Intro to Comp Networks Final Exam

Homeworks, Quizzes, Exam 1 & 2, Ch 6

1824

* Suppose that the RTT delay between the client and server is 30 msecs; the time a server needs to transmit an object into its outgoing link is 1 msecs; and any other HTTP message not containing an object has a negligible (zero) transmission time. Suppose the client again makes 60 requests, one after the other, waiting for a reply to a request before sending the next request.
* Assume the client is using HTTP 1.1 and the IF-MODIFIED-SINCE header line. Assume 60% of the objects requested have NOT changed since the client downloaded them (before these 60 downloads are performed)

How much time elapses (in milliseconds) between the client transmitting the first request, and the completion of the last request?

false

(T/F) 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 messaes.

false

(T/F) With nonpersistent connections between browser and origin server, it is possible for a single TCP segment to carry two distinct HTTP request messages.

a) The cookie value itself doesn’t mean anything. It is just a value that was returned by a web server to this client during an earlier interaction.

What is the purpose of a cookie value in the HTTP GET request?

* a) The cookie value itself doesn’t mean anything. It is just a value that was returned by a web server to this client during an earlier interaction.
* b) The cookie value indicates whether the user wants to use HTTP/1, HTTP/1.1, or HTTP/2 for this GET request
* c) none of the others
* d) The cookie value encodes the format of the reply preferred by the client in the response to this GET request
* e) The cookie value in encoding of a user email address associated with the GET request

a) all of the others

When a TCP segment arrives to a host, the socket to which the segment is directed depends on

* a) all of the others
* b) the source IP address of the datagram that encapsulated the segment
* c) the destination port number
* d) the source port number

d) none of the others

UDP has which of the following characteristics:

* a) connection state at the server
* b) three-way handshake for the connection establishment
* c) regulated send rate
* d) none of the others

d) host A will retransmit neither segments

Over a TCP connection, suppose host A sends two segments to host B, host B sends an acknowledgement for each segment, the first acknowledgement is lost, but the second acknowledgement arrives before the timer for the first segment expires.

* a) host A will retransmit both segments
* b) host A will retransmit the second segment
* c) host A will retransmit the first segment
* d) host A will retransmit neither segments

d) all of the others

Pipelining requires which of the following

* a) transmitting many packets before receiving acknowledgements
* b) sender-side buffering of unacknowledged packets
* c) unique sequence numbers for each in-transit packet
* d) all of the others

true

(T/F) In the End-End congestion control approach, congestion is inferred from observed loss or delay.T

false

(T/F) The size of the TCP RcvWindow never changes throughout the duration of the connection.

false

(T/F) Host A is sending a large file to host B over a TCP connection. If the sequence number for a segment of this connection is m, then the sequence number for the subsequent segment will necessarily be m+1.

b) increases utilization

TCP uses pipelining to:

* a) none of the others
* b) increases utilization
* c) establish connections
* d) control congestion

segments

On the sending side, the transport layer converts the application-layer messages it receives from a sending application process into transport-layer packets, known as transport-layer ______________________.

001001010000011

What is the sum of these two 16 bit numbers?

* 10001011 01001110
* 10011001 10110111

110110101111100

What is the checksum of these two 16 bit numbers?

* 10001011 01001110
* 10011001 10110111

183,1118,2053,2988; 1118,2053,2988,x

Consider the figure below in which a TCP sender and receiver communicate over a connection in which the sender->receiver segments may be lost. The TCP sender sends an initial window of 4 segments. Suppose the initial value of the sender->receiver sequence number is 183 and the first 4 segments *each* contain 935 bytes. The delay between the sender and receiver is 7 time units, and so the first segment arrives at the receiver at t=8. As shown in the figure below, 1 of the 4 segment(s) are lost between the segment and receiver.

* What is the sequence numbers associated with each of the 4 segments sent by the sender. Format your answers as: a,b,c,… (no spaces)
* Give the ACK numbers the receiver sends in response to each of the segments. If a segment never arrives use ‘x’ to denote it, and format your answer as: a,b,c,…

d) there is no queueing delay in the router

Suppose a router has n input ports each with identical line speeds, n output ports each with identical line speeds, and the line speed of an output port is at least n times as that of an input port. Further suppose that the switching fabric speed is at least n times as fast as an input line speed. Then

* a) queueing can occur in an output port
* b) queueing can occur in an input port
* c) queueing can occur in the switching fabric
* d) there is no queueing delay in the router

b) in the input ports and in the output ports

In a router, queueing can occur

* a) only in the output ports
* b) in the input ports and in the output ports
* c) none of the others
* d) only in the input ports

d) the sending IPv6 router creates an IPv6 datagram and puts it in the data field of an IPv4 datagram

