ELE00060M Page 1 of 11 MSc Degree Examinations 2020-1 Department: Electronic Engineering Title of Exam: Internet & LAN Protocols Time Allowed: 24 Hours (PLEASE NOTE: papers submitted more than 30 minutes after the deadline will not be marked) Time Recommended: TWO hours Allocation of Marks: All questions carry equal marks Instructions for Candidates: You should attempt 2 of the 3 questions. Write all of your answers by hand (unless you have a Student Support Plan which allows use of a PC) and submit your handwritten answers in a single pdf document. Use only black or blue pen for any handwritten answers. Clearly write your examination number on each page submitted. Begin each question on a new page and clearly write the question number on each page. More detailed instructions regarding submission of your work and conduct during the open exam is given on the next page. Please read this carefully before you begin, including the information regarding the conduct expected of you during the exam. Paper Queries: Please see the detailed instructions on the next page regarding exam queries. The exam setter for this exam is Dr Cuma Kanapathippillai who if necessary can be contacted by email at [email protected]. Please copy any email that you send to the Chair of Board of Examiners ([email protected]) and to [email protected]. Page 2 of 11 ELE00060M A note on Academic Integrity: We are treating this online examination as a time-limited open assessment, and you are therefore permitted to refer to written and online materials to aid you in your answers. However, you must ensure that the work you submit is entirely your own, and for the whole time the assessment is live you must not: ● communicate with departmental staff on the topic of the assessment, except for the exam setter. ● communicate with other students on the topic of this assessment. ● seek assistance with the assignment from the academic and/or disability support services, such as the Writing and Language Skills Centre, Maths Skills Centre and/or Disability Services. (The only exception to this will be for those students who have been recommended an exam support worker in a Student Support Plan. If this applies to you, you are advised to contact Disability Services as soon as possible to discuss the necessary arrangements.) ● seek advice or contribution from any third party, including proof-readers, friends, or family members. We expect, and trust, that all our students will seek to maintain the integrity of the assessment, and of their award, through ensuring that these instructions are strictly followed. Failure to adhere to these requirements will be considered a breach of the Academic Misconduct regulations, where the offences of plagiarism, breach/cheating, collusion and commissioning are relevant – see AM.1.2.1” Please make sure you note the following detailed instructions: If you do not submit by the deadline you will score a mark of zero unless you submit in the first 30 minutes after the deadline in which case your mark will be subject to a 5% late penalty. The deadline is not flexible, it may take a while for your file to be processed through the system. Make sure you submit in good time to allow for this. You must submit your answers as a single pdf file. Please check that all scanned pages are clear and visible BEFORE you submit. The Adobe Scan app is a free app that works on all phones and can be used to photograph and then connect together all the scans into a single document – ensure all your pages are in the correct order. Please make sure that every page is clearly labelled with both your examination number (NOT your name) and the question number. It would be useful if you numbered the pages. The file size limit for anonymised work submitted online is 30MB per file. Please see Compressing File Sizes (Student Guide) for details on reducing the file sizes. If your submission remains too large or if you experience genuine technical difficulties when trying to submit, then you should email your submission to elec- [email protected]. If the assessment is too large to send by email, you may use the University of York Deposit Service. If using this service as the back-up please specify [email protected] as the recipient of the drop-off. Please do not use this backup option if the VLE submission has worked properly and you have received a receipt. University policy is that corrections or clarifications to the questions in the exam paper will only be issued within the first hour of the submission window. Therefore if outside the first hour you should answer the question as best as you can and note the assumptions that you have made to allow you to proceed. All submissions may be screened for collusion and plagiarism. By submitting your assignment you agree to the University rules on Collusion and Plagiarism. The Department will run submissions through Turnitin wherever possible. For more information visit york.ac.uk/integrity You may make multiple submissions up to the assessment deadline but by default, we will mark your last submission before the deadline. IT IS YOUR RESPONSIBILITY TO MAKE SURE THAT YOUR SUBMISSION IS CORRECT. Once you have submitted your assignment via the VLE, a ‘receipt’ screen appears that has a ELE00060M Page 3 of 11 link to the submitted file, so you can click the link and check the file to make sure it is the correct one. You can also click back into the submission point and see links to the file(s) you have submitted. Page 4 of 11 ELE00060M 1 (a) [14 Marks in total] (i) Discuss two advantages and two disadvantages of computer networking. (4 marks) (ii) Discuss two advantages and two disadvantages of OSI model in computer networking as opposed to having no layers in the protocols at all. (4 marks) (iii) Describe the technologies that are used to solve the incompatibility issues between IPv4 and IPv6 addresses. (6 marks) (b) [5 Marks] The distance between two stations M and N is L kilometers. All frames are K bits long. The propagation delay per kilometer is t seconds. Let R bits/second be the channel capacity. Assuming that processing delay is negligible, derive the window size for maximum utilization, when the sliding window protocol is used. The answer should be in terms of L, K, t and R. (c) [12 Marks in total] A communication link runs from computer A to computer B through two routers R1 and R2 as shown below. The bit rates and lengths
