Computer Networks Chapters 1-3
Which of the following best completes this sentence: "In the absence of loss, TCP slow start increases the sending rate ... "
"... faster than AIMD. In fact, slowstart increases the sending rate exponentially fast per RTT."
Suppose a packet is L = 1200 bytes long (one byte = 8 bits), and link transmits at R = 100 Mbps (i.e., a link can transmit bits 100,000,000 bits per second). What is the transmission delay for this packet?
(1200*8)/100,000,000
Suppose a packet is L = 1500 bytes long (one byte = 8 bits), and link transmits at R = 1 Gbps (i.e., a link can transmit bits 1,000,000,000 bits per second). What is the transmission delay for this packet?
(1500*8)/1,000,000,000=0.000012 secs
Consider the network shown in the figure below, with three links, each with the specified transmission rate and link length. Assume the length of a packet is 8000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec What is the propagation delay at (along) link 2? (Link 2 is: Transmission rate: 100 Mbps, Link Length: 1000 Km)
0.0033 secs (1,000Km*1,000m/3*10^8)
Suppose a packet is 10K bits long, the channel transmission rate connecting a sender and receiver is 10 Mbps, and the round-trip propagation delay is 10 ms. What is the maximum channel utilization of a stop-and-wait protocol for this channel?
0.1
Consider the figure below, which shows the application-to-application throughput achieved when two senders are competing at a shared bottleneck link. Suppose that when the overall arrival rate, lambdain' (for each sender) is close to R/2, the throughput to the application layer (at each receiver), lambda out, is equal to 0.8 * lambda in'.
0.20
How is the sending rate typically regulated in a TCP implementation?
By keeping a window of size cwnd over the sequence number space, and making sure that no more than cwnd bytes of data are outstanding (i.e, unACKnowledged). The size of cwnd is regulated by AIMD.
What are some reasons for not discarding received-but- out-of-sequence packets at the receiver in GBN? Indicate one or more of the following statements that are correct.
Even though that packet will be retransmitted, its next retransmission could be corrupted, so don't discard a perfectly well-received packet, silly!
Consider TCP use of an exponentially weighted moving average (EWMA) to compute the nth value of the estimated RTT:EstimatedRTTn = (1- a)*EstimatedRTTn-1 + a*SampleRTTnTrue or False: with this EWMA algorithm the value of EstimatedRTTn has no dependence on the earlier sample, SampleRTTn-1
False
True or False: On the sending side, the TCP sender will take each application-layer chunk of data written into a TCP socket and send it in a distinct TCP segment. And then on the receiving side, TCP will deliver a segment's payload into the appropriate socket, preserving the application-defined message boundary.
False
True or False: 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.
False
True or False: When multiple TCP clients send TCP segments to the same destination port number at a receiving host, those segments (from different senders) will always be directed to the same socket at the receiving host.
False
Which of the following physical layer technologies has the highest transmission rate and lowest bit error rate in practice?
Fiber optic cable
Suppose now the server sends the following HTTP response message the client: HTTP/1.0 200 OK Date: Wed, 09 Sep 2020 23:46:21 +0000Server: Apache/2.2.3 (CentOS)Last-Modified: Wed, 09 Sep 2020 23:51:41 +0000ETag:17dc6-a5c-bf716880.Content-Length: 418 Connection: CloseContent-type: image/html Will the web server close the TCP connection after sending this message?
Yes, the server will close this connection because version 1.0 of HTTP is being used, and TCP connections do not stay open persistently.
When an application uses a TCP socket, what transport services are provided to the application by TCP? Check all that apply.
Flow Control. The provided service will ensure that the sender does not send so fast as to overflow receiver buffers. Loss-free data transfer. The service will reliably transfer all data to the receiver, recovering from packets dropped in the network due to router buffer overflow. Congestion control. The service will control senders so that the senders do not collectively send more data than links in the network can handle.
Choose one the following two definitions that makes the correct distinction between routing versus forwarding.
Forwarding is the local action of moving arriving packets from router's input link to appropriate router output link, while routing is the global action of determining the source-destination paths taken by packets.
Which of the following are changes between HTTP 1.1 and HTTP/2? Note: select one or more answers.
HTTP/2 allows a large object to be broken down into smaller pieces, and the transmission of those pieces to be interleaved with transmission other smaller objects, thus preventing a large object from forcing many smaller objects to wait their turn for transmission. HTTP/2 allows objects in a persistent connection to be sent in a client-specified priority order.
