CSCI 278 : COMPUTER NETWORKS Instructor : Seung Bae Im MIDTERM EXAM ----- Fall 1997 Closed book, closed notes. Print your name on each page of the answer sheets. Do not write on the back of a page(they will not be graded). State all assumptions. Majority of the questions require Brief answers(But the answers should not be a simple list from memory. You should describe them briefly). Use time efficiently!!!. 1.(10 points) List standardization organizations with brief description(as many you know which are related to networking--distinguish between national/regional/international organizations). 2.(20 points) Define/describe the following terms: (a) Nth Layer Protocol (b) OSI 7 layer model--what is it? Not the list of layers (c) Data Encapsulation /decapsulation (d) Peer-to-peer Òvirtual communicationÓ (e) Main difference between 100BaseT and 100BaseVGAnyLan 3.(10 points) (a) Digital communication systems achieve Òhiger S/N(Signal to Noise ratio) than analog systems. Explain how? (b) List the advantages of fiber optics compared to electromagnetic medium (twisted pair, Coaxial cables, ...) 4.(8 points) (a) Difference between BPS and Baud. (b) What is ShannonÕs Capacity? Why canÕt we achieve ShannonÕs capacity in practical systems? ( C = H log2( 1 + S/N ) ) 5.(10 Points) Answer the questions. (a) Why do we twist wires(UTP/STP)? (b) The European version of T1 carrier is called E1. E1 uses 8 bits per sample, 4Khz bandwidth for each voice signal. It multiplexes 30 voice channels and use 2 extra channels for signaling and synchronization. (1) Calculate the total rate(bps) of E1. (2) Now, we like to carry an E1 on a transmission line. If you are given a line with 10MHz bandwidth, calculate the S/N(Signal to Noise ratio) in decibel. Exact value is not needed. 6.(10 points) (a) Compare CSMA/CD and Token Ring in terms of utilization. (b) The current trend in networking is going from Òshared mediaÓ to Òswitched mediaÓ. Discuss the difference. 7.(32 points) Discuss/describe briefly (a) IEEE 802 Project (b) CRC error checking scheme (c) Difference between Connectionless service and connection-oriented service (d) Advantages and disadvantages of the above two services (e) State why Ethernets can not provide services for Òisochronous(time-sensitive)Ó traffic? (f) ÒCharacter stuffingÓ and ÒBit stuffingÓ