CN T2

3.5-5 TCP RTT Estimation: EWMA. Consider TCP use of an exponentially weighted moving average (EWMA) to compute the nth value of the estimated RTT:

False

3.7-3 TCP's Slowstart algorithm. 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."

7.3-2. Use of ACKs in WiFi. Why are link-layer ACKs used in WiFi (802.11) networks? [Hint: check two of the boxes below].

-> Because of the hidden terminal problem, a node that is transmitting and hears no collisions still doesn't know if there was a collision at the receiver. -> Wireless links are noisier than wired links, and so bit level errors are more likely to occur, making link-layer error recovery more valuable that in less-noisy wired links.

7.2-1. Characteristics of wireless links. Which of the following statements about the characteristics of wireless links are true?

- The "hidden terminal problem" happens when A sends to B over a wireless channel, and an observer, C (that can be even closer to A than B), does not detect/receive A's transmission because of physical obstacles in the path between A and C. -The bit error rate (BER) of a wireless channel decreases as the signal-to-noise ratio (SNR) increases. -Multipath propagation occurs when portions of the electromagnetic wave reflect off objects and the ground taking paths of different lengths between the sender and a receiver, and thus arriving at the receiver at slightly different points in time.

3.7-5 TCP CUBIC. Assuming that the congestion window size, cwnd, has not yet reached Wmax, TCP CUBIC will ... (check all that apply)

-> ... 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). -> ... 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

7.3-4. RTS/CTS frames. What is the purpose of RTS (request to send) and CTS (clear to send) frames in WiFi (802.11) networks? Select one or more of the answers below. [Hint: check two answers below].

-> A CTS that is sent allows a receiver to force other nodes (other than the intended sender who sent the RTS) to refrain from transmitting, thus allowing the sender who sent the RTS to then transmit a frame with less likelihood of a collision. -> RTC/CTS frames helps nodes in a wireless network mitigate the effects of the hidden terminal problem.

3.3-4a. What is a checksum? Which of the following statements are true about a checksum? Hint: more than one statement is true.

-> A checksum is computed at a sender by considering each byte within a packet as a number, and then adding these numbers (each number representing a bytes) together to compute a sum (which is known as a checksum). -> The sender-computed checksum value is often included in a checksum field within a packet header. -> The receiver of a packet with a checksum field will add up the received bytes, just as the sender did, and compare this locally-computed checksum with the checksum value in the packet header. If these two values are different then the receiver knows that one of the bits in the received packet has been changed during transmission from sender to receiver.

3.4-10 Pipelining. Which of the following statements about pipelining are true? One or more statements may be true.

-> A pipelined sender can have transmitted multiple packets for which the sender has yet to receive an ACK from the receiver. -> 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.

2.1-2 The peer-to-peer (P2P) paradigm. Which of the characteristics below are associated with a P2P approach to structuring network applications (as opposed to a client-server approach)?

-> A process requests service from those it contacts and will provide service to processes that contact it. -> There is not a server that is always on.

2.2-11 What's in an HTTP reply? Which of the following pieces of information will appear in a server's application-level HTTP reply message? (Check all that apply.)

-> A response code -> A response phrase associated with a response code

3.7-1 TCP's AIMD algorithm. Which of the following statements about TCP's Additive-increase-multiplicative-decrease (AIMD) algorithm are true? Check all that are true.

-> AIMD is a end-end approach to congestion control. -> AIMD cuts the congestion window size, cwnd, in half whenever loss is detected by a triple duplicate ACK. -> AIMD cuts the congestion window size, cwnd, i to 1 whenever a timeout occurs.

3.8-3 QUIC: an application-layer protocol. 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.

2.4-1 DNS functions. 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).

-> Authoritative DNS server -> Local DNS server -> Top Level Domain (TLD) servers -> DNS root servers

2.6-2 Streaming video definitions. 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.

-> Chunk -> Manifest -> DASH -> Enter deep

2.4-2 Why does the DNS perform caching? What is the value of caching in the local DNS name server? Check all that apply.

-> DNS caching results in less load elsewhere in DNS, when the reply to a query is found in the local cache. -> DNS caching provides for faster replies, if the reply to the query is found in the cache.

2.1-1 The client-server paradigm. Which of the characteristics below are associated with a client-server approach to structuring network applications (as opposed to a P2P approach)?

-> HTTP uses this application structure. -> There is a server that is always on. -> There is a server with a well known server IP address.

2.2-10 HTTP/2 versus HTTP/1.1. Which of the following are changes between HTTP 1.1 and HTTP/2? Note: select one or more answers.

-> HTTP/2 allows objects in a persistent connection to be sent in a client-specified priority order. -> 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.

3.5-9 TCP Fast Retransmit. 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.

3.3-2 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.]

-> Internet Checksum -> Source port number -> Destination port number -> Length (of UDP header plus payload)

2.3-4 Comparing and contrasting HTTP and SMTP (3). 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.

2.1-4 TCP service. When an application uses a TCP socket, what transport services are provided to the application by TCP? Check all that apply.

-> 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. -> Flow Control. The provided service will ensure that the sender does not send so fast as to overflow receiver buffers.

