Exam 1 and 2 Questions COSC 4360
A user requests a web page that consists of some text and three images. For this page, the client will send one request message and receive four response messages.
False
An email client sends emails to the email server using the POP3 protocol.
False
Application layer is not accessible by the users of a computer.
False
Consider congestion control in TCP. When the timer expires at the sender, the value of ssthresh is set to one half of its previous value.
False
Encapsulation occurs at the receiver of a message.
False
Generalized forwarding and destination-based forwarding are synonymous.
False
HOL blocking occurs in a router's output ports.
False
HTTP is a push protocol while SMTP is a pull protocol.
False
If an IPv6 datagram received by a router is too large to be forwarded over the outgoing link, the router fragments the datagram.
False
If two packets arrive at two different input ports of a router at the same time and these two packets are to be forwarded to the same output port of the router, then these two packets can be switched through the fabric at the same time only when the fabric is a crossbar.
False
In IPv6 datagram structure, the fragmentation offset field is set a value in 8 byte blocks.
False
In network security, DDoS stands for Distributed Duplication of Service.
False
In store-and-forward packet switching, the formula for end-to-end delay (in seconds when we ignore queuing, processing, and propagation delays) for sending P packets each of length L bits back-to-back over N links each of rate R bps is (P+N−1)R/L
False
In the TCP's 3-way handshake, when the segment with the ACK for the SYNACK is sent, no application data can be sent with this segment.
False
One of the golden rules in network traffic engineering is to design the system so that the traffic intensity is always greater than one.
False
Only the client can initiate the closure of a TCP connection.
False
Propagation delay is the time taken to put all bits of a packet on the link and transmission delay is the time taken by a bit to travel from source to destination.
False
Queuing delays occur at the network edges.
False
Ranking of home access technologies by speed from lowest to highest is: dialup, HFC, DSL, and FTTH.
False
Root servers of the DNS are running on the premises of your ISP
False
Selective Repeat uses a single timer for timeouts.
False
Suppose two packets arrive at two different input ports of a router at exactly the same time. Also suppose there are no other packets anywhere in the router. A shared bus switch fabric router can forward these two packets to different output ports at the same time.
False
TCAM returns the data at an address in the memory in variable time - that is, once it may return the data in 50 ns and the next time it may return the data in 100 ns.
False
TCP Reno is a version older than TCP Tahoe.
False
TCP Tahoe supports fast recovery.
False
The following figure correctly shows the minimum distribution time curves for ClientServer and P2P architectures.
False
The formula for traffic intensity is R/La, where R is the link rate, a is the packet arrival rate, and L is the packet size.
False
The transport layer is present in all devices in the core of the Internet.
False
Throughput and bandwidth are synonymous.
False
UDP stands for Useful Datagram Protocol.
False
When a large datagram is fragmented into multiple smaller datagrams, all the fragments necessarily follow the same route from source to destination.
False
When we apply the Dijkstra's algorithm at a node in a network, we get the forwarding table first and then determine the routing table.
False
When you read emails you use the SMTP protocol.
False
A tunnel is used to connect IPv6 nodes through an IPv4 network.
True
Akamai is an example of third-party CDN.
True
All computers on a subnet have the same subnet mask.
True
Dijkstra's algorithm we studied is an example of link-state routing algorithm.
True
During the TCP slow start phase, the number of segments transmitted doubles every transmission round.
True
Host A sends two segments to host B, the first containing sequence number 92 and the second containing sequence number 100; this means that the first segment contained 8 bytes of data.
True
In GBN, if a timeout occurs, the sender resends all packets that have been previously sent but that have not yet been acknowledged.
True
In a IPv4 datagram, the header length field has a value of 5 for the standard header (without options).
True
In a network, we need to apply the Dijkstra's algorithm at every node to get the routing and forwarding tables for each node.
True
In a packet switched network, when a router in the path of a packet drops the packet then that packet is lost.
