Homework4Answers - CNT4704 (Fall 2010) Homework 4 Solution...

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CNT4704 (Fall 2010) Homework 4 Solution 1. (10 points) a). Ethernet MAC protocol is CSMA/CD – Carrier Sense Multiple Access with Collision Detection 802.11 wireless LAN is CSMA/CA – Carrier Sense Multiple Access with Collision Avoidance b). Ethernet efficiency is much higher than ALOHA because: 1> Ethernet protocol provides “listen before transmit”, which makes a node to delay transmission if the channel is using by others. This can avoid destroying the current transmission. 2> Ethernet protocol can stop transmission once it detects collision, while slotted ALOHA does not stop upon collision. Thus Ethernet can quickly recover from a collision. 3> Ethernet uses an “exponentially back-off” mechanism in determining the time to retransmit, which can adjust the transmission speed according to the congestion situation. Slotted ALOHA always back-off with the same probability no matter how congested the network is. c). Hub connects all LAN segments into one large Ethernet collision domain; Switch isolates LAN segments. In addition, Hub does not store packet while Switch does; Hub is a physical signal repeater, switch is a device processing data-link layer. 2.
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Homework4Answers - CNT4704 (Fall 2010) Homework 4 Solution...

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