Suppose one IPv6 router wants to send a datagram to another IPv6 router, but are connected together by intervening IPv4 routers. If the two routers use tunneling, then

* a) none of the others
* b) the sending IPv6 router creates one or more IPv6 fragments, none of which is larger than the maximum size of an IPv4 datagram
* c) the sending IPv6 router creates an IPv4 datagram and puts it in the data field of an IPv6 datagram
* d) the sending IPv6 router creates an IPv6 datagram and puts it in the data field of an IPv4 datagram

true

(T/F) With a datagram network layer, each packet carries the address of the destination host

true

(T/F) The network portion of an IP address is the same for all the hosts on the same IP network

b) could increase the end-end delay

Increasing the amount of per-hop buffer

* a) could decrease the end-end delay
* b) could increase the end-end delay
* c) will not decrease packet loss
* d) none of the others

true

(T/F) Multiple packets can be transferred by the switch fabric in parallel, as long as their output ports are different

b) the transmission of packet A will not be interrupted. so, packet B has to wait after fully transmitting packet A

Assume packet A has begun transmission. If packet B (a high-priority packet) arrives during the transmission of packet A (a low-priority packet), then

* a) packet B will be transmitted immediately while packet A is still being transmitted
* b) the transmission of packet A will not be interrupted. so, packet B has to wait after fully transmitting packet A
* c) the transmission of packet A will be interrupted to allow the transmission of packet B
* d) transmission cannot be based on priorities

10\.0.1.13

Suppose that the host with IP address 10.0.1.13 sends an IP datagram destined to host 128.119.173.181. The source port is 3461, and the destination port is 80.

* Consider the datagram at step 1, after it has been sent by the host but before it has reached the router. What is the source IP address for this datagram?

135\.122.201.210

Suppose that the host with IP address 10.0.1.13 sends an IP datagram destined to host 128.119.173.181. The source port is 3461, and the destination port is 80.

* Now consider the datagram at step 2, after it has been transmitted by the router. What is the source IP address for this datagram?

yes

Suppose that the host with IP address 10.0.1.13 sends an IP datagram destined to host 128.119.173.181. The source port is 3461, and the destination port is 80.

* Will the source port (at step 2) have changed (from step 1)? y/n

no

Suppose that the host with IP address 10.0.1.13 sends an IP datagram destined to host 128.119.173.181. The source port is 3461, and the destination port is 80.

* Has a new entry been made in the router’s NAT table (between step 3 and step 4)? y/n

c) all of the others

The link-state algorithm (covered in class) has the following properties:

* a) it determines the shortest path from the source node to all other nodes
* b) after the kth iteration, the least-cost paths are known to k nodes
* c) all of the others
* d) it requires the source node to know the costs between every pair of adjacent nodes in the graph

c) policy

In routing among ASs, which of the following issues dominants:

* a) number of ASs traversed
* b) current congestion levels in the ASs
* c) policy
* d) geographical distance between ASs

c) runs directly on top of IP

The ICMP protocol

* a) none of the others
* b) runs on top TCP
* c) runs directly on top of IP
* d) runs on top UDP

c) chooses the gateway that has the smallest cost

As part of hierarchical routing, hot-potato routing does the following:

* a) determines the number of ASes in the shortest As path from router to destination
* b) provides information to a router about the existence of external networks
* c) chooses the gateway that has the smallest cost
* d) labels suspicious packets as “hot”

false

(T/F) In a distance-vector routing algorithm, each node has a map of the entire network and determines the shortest path from itself to all other nodes in the network.

false

(T/F) In the BGP routing algorithm, each AS advertises to its neighbors its estimates of the shortest distances from the AS to all possible destination ASs.

false

(T/F) Every autonomous system must use the same intra-autonomous system routing algorithm.

false

(T/F) OSPF uses BGP for routing among areas.