True
In the first lab we saw that uttyler.edu used TLS; TLS this stands for Transport Layer Security and encrypts application layer data.
True
The DASH video streaming protocol encodes a video into several different versions with each version having a different bit rate.
True
The first step in the DHCP protocol is the DHCP server discovery step.
True
The maximum payload in a IPv6 datagram is 65535 bytes.
True
The problem of oscillations can occur in the link state routing algorithm.
True
The product of bandwidth and transmission delay for a link gives the number of bits currently on the link.
True
There are 13 root servers in the DNS system.
True
Transport layer multiplexes several messages leaving the system and demultiplexes messages received from outside.
True
UDP has a 8-byte header.
True
When a network drops packets due to congestion they are actually dropped at the input and output buffers of router interfaces due to the finite size of these buffers.
True
Wireshark is a packet sniffer.
True
A router with 48 interfaces needs only one IP address for itself.
False
A DDoS attack uses a botnet to attack a target.
True
We are transferring a 100 kbyte file. Each frame of the data link layer can carry 1460 bytes of this payload while at the same time each frame also has an overhead of 46 bytes from the network and data link layers. Transmission efficiency is the ratio of application layer bytes to the total number (or actual number) of bytes transmitted. If TCP with no options is used, what is the transmission efficiency in percentage? Give the answer to two decimal digits. (6 points) What is the transmission efficiency (in percentage to two decimal digits) if UDP is used instead of TCP for this file transfer? (4 points) Write all steps in your answers. Your Answer:
(100 x 10^3)/1460 = 69 Frames TCP Overhead = 20(TCP) + 46 = 66 TCP Efficiency = (100 x 10^3) / ((100 x 10^3) / (66 x 69)) = 95.64% UDP Overhead = 8 + 46 = 54 UDP Efficiency = (100 x 10^3) / ((100 x 10^3) / (54 x 69)) = 96.41%
Two hosts A and B are connected by a single link of 56 kbps. They are separated by 1000 km and the propagation speed along the link is 2.5 * 108 m/s. Host A is to send a packet of size 120 bits to Host B. What is dprop for this packet in whole number ms?
4
Two applications on hosts A and B are communicating over a TCP connection, and the application on host B has already received from the application on host A all bytes from zero through 198. Application on host A is bound to port number 5012 and the application on host B is the web server listening on the HTTP port. Suppose the application on host A then sends two segments to Host B back-to-back: the first and second segments contain 100 and 50 bytes of data, respectively. Host B sends an acknowledgement whenever it receives a segment from Host A. 1. In the first segment sent from Host A to B, what are the sequence number, source port number, and destination port number? (3 points) 2. If the first segment arrives before the second segment, in the acknowledgement of the first arriving segment, what is the acknowledgement number, the source port number, and the destination port number? (3 points) 3. In the acknowledgement of the second segment (assume the first segment has already been received), what is the acknowledgement number, the source port number, and the destination port number? (3 points) 4. Why does TCP need sequence numbers? (1 point)
1. Sequence = 298, Source Port = 5012, Destination Port = 80 2. ACK = 298, Source Port = 80, Destination Port = 5012 3.ACK = 348, Source Port = 80, Destination Port = 5012 4. Ensure Priority Queue
Consider the graph below which shows TCP window as a function of time: horizontal axis is the transmission round and the vertical axis is the congestion window size in segments. Now answer the following questions: 1. Is this figure representing TCP Tahoe or TCP Reno? (1 point) 2. Identify the intervals of time when TCP congestion avoidance is operating. (2 points) 3. After the 8th transmission round, is segment loss detected by a triple duplicate ACK or by a timeout? Why? (2 points) 4. What is the value of ssthresh at the 12th transmission round? Why?(2 points) 5. If one RTT = 200ms, what is the transmission rate in bps during the 9th transmission round when one MSS = 1500 bytes? (3 points) Your Answer:
1. TCP Reno 2. Time Interval 4 - 8, and 9 - 15 3. Triple Duplicate ACK, because TCP Reno only resets to 1 after a timeout, not a Triple Duplicate 4. 12, while ssthresh was reduced to 6 at 9, it has since then recovers to 12 5. 540,000 bps
What is the 1's complement of the sum of the two bytes 11011010 and 01100101?
