (:) separators.

Question 6

Which protocol allows files to be copied from one computer to another across the Internet?

• SMTP
• HTTP
• FTP
• SNMP

Answer 6

FTP (File Transfer Protocol).

Question 7

Which of the following is an advantage of SEO, compared to sponsored advertising?

• Able to understand customers’ intents better.
• Able to target specific demographic groups.
• Customers are more inclined to click links on search engine result pages.
• Able to improve site traffic immediately.

Answer 7

Customers are more inclined to click links on search engine result pages.

Question 8

Advertisers A, B, C with:
CTR A = 0.5,
CTR B = 0.2,
CTR C = 0.1

bid for two slots:
bid A = 1.5,
bid B = 2,
bid C = 1 per click.

By the GSP rule which advertiser wins which slot and what are their actual payments per click?

Answer 8

1) A
2) B
3) C

Pa = Bid_B * CTR B/CTR A = 0.4/0.5 = 0.8

Pb = Bid_C * CTR_c/CTR_B = 0.1/0.2 = 0.5

Pc = 0

Question 9

Which of the following best describes the Brokerage business model?

• B2C
• C2C
• B2B
• All of them

Answer 9

All of them.

Question 10

What layer of the Internet Protocol 5-layer Stack model contains the TCP and UDP protocols?

Answer 10

Transport layer.

Question 11

Which can shopbots not do?

• Product search
• Comparison shopping
• Participate in auctions
• Collect data from Flash-based banners

Answer 11

Collect data from Flash-based banners.

Question 12

In a sealed-bid auction the valuations and bids are:

1) v1 = 5, b1 = 4,
2) v2 = 4, b2 = 2,
3) v3 = 1, b3 = 3.

Who wins in a first-price sealed-bid auction?

Answer 12

1) v1 = 5, b1 = 4

With payoff 5-4=1.

Question 13

Is the first-price sealed-bid auction truthful?

Answer 13

No.

Question 14

In a second-price sealed-bid auction the valuations of 3 bidders are:

1) v1 = 5
2) v2 = 4
3) v3 = 1.

If all bidders in this auction bid truthfully, who wins and what is their payoff?

Answer 14

1) v1 = 5 with a bid of b1=4, and a payoff of 5-4=1.

Question 15

Is the second-price sealed-bid auction truthful?

Answer 15

Yes.

Question 16

All bids are private. The bidder with a highest bid gets the item, but neither gets nor pays any money. Everyone else gets the highest bid.

Is this auction truthful?

Answer 16

Yes.

Question 17

Which player prefers the highest expected payoff?

• Risk-averse
• Risk-neutral
• Risk-seeking
• None of the above

Answer 17

Risk-neutral.

Question 18

Name two sources of privacy risks on the internet ?

Answer 18

HTTP cookies, search engines.

Question 19

In which type of attack an intruder modifies data stored in a database ?

• Integrity
• Confidentiality
• Denial-of-service
• Authentication

Answer 19

Integrity.

Question 20

Compute 213 (mod 85), which is between 0 and 84 ?

Answer 20

26 = 64 is close enough to 85, so at least 26 21 (mod 85) is simpler than 64.

Then 2^7 = 2 * ( 21) (mod 85) and
2^8 = 4 * ( 21) (mod85) = 1 (mod 85).

Then 2^13 = 2^(8+5) = 2^5 * (mod 85) = 32 * (mod 85).

Question 21

Compute 32^5 (mod 85), which is between 0 and 84 ?

Answer 21

32^5 = (2^5)5 = 2^(5*)5 = 2^(25).

We’ll find 2^(25) (mod 85).

2^(25) = 2^(8*3+1) = 2 * (mod 85)

Question 22

Describe one strength and one weakness of asymmetric key encryptions ?

Answer 22

Strength: a public key distribution, which is needed for encryption.

Weakness: computational cost for long messages

Question 23

Which cryptographic protocol requires two keys (public and private)?

• Digital signatures
• Symmetric encryption
• Private key encryption
• All of the above
• None

Answer 23

Digital signatures.