COMP247 Data Communications Assignment 2, 2016 Due: Tuesday 31st May, 2016, 6 pm Marks: 60 Value: 15% This assignment is designed to help you develop skills and strengthen your understanding of data communications. Answer the questions as if they are a professional presentation to a client. Thus justify what you say in terms of what will work well for the client. Your submission should be around 5 to 10 pages, but be succinct. Your assignment will be submitted electronically as below with TurnItIn on the COMP247 iLearn page. Before doing assignment 2, please read the Assignment 1 Comments and the following Assignment Typography document in 14 Assignment Specifications on the COMP247 iLearn page. You will lose marks if these guidelines are not followed – or to put it more positively, these guidelines are to help you get the best marks. Question 1 (20 marks) – Physical Layer Part A We presented four impairments to physical transmission of signals – attenuation, noise, attenuation distortion, and delay distortion. How will these affect the guided media of copper wires and optical fibre cable, and wireless media? Suggest some techniques that are used at the physical layer to counteract these effects (that is ignore techniques like error detection and correction used at higher layers). Part B Consider again the above three media, but in this case how does security affect these media and again what physical measures can be taken to secure these media. Question 2 (20 marks) – Wireless LAN Boojum Enterprises intends letting their workers bring their own device (BYOD) to work, so that workers can use a device that they are personally comfortable with. The office measures 50 metres by 20 metres. It is already serviced by a 1000Base-T Ethernet LAN. What would you recommend for a wireless LAN installation? What 2016 802.11 technology would you recommend? How many access points are required and how would they be positioned for the particular version of 802.11 you have chosen? Question 3 (10 marks) – Backbone Networks A backbone network can be constructed as a switched backbone, a routed backbone or a VLAN backbone. Each of these approaches has its advantages and disadvantages. a) (6 marks) Discuss the advantages and disadvantages of each approach. [Up to 400 words] b) (2 marks) Describe an example of a situation where a switched backbone would be preferred. [Up to 150 words] c) (2 marks) Describe an example of a situation where a VLAN backbone would be preferred. [Up to 150 words] Question 4 (10 marks) – Data Link Layer a) (2 marks) Senders and receivers have agreed to use even parity. Acting as a sender, add a parity bit to the following bit sequences. 010 01100 011010 01100100 b) (2 marks) Senders and receivers have agreed to use odd parity. Are the following received bit sequences correct? 1001 010101 0110110 011101101 c) (3 marks) An ASCII transmission scheme uses DLE STX control characters to start a frame and DLE ETX to end a frame. Using character stuffing (hint: only DLE needs to be escaped), what are the ASCII sequences to transmit the following data streams? ABCD AB DLE STX CD ABC ETX DLE D ETX d) (3 marks) A bit-oriented protocol uses the flag bits 01111110 to start and end the frame. What will be the transmitted frames for the following streams of bits? 01010111000 01111110 00001110111110000111111111111110000 Assessment For all questions in this assignment not only content but also presentation will affect your mark. You will lose marks 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 correct, clear, and coherent. The standards of marking described in the unit outline L.O. 1 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 more 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. Submission Submit on the iLearn page under 'Assignments Section'. The submission is with a tool called TurnItIn. This cross checks for online papers and other student papers for any plagiarism (copying). In short – DON'T COPY – or get others to do your assignment, we are pretty good at catching people out and the consequences can be severe. Do not trust anyone who will take money to do assignments. They can take money from several students, return the same assignment, and you get caught. They don't care about you, but we do! Please do not include text of questions – TurnItIn reports this as copied text.