Data and Computer Exam III

1. Data and Computer Exam 3
Question 1
Consider a slotted ring of length 2 km with a data rate of 100 Mbps and 100 repeaters, each of
which introduces a 1-bit delay. Each slot contains room for one source address byte, one
destination address byte, two data bytes, and five control bits for a total length of 37 bits. How
many slots are on the ring?
(Assume propagation speed of 2 x 10^8 m/s)
Answer:
2 x 10^3/2x10^8 + 100/10^7=10000000000(or 10^-6) 100 x 10^-6 x 10^7 = 1000 bits / 37 =
27.03 = 27 slots
29.73 slots
Question 2
Assume a LAN with a Bus topology in which each station is given permission to send a fixed-
size frame. However, other stations are not allowed to send data until this frame reaches the
destination. Using the following information, calculate the efficiency.
Medium length = 5000 m
Capacity = 100 Mbps
Propagation speed = 200,000,000 m/s
Frame length = 500 bits
Answer: 16.7%
Question 3
Calculate the theoretical efficiency of a typical CSMA/CD network using the following
information:
Medium length = 10,000 m
Capacity = 10 Mbps
Propagation speed = 200,000,000 m/s
Frame length = 256 bits

2. Answer:
10 x 10^6/2x10^8 (10x10^3) = 500 500/256 =
1.9531 1/1+3.4(1.95) = 0.131 or 13.1%
Question 4
Calculate the efficiency of a Token Ring network using the following information:
Medium length = 5,000 m
Number of stations = 50
Capacity = 16 Mbps
Propagation speed = 200,000,000 m/s
Frame length = 4,000 bits
Assume that each station has data to send. When a station receives a token holds the token and
sends its data. After sending one frame, the station releases the token so that the next station can
have the opportunity to send.
Answer:
16x10^6/2x10^8 (5x10^3)= 400 400/4000=.1
1/1+a/n = 1/1+0.1/50 = 0.99800 or 99.98%
Question 5
In a Token Ring Network, a Token is released when………………………
A frame arrives at a station
A frame arrives at its originating station
A frame arrives at its destination station
A station becomes the responsible station
Question 6
List four application areas for wireless LANs.
Answer for blank # 1: LAN Extension
Answer for blank # 2: Cross-Building Interconnect

3. Answer for blank # 3: Nomadic Access
Answer for blank # 4: Ad Hoc Networking
Question 7
Wireless LANs are generally categorized according to the transmission technique that is used .
All current wireless LAN products fall into one of the following categories:
Answer for blank # 1: Infared (IR) LANs
Answer for blank # 2: Spread Spectrum LANs
Answer for blank # 3: Narrowband Microwave
Question 8
There are three ways to incorporate ATM technology in a LAN architecture: (Name two).
Answer for blank # 1: Pure ATM Architecture, Mixed Architecture
Answer for blank # 2: Legacy ATM LAN, Pure, Legacy
Question 9
In a …………….ATM LAN, all stations are connected to the ATM switch.
Pure
Legacy
Mixed Architecture
any of the above

4. Question 10
In a mixed architecture ATM LAN, a converter lies between the ATM switch and……………….
a station
a traditional LAN
a server
any of the above
Question 11
The probability that a station on a LAN using CSMA/CD successfully finds a time slot with no
collision is…………………
0.99
0.50
0.36
0.25
If the length of the medium in an Ethernet LAN is 5000 bits and the value of the
“a” parameter is 2, then the length of the frame is ……………………bits.
1000
2500
5000
10000

5. What is the value of "a" parameter for an Ethernet LAN that has a theoretical
efficiency of 59%.
0.123
0.204
0.459
0.461