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03_final_3 - We studied a reanber of multiple access...

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Unformatted text preview: We studied a reanber of multiple access protocols in this course, including (1') TDMA, (2) CSMA, (3) Slotted Aloha and (4) Token passing. 6 points each. 0 Suppose you were charged with putting together a LAN to support IP telephony {only} and that multiple users may want to carry on a phone call at the same time. Recall that IP telephony digitites and packetites voice ata constant bit rate when a user is making an LP phone call. How well suited are these four protocols for this scenario?r Provide a brief {e.g. one sentence) explanation of each answer. TDMA: works well here since it provides a constant bit rate service of 1 slot per frame CSMA: will NOT work well here due to collisions and variable amount of time to access the channel. Channel access delays can be unbounded Slotted Aloha: same answer as CSL'LA Token passing: works well here since each station gets a turn to transmit once per token round, yielding an essentially constant bit rate service. I» Now signpost: you were charged with putting together a LAN to strip-port the occasional exchange of data between nodes. That is, any individual node does not have data to send very often. How well suited are these four protocols for this scenario? Provide a brief fag. one sentence) explanation of each answer. TDMA: TDMA would not work well here as if there is only one station with something to send, it can only send once per frame. Hence the access delays are long, and the throughput over a long period of time is only UN of the channel capacity. CSMA: This would work well since at low utilization, a node will get to use the channel as soon as it need to. Slotted Aloha: same answer as CSL'LA Token passing: This would work better than TDMA but slightly less well than CSMA and Slotted Aloha, since it must wait for the token to be passed to the other stations {who likely wouldn’t use it) before sending again. It Now signpose the LAN must signport both voice and data and you must choose one of these multiple access strategies in order to support both applications on the same network, with the understanding that voice calls are more important than data. Which would you choose and why? How would voice and data he sent in this scenario? That is, which access protocol would you use, or adapt’modijf'jr, and who}? Here are two possible answers: Assign some number of TDMA slots for voice calls {e.g., one slot to each user). Also add some additional slots and allow the stations with data to send to perform random access (e.g., slotted aloha or CSMA) within those slots only. Alternatively, use token passing with priorities and give priority to voice packets. Question 4: Secure and authenticated message transfer (21 points, 23 minutes) ...
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