Consider the figure below, showing a link-layer frame heading from a host to a router. There are three header fields shown. Match the name of a header with a header label shown in the figure. Header H1 Header H2 Header H3 A. Transport layer B. Link layer C. Network Layer
Header H1 - B Header H2 - C Header H3 - A
Consider the transport-layer flows interacting at a congested link. In the face of such congestion, what happens at this link to a transport-layer flow that does not cut back on its sending rate?
Nothing different from the other flows crossing the congested link.
For delay-based congestion control, match the sender action to the relationship of the currently measured throughput to the value of cwnd/RTTmin The currently measured throughput is greater than cwnd/RTTmin The currently measured throughput is equal to or a bit less than than cwnd/RTTmin The currently measured throughput is much less that than cwnd/RTTmin A. decrease the sending rate B. This should never happen. C. increase the sending rate
The currently measured throughput is greater than cwnd/RTTmin - B The currently measured throughput is equal to or a bit less than than cwnd/RTTmin - C The currently measured throughput is much less that than cwnd/RTTmin - A
What is meant by transport-layer demultiplexing?
Receiving a transport-layer segment from the network layer, extracting the payload (data) and delivering the data to the correct socket.
Check all of the services below that are provided by the TCP protocol.
Reliable data delivery. A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender. A congestion control service to ensure that multiple senders do not overload network links. A flow-control service that ensures that a sender will not send at such a high rate so as to overflow receiving host buffers. In-order data delivery
What is meant by transport-layer multiplexing?
Taking data from one socket (one of possibly many sockets), encapsulating a data chuck with header information - thereby creating a transport layer segment - and eventually passing this segment to the network layer.
Over what set of bytes is the checksum field in the UDP header computed over?
The entire UDP segment, except the checksum field itself, and the IP sender and receive address fields
Which of the definitions below describe what is meant by the term "encapsulation"?
Taking data from the layer above, adding header fields appropriate for this layer, and then placing the data in the payload field of the "packet" for that layer.
What is the purpose of the HTTP GET message?
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.
When we say that the Internet is a "network of networks," we mean? Check all that apply (hint: check two or more).
The Internet is made up of access networks at the edge, tier-1 networks at the core, and interconnected regional and content provider networks as well. The Internet is made up of a lot of different networks that are interconnected to each other.
How does the networked application running on a server know the client IP address and the port number to reply to in response to a received datagram?
The application code at the server determines client IP address and port # from the initial segment sent by client, and must explicitly specify these values when sending into a socket back to that client.
The utilization of client link is:
The client's utilization = Rbottleneck / RC = 50/90 = 0.56
What is the purpose of a cookie value in the HTTP GET request?
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 are some reasons for discarding received-but- out-of-sequence packets at the receiver in GBN? Indicate one or more of the following statements that are correct.
The implementation at the receiver is simpler. The sender will resend that packet in any case.
Check all of the phrases below that state a true property of a local DNS server.
The local DNS server can decrease the name-to-IP-address resolution time experienced by a querying local host over the case when a DNS is resolved via querying into the DNS hierarchy.
Which of the characteristics below are associated with a client-server approach to structuring network applications (as opposed to a P2P approach)?
There is a server with a well known server IP address. HTTP uses this application structure. There is a server that is always on.
What happens when a socket connect() procedure is called/invoked?
This procedure creates a new socket at the client, and connects that socket to the specified server.
True or False: It is possible for two TCP segments with source port 80 to be sent by the sending host to different clients.
True
True or False: It is possible for two UDP segments to be sent from the same socket with source port 5723 at a server to two different clients.
True
True or False: On the sending side, the UDP sender will take each application-layer chunk of data written into a UDP socket and send it in a distinct UDP datagram. And then on the receiving side, UDP will deliver a segment's payload into the appropriate socket, preserving the application-defined message boundary.
True
True or False: The transport layer provides for host-to-host delivery service?
True
True or False: When computing the Internet checksum for two numbers, a single flipped bit (i.e., in just one of the two numbers) will always result in a changed checksum.
True
True or False: When multiple UDP clients send UDP segments to the same destination port number at a receiving host, those segments (from different senders) will always be directed to the same socket at the receiving host.
True
True or False: with TCP's flow control mechanism, where the receiver tells the sender how much free buffer space it has (and the sender always limits the amount of outstanding, unACKed, in-flight data to less than this amount), it is not possible for the sender to send more data than the receiver has room to buffer.
True
Which of the characteristics below are associated with the technique of packet switching?
This technique is used in the Internet. Data may be queued before being transmitted due to other user's data that's also queueing for transmission. Resources are used on demand, not reserved in advance. Congestion loss and variable end-end delays are possible with this technique.
Which of the characteristics below are associated with the technique of circuit switching?
