TELECOMMUNICATION AND NETWORKING EXAM

Name: ____________________________ SID: ____________________________
Midterm Exam 2
Certification of identity: I certify that I am registered for this class (CSC 38000, Spring 2015) and that I am the person whose name and student ID number are stated on this exam (please show your Student ID to the proctor or instructor when turning in your exam). Signature: ________________________________ Date: _______________
Exam Instructions You may not talk to anyone else regarding the exam. You may not look at anyone else’s exam or papers while completing the exam. You may use a calculator during the exam, as long as the calculator is not capable of running programs, or storing formulas or text. Any cheating on this exam will be dealt with immediately and harshly. Cheating on this, or any other, exam in this class will result in an immediate F in the course and possibly suspension/expulsion from the University. Please read the instructions for each question carefully. Weights for each question are given in parentheses. When more than one answer is correct, give the best answer. When program code is to be supplied, give your answer in the C++ programming language. Please write clearly. Answers that
can’t be deciphered will be marked as wrong. Give your answers on the question side of the page. The backs of the pages may be used for scratch work, but will not be graded. Please put your name and student ID on EVERY page of this exam. Failure to do so could result in lost pages during grading, and/or points taken off your exam. When you turn in your exam, please show your Student ID to the proctor, or instructor.
Certification of integrity: I certify that I did not give or receive any help from any source other than those outlined as acceptable above or by the instructor during this exam. Signature: ________________________________ Date: _______________ Name: ____________________________ SID: ____________________________ Page 1
Midterm Exam 2 1. (8 pts) Consider the following subnet in which the routers are labeled A through F. Distance vector routing is used, and D’s routing table initially contains only information about reaching C and F (its nearest neighbors). In other words, D has not received any update messages yet. Suppose the following vectors have just come into router D: From C: (13, 4, 0, 6, 6, 14) From F: (10, 12, 16, 14, 2, 0) The measured delays to C and F are 4 and 97 respectively. What is C’s new routing table? Give both the outgoing line and the expected delay. Dest. Outgoing Line Delay A B C E F 2. (8 pts) What is the fastest line speed at which a host can blast out 1500-byte TCP payloads with a 120- sec maximum packet lifetime without having the sequence numbers wrap around? Take TCP, IP, and Ethernet overhead into consideration. Assume that Ethernet frames may be sent continuously. Name: ____________________________ SID: ____________________________ Page 2 3. (10 pts) Consider the network shown: Assume that the weight on the lines is the currently known link delay. Run Dijkstra’s algorithm to find the shortest paths from source node A to all other nodes in the network. Show all your work (show the intermediate tables you generate) Name: ____________________________ SID: ____________________________ Page 3 4. (10 pts) Consider the network shown in the previous problem. Run the non-distributed Bellman-Ford algorithm to find the shortest paths from source node A to all other nodes in the network. Show all your work (show the intermediate tables you generate) Name: ____________________________ SID: ____________________________ Page 4 5. (8 pts) Given a router with 4 interfaces/links which are labeled 0 – 3, and a forwarding table as follows:
IP Prefix Output Link 192.168.0/17 0 192.168.32/19 1 192.168.64/18 2 192.168.127/24 3 192.168.128/18 0 192.168.160/19 1 192.168.186/24 2 192.168.191/24 3 192.168.192/18 0 What interface will a packet with a destination IP address of 192.168.96.75 be sent out on? 6. (8 pts) Suppose Host A sends three TCP segments back to back to Host B over a TCP connection. The first segment has sequence number 120. The second segment has sequence number 121. The third segment has a sequence number of 1145. How much data is in the first segment? How much data is in the second segment? How do you know? 7. (8 pts) Consider the Go Back N protocol with 8 bit sequence numbers (i.e., a sequence number space of size 256). What is the largest allowable sender window that will avoid the occurrence of the problem where a new packet is indistinguishable from a retransmission? 8. (8 pts) Consider the Selective Repeat protocol with 8 bit sequence numbers (i.e., a sequence number space of size 256). What is the largest allowable sender window that will avoid the occurrence of the problem where a new packet is indistinguishable from a retransmission? Name: ____________________________ SID: ____________________________ Page 5 9. (8 pts) Consider the effect of using slow start on a line with a 10-msec round-trip time and no congestion. The receive window is 24 KB and the maximum segment size is 2 KB. How long does it take before the first full window can be sent? 10. (8 pts) Suppose datagrams are limited to 1500 bytes (including the header) between source and destination. Assuming a 20 byte IP header (with no options present), how many datagrams would be required to transfer a video file consisting of 500,000,000,200 bytes. Name: ____________________________ SID: ____________________________ Page 6 11. (8 pts) Suppose a UDP segment contains the following data: 00001001 01101001 00100011 01111100 00000000 00010100 00000000 00000000 11110000 11110000 00001111 00001111 10101010 01010101 01010101 10101010 11111111 00000000 11001100 00110011 Look at figure 3.7 on p. 202 of the book to see how the data is laid out in this segment. Suppose a segment checksum needs to be computed for this segment. What is the checksum value that is computed? Where is this checksum placed in the segment? Assuming there are no errors during transmission of the segment, what do you expect the verification step to produce as a result when verifying the checksum on the receiver? 12. (8 pts) Suppose two packets arrive to two different input ports of a router at exactly the same time. Also, suppose there are no other packets anywhere in the router. If the packets are to be forwarded to two different output ports, is it possible to forward the packets through the switch fabric at the same time when the fabric uses a shared bus? Is it possible to forward the packets through the switch fabric at the same time when the fabric uses a crossbar? Explain.