4,u

* Consider the 6-node network shown below, with the given link costs.
* Using Dijkstra's algorithm, find the least cost path from source node U to all other destinations and answer the following questions:

What is the shortest distance to node x and what node is its predecessor? Write your answer as n,p

7,w

* Consider the 6-node network shown below, with the given link costs.
* Using Dijkstra's algorithm, find the least cost path from source node U to all other destinations and answer the following questions:

What is the shortest distance to node z and what node is its predecessor? Write your answer as n,p

8,w

* Consider the 6-node network shown below, with the given link costs.
* Using Dijkstra's algorithm, find the least cost path from source node U to all other destinations and answer the following questions:

What is the shortest distance to node y and what node is its predecessor? Write your answer as n,p

x,x,x,9,0

* Consider the 6-node network shown below, with the given link costs:
* What are the initial distance vectors for router 'Y'? Write your answer as u,v,w,x,y and if a distance is ∞, write 'x'

0,2,6,4,13

* Consider the 6-node network shown below, with the given link costs:
* When the algorithm converges, what are the distance vectors from router 'U' to all routers? Write your answer as u,v,w,x,y

false

(T/F) In a Client-SErver paradigm, clients can communicate directly with each other.

true

(T/F) In order for 2 processes running on different hosts to exchange messages, two sockets must be involved: one on each side.

80

The default port for processes running on an HTTP server is ____________.

false

(T/F) Generally, a file transfer application can tolerate some loss of data

c) at most one object is sent

In a non-persistent HTTP connection:

* a) the connection will remain open until all objects are sent
* b) multiple objects can be sent
* c) at most one object is sent
* d) the objects that are sent will not be persisted

* d) cookies

In order for web sites and client browsers to maintain some state between transactions, they use:

* a) persistent TCP
* b) none of the others
* c) persistent HTTP connections
* d) cookies

true

(T/F) HTTP/2 increased flexibility at server in sending objects to client

false

(T/F) One similarity between HTTP and SMTP is that both are pull protocols.

a) IMAP

When a user agent retrieves an e-mail message from its e-mail server, it uses this protocol:

* a) IMAP
* b) UDP
* c) none of the others
* d) SMTP

a) The HTTP GET request message is used by a web client to request a web server to send the requested object from the server to the client

What is the purpose of the HTTP GET?

* a) The HTTP GET request message is used by a web client to request a web server to send the requested object from the server to the client
* b) The HTTP GET request message is sent by a web server to a web client to get the next request from the web client
* c) The HTTP GET request message is used by a web client to post an object on a web server
* d) The HTTP GET request message is sent by a web server to a web client to get the identity of the web client

a) yes, because this is a conditional GET, as evidenced by the If-Modified-Since field

* Suppose the client-to-server HTTP GET message is the following:

GET /kurose_ross_sandbox/interactive/quotation1.htm HTTP/1.1 \\n Host: gaia.cs.umass.edu \\n Accept: text/plain, text/html, image/png, image/gif, audio/mp4, audio/basic, video/mp4, video/wmv, \\n Accept-Language: en-us, en-gb;q=0.3, en;q=0.7, fr, fr-ch, zh, de, fi, ar, cs \\n If-Modified-Since: Mon, 12 Dec 2022 17:09:47 -0800 \\n User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3) AppleWebKit/534.53.11 (KHTML, like Gecko) Version/5.1.3 Safari/534.53.10

* Does the client have a cached copy of the object being requested?
* a) yes, because this is a conditional GET, as evidenced by the If-Modified-Since field
* b) There’s not enough information in the header to answer this question
* c) no, because a client would not request an object if it had that object in its cache
* d) yes, because HTTP 1.1 is being used

1512\.5

Assume that the RTT delay between the client and server is 30 msecs and the TCP connection is already established

* the time a server needs to transmit an object into its outgoing link is 0.5 msecs
* any other HTTP message not containing an object has a negligible (zero) transmission time.

Suppose the client again makes 50 requests, one after the other, waiting for a reply to a request before sending the next request.

* Assume the client is using HTTP 1.1 and the IF-MODIFIED-SINCE header line.
* Assume 50% of the objects requested have NOT changed since the client downloaded them (before these 50 downloads are performed)

How much time elapses (in milliseconds) between the client transmitting the first request, and the completion of the last request?

40

* Assume an RTT of 10 msec is needed for each:
* to initiate and establish a TCP connection
* for HTTP request and first few bytes of HTTP response to return
* Assume an object transmission time is 0.5 msec
* Assume the HTML page being requested references % objects in addition to the base HTML file and that HTTP/1.0 is being used.

What is the total response time for the entire page to be delivered to the browser?

a) none of the others

Which of the following is not true about UDP?

* a) none of the others
* b) connection setup is not needed
* c) segments may be delivered out of order
* d) segments may be lost

e) data (payload)

Which of the fields below are not in a UDP segment header?

* a) checksum
* b) none of the other
* c) source port number
* d) length
* e) data (payload)

false

(T/F) When computing the Internet checksum for two numbers, a single flipped bit in each of the two numbers will always result in a changed checksum

true

(T/F) It is possibly for two UDP segments to be sent from the same socket with source port 5723 at a server to two different clients

segments, network

The transport protocol in the sender host breaks application messages into __________, and passes to _________ layer

111010110000001

What is the sum of these two 16 bit numbers?