This technique was the basis for the telephone call switching during the 20th century and into the beginning of this current century. Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two approaches for implementing this technique. Reserves resources needed for a call from source to destination.
Suppose a client is sending an HTTP GET message to a web server, gaia.cs.umass.edu. Suppose the client-to-server HTTP GET message is the following: GET /kurose_ross_sandbox/interactive/quotation2.htm HTTP/1.1Host: gaia.cs.umass.eduAccept: text/plain, text/html, text/xml, image/jpeg, image/gif, audio/mpeg, audio/mp4, video/wmv, video/mp4,Accept-Language: en-us, en-gb;q=0.1, en;q=0.7, fr, fr-ch, da, de, fiIf-Modified-Since: Wed, 09 Sep 2020 16:06:01 -0700User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11 Does the client have a cached copy of the object being requested?
Yes, because this is a conditional GET.
Consider the rdt2.1 sender and receiver FSMs shown below, with labeled transitions S1 through S6 at the sender, and transitions R1 through R6 at the receiver. The sender and receiver start in the "Wait for call 0 from above" and "Wait for 0 from below" states, respectively. Suppose that no channel errors occur. A sequence of interleaved sender and receiver transitions is given below. Transitions S1 and S4 are already provided. Choose the sender or receiver transition for the unlabeled transitions x1, x2, x3, and x4 below to indicate the time-ordered sequence of transitions (interleaved sender and receiver transitions) that will result in two messages being delivered at the receiver, with the sender and receiver returning to their initial states (again, given that no channel errors occur). S1, x1, x2, S4, x3, x4 A. S3 B. R1 C. R4 D. S6
transition x1 - B transition x2 - A transition x3 - C transition x4 - D
Consider the rdt2.1 sender and receiver FSMs shown below, with labeled transitions S1 through S6 at the sender, and transitions R1 through R6 at the receiver. The sender and receiver start in the "Wait for call 0 from above" and "Wait for 0 from below" states, respectively. Suppose that the first packet from the sender is correctly received at the receiver but that ACK message sent from receiver-to-sender is corrupted; all other messages (before or after that ACK) are transmitted error-free. Match the unlabeled transitions x1, x2, x3, x4, x5 in the time-ordered sequence of transitions below (interleaved sender and receiver transitions) that will occur following the initial S1 transition, which is followed by a corrupted ACK transmission, that will result in a message being delivered at the receiver, with the sender and receiver returning to their initial states. Note that some transitions are already provided below.S1, x1 (ACK corrupted), x2, x3, x4, S4, x5, S6. A. R4 B. R1 C. R3 D. S3 E. S2
transition x1 - B transition x2 - E transition x3 - C transition x4 - D transition x5 - A
Suppose that the local DNS server caches all information coming in from all root, TLD, and authoritative DNS servers for 20 time units. (Thus, for example, when a root server returns the name and address of a TLD server for .com, the cache remembers that this is the TLD server to use to resolve a .com name). Assume also that the local cache is initially empty, that iterative DNS queries are always used, that DNS requests are just for name-to-IP-address translation, that 1 time unit is needed for each server-to-server or host-to-server (one way) request/response, and that there is only one authoritative name server (each) for any .edu or .com domain. Consider the following DNS requests, made by the local host at the given times: t=0, the local host requests that the name gaia.cs.umass.edu be resolved to an IP address. t=1, the local host requests that the name icann.org be resolved to an IP address. t=5, the local host requests that the name cs.umd.edu be resolved to an IP address. (Hint: be careful!) t=10, the local host again requests that the name gaia.cs.umass.edu be resolved to an IP address. t=12, the local host requests that the name cs.mit.edu be resolved to an IP address. t=30, the local host again requests that the name gaia.cs.umass.edu be resolved to an IP address. (Hint: be careful!) Which of the requests require 8 time units to be resolved?
**FIX**
In DASH (Dynamic, Adaptive Streaming over HTTP), a server divides a video file into chunks that ... (pick best completion from below)
... are stored, each encoded at multiple rates (video quality). The client plays the video chunk-by-chunk, with each chunk requested at encoding rate that fits the available bandwidth at the time.
Assuming that the congestion window size,cwnd, has not yet reached Wmax, TCP CUBIC will ... (check all that apply)
... increase its sending rate faster than AIMD when cwnd is far away from Wmax, but increase slower than AIMD when cwnd is closer to Wmax ... always have a window size, cwnd, and hence a sending rate, higher than that of AIMD (assuming a given window size, Wmax, at which loss would occur).
