Title DCCN Theory (CSC339) - Final Term SP20 [v01] - CUI Lahore (By Mr. Imran Raza).pdf ✅

COMSATS University Islamabad, Lahore Campus Terminal Examination – Semester Spring 2020 Course Title: Data Communications and Computer Networks Course Code: CSC339 Credit Hours: 3(2,1) Course Instructor/s: Mr. Imran Raza, Dr. M. Hasanain Ch., Dr. Shahbaz Akhtar, Dr. Atif Saeed, Mr. Shuja Program Name: BS Computer Science, BS Software Engineering Semester: 5th & 6th Batch: Section: All sections Date: Time Allowed: 3 Hours Maximum Marks: 100 Important Instructions / Guidelines: • All questions are compulsory 1. Suppose a new TCP congestion protocol TCPN is developed. It is similar to the congestion protocol we have discussed in the class but only has 2 phases: The Slow-Start phase and the Congestion-Avoidance phase. TCPN starts in the Slow-Start phase with CWND initially set to 1 (i.e., at RTT 0, CWND = 1), and ssthresh (slow-start threshold) set to 37. Its actions upon receiving each acknowledgement (Ack) in each of its phases are defined as follows. [15] • Slow-start phase: for each Ack, CWND +=2 • Congestion-Avoidance Phase: for each Ack, CWND = CWND +2 / CWND When CWND ≥ ssthresh, TCPN exits Slow-Start and enters the Congestion-Avoidance phase. On a packet loss, TCPN always goes back to the Slow- Start phase and adjusts as follows. • ssthresh = CWND / 4 • CWND = 1 Finally, when dividing, TCPN rounds numbers up to the nearest integer (e.g., 5/4 = 2, 9/2 = 5). Based on the protocol described above, answer the following questions: a. Using TCPN, draw a CWND-size vs. RTT graph for the first 14 RTTs. Assume a packet loss is detected right after the 7th RTT has passed. Clearly label the CWND size value for each RTT. (10) b. Does TCPN ensure equal bandwidth sharing among multiple flows? Briefly explain why or why not. (2) c. Assume no loss happens and header size is negligible. Assume the MSS of your transport protocol to be 1500 bytes and RTT is fixed at 200 ms. Calculate the average throughput (in Mbps) using TCPN for the first 5 RTTs. Assume 1 Mbps = 106 bps. (3) 2. Consider the given network setup, suppose that the ISP assigns the router the address 12.14.102.215 and that the network address of the home network is 172.16. 0.0/16. [10] a. Assign addresses to all interfaces in the home network. (3) b. Suppose each host has six ongoing TCP connections, all to port 20 at host 118.109.20.96. Provide all corresponding entries in the NAT translation table. (7)