CSCI 278 : COMPUTER NETWORKS

Instructor : Seung Bae Im

MIDTERM EXAM ----- Fall 2004

 

Closed book, closed notes. Write neatly.

 

Name : _____________________________

 

1.(28 points) Describe the following terms and answer the questions.

(a)    Network architecture & give example architectures

 

 

 

 

 

 

 

 

 

(b)   Show the layers of OSI and TCP/IP protocol suites.

 

 

 

 

 

 

 

 

 

 

 

 

(c)    Decibel is defined as dB = 10 log 10 S/N. Calculate in dB for S/N=100/1 and for S/N=1000/1.

 

 

 

 

 

 

 

 

(d)   State why the OSI Model is important?

 

 

 

(e)    Discuss the overlap of functions between ISO and ITU-T and also discuss how they cooperate.

 

 

 

 

 

 

 

 

 

 

(f)     Discuss the role of IEEE in the arena of network standards.

 

 

 

 

 

 

 

 

 

(g)    List the kinds of rfcs?

 

 

 

 

 

 

 

 

 

2.(6 points) State the reasons why TCP/IP protocol suite is dominant(used almost everywhere, used on  almost every machine) over all other protocols including OSI protocols.

 

 

 

 

 

 

 

 

 

 

 

 

 

3.(20 points) Describe/discuss

(a)    Bridges have “closed loop problem”. Describe the problem and state how it is solved.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(b)   Discuss how all the generations of Ethernets(different speeds) can coexist. Include the word, “autonegotiation”.

 

 

 

 

 

 

 

 

 

 

 

 

(c)    Discuss how WDM increases data rate of fiber optics.

 

 

 

 

 

 

 

 

(d)   Discuss the significance of Shannon’s Law.

 

 

 

 

 

 

 

4.(20 Points) Answer the questions.

(a)    Describe the difference between Ethernet hubs and Ethernet switches.

 

 

 

 

 

 

 

 

 

(b)   What is ISM(Industrial, Scientific, Medical) band? What is the restriction of the band?

 

 

 

 

 

 

 

 

 

 

(c)    Discuss how Full duplex Ethernet is possible using Ethernet switches.

 

 

 

 

 

 

 

 

 

(d)   In 802.11 wireless Lans, there are two problems; (a) Hidden station problem (b) Exposed station problem. Describe them.

 

 

 

 

 

 

 

 

 

 

 

 

 

5.(10 points) Show a diagram which illustrates how T-1 carrier multiplexes 24 digitized voices. Also, show the calculation to derive its data rate of 1.544 Mbps. In the calculation, clearly mark each component.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6.(16 points) Discuss/describe

(a)    Synchronization occurs in two bottom layers of OSI model. Identify them and describe them.

 

 

 

 

 

 

 

 

 

 

 

(b)   Draw the protocol diagram(showing layers and sublayers) for the LAN protocols—Show IEEE 802.2, 802.3, 802.11.  Also clearly show the Physical, MAC and LLC layers on the diagram. Also discuss why IEEE divided the Data Link layer into two sublayers.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(c)    List the 3 services a 2nd layer can offer and briefly describe each.

 

 

 

 

 

 

 

 

 

 

 

 

(d)   Describe the difference between “go-back-n ARQ” & “Selective Repeat ARQ”.