Compute the Internet checksum value for these two 16-bit words: 11110101 11010011 and 10110011 01000100
01010110 11100111 (add the two numbers and find the one's compliment [invert], in this question, the addition came up with an overflow 1. Take this overflow to the right side and keep adding it until it cannot)
Which of the following pieces of information will appear in a server's application-level HTTP reply message?
A response code A response phrase associated with a response code
Suppose a packet is 10K bits long, the channel transmission rate connecting a sender and receiver is 10 Mbps, and the round-trip propagation delay is 10 ms. What is the channel utilization of a pipelined protocol with an arbitrarily high level of pipelining for this channel?
1.0
Suppose a client is sending an HTTP GET request message to a web server, gaia.cs.umass.edu. Suppose the client-to-server HTTP GET message is the following: GET /kurose_ross_sandbox/interactive/quotation2.htm HTTP/1.1Host: gaia.cs.umass.eduAccept: text/plain, text/html, text/xml, image/jpeg, image/gif, audio/mpeg, audio/mp4, video/wmv, video/mp4,Accept-Language: en-us, en-gb;q=0.1, en;q=0.7, fr, fr-ch, da, de, fiIf-Modified-Since: Wed, 09 Sep 2020 16:06:01 -0700User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11 What version of HTTP is the client using?
1.1
What is the maximum throughput achievable between sender and receiver in the scenario shown below? (link capacity 1: 1.5 Mbits/sec, link capacity 2: 10 Mbits/sec)
1.5Mbps because it is the lowest
Suppose a packet is 10K bits long, the channel transmission rate connecting a sender and receiver is 10 Mbps, and the round-trip propagation delay is 10 ms. How many packets can the sender transmit before it starts receiving acknowledgments back?
10
Compute the Internet checksum value for these two 16-bit words: 01000001 11000100 and 00100000 00101011
10011110 00010000
Consider the circuit-switched network shown in the figure below, with four circuit switches A, B, C, and D. Suppose there are 20 circuits between A and B, 19 circuits between B and C, 15 circuits between C and D, and 16 circuits between D and A. What is the maximum number of connections that can be ongoing in the network at any one time?
20+16+19+15=70. Add up all the circuits
How many RTTs are there from when a client first contacts an email server (by initiating a TCP session) to when the client can begin sending the email message itself - that is following all initial TCP or SMTP handshaking required?
3
What are advantages of implementing transport-layer functionality in QUIC at the application layer? Select all that apply.
As an application-layer protocol, QUIC can be updated/modified at "app frequency" rather than at the frequency of operating system updates. QUIC can establish all connection parameters (security, reliability, flow and congestion control)in just one handshake rather than separately in two.
Suppose a Web server has five ongoing connections that use TCP receiver port 80, and assume there are no other TCP connections (open or being opened or closed) at that server. How many TCP sockets are in use at this server?
6
Consider the network shown in the figure below, with three links, each with the specified transmission rate and link length. Assume the length of a packet is 8000 bits. What is the transmission delay at link 2? (Link 2 is: Transmission rate: 100 Mbps, Link Length: 1000 Km)
8 x 10^(-5) secs (8000bits/(100Mbps*1,000,000bits)
Which of the following descriptions below correspond to a "nuts-and-bolts" view of the Internet?
A collection of billions of computing devices, and packet switches interconnected by links. A collection of hardware and software components executing protocols that define the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event. A "network of networks".
What is an HTTP cookie used for?
A cookie is a code used by a server, carried on a client's HTTP request, to access information the server had earlier stored about an earlier interaction with this Web browser. [Think about the distinction between a browser and a person.]
What is meant by a cumulative acknowledgment, ACK(n)?
A cumulative ACK(n) acks all packets with a sequence number up to and including n as being received.
What information does the type "A" resource record hold in the DNS database? Check all that apply.
A hostname and an IP address
Check all of the services below that are provided by the UDP protocol.
A message abstraction, that preserves boundaries between message data sent in different socket send calls at the sender.
Which of the following descriptions below correspond to a "services" view of the Internet?
A platform for building network applications. A place I go for information, entertainment, and to communicate with people.
Match the definition/function of an element or approach in a networked streaming video system, with its name. A unit of video, each of which may be encoded at multiple different rates, stored in different files. A file containing the location and encoding rate of files corresponding to video segments in a video. An approach that allows a client to adapt the encoding rate of retrieved video to network congestion conditions. A CDN approach that stores content in access networks, close to clients. A. Enter deep B. DASH C. Manifest D. Chunk
A unit of video, each of which may be encoded at multiple different rates, stored in different files. - D A file containing the location and encoding rate of files corresponding to video segments in a video. - C An approach that allows a client to adapt the encoding rate of retrieved video to network congestion conditions. - B A CDN approach that stores content in access networks, close to clients. - A
What do we mean when we say "HTTP is stateless"? In answering this question, assume that cookies are not used. Check all answers that apply.
