assn4.odt - Nova Southeastern University College of...

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Nova Southeastern University College of Engineering and Computing Assignment 4 CISC650 Computer Networks Winter 2017 Due Date: 4/16/2017 11:59 PM EST Total Points: 100 Part 1. Text reading Chapter 7, Chapter 8, Chapter 9 Part 2. Textbook questions Chapter 7 [25 points] 7.1 What are the services that can be provided using IEEE 802.11? The 802.11 standard defines services that provide the functions that the LLC layer requires for sending MAC Service Data Units (MSDUs) between two entities on the network . These services, which the MAC layer implements, fall into two categories: Station Services These include Authentication, Deauthentication, Privacy, and MSDU delivery. Distribution System Services These include Association, Disassociation, Distribution, Integration, and Reassociation. 9.1 What are the differences between the infrastructure mode and the ad-hoc mode in wireless networks? Infrastructure mode requires a central access point that all devices connect to. Ad - hoc mode is also known as “peer-to-peer” mode . Ad - hoc networks don't require a centralized access point. Instead, devices on the wireless network connect directly to each other. 9.2 Why are acknowledgments used in 802.11 but not in a wired Ethernet? Acknowledgments are used in an 802.11 network due to the high rate of errors in wireless networks due to signal loss, signal to noise ratio, fading, collisions, multi-path propagation and interference. If there were no acknowledgements sent back to the sender the sender would have no way of knowing that the receiver received the data intact and without error. 9.3 Suppose the IEEE 802.11 RTS and CTS frames were as long as the standard DATA and ACK frames. Would there be any advantages to using the CTS and RTS frames? Why or why not? RTS/CTS (Request to Send / Clear to Send) is the optional mechanism used by the802.11 wireless networking protocol to reduce frame collisions introduced by the"hidden node problem". Originally the protocol fixed the exposed node problem aswell, but modern RTS/CTS includes ACKs and does not solve the exposed nodeproblem. There is no advantage, RTS/CTS is an additional method to implementvirtual carrier sensing in Carrier
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sense multiple access with collision avoidance(CSMA/CA). By default, 802.11 relies on physical carrier sensing only which isknown to suffer from the hidden node problem.
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