FinalExamSolution - CNT 4704: Network Analysis Final Exam...

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CNT 4704: Network Analysis Final Exam Solution Prof. Cliff Zou Dec. 07, 2010 Question 1: Knowledge questions (25points) Answer each of the following questions briefly. a). What is the size of TCP header? UDP header? IP header? TCP: 20 bytes UDP: 8 bytes IP: 20 bytes b). What is the order of efficiency of the following three MAC protocols: pure ALOHA, slotted ALOHA, CSMA/CD? What assumptions do they have, respectively? Ordered Most-to-Least Efficient CSMA/CD slotted ALOHA pure ALOHA Assumptions CSMA/CD Only send when channel is idle (carrier sense) Collision can be detected within a short time (collision detection) colliding transmissions are aborted, reducing channel waste Exponential back-off algorithm makes the MAC protocol intelligent Slotted ALOHA all frames have the same size time is divided into equal size slots (the time to transmit 1 frame) nodes start to transmit frames only at beginning of slots nodes are synchronized if 2 or more nodes transmit in slot, all nodes detect collision pure ALOHA all frames have the same size no synchronization between nodes a node can detect collision only after it transmits c). What is the full names of CSMA/CA and CSMA/CD? Why wireless LAN uses CSMA/CA instead of CSMA/CD?
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CSMA/CA: Carrier Sense Multiple Access/Collision Avoidance CSMA/CD: Carrier Sense Multiple Access/Collision Detection Wireless LAN doesn’t use collision detection because collisions are difficult to detect in wireless environment. It is due to two reasons: First, fading of signal quality and strength as well as the issue of having a hidden terminal, Second, a node cannot sense a channel for collision detection when it is transmitting at the same time. d). What is the full names of RIP, OSPF, BGP? In the two-level Internet routing, which level are they used on, respectively? Routing Information Protocol (RIP) : intra-AS routing Open Shortest Path First (OSPF): intra-AS routing Border Gateway Protocol (BGP): inter-AS routing e). What is public/symmetric key cryptography? The advantage and disadvantage of each? Public cryptography
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This note was uploaded on 04/24/2011 for the course CNT 4704 taught by Professor Guha,r during the Fall '08 term at University of Central Florida.

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FinalExamSolution - CNT 4704: Network Analysis Final Exam...

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