CSCI 278:   Computer Networks         Midterm Exam                    Fall 2002

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Question 1: (6 points) Standard Organizations

List two of the most important international standards organizations and discuss the relationships between them.

 

 

 

 

 

 

 

Question 2:  (6  points) OSI model

Discuss the following terms: Layer services, service access points, service users, service providers.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question 3:  (3 points) OSI model

What is peer-to-peer Virtual communication? Why is it called “virtual”?

 

 

 

 

 

 

 

Question 4:  (3 points) OSI model

What is Nth layer protocol?

 

 

Question 5:  (14 points) OSI vs TCP/IP

Point out the differences between OSI model and TCP/IP model in terms of:

a) Number of layers 

b) Equivalent layers between the 2 models—draw a diagram

c) Reasons why TCP/IP model dominates

d) OSI model is still important. Why?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question 6:  (8 points) A New Digital Carrier

X1 carrier(a new digital carrier that you are designing) is designed to carry 48 channels(46 voice channels plus one signaling channel and one synchronization channel). Each sample of a voice will be represented with 8 bits and the voice bandwidth is limited to 4Khz. What is the total data rate of your digital carrier system including the overheads? Show your calculations

 

 

 

 

 

 

 

 

Question 7:  (10 points) LAN Protocol Architecture

Show in a diagram the LAN protocol architecture: its sublayers, names for the sublayers. Also include the following and clearly mark them in the diagram: IEEE 802.3, CSMA/CD, IEEE 802.5, Token Ring

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question 8:  (10 points) LAN Evolution

Local Area Networks have been evolving through 3 generations(4th in sight) so far. Describe each generation: Their speeds, MAC protocols, Standards(IEEE xxx.x). Also discuss the usage of switches as interim solutions between generations.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question 9:  (6 points) Ethernet's Dominance

State the main reasons why Ethernet dominates in LAN technologies throughout all the generations of LANs.

 

 

 

 

 

 

 

 

Question 10:  (8 points) Data Encoding

Describe the following encoding schemes:

a)      Manchester code

 

 

 

 

 

 

b)      4B/5B code

 

 

 

 

 

 

Question 11:  (8 points) Bridges

Describe the problem of bridged networks called “Closed loop problem” and how the problem is solved.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question 12:  (10 points)Connection-Oriented Service

What are the functions of a protocol layer(list of things that a layer should achieve) to provide a connection-oriented service to its upper layer?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question 13: (8 points) Classful Internet Addressing

a)      What is “Classful Internet Addressing”?

 

 

 

 

 

 

 

 

b)      What are the disadvantages of it?