Activity27 Soln - In-Class Activity #27 Due 4-24-01 Last...

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ECSE-2660 Computer Architecture, Networks, & Operating Systems, Spring 2001 Page 1 of 4 In-Class Activity #27 Due 4-24-01 Last Name First Name Student ID Number Email 27.1 27.2 Total Assigned grader Grader Initials 100 points - 100 points - 4/25/01 10:14 AM Activity 27.1 (First Hour) Grading Policy for all questions: 2 pts for trying, 7pts for partial answer, 10 points for correct answer. For 15-point questions, use the numbers 4 points, 8 points, and 15 points instead. 1. (10 Points). The attached pages show excerpts from the file /etc/services on the RCS system. What protocols and port numbers are used by ftp-data, sftp (secure ftp) and tftp (trivial ftp) services? Explain these choices. ftp-data Port # 20 TCP sftp Port #115 TCP tftp Port #69 UDP tftp is used by web servers for voice, image and video data. The fancy error checking of TCP is not needed and burdensome for these applications. 2. (10 points) How many UDP ports are possible on a given computer? What are the implications of this limit? Answer: We have 16 bits for specifying ports, so 64K ports are possible. Keep in mind that there are many more processes on the internet. So, port numbers are reckoned for each host. Therefore, UDP can only support upto 64K processes on each host – usually sufficient. 3. (10 points) Suppose that a UDP packet has been mis-delivered. How would this situation be detected? Answer: This can be detected by a checksum error. This is the primary purpose of the checksum. 4. (15 points) Recall that the 4-tuple {Client IP Address, Client Port#, Server IP Address, Server Port#} uniquely identifies a TCP connection. While the Server port numbers for the standard Internet applications are fixed and published, the client port numbers are not. Instead, client port numbers are generally either randomly or sequentially assigned from a pool of unused numbers at the client. Why is this approach necessary? Hint : Think of what will happen if client sends two different messages in succession. Answer:
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This note was uploaded on 04/25/2010 for the course ECSE ecse-2340 taught by Professor Wozny during the Spring '09 term at Rensselaer Polytechnic Institute.

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Activity27 Soln - In-Class Activity #27 Due 4-24-01 Last...

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