University of Southern California EE450 Introduction to Computer Networks Final Exam 210 hours May 6 2022 Last Name First Name Part 1 T F Part 2 Fill in the Blank Part 3 Routing Algorithms Part 4 Subnetting Part 5 TCP Congestion Control Total 30 30 15 10 15 100 Notes All your answers should be on the exam paper You can work the problems in any order you wish the goal is to try to accumulate as many points as you can Try your best to be clean and to show all the steps of your work Rules This is a closed book closed notes exam One 8 x11 containing formulas only is allowed along with a calculator Any other electronic gadget including a smart phone or an IPad is strictly prohibited Adherence to the University s Code of Ethics will be strictly monitored and enforced Academic Integrity violations such as cheating will result in a series of actions and penalties including the student failing the class EE450 Spring 2022 Final Zahid 1 Part 1 True False Multiple Choice 1 A subnet mask is used to identify the boundary between network bits and host bits in an IP address 2 Unlike Routers L2 switches built their tables based on destination MAC address 3 An IPv 4 packet can be fragmented and reassembled multiple times in transit 4 A NAT PAT maintains end to end addressing and improves network performance 5 The following masks in slash notation for simplicity are only used as default masks 8 16 and 24 for classes A B and C respectively 6 Link state routing protocols compute the least cost path between source and destination using complete global knowledge of the network 7 SSID is a technical term for a Wi Fi network address 8 In DV protocol shortest path computations and updates are asynchronous 9 The entire Class C address space can be expressed as a single CIDR notation of 192 3 10 In 802 11 CSMA CA the sender can detect a collision without feedback from receiver 11 In 802 11 when two stations transmit RTS frames simultaneously a collision will occur and no CTS frame is received Each station will wait a random period and try again 12 A host sends a segment with a sequence number 100 and payload size of 100 Bytes The ACK sequence number in that segment is 200 13 IP Tunneling is most related to the concept of encapsulation 14 If an IP fragment does not arrive at the destination the source host retransmits that fragment only not the entire packet 15 Every port of a router constitute a broadcast domain while every port of a L2 switch constitute a collision domain EE450 Spring 2022 Final Zahid 2 16 A 1000 Byte packet is fragmented when sent over a link with an MTU of 600 The resulting fragments are then sent over a link with 500 The minimum number of fragments received at destination is four 17 At the network layer a spanning tree is used to ensure that no redundant packets are 18 In 802 3 standard if the coverage distance is increased the minimum frame size 19 In 802 3 standard if the bandwidth is increased the minimum frame size would 20 In 802 3 if an ACK is not received within a specified time timeout the sender will 21 The results of connecting multiple L2 switches together is increasing the size of the received by any node would decrease increase as well retransmit the frame broadcast domains 22 In Wi Fi a wireless host needs only the MAC address of the AP It does not need the MAC address of the default router 23 If a TCP and a UDP flows share the same bottleneck the UDP flow is more likely to get a greater percentage of the available bandwidth 24 Suppose a Certificate Authority CA has Bob s certificate registered with it binding Bob s public key to Bob This certificate is signed with a Bob s public key b The CA s public key c Bob s private key d The CA s private key EE450 Spring 2022 Final Zahid 3 25 A sender sends an unencrypted message and its encrypted digest over a network Which of the following types of information assurance is provided in this scenario 26 A sender sends a message encrypted by a public key of the recipient Which of the following is NOT provided in this scenario 27 A sender sends a message encrypted by his own private key Which of the following is NOT provided in this scenario a Data Confidentiality b Authentication c Data Integrity d None of the above a Data Integrity b Data Confidentiality c Authentication d All the above a Data Confidentiality b Authentication c Data Integrity d All the above 28 A switch will never learn a broadcast address because a Broadcast frames are never sent to the switch b A broadcast address will never be the source address of a frame c Broadcasts only use network layer addresses d A switch never forwards a broadcast frame e None of the above EE450 Spring 2022 Final Zahid 4 29 Considering the addresses already used and having to remain within the 10 16 10 0 24 network range which subnet address could be assigned to the network containing 25 hosts 30 Given the network address of 192 168 5 0 and a subnet mask of 255 255 255 224 how many total host addresses are unused in the assigned subnets a 10 16 10 160 26 b 10 16 10 128 28 c 10 16 10 64 27 d 10 16 10 224 26 e 10 16 10 240 27 f 10 16 10 192 27 a 56 b 60 c 64 d 68 e 72 EE450 Spring 2022 Final Zahid 5 Part 2 Fill in the Blank 1 Suppose a group of 4 nodes are connected to a 10 Mbps Ethernet hub The average bandwidth available to each node is Mbps Now suppose these 4 nodes are connected to a 4 port 10 Mbps Ethernet Switch the maximum bandwidth available to each node is Mbps The aggregate capacity of the switch is Mbps 2 A TCP sender is sending a full window of 216 Bytes over a 1 Gbps channel that has a 1msec propagation delay a The link utilization is b The maximum throughput is Bytes sec 3 Assume you have a 10 Mbps hub based i e shared Ethernet network with 3 hosts Each computer is connected to the hub with a cable of different length Host H1 is connected via a 100 m cable Host H2 is connected via a 200 m cable and H3 which is connected via a 300 m cable The speed of propagation is 2x108 m sec The minimum frame length used in this network so that CSMA CD protocol will function correctly should be bits 4 Two nodes A and B that are attached at the opposite ends of 500 m Ethernet cable They both have a 1000 bit frame to send to each other Both nodes attempt to transmit at t 0 Assume …