• October 3rd, 2018

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ITEC851 Mobile Data Networks Assignment 1 Due: Friday (Week 8) – 5 th of October, 2018, 6 pm (Via Turnitin). Total Marks: 60 Weighting (Value): 15% Submission · On line submission via Turnitin. Assignments will normally be marked and returned online. There are no hardcopy submissions for written assignments. Ensure you submit the correct file. The submission process shows you a complete preview of your entire assignment after you have uploaded it but before you have submitted it. Carefully check through every single page to ensure everything is there and the correct version has been uploaded, and only then press CONFIRM. Multiple submissions may be possible via Turnitin prior to the final due date and time of an assessment task and originality reports may be made available to students to view and and check their levels of similarity prior to making a final submission. Students are encouraged to use these reports to ensure that they do not breach the Academic Honesty Policy through high levels of similarity (plagiarism). Teaching staff will use the report to judge whether plagiarism has occurred and whether penalties should apply for breaches of the Academic Honesty Policy. Any similar text identified by Turnitin will be considered carefully to see if it is indeed a breach of the Academic Honesty Policy. Objectives This assignment has been designed to test the following areas: · Medium Access Control · Wireless LAN · Mobile IP Note · Answers must be within the specified word limit. This is an absolute word limit and no excess will be allowed. · Assumptions (if any) must be stated clearly in your answers. Remember, there may not be one right answer for some of the questions. Rather, your explanations do need to present your case clearly. The explanations you provide do not have to be long, concise is preferred to meandering Assessment For all questions in this assignment not only content but also presentation will affect your mark. You will lose marks (and not necessarily only a small portion) if there are problems with the presentation, particularly with clarity. This means that your answers to each question should be a coherent statement and that the spelling and grammar of your submission will be taken into account in assessing its presentation. For full marks, your answers should all be clear, coherent and correct. The standards of marking described in the unit outline L.O. 1-6 will be applied to this assignment as relevant to the assignment topics. In addition, the following particular standards will be applied in marking this assignment: · Spelling and grammar: o Assignment submissions with more than 4 spelling or grammatical errors will not achieve a grade higher than distinction; submissions with mo than 8 such errors will not achieve a grade higher than credit. · Clarity: o Ambiguous or poorly worded answers will receive a grade no more than a pass for the individual question. o Minor issues of clarity will receive a grade no more than credit for the individual question. · Correctness of approach taken and answer obtained: o Incorrect answers with the correct logic or approach will receive no more than a pass for the individual question. o Correct answers with incorrect logic or approach will receive no more than pass for the individual question. o Incorrect answers with no explanation of the approach taken or with the incorrect approach will receive a fail grade for the individual question. The questions will be marked individually, the marks totalled, and a final grade assigned that is no more than indicated by the total marks, and no more than allowed by the standards specified above and in the unit outline. 1. [12 marks] Consider a CDMA system in which there are 4 stations with the following chip sequences assigned to them: · A: (-1 -1 -1 +1 +1 -1 +1 +1) · B: (-1 -1 +1 -1 +1 +1 +1 -1) · C: (-1 +1 -1 +1 +1 +1 -1 -1) · D: (-1 +1 -1 -1 -1 -1 +1 -1) a. (4 marks) A receiver receives the following chip sequence (-1 +1 -3 +1 -1 -3 +1 +1). Using this chip sequence determine the stations that have sent out any data and the actual bits that were transmitted. b. (4 marks) Assume that there is some noise in the environment and that (4 marks) A receiver receives the following chip sequence (-1 +1 -3 +1 -1 -3 +1 +1). Using this chip sequence determine the stations that have sent out any data and the actual bits that were transmitted. b. (4 marks) Assume that there is some noise in the environment and that the noise adds to the signal as a transmission of additional station. This noise can be represented as (-1 -1 +1 +1 -1 +1 +1 +1). Does this impact the above communication pattern of part (a) in any way? c. (4 marks) How does the above situation change if there is no power control in the system? This implies that stations can send information at different power levels. 