- B Dijkstra S Algorithm Is An Example Of A Link State Routing Algorithm In Practice Many Of The Common Routing Protoc 1 (70.48 KiB) Viewed 54 times
2. Two engineering students are developing an instant messaging app. In order to protect the content of any messages sent they are implementing a simple encryption system. (a) In the initial iteration of their design, the students generate the ciphertext message "IOCCH VHMCW” using a Caesar-style substitution cipher with the keyword “networking”. Write down the plain and cipher alphabets using lowercase for the plaintext and UPPERCASE for the ciphertext, and then decrypt the message. [2] (b) Having discussed their work with a colleague, the students decide that the Caesar- style cipher they've implemented will be too easy to break. They next try a solution based on the symmetric key encryption in WEP. Using the keystream 01101010, generate the WEP ciphertext for the data stream 10001101. You may assume this data stream already includes the CRC. [2] (c) It is not practical to manage the symmetric key within the instant messaging app, so instead a public/private key solution is implemented (RSA). Encrypt the message m (where m="BIRMINGHAM”) with the RSA algorithm using p=5, q=13 and e=11. You may assume a simple character encoding beginning with “A”=1 and leave your encrypted message in numerical form. Indicating where you would insert your encrypted value, c, also write down the decryption formula that would be used to recover m. [6]
3. A multiplexer is used to connect sensor nodes to a single external networking link as part of an industrial sensor network. The multiplexer has an arrival rate (a) of 1500 packets per second, and a service rate (u) of 3000 packets per second. (a) What is the load (p) on the multiplexer? [2] (b) If the maximum number of packets in the system (k) is 3, and the multiplexer can be modelled using an M/M/1/k queuing model, what is the probability of packet loss in the network? [3] (C) If the average number of packets in the multiplexer is given by: р (k + 1)pk+1 E[N] = 1 - pk+1 What is the average packet delay on the network? 1-P [5]
4. An engineer has been asked to review network provision within a small company that is currently planning an expansion, and to make suggestions for restructuring of the address space to support additional users. (a) A group of network users share a 6Mbps network link. Each user requires 125kbps when transmitting, but only transmits for 10% of the time. If the network is circuit-switched, how many users can be supported? (b) Due to planned growth in staff numbers, the engineer wants to update the network to use packet-switching. Assume there are now 70 possible users at any one time. With reference to your answer to part (a) describe how the performance of the packet switched network compares to that of the circuit switched network, and how it is possible for all 70 users to user the packet- switched network. (c) ) Subnet masks allow an organisation to manage its address space more easily by dividing it into subnets. Explain how subnet masks allow routers to forward packets to the correct network within an organisation. Demonstrate the process by deriving an appropriate binary subnet mask for an organisation with a number of networks, each containing less than 100 hosts. Combine the mask with the (binary form) IP address shown below and state the subnet number in dotted decimal notation. 10010110011001000000110010110000