3.1-3 Transport layer services using TCP. Check all of the services below that are provided by the TCP protocol.

-> Reliable data delivery -> In-order data delivery -> A flow-control service that ensures that a sender will not send at such a high rate so as to overflow receiving host buffers. -> A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender.

2.3-5 Which e-mail protocol? 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.

-> SMTP -> Neither SMTP nor IMAP does this. -> IMAP

-> A message from client to server initiating a connection request. -> A message from server to client ACKing receipt of a SYN message and indicating the willingness of the server to establish a TCP connection with the client. -> A message indicating that the sending side is initiating the protocol to terminate a connection. -> A message sent in response to a request to terminate a connection, ACKing that the side receiving this message is also willing to terminate the connection -> A general purpose error message used during connection set up or tear down to let the other side know that an error has occurred, and that the referenced connection should be shut down.

-> SYN mesage -> SYNACK message -> FIN message ->FINACK message -> RESET message

-> This field contains the port number associated with the sending socket for this TCP segment. -> This field contains application data that was written into a socket by the sender of this TCP segment. -> This field contains the index in the sender-to-receiver byte stream of the first byte of that data in the payload carried in this segment. -> This field contains the index in the byte stream of the next in-order byte expected at the receiver -> If set, this segment cumulatively ACKs all data bytes up to, but not including, the byte index in the ACK value field of this segment. -> This field contains the number of available bytes in the TCP receiver's buffer. -> This field contains the Internet checksum of the TCP segment and selected fields in the IP datagram header. -> This field contains the number of bytes in the TCP header.

-> Source port number -> Data (or payload). -> sequence number -> ACK number field -> ACK bit -> Reciever advetised window -> checksum -> header length field

3.8-2 QUIC streams. What are advantages of the streams concept in QUIC? Select all that apply.

-> Streams allow concurrent retrieval of web objects, while avoiding Head of the Line (HOL) blocking. -> 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.

2.4-7 The local DNS server. Check all of the phrases below that state a true property of a local DNS server.

-> The local DNS server record for a remote host is sometimes different from that of the authoritative server for that host. -> 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.

Overlapping WiFi networks. Suppose there are two ISPs providing WiFi access in a particular café, with each ISP operating its own AP and having its own IP address block. Further suppose that by accident, each ISP has configured its AP to operate over channel 11. Which of the following statements are true? [Hint: ]ore than one of the following statements is true].

-> Two devices transmitting at the same time will interfere with each other, regardless of the network to which they are associated. -> Devices will still be able to associate with one network or the other.

2.7-1 UDP client-side socket actions. Match the general client-side action stated with the specific UDP socket-related action that implements it. -> Create a socket. ->When sending to the server, this is how a specific server is identified. -> Send to server, using this socket.

-> Use the call socket(AF_INET, SOCK_DGRAM) -> The client explicitly includes the destination IP address and port #, when sending -> Send using the socket created using socket(AF_INET, SOCK_DGRAM)

2.7-2 UDP server-side socket actions. Match the general server-side action stated with the specific UDP socket-related action that implements it. -> Create a socket -> When sending to a client, this is how a specific client is identified. -> Send to client, using this socket. -> When sending to the client, this is how the server knows the client IP address and port number.

-> Use the call socket(AF_INET, SOCK_DGRAM) -> The client explicitly includes the destination IP address and port #, when sending -> Send using the socket created using socket(AF_INET, SOCK_DGRAM) -> The server determines the client IP address and port # from an earlier datagram sent by this client.

2.7-4 TCP server-side socket actions. Match the general server-side action stated with the specific TCP socket-related action that implements it. -> create a socket -> When sending to a client, this is how a specific client is identified. -> Send to server, using this socket.

-> Use the call socket(AF_INET, SOCK_STREAM) -> As the result of an accept(), a new socket is created, which binds the client that made the corresponding connect() and server together via this new socket without the need to to explicitly specify the destination IP address and port # when sending. -> Send using a socket not explicitly created via a call to socket()

2.7-3 TCP client-side socket actions. Match the general client-side action stated with the specific TCP socket-related action that implements it. -> Create a socket -> When sending to a server, this is how a specific server is identified. -> Send to server, using this socket.

-> Use the call socket(AF_INET, SOCK_STREAM) -> The client uses connect() to explicitly bind its socket to specific server, and so the server IP address and port number need not be explicitly stated in a send operation. -> Send using the socket created using socket(AF_INET, SOCK_STREAM)

2.3-3 Comparing and contrasting HTTP and SMTP (2). 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.

2.3-2 Comparing and contrasting HTTP and SMTP. Which of the following characteristics apply to HTTP only (and do not apply to SMTP)? Note: check one or more of the characteristics below.

-> Uses a blank line (CRLF) to indicate end of request header. -> Uses server port 80. -> Operates mostly as a "client pull" protocol.

7.4-3. Comparing three wireless network types. Consider three wireless networks that we learned about: WiFi (802.11), 4G LTE, and Bluetooth. Match each of these types of networks to a characteristic on the right.

-> WiFi (802.11) - Has the maximum link capacity (i.e., can deliver more bits/sec to the edge device). -> 4G/LTE - Can provide the farthest coverage (i.e., longest range wireless communication) from a base station. -> Bluetooth - Consumes the least amount of power.

2.2-9 Why Web Caching? Which of the following are advantages of using a web cache? Sselect one or more answers.

->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. -> Caching uses less bandwidth coming into an institutional network where the client is located, if the cache is also located in that institutional network.

2.6-3 What is DASH? 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.

3.06.a.2 Consider again rdt3.0 and the diagram of messages exchanges above. What is the ACK number on the packet sent by the receiver at time t1? (Note: there is only one correct answer below).

0

7.3-1. Beacon Frames. What is the purpose of a beacon frame in WiFi (802.11) networks

A beacon frame allows an access point to advertise its existence, and the frequency channel it is operating on, to devices that want to connect to an access point.

3.03-1 Internet Checksum. Consider the two sixteen bit numbers: 10110100 01000110 01001000 01101111

00000011 01001010

3.3-5 Computing the Internet Checksum (1). Compute the Internet checksum value for these two 16-bit words: 11110101 11010011 and 10110011 01000100

01010110 11100111

2.2-2 HTTP cookies. 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.]

3.08-1 TCP sequence and ACK numbers (a). Consider the figure below, where a TCP sender sends 8 TCP segments at t = 1, 2, 3, 4, 5, 6, 7, 8. Suppose the initial value of the sequence number is 0 and every segment sent to the receiver each contains 100 bytes. The delay between the sender and receiver is 5 time units, and so the first segment arrives at the receiver at t = 6. The ACKs sent by the receiver at t = 6, 7, 8, 10, 11, 12 are shown. The TCP segments (if any) sent by the sender at t = 11, 13, 15, 16, 17, 18 are not shown.

100

3.3-6 Computing the Internet Checksum (2). Compute the Internet checksum value for these two 16-bit words: 01000001 11000100 and 00100000 00101011

10011110 00010000

3.07-1 TCP RTT estimation and timeout value (a). Suppose that TCP's current estimated values for the round trip time (estimatedRTT) and deviation in the RTT (DevRTT) are 300 msec and 13 msec, respectively. Suppose that the next two measured RTTs are 330 msec and 240 msec respectively. We want to calculate TCP's RTT estimate, and the value of TCP's timeout interval. Note that given a new measured RTT, you should first compute devRTT, then estimatedRTT (the textbook incorrectly reverses those computations), and then (lastly) the timeout interval. Use the values of α = 0.125, β = 0.25.

17

3.4-6 Cumulative ACK. 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.

2.4-3 What's in the DNS type A resource record? What information does the type "A" resource record hold in the DNS database? Check all that apply.

A hostname and an IP address.

2.2-1 Simple HTTP GET request response time. Suppose an HTTP client makes a request to the gaia.cs.umass.edu web server. The client has never before requested a given base object, nor has it communicated recently with the gaia.cs.umass.edu server. You can assume, however, that the client host knows the IP address of gaia.cs.umass.edu.

2.5 RTT

3.07-4 TCP RTT estimation and timeout value (d). Suppose that TCP's current estimated values for the round trip time (estimatedRTT) and deviation in the RTT (DevRTT) are 300 msec and 13 msec, respectively. Suppose that the next two measured RTTs are 330 msec and 240 msec respectively. We want to calculate TCP's RTT estimate, and the value of TCP's timeout interval. Note that given a new measured RTT, you should first compute devRTT, then estimatedRTT (the textbook incorrectly reverses those computations), and then (lastly) the timeout interval. Use the values of α = 0.125, β = 0.25.

29

3.07-5 TCP RTT estimation and timeout value (e). Suppose that TCP's current estimated values for the round trip time (estimatedRTT) and deviation in the RTT (DevRTT) are 300 msec and 13 msec, respectively. Suppose that the next two measured RTTs are 330 msec and 240 msec respectively. We want to calculate TCP's RTT estimate, and the value of TCP's timeout interval. Note that given a new measured RTT, you should first compute devRTT, then estimatedRTT (the textbook incorrectly reverses those computations), and then (lastly) the timeout interval. Use the values of α = 0.125, β = 0.25.

296

2.3-1 E-mail delays. 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

3.07-2 TCP RTT estimation and timeout value (b). Suppose that TCP's current estimated values for the round trip time (estimatedRTT) and deviation in the RTT (DevRTT) are 300 msec and 13 msec, respectively. Suppose that the next two measured RTTs are 330 msec and 240 msec respectively. We want to calculate TCP's RTT estimate, and the value of TCP's timeout interval. Note that given a new measured RTT, you should first compute devRTT, then estimatedRTT (the textbook incorrectly reverses those computations), and then (lastly) the timeout interval. Use the values of α = 0.125, β = 0.25.

304

3.1-4 Transport-layer services using UDP. 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.

3.07-3 TCP RTT estimation and timeout value (c). Suppose that TCP's current estimated values for the round trip time (estimatedRTT) and deviation in the RTT (DevRTT) are 300 msec and 13 msec, respectively. Suppose that the next two measured