# ECE486 Test.pdf

29 de Jun de 2022
1 de 3

### ECE486 Test.pdf

• 1. ECE 486/586: Computer Networks Fall 2021 9 Problems, 11 pts each, you get 1 pt for free. 1. If a binary signal is transmitted through a 32kHz noiseless channel, what is the maximum data rate? If the SNR of the channel is 30dB, what is the maximum data rate? 2. Consider building a CSMA/CD network running at 1 Gbps over a 1-km cable with no repeaters. The signal speed in the cable is 200,000 km/sec. What is the minimum frame size? 3. Consider the subnet in the following. Distance vector routing is used, and the following vectors have just come in to router C: from B: (5, 0, 8, 12, 6, 2); from D: (16, 12, 6, 0, 9, 10); and from E: (7, 6, 3, 9, 0, 4). The measured delays to B, D, and E, are 6, 3, and 5, respectively. B C A E F D 2 8 Figure 1. Illustration of the original subnet topology. (a) What is C’s original routing table? Give both the outgoing line (next-hop table) to use and the expected delay. (b) What is C’s new routing table? 4. According to Fig. 1, determine the routing table for node F using Dijkistra algorithm. Show the steps.
• 2. 5. In Transport Layer, symmetric connection release can be achieved by using a three- way handshake, as shown in Fig. 2. Figure 2. Three-way handshake protocol for connection release. (a) Assuming a timer is NOT applied in the protocol, explain the two-army problem in this protocol. (b) Assuming a timer is used in the protocol, explain how the connection is released if the ACK in the third handshake is lost. 6. In Fig. 3, the maximum flow between two adjacent routers are set as 1. Router 1 Router 2 Router 3 Router 4 Router 5 Router 6 A B C A B C Figure 3. Flow control. (a) Determine flow control using Max-Min fairness. (b) Explain why your flow control is optimal. (Note: you need to illustrate 3 possible scenarios, which are increasing the flow for A/B/C respectively.) 7. Congestion prevention policies applied to Data Link layer and Transport layer are similar. (a) List the congestion prevention policies in Data Link layer and Transport layer. (b) Is it acceptable to adopt the policies used in Data Link layer and apply them to the Transport layer? Why or why not?