An HTTP server does not remember anything about what happened during earlier steps in interacting with this HTTP client.
Match the name of an Internet layer with unit of data that is exchanged among protocol entities at that layer, using the pulldown menu. Application layer Transport layer Network layer Link layer Physical layer A. Frame B. Datagram C. Message D. Segment E. Bit
Application layer - C Transport layer - D Network layer - B Link layer - A Physical layer - E
Why is the UDP header length field needed?
Because the payload section can be of variable length, and this lets UDP know where the segment ends.
Consider the TCP Telnet scenario below (from Fig. 3.31 in text). Why is it that the receiver sends an ACK that is one larger than the sequence number in the received datagram?
Because the send-to receiver segment carries only one byte of data, and after that segment is received, the next expected byte of data is just the next byte (i.e., has an index that is one larger) in the data stream.
In SR, why does the receiver have to acknowledge packets with sequence numbers that are less than (and to the left of) those in its window, which starts at rcv_base.
Because the sender may not have received an ACK for that packet yet.
When an application uses a UDP socket, what transport services are provided to the application by UDP? Check all that apply.
Best effort service. The service will make a best effort to deliver data to the destination but makes no guarantees that any particular segment of data will actually get there.
Which of the following are advantages of using a web cache? Sselect one or more answers.
Caching uses less bandwidth coming into an institutional network where the client is located, if the cache is also located in that institutional network. Caching generally provides for a faster page load time at the client, if the web cache is in the client's institutional network, because the page is loaded from the nearby cache rather than from the distant server.
Consider the TCP Telnet scenario below (from Fig. 3.36 in text). What timer-related action does the sender take on the receipt of ACK 120?
Cancels any running timers
The transport layer sits on top of the network layer, and provides its services using the services provided to it by the network layer. Thus it's important that we know what is meant by the network layer's "best effort" delivery service. True or False: The network layer's best-effort delivery service means that IP makes its "best effort" to deliver segments between communicating hosts, but it makes no guarantees. In particular, it does not guarantee segment delivery, it does not guarantee orderly delivery of segments, and it does not guarantee the integrity of the data in the segments.
Correct! The network layer's best effort service doesn't really provide much service at all, does it?
What is the value of caching in the local DNS name server? Check all that apply.
DNS caching provides for faster replies, if the reply to the query is found in the cache. DNS caching results in less load elsewhere in DNS, when the reply to a query is found in the local cache.
Consider a scenario in which 5 users are being multiplexed over a channel of 10 Mbps. Under the various scenarios below, match the scenario to whether circuit switching or packet switching is better. Each user generates traffic at an average rate of 2.1 Mbps, generating traffic at a rate of 15 Mbps when transmitting Each user generates traffic at an average rate of 2 Mbps, generating traffic at a rate of 2 Mbps when transmitting Each user generates traffic at an average rate of 0.21 Mbps, generating traffic at a rate of 15 Mbps when transmitting A. Packet switching B. Circuit switching C. Neither works well in this overload scenario
Each user generates traffic at an average rate of 2.1 Mbps, generating traffic at a rate of 15 Mbps when transmitting - C Each user generates traffic at an average rate of 2 Mbps, generating traffic at a rate of 2 Mbps when transmitting - B Each user generates traffic at an average rate of 0.21 Mbps, generating traffic at a rate of 15 Mbps when transmitting - A
Match the networking event with the time frame when the event occurred. Early studies of packet switching by Baran, Davies, Kleinrock. First ARPAnet node operational. Internetting: DARPA researchers connect three networks together. The Internet Protocol (IP) is standardized in RFC 791. Congestion control is added to the TCP protocol. The WWW starts up (note: the WWW design started at the end of previous decade). Software-defined networking begins. The number wireless Internet-connected devices surpasses the number of connected wired devices. A. 1970's B. Late 1980's C. 1990's D. 2010 - 2020 E. Early 1960's F. 2000-2010 G. Early 1980's H. Late 1960's
Early studies of packet switching by Baran, Davies, Kleinrock. - E First ARPAnet node operational. - H Internetting: DARPA researchers connect three networks together. - A The Internet Protocol (IP) is standardized in RFC 791. - G Congestion control is added to the TCP protocol. - B The WWW starts up (note: the WWW design started at the end of previous decade). - C Software-defined networking begins.- F The number wireless Internet-connected devices surpasses the number of connected wired devices. - D
Match the access network with the approximate speeds that a subscriber might experience. (Note: if you look these up, do so in the 8E textbook, slides,or video -- not in the 7E or earlier versions, since link access speeds are always increasing over the years). Ethernet 802.11 WiFi Cable access network Digital Subscriber Line 4G cellular LTE A. Wireless. 10's to 100's of Mbps per device. B. Wired. Up to 10's of Mbps downstream per user. C. Wireless. Up to 10's Mbps per device. D. Wired. Up to 10's to 100's of Mbps downstream per user. E. Wired. Up to 100's Gbps per link.
