2006 Summer Midterm 1

2006 Summer Midterm 1 - CS 198:352 Internet Technology 1st...

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CS 198:352 Internet Technology 1 st Midterm – Summer 2006 (Time: 120 Minutes) Name: SID: Section: For TA use only: 1 2 3 4 5 6 7 8 Total Do not open the exam until you are told to begin. Write your name on every page including your notes page. There is no leaving the room while taking the exam. If you think you might need to leave the room during the exam, you must do so before starting the exam. Leave your ID out on your desk; these will be checked during the exam. You must show all work to get full credit. No electronic devices other than a calculator with a memory that can be cleared are allowed. This exam has 8 questions Not all points are created equal. Go for the easy points first! Make sure you have all 11 pages, including the cover page, of the exam before you hand it in. 1
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1. SMTP Figure 1 shows how Bob and Alice can communicate to each other through email. Suppose SMTP is used for the email transfer. (a) Bob has sent Alice an email. Suppose direct mode of SMTP is used in this email transfer. We know that Alice has not checked this mail (assume Alice’s PC is off till now). Where is this email currently stored? i. Email Server 1 ii. Email Server 2 iii. Email Server 1 or 2 iv. Bob’s PC Answer: ii (b) Bob has sent Alice an email and Alice has checked the email. Suppose indirect mode of SMTP is used in this email transfer. What are the links that SMTP has been used for transfer? i. Bob’s PC → Email Server 1, Email Server 1 → Alice’s PC ii. Bob’s PC → Email Server 2 iii. Bob’s PC → Email Server 2, Email Server 2 → Alice’s PC iv. Bob’s PC → Email Server 1, Email Server 1 → Email Server 2 Answer: iv 2. Switching Considering a small network of four hosts and three links as depicted in the figure below. A 1,024,000 bits message is to be sent from A to D. The bandwidth of the first two links is 0.4 Mbyte/second, but the link between C and D is 1.6 Mbyte/sec. Propagation delays of the links are negligible. A → B → C → D 2
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(a) Assume that circuit switching is used and the total circuit set-up time is 100 ms, what is the time to send the message from A to D? Answer: Circuit bandwidth = min (bandwidth of links) = 0.4 MB/s.
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2006 Summer Midterm 1 - CS 198:352 Internet Technology 1st...

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