NAME: ______________________________
CS 450 Computer Networks
Test on Chapters 1 – 4 and other Reading Assignments
Short answers (total 51 points):
1) (5 points) What is Metcalfe’s Law?
2) (10 points) Explain the difference between packet switching and circuit switching.
3) (10 points) Give two reasons why networks might use an error-correcting code instead of doing
error detection and retransmission.
4) Consider five wireless stations using IEEE 802.11, A, B, C, D, and E. Station A can communicate with
all other stations. B can communicate with A, C, and E. C can communicate with A, B, and D. D can
communicate with A, C, and E. E can communicate with A, D, and B.
i)
(5 points) When A is sending to B, what other communications are possible?
ii) (5 points) When B is sending to A, what other communications are possible?
iii) (5 points) When B is sending to C, what other communications are possible?
1
5) (6 points total)The following picture was shown during the telephony lecture:
Trunk
Connection
B
Connection
A
Connection
C
i)
(3 Points) Are Connections A and C analog or digital links?
(choose 1 by circling: analog or digital)
ii) (3 Points) Is Connection B an analog or a digital link? (choose 1 by circling: analog or digital)
6) (5 points total) Consider the extended LAN connected using bridges B1 and B2 in the following figure
(which was Figure 4-41 in the textbook). Suppose the hash tables in the two bridges are empty. List
all ports on which a packet will be forwarded for the following sequence of data transmissions:
(a) Bridge connecting two multidrop
i)
(1 point) A sends a packet to C
ii) (2 points) E sends a packet to F
iii) (2 points) F sends a packet to E
TRUE or FALSE – circle the appropriate answer (33 points total)
1. (3 points) In Traditional Telephony (i.e., POTS = PSTN) the computer-serviced trunk lines
between Central Offices multiplex using frequency division multiplexing.
True or False
2
2. (3 points) In the OSI Reference Model the Network Layer provides services to the Data Link
Layer.
True or False
3. (3 points) The textbook mentioned four methods by which frames can be delineated (i.e., ways
to identify when frames begin and end): 1) byte count, 2) flag bytes with bit stuffing, 3) flag bits
with bit stuffing, and 4) physical layer coding violations.
True or False
4. (3 points) In telephony both a T1 circuit and an OC-1 circuit have a lower data rate (i.e., are
slower) than a T3 circuit.
True or False
5. (3 points) Both Safety-oriented and Security-oriented industries have data communications
requirements for integrity and availability. These industries differ in that Safety-oriented
industries additionally have a requirement for minimal latency versus Security-oriented
industries that have a confidentiality requirement.
True or False
6. (3 points) Computer networks can be accurately modeled using Poisson Traffic Models.
True or False
7. (3 points) Complexity Theory evaluates how agents respond to feedback loops.
True or False
8. (3 points) Bayes Theory presumes that a chain of events have memory and that the behavior of
an event is conditional upon a prior event.
True or False
9. (3 points) Medium Access Control (MAC) is a part of the Data Link Layer.
True or False
10. (3 points) The 2.4 MHz unlicensed frequency band is used by IEEE 802.11 b/g/n.
True or False
11. The Cyclic Redundancy Check (CRC) is computed by dividing the frame’s contents by a generator
polynomial using modulo 2 arithmetic.
True or False.
Multiple Choice – select the best answer to each question (16 points total)
1. (4 points) Multiplexing approach that is based on Shannon’s Information Theory
a. Time Division Multiplexing (TDM)
b. Frequency Division Multiplexing (FDM)
c. Code Division Multiplexing (CDM)
d. Extended InterFrame Spacing (EIFS)
2. (4 points) The OSI Reference Model has
a. 4 Layers
b. 5 Layers
c. 6 Layers
3
d. 7 Layers
e. 8 Layers
3. (4 points) How many octets (i.e., bytes) are in a standard IEEE 802 address?
a. 4 octets
b. 5 octets
c. 6 octets
d. 8 octets
e. Addresses are variable length
f. It depends upon the implementation
4. (4 points) In an environment that has a Hamming Distance of 5 between codewords, how many
bit errors can be detected and how many can be corrected?
a. Detect 3 correct 2
b. Detect 3 correct 1
c. Detect 2 correct 1
d. Detect 4 correct 3
e. Detect 4 correct 2
4