Ethernet - E 802.11 WiFi - A Cable access network - D Digital Subscriber Line - B 4G cellular LTE - C
Consider TCP's Fast Retransmit optimization (see Figure 3.37 from the text, below). Of course, the sender doesn't know for sure that the segment with sequence # 100 is actually lost (it can't see into the channel). Can a sender get three duplicate ACKs for a segment that in fact has not been lost? Which of the following statements are true? Suppose a channel can lose, but will not corrupt, messages.
If the channel cannot reorder messages, a triple duplicate ACK indicates to the sender that a segment loss has happened for sure. Actually (again assuming the channel cannot corrupt or reorder messages), even a single duplicate ACK would indicate that a segment loss has happed for sure. If the channel can reorder messages, a triple duplicate ACK can occur even though a message is not lost; since it's possible that a message has just been reordered and has not yet arrived when the three duplicate ACKs were generated.
Which of the following characteristics apply to both HTTP and SMTP? Note: check one or more of the characteristics below.
Is able to use a persistent TCP connection to transfer multiple objects. Has ASCII command/response interaction, status codes.
What is the role of an authoritative name server in the DNS? (Check all that apply)
It provides the definitive answer to the query with respect to a name in the authoritative name server's domain.
UDP header fields. Which of the fields below are in a UDP segment header? [Hint: note the use of the word "header" in this question statement.]
Length (of UDP header plus payload) Source port number Internet checksum Destination port number
Consider the purposes/goals/use of different reliable data transfer protocol mechanisms. For the given purpose/goal/use match it to the RDT mechanism that is used to implement the given purpose/goal/use. Lets the sender know that a packet was NOT received correctly at the receiver. Used by sender or receiver to detect bits flipped during a packet's transmission. Allows for duplicate detection at receiver. Lets the sender know that a packet was received correctly at the receiver. Allows the receiver to eventually receive a packet that was corrupted or lost in an earlier transmission. A. ACK B. Retransmission C. Checksum D. NAK E. Sequence numbers
Lets the sender know that a packet was NOT received correctly at the receiver. - D Used by sender or receiver to detect bits flipped during a packet's transmission. - C Allows for duplicate detection at receiver. - E Lets the sender know that a packet was received correctly at the receiver. - A Allows the receiver to eventually receive a packet that was corrupted or lost in an earlier transmission. - B
Suppose a UDP segment (A in the figure below) arrives at a host with an IP address of 128.119.40.186. The source port in the UDP segment is 4829 and the destination port is 3546. The IP address of the sending host is 60.54.75.24. Now consider the UDP datagram (and the IP datagram that will encapsulate it) sent in reply by the application on host 128.119.40.186 to the original sender host, labeled B in the figure above. Complete the sentences below ... What are the source and destination port numbers and IP addresses? (Enter the integer port number or the 4-part dotted decimal IP address, included the period) The source port number of the UDP segment (B) sent in reply is: The source IP address of the IP datagram containing the UDP segment (B) sent in reply is: The destination port number of the UDP segment (B) sent in reply is: The destination IP address of the IP datagram containing the UDP segment (B) sent in reply is: A. 60.54.75.24 B. 4829 C. 128.119.40.186 D. 3546
Now consider the UDP datagram (and the IP datagram that will encapsulate it) sent in reply by the application on host 128.119.40.186 to the original sender host, labeled B in the figure above. Complete the sentences below ... What are the source and destination port numbers and IP addresses? (Enter the integer port number or the 4-part dotted decimal IP address, included the period) The source port number of the UDP segment (B) sent in reply is: D The source IP address of the IP datagram containing the UDP segment (B) sent in reply is: C The destination port number of the UDP segment (B) sent in reply is: B The destination IP address of the IP datagram containing the UDP segment (B) sent in reply is: A
Which of the following characteristics apply to HTTP only (and do not apply to SMTP)? Note: check one or more of the characteristics below.
Operates mostly as a "client pull" protocol. Uses server port 80. Uses a blank line (CRLF) to indicate end of request header.
What is the maximum achievable end-end throughput (an integer value, in Mbps) for each of four client-to-server pairs, assuming that the middle link is fairly shared (divides its transmission rate equally) and all servers are trying to send at their maximum rate?