10111111
Consider a subnet with prefix 128.119.128.0/22. Give one IP address (of form xxx.xxx.xxx.xxx) that can be assigned to a computer in this network. Explain your answer. (2 points) Suppose we want to create four maximally sized subnets within this subnet, with each block having the same number of IP addresses. What are the prefixes (of form a.b.c.d/x) for each of the four subnets? Show all work. (4 x 2 points) Your Answer:
128.119.128.255, IP can fit because subnet allows IP's Ranging from 128.119.128.0 - 128.119.131.255. 128.119.10000000.0/24 = 128.119.128.0/24 128.119.10000001.0/24 = 128.119.129.0/24 128.119.10000010.0/24 = 128.119.130.0/24 128.119.10000011.0/24 = 128.119.131.0/24
An IPv4 router that uses longest prefix matching has an entry in its forwarding table that reads "if the prefix is 1110 then forward to interface 3". If this is the only entry that forwards datagrams to interface 3, how many IP addresses will be forwarded by this router to interface 3?
16
When a packet arrives at a router, one other packet is halfway done being transmitted on the outbound link and three other packets are waiting to be transmitted. Packets are transmitted in order of arrival. Suppose all packets are 1000 bytes and the link rate is 10 Mbps. What is the queuing delay for the packet in milliseconds (to one decimal place)?
2.8
Suppose datagrams are limited to 1500 byes (including header) between source Host A and destination Host B. Assuming a 20-byte IP header, how many datagrams would be required to send an MP3 consisting of 5 million bytes using UDP?
3,397
Consider transferring an enormous file of L bytes from Host A to Host B. Assume an MSS of 800 bytes. Given that L is the maximum number that can be supported by the TCP sequence number field (4 bytes wide), how many TCP segments will be needed for transferring this file?
5,368,710
A web browser requests a 5000 byte HTML file over a 10Mbps link. The client-server RTT is 150ms and the DNS lookup round-trip time is 200ms. Ignore all transmission times except for the HTTP response. Also ignore any processing delays and queuing delays. How long does it take for this file to be received by the browser after the URL is entered on the browser? Assume the browser does not know the IP address of the server. Give the answer in whole number ms.
504
A UDP segment has 16 bits allocated for its length. What is the maximum number of bytes of application data (that is, the payload) a UDP segment can carry?
65,527
The IP address for a host is 192.169.225.87/26. What are its network address, broadcast address, and subnet mask? (3 x 3 points) What is the maximum number of hosts that can be there on this subnet? (1 point) Show all work.
Network = 192.169.225.64 Broadcast = 192.169.225.127 Subnet Mask = 255.255.255.192 Maximum Number of hosts = 64 - 2 = 62
Consider the following network. Apply Dijkstra's algorithm to find the shortest path from node A to all other nodes. Show your work using a table as discussed in class. (7 points) If node A is sending a packet to node D, what is the distance traversed by the packet, if the costs given in the network below represent distances in miles? What nodes does this packet go through? Justify your answers using the table you developed for the Dijkstra's algorithm. (3 points) Your Answer:
The Packet from Node A travels 25 Miles, going from A to B to C and finally to D.
A UDP segment is carrying 946 bytes of application data. What is the value in the length field of this segment in binary? If a TCP segment is carrying this same application data, what will be the length of the segment (in decimal) assuming a header with no options is used? Write all steps in your answer. Your Answer:
UDP total size = 946 + 8 = 954 In Binary = 1110111010 or 0000001110111010 TCP total size = 946 + 20 = 966