2. [10 marks] The IEEE 802.11’s exponential back-off scheme is considered to be unfair. Explain Why. Explain how MACAW solves this unfairness problem? Do the techniques suggested by MACAW work well under any network condition? Explain why or why not. (400 words) 3. [10 marks] MACA-BI performs better than the four-way handshake of the IEEE 802.11 when traffic characteristics are known or predictable. However, this protocol is not known to perform well under dynamic network conditions wherein the traffic is unforeseen. Explain why. Suggest a simple change/s to this protocol to rectify this problem. (200 Words) 4. [8 marks] In a scenario that uses distance vector routing, routing updates that reflect changes in the network are exchanged only between the neighbouring routers. What pitfalls do we encounter when we use this routing strategy to propagate updates about a node that is mobile and which frequently changes its location? (300 Words) 5. [8 marks] Assume that a Correspondent Node (CN) is sending packets to a Mobile Host (MH) currently located in a Foreign Network X (under the jurisdiction of Foreign Agent FAX). Further assume that the CN itself is mobile and has initiated this communication session with the MH upon moving to a Foreign Network Y (under the jurisdiction of Foreign Agent FAY). Outline the steps involved in routing packets between the CN and the MH. Outline the steps if reverse tunnelling is allowed. Illustrate these scenarios with the help of diagrams. (350 words) 6. [12 marks] An organization has deployed a campus network using cellular IP. The cellular IP network extends the wired infrastructure of the campus as shown in provides layer 3 functionality (in other words, they act as IP forwarding engines). The campus network supports multicast routing. All the components in the wireless part strictly adhere to cellular IP standard. Assume that this campus network deploys Source Based Multicast Routing scheme – a protocol that builds source based multicast distribution trees (Refer to Appendix for a brief explanation on Source Based Multicast Routing). A visiting mobile node MN enters the wireless network and initially gets registered to its home network via BS1-G1 and acquires a Care of Address (CoA – an address from the campus network address space). The CoA assigned to the MN remains unchanged irrespective of MN’s movements within the campus network. In other words, MN does not need to acquire a new CoA upon moving to a wireless segment under the same or under a different gateway. While initially at BS1, the MN joins a multicast group G whose scope is local to this campus network (all sources, and members reside in the campus network). Assume that hosts H1, H3, H5, and H7 are members of this group with H1 and H7 also acting as Multicast sources. Furthermore, assume that MN itself is a source for multicast traffic. In this scenario, explain what problems can arise in multicast communication due to MN’s mobility. (300 Words) Appendix Source Based Multicast Routing Consider a single sender. In source based multicast Routing, the routing process builds shortest path trees rooted at the sender. The router delivers packets to each receiver along the shortest path. In a nutshell, it builds a shortest path spanning tree routed at source to all intended destinations. Source Based Multicast Routing (SBMR) The SBMR techniques implement the Reverse Path Multicast (RPM) algorithm. The RPM constructs an implicit spanning tree for each source. l It accepts a packet from a source S, on link L, if S. (Reverse Path Check) l Uses unicast routing table which contains shortest paths to each node in the network. In this technique, the first packet flooded across the internetwork. The packet scope is restricted by a TTL value. Due to flooding, all routers in the network get a copy of the packet. Routers not having any downstream router in multicast tree are called leaf routers. If a leaf router has no group members on its sub-networks, a Prune message is sent upstream to parent router (one hop up). The prune state is maintained in every router. This process is repeated every hop upwards. These cascaded prune messages create/truncate the original RPM tree. Prune information only held for a certain lifetime (soft state). A Graft message is sent to quickly recover back a previous pruned branch. It cancels out the previously received prune message. Graft cascades reliably hop by hop toward the source. Due to this graft and prune feature, messages are forwarded on only those links leading to a group member.

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