Pick the lowest amount
Match the function of a layer in the Internet protocol stack to its its name in the pulldown menu. Protocols that are part of a distributed network application. Transfer of data between one process and another process (typically on different hosts). Delivery of datagrams from a source host to a destination host (typically). Transfer of data between neighboring network devices. Transfer of a bit into and out of a transmission media. A. Link layer B. Network layer C. Application Layer D. Physical layer E. Transport layer
Protocols that are part of a distributed network application. - C Transfer of data between one process and another process (typically on different hosts). - E Delivery of datagrams from a source host to a destination host (typically). - B Transfer of data between neighboring network devices. - A Transfer of a bit into and out of a transmission media. - D
Match the function of a server to a given type of DNS server in the DNS server hierarchy. Provides authoritative hostname to IP mappings for organization's named hosts. Replies to DNS query by local host, by contacting other DNS servers to answer the query. Responsible for a domain (e.g., *.com, *.edu); knows how to contact authoritative name servers. Highest level of the DNS hierarchy, knows how to reach servers responsible for a given domain (e.g., *.com, *.edu). A. DNS root servers B. Authoritative DNS server C. Local DNS server D. Top Level Domain (TLD) servers
Provides authoritative hostname to IP mappings for organization's named hosts. - B Replies to DNS query by local host, by contacting other DNS servers to answer the query. - C Responsible for a domain (e.g., *.com, *.edu); knows how to contact authoritative name servers. - D Highest level of the DNS hierarchy, knows how to reach servers responsible for a given domain (e.g., *.com, *.edu). - A
Match the functionality of a protocol with the name of a the email protocol (if any) that implements that functionality. Pushes email from a mail client to a mail server. Pulls mail from one mail server to another mail server. Pulls email to a mail client from a mail server. A. IMAP B. Neither SMTP nor IMAP does this C. SMTP
Pushes email from a mail client to a mail server. - C Pulls mail from one mail server to another mail server. - B Pulls email to a mail client from a mail server. - A
What are advantages of the streams concept in QUIC? Select all that apply.
Since each stream has its own error control, if one stream experiences an error (e.g., lost or damaged segment), the other streams are unaffected. Streams allow concurrent retrieval of web objects, while avoiding Head of the Line (HOL) blocking.
Match the description of a security defense with its name. Specialized "middleboxes" filtering or blocking traffic, inspecting packet contents inspections Provides confidentiality by encoding contents Used to detect tampering/changing of message contents, and to identify the originator of a message. Limiting use of resources or capabilities to given users. Proving you are who you say you are. A. Authentication B. Firewall C. Digital signatures D. Access control E. Encryption
Specialized "middleboxes" filtering or blocking traffic, inspecting packet contents inspections - B Provides confidentiality by encoding contents - E Used to detect tampering/changing of message contents, and to identify the originator of a message. - C Limiting use of resources or capabilities to given users. - D Proving you are who you say you are. - A
What approach is taken by a CDN to stream content to hundreds of thousands of simultaneous users?
Store/serve multiple copies of videos at multiple geographically distributed sites.
Use the pulldown menu to match a congestion control approach to how the sender detects congestion. The sender infers segment loss from the absence of an ACK from the receiver. Bits are set at a congested router in a sender-to-receiver datagram, and bits are in the returned to the sender in a receiver-to sender ACK, to indicate congestion to the sender. The sender measures RTTs and uses the current RTT measurement to infer the level of congestion. A. network-assisted B. delay-based C. end-end
The sender infers segment loss from the absence of an ACK from the receiver. - C Bits are set at a congested router in a sender-to-receiver datagram, and bits are in the returned to the sender in a receiver-to sender ACK, to indicate congestion to the sender. - A The sender measures RTTs and uses the current RTT measurement to infer the level of congestion. - B
The utilization of the server links is:
The server's utilization = Rbottleneck / RS[server] = 50 / 50 = 1.00
The utilization of shared link is:
The shared link's utilization = Rbottleneck / (R / [amount of computers sharing]) = 50 / (300/ 4) = 0.67
Which of the characteristics below are associated with a P2P approach to structuring network applications (as opposed to a client-server approach)?
There is NOT a server that is always on. A process requests service from those it contacts and will provide service to processes that contact it.
In the SR receiver window (see diagram below, taken from PPT slides and video), why haven't the red packets been delivered yet? Check the one or more reasons below that apply.
There is a packet with a lower sequence number than any of the red packets that has yet to be received, so in-order delivery of data in the red packets up to the application layer is not possible.