* 00010100 01110001
* 11010110 10010010

000101001111110

What is the checksum of these two 16 bit numbers?

* 00010100 01110001
* 11010110 10010010

forwarding

Moving packets from a router’s input link to appropriate router output link is called _____________.

32

In Internet protocol version 4, the IP address consists of ______________ bits.

128

In Internet protocol version 6, the IP address consists of ______________ bits.

b) none of the others

Network-layer service model guarantee(s) on:

* a) bandwidth available to end-end flow
* b) none of the others
* c) delivery to destination
* d) timing or order of delivery

buffering

Because datagrams might arrive from switch fabric faster than link transmission rate, ___________ is required at the output port.

subnet

We refer to device interfaces that can physically reach each other without passing through an intervening router as a _______________.

false

(T/F) Before sending a packet into a datagram network, the source must determine all of the links that packet will traverse between source and destination

false

(T/F) The HTTP protocol was invented at Netscape in the early 1990s.

10

Suppose there are two links between a source and a destination. The first link has transmission rate 100 Mbps and the second link has transmission rate 10 Mbps. Assuming that the only traffic in the network comes from the source, what is the throughput for a file transfer?

a) loss-intolerant and time insensitive

The transfer of an html file from one host to another is:

* a) loss-intolerant and time insensitive
* b) loss-intolerant and time sensitive
* c) loss-tolerant and time insensitive
* d) loss-tolerant and time sensitive

d) 304 Not Modified

Suppose a client sends an HTTP request message with the If-modified-since header. Suppose the object in a server has not changed since the last time a client retrieved the object. Then the server will send a response message with the status code:

* a) 404 Not Found
* b) none of the others
* c) 200 OK
* d) 304 Not Modified

c) cache resource records, but discard them after a period of time that is on the order of a few days

Local DNS name servers:

* a) never cache resource records
* b) obtain resource records from Web caches
* c) cache resource records, but discard them after a period of time that is on the order of a few days
* d) cache resource records and never discard them

b) all of the others

For BitTorrent, which of the following is true?

* a) at a given instant of time, a peer A may upload to a peer B, even is peer B is not sending anything to A
* b) all of the others
* c) Among the chunks that a peer does not have, the peer will request chunks that appear to be relatively rare in the torrent
* d) Although a peer may have 50 concurrent TCP connections with other peers, at any given instant of time it sends data to less than 10 other peers

true

(T/F) With SMTP, it is possible to send multiple mail messages over the same TCP connection.

false

(T/F) In a Client-server paradigm, the clients can either communicate with the server or communicate directly with each other.

b) real-time audio

Which of the following applications can tolerate some data transfer loss?

* a) file transfer
* b) real-time audio
* c) none of the others
* d) all of the others
* e) web transactions

port

To receive messages, processes must have identifier which includes both IP address and _________ number associated with process on host.

true

(T/F) File transfer applications are elastic applications and can make use of whatever throughput they get.

true

(T/F) Interactive game applications can use TCP or UDP.

false

(T/F) In HTTP/1.1, objects are divided into frames which are scheduled to mitigate HOL blocking.

c) Application-layer protocol

The Domain Name System is implemented as:

* a) Transport-layer protocol
* b) Network-layer protocol
* c) Application-layer protocol
* d) none of the others

b) none of the others

When a host makes DNS query, the query is normally sent to:

* a) Top-Level Domain DNS server
* b) none of the others
* c) Authoritative DNS server
* d) Root DNS server

b) the client determines what encoding rate to request

In a streaming stored videos application that uses DASH

* a) none of the others
* b) the client determines what encoding rate to request
* c) the CDN closest to the client determines which encoding rate to provide
* d) the server determines what encoding rate to provide

0\.00012

* Assume a single router is transmitting packets, each of length L bits, over a single link with transmission rate R Mbps to another router at the other end of the link.
* Suppose that the packet length is L = 12000 bits, and that the link transmission rate along the link to router on the right is R = 100 Mbps.

What is the transmission delay?

8333

* Assume a single router is transmitting packets, each of length L bits, over a single link with transmission rate R Mbps to another router at the other end of the link.
* Suppose that the packet length is L = 12000 bits, and that the link transmission rate along the link to router on the right is R = 100 Mbps.

What is the maximum number of packets per second that can be transmitted by this link?

