CSCI 278 : COMPUTER NETWORKS Instructor : Seung Bae Im MIDTERM EXAM ----- March 1994 Closed book, closed notes. Print your name on each page of the answer sheets. Do not write on the back of a page. State all assumptions, if necessary. Show all your work. Majority of the questions require Brief answers! 1.(8 points) Discuss the main advantages and disadvantages of digital communication compared to analog communication. Note: Explain each briefly. Simple listing will not get much points. 2.(6 points) Define: Virtual communication, Layer interface 3.(5 points) What are the main purposes of LANs? 4.(38 Points) Answer the questions regarding transmission media. ( C = H log2( 1 + S/N ) ) (a) What is Delay Distortion? What do you do to reduce it? (b) The European version of T1 carrier is called E1 which has 2.048MBPS data rate. Now, we like to carry an E1 on a transmission line. Assuming 30 dB signal-to- noise ratio(for the line), calculate the required bandwidth of the line. (c) Discuss the trade-offs(Advantages/Disadvantages) between "Baseband signaling" and "Broadband signaling". (d) Major Advantages of coaxial cables over twisted pairs. (e) Twisted pair cabling is probably the most widely used cabling for LANs. Why do we twist the cables? (f) Discuss the advantages of fiber optic cables compared to Electromagnetic media(Twisted pair, coaxial cable, microwave, ...) 5.(4 points) MAP(Manufacturing Automation Protocols) chose 802.4(Token Bus) as its LAN protocol. Why did they choose it instead of token-ring or Ethernet? 6.(20 points) (a) Describe the differences between 10Base5, 10Base2 and 10BaseT. (b) Describe the function of ÒEthernet 10BaseT HubÓ. What are the advantages of the hub compared to 10Base5 or 10Base2? 7.(6 points) Compare the performances of CSMA/CD and Token-passing protocols(Token Ring and Token Bus) for the cases of "light load" and "heavy load". 8.(6 points) What are the trade-offs between connection-oriented service and connectionless service? 9.(7 points) Compare/contrast the 3 ARQ schemes(Stop-and-wait, Go-back-N, Selective-Repeat) in terms of efficiency, buffer requirements, complexity.