Match the description of each component of packet delay to its name in the pull down list. Time needed to perform an integrity check, lookup packet information in a local table and move the packet from an input link to an output link in a router. Time spent waiting in packet buffers for link transmission. Time spent transmitting packets bits into the link. Time need for bits to physically propagate through the transmission medium from end one of a link to the other. A. Propagation delay B. Processing delay C. Queueing delay D. Transmission delay
Time needed to perform an integrity check, lookup packet information in a local table and move the packet from an input link to an output link in a router. - B Time spent waiting in packet buffers for link transmission. - C Time spent transmitting packets bits into the link. - D Time need for bits to physically propagate through the transmission medium from end one of a link to the other. - A
What is the purpose of the conditional HTTP GET request message?
To allow a server to only send the requested object to the client if this object has changed since the server last sent this object to the client.
What is the purpose of the If-Modified-Since field in a HTTP GET request message
To indicate to the server that the client has cached this object from a previous GET, and the time it was cached.
Manifest file. What is the purpose of a manifest file in a streaming multimedia setting?
To let a client know where it can retrieve different video segments, encoded at different rates
Where is transport-layer functionality primarily implemented?
Transport layer functions are implemented primarily at the hosts at the "edge" of the network.
Which of the following human scenarios involve a protocol (recall: "Protocols define the format, order of messages sent and received among network entities, and actions taken on message transmission, receipt")?
Two people introducing themselves to each other. One person asking, and getting, the time to/from another person. A student raising her/his hand to ask a really insightful question, followed by the teaching acknowledging the student, listening carefully to the question, and responding with a clear, insightful answer. And then thanking the student for the question, since teachers love to get questions.
Which of the following characteristics apply to SMTP only (and do not apply to HTTP)? Note: check one or more of the characteristics below.
Uses CRLF.CRLF to indicate end of message. Uses server port 25. Operates mostly as a "client push" protocol.
Which of the following statements about pipelining are true? One or more statements may be true.
With a pipelined sender, there may be transmitted packets "in flight" - propagating through the channel - packets that the sender has sent but that the receiver has not yet received. A pipelined sender can have transmitted multiple packets for which the sender has yet to receive an ACK from the receiver.
Suppose an HTTP server sends the following HTTP response message a client:HTTP/1.0 200 OKDate: Wed, 09 Sep 2020 23:46:21 +0000Server: Apache/2.2.3 (CentOS)Last-Modified: Wed, 09 Sep 2020 23:51:41 +0000ETag:17dc6-a5c-bf716880.Content-Length: 418Connection: CloseContent-type: image/html Will the web server close the TCP connection after sending this message?
Yes, because this is HTTP 1.0
Which of the following characteristics below are associated with a TCP socket? Check one or more that apply.
a server can perform an accept() on this type of socket socket(AF_INET, SOCK_STREAM) creates this type of socket provides reliable, in-order byte-stream transfer (a "pipe"), from client to server when contacted, the server will create a new server-side socket to communicate with that client
Which of the following characteristics below are associated with a UDP socket? Check one or more that apply.
provides unreliable transfer of a groups of bytes ("a datagram"), from client to server the application must explicitly specify the IP destination address and port number for each group of bytes written into a socket socket(AF_INET, SOCK_DGRAM) creates this type of socket data from different clients can be received on the same socket
Perform a traceroute from your computer (on whatever network you happen to be on) to gaia.cs.umass.edu. Use traceroute (on Mac terminal) or tracert (on Windows command line) or tracepath (on a Linux command line). Enter the missing part of the name of the router just before the host gaia.cs.umass.edu is reached: ??.cs.umass.edu
nscs1bbs1 (on windows cmd use: tracert gaia.cs.umass.edu)
Consider the rdt2.1 sender and receiver FSMs shown below, with labeled transitions S1 through S6 at the sender, and transitions R1 through R6 at the receiver. The sender and receiver start in the "Wait for call 0 from above" and "Wait for 0 from below" states, respectively. Suppose that the initial message transmission by the sender is corrupted, but that no other message transmissions are corrupted. Match the unlabeled transitions x1, x2, x3, x4, x5 in the time-ordered sequence of transitions below (interleaved sender and receiver transitions) that will occur following the initial S1 transition (which is corrupted), that will result in two messages being delivered at the receiver, with the sender and receiver returning to their initial states (again, given that the initial message transmission by the sender is corrupted). Note that transitions S1, S4, and S6 are already provided below. S1 (message corrupted), x1, x2, x3, x4, S4, x5, S6. A. R1 B. S2 C. R6 D. S3 E. R4
transition x1 - C transition x2 - B transition x3 - A transition x4 - D transition x5 - E
