sit202-a4-solutions

sit202-a4-solutions - Solutions Task 1: Wireless networks...

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Solutions Task 1: Wireless networks (2+2+1 = 5 marks) 1. What does it mean for a wireless network to be operating in “infrastructure mode”? If the network is not in infrastructure mode, what mode of operation is it in, and what is the difference between that mode of operation and infrastructure mode? A wireless BSS operating in infrastructure mode implies that the hosts in the BSS are associated with a base station. This base station could be a Cell Tower in a cellular network and an AP (access point) in a 802.11 LAN. It is a task for the base station to coordinating the transmission of its associated hosts and relay frames to the appropriate network(s). The other type of mode is Ad-Hoc where the wireless hosts have no infrastructure (such as DHCP and routing) to make use of. Therefore it is up to the hosts to provide the desired services in order to communicate accordingly. In contrast infrastructure mode allows access to other network infrastructure through a base station and to other wireless clients in the BSS indirectly . The base station is similar to a switch in an Ethernet network. Where as Ad-Hoc is a peer-to-peer topology where hosts communicate directly. 2. What are the differences between the following types of wireless channel impairments: path loss, multipath propagation, interference from other sources? Pass loss refers to the fact that electromagnetic radiation attenuates as it passes through matter. Thus as the distance between the hosts increases, the signal strength in turn will decrease. Where as, multipath propagation refers to the bluring of signals in the electromagnetic wave as it reflects of objects causing it to take paths of different lengths between the peers. And interference from other sources occurs when radio sources transmitting in the same frequency band interfere with each other. This can also be caused by electromagnetic noise within the environment such as microwaves, motors etc. 3. Describe the role of the beacon frames in 802.11 The role of beacon frames in 802.11 is to advertise the AP to nearby stations. These beacons contain the SSID and MAC of the access point to the user can determine if it’s the appropriate AP to connect to. The station will scan through the available channels (varies depending on chipsets) to identify all the AP’s available for association. Note: the user can also make their decision based on the strength of the received signal also.
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Task 2: Communication security (1+ (2+1)3+(1+1)2+2 = 8 marks) 1. List and briefly describe the desirable properties of secure communication. Confidentiality – Only the 2 hosts who are communicating should be able to understand
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sit202-a4-solutions - Solutions Task 1: Wireless networks...

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