of individual links are given. 4 Mbit/s 200 m 2 Mbit/s 1500 km 12 Mbit/s 2500 m A B R1 R2 ELE00060M Page 5 of 11 This network uses a reliable transport layer protocol with stop- and-wait error control. Assume that signal travels along the cables at a speed of 2 × 108 ms-1 and state any assumptions you make. (i) Estimate the minimum time-out period of the retransmission timer at the source node, if packets are 1500 bytes long. Assume that there is no traffic on any of the links except that between these two computers. (10 marks) (ii) Determine the minimum delay through this network in the case for packets that have to be re-transmitted once. (2 marks) (d) [7 Marks in total] To provide mobility, the link between computer A and router R1 in (c) was replaced by 4 Mbit/s wireless link, and as result the packet error rate on this link suddenly increased. (i) To reduce the minimum delay through this network for packets that have to be re-transmitted once, the wireless data-link layer is made reliable. By how much does this change the delay of packets that have to be re transmitted due to loss in this first wireless link. Provide your answer in microseconds (μs). (4 marks) (ii) What are the disadvantages of making this change to the data-link layer (3 marks) (e) [6 Marks] If the stop-and-wait flow control in (c) was replaced by sliding window flow control to increase the utilisation, what is the minimum window size that could be used to keep this connection running at its maximum capacity (f) [6 Marks in total] The link from router R2 to computer B has bit error rate pbit = 10-6. (i) Determine the packet error rate ppkt on the link. (3 marks) Page 6 of 11 ELE00060M (ii) Determine the throughput of the link R2 to computer B with a window size N when the errors are present if the link uses go-back-N-ARQ with the packet error rate calculated in part (f) (i). (3 marks) ELE00060M Page 7 of 11 2 (a) [20 Marks in total] (i) Subnetting is the procedure to divide the network into sub- networks or small networks. Discuss the three advantages and three disadvantages of subnetting. (6 marks) (ii) Discuss how IPv6 addresses are assigned to devices and hosts in the network. (5 marks) (iii) Discuss the differences between IPv4 and IPv6 addressing. (5 marks) (iv) List three features of an IPv6 header that make IPv6 header is simpler than an IPv4 header. (4 marks) (b) [10 Marks in total] Port B Port A Port C Router R31 Gbit/s Ethernet E3 (130 stations) Ethernet E4 (61 stations) To the Internet Port A Port C Port B Router R1 Ethernet E1 (58 stations) 100 Mbit/s Router R2 Port B Port A Port C Ethernet E2 (37 stations) Port D 1 Mbit/s Port A Port B Bridge B1 Page 8 of 11 ELE00060M The sub-network shown above is required to be connected to the Internet. The IPv4 address range 144.32.64.0/23 has been allocated. A web-server on Ethernet E1 should be assigned the IP address 144.32.64.1. (i) Suggest a suitable assignment of IP addresses to the four Ethernet segments. (8 marks) (ii) How would you assign addresses to the links between the routers (2 marks) (c) [9 Marks] Describe a possible routeing table for router R3, in the form: giving the links appropriate cost functions. Justify the cost you choose. (d) [7 Marks in total] (i) The network manager is considering an upgrade to IPv6. What are the main advantages of using IPv6 over IPv4 (4 marks) (ii) In particular, how would the process of assigning IP addresses to computers change in IPv6 What are the benefits of using this new approach (3 marks) Subnet mask Cost Port X.X.X.X/Y Z P1 X.X.X.X/Y Z P1 … … … ELE00060M Page 9 of 11 (e) [5 Marks in total] Two subnetworks A and B are connected to a router R1 as shown below. The IPv4 address range 152.72.45.0/24 has been allocated. (i) Describe a possible routeing table for router R1 in the form: (3 marks) (ii) Router R1 receives a packet with an IP address 152.72.45.12 from the Internet and the IP address matches with two entries in the routeing table in part e (i). Explain how the router determines which port to send this packet. (2 marks) Router R1 Subnet A (28 stations) Subnet B (220 stations) To the Internet Port 1 Port 2 Port 3 IP Addresses Send Packet to: Send Packet from: Page 10 of 11 ELE00060M 3 (a) [18 Marks in total] (i) Discuss five features of Enhanced Interior Gateway Routing Protocol (EIGRP). (5 marks) (ii) Why is IPv4 fragmentation required How is fragmentation done in IPv4 (4 marks) (iii) List the three key differences between each of the following pair of terms. (9 marks) a. DNS and ARP b. IPV4 address and MAC address c. Internet checksum and Cyclic Redundancy Check (CRC) (b) [11 Marks in total] (i) When routers generate ICMP messages, to where do they send them Along with the ICMP header at the beginning, what additional contextual information do routers include in the messages (4 marks) (ii) Name two circumstances under which an end-host (not a router) will send an ICMP message. (3 marks) (iii) Briefly describe how the “traceroute” tool works (i.e., what does it do in order to identify the routers that make up an Ineternet path). (4 marks) (c) [10 Marks in total] (i) Discuss five differences between “Distance vector” routeing protocol and “link-state” routeing protocol. (5 marks) (ii) Name two problems that would arise if all routeing in the Internet was done using link-state routeing protocol and Dijkstra’s algorithm. Does Distance vector routing suffer from these How about path-vector (5 marks) ELE00060M Page 11 of 11 (d) [11 Marks in total] (i) Briefly describe how Ethernet’s exponential backoff works. What is one reason why Ethernet’s exponential backoff might be better than randomizing retransmission attempts over a fixed-length time interval (4 marks) (ii) A 2 km long broadcast LAN has a capacity of 107 bps and uses CSMA/CD. The signal travels along the wire at 2×108 ms-1. What is the minimum packet size that can be used on this network (4 marks) (iii) The message 11001001 is protected by a cyclic-reduncancy check (CRC) with a polynomial x3 + 1. Determine the CRC that need to be appended at the end of the message. (3 marks) End of Paper