583\.33

We need to distribute a file that is initially located at a server to clients via either client-server download or peer-to-peer download.

* The problem is to distribute a file of size F = & Gbits to each of these 7 peers. Suppose the server has an upload rate of u = 84 Mbps.
* The 7 peers have upload rates of: u1 = 24 Mbps, u2 = 23 Mbps, u3 = 27 Mbps, u4 = 25 Mbps, u5 = 18 Mbps, u6 = 29 Mbps, and u7 = 27 Mbps
* The 7 peers have download rates of: d1 = 27 Mbps, d2 = 20 Mbps, d3 = 22 Mbps, d4 = 39 Mbps, d5 = 32 Mbps, d6 = 33 Mbps, and d7 = 17 Mbps

What is the minimum time needed to distribute this file from the central server to the 7 peers?

Formula: Dc-s = max{NF/us, F/dmin}

411\.76

We need to distribute a file that is initially located at a server to clients via either client-server download or peer-to-peer download.

* The problem is to distribute a file of size F = & Gbits to each of these 7 peers. Suppose the server has an upload rate of u = 84 Mbps.
* The 7 peers have upload rates of: u1 = 24 Mbps, u2 = 23 Mbps, u3 = 27 Mbps, u4 = 25 Mbps, u5 = 18 Mbps, u6 = 29 Mbps, and u7 = 27 Mbps
* The 7 peers have download rates of: d1 = 27 Mbps, d2 = 20 Mbps, d3 = 22 Mbps, d4 = 39 Mbps, d5 = 32 Mbps, d6 = 33 Mbps, and d7 = 17 Mbps

What is the minimum time needed to distribute this file using peer-to-peer download?

Formula: DP2P = max{F/us, F/dmin, NF/(us + Sigma ui)}

64

Consider the circuit-switched network shown in the figure below, with circuit switches A, B, C, and D. Suppose there are 15 circuits between A and B, 14 circuits between B and C, 18 circuits between C and D, and 17 circuits between D and A.

What is the maximum number of connections that can be ongoing in the network at any one time?

31

Suppose that every connection requires 2 consecutive hops, and calls are connected clockwise. For example, a connection can go from A to C, from B to D, from C to A, and from D to B.

With these constraints, what is the maximum number of connections that can be ongoing in the network at any one time?

c) all of the others

When a TCP segment arrives to a host, the socket to which the segment is directed depends on:

* a) the source port number
* b) the destination port number
* c) all of the others
* d) the source IP address of the datagram that encapsulated the segment

a) none of the others

UDP has which of the following characteristics?

* a) none of the others
* b) regulated send rate
* c) connection state at the server
* d) three-way handshake for connection establishment

b) host A will retransmit neither segments

Over a TCP connection, suppose host A sends two segments to host B, host B sends an acknowledgement for each segment, the first acknowledgement is lost, but the second acknowledgement arrives before the timer for the first segment expires.

* a) host A will retransmit both segments
* b) host A will retransmit neither segments
* c) host A will retransmit the first segment
* d) host A will retransmit the second segment

d) breaking application messages into segments and passing them to network layer

The transport protocols actions in send end systems involves:

* a) breaking application messages into datagrams and passing them to network layer
* b) breaking application messages into frames and passing them to link layer
* c) none of the others
* d) breaking application messages into segments and passing them to network layer

a) network layer represents a logical communication between hosts while transport layer represents a logical communication between processes

One important difference between the network and transport layer is:

* a) network layer represents a logical communication between hosts while transport layer represents a logical communication between processes
* b) network layer represents a logical communication between hosts while transport layer represents a logical communication between processes as well as between hosts
* c) none of the others
* d) network layer represents a logical communication between processes while transport layer represents a logical communication between hosts

a) no RTT required for connection establishment

Potential benefit(s) for using UDP over TCP:

* a) no RTT required for connection establishment
* b) reliable
* c) maintains connection state
* d) will decrease sending rate when congestion is detected to avoid packet loss

d) sender allows multiple, “in-flight”, yet-to-be-acknowledged packets

In pipelining:

* a) sender allows single yet-to-be-acknowledged packets
* b) sender waits for acknowledgements before sending another packet
* c) none of the others
* d) sender allows multiple, “in-flight”, yet-to-be-acknowledged packets

0001010100100000

What is the sum of these two 16 bit numbers? Do not put spaces.

* 11010000 10111011
* 01000100 01100100

1110101011011111

What is the checksum of these two 16 bit numbers? Do not put spaces.

* 11010000 10111011
* 01000100 01100100

true

(T/F) TCP can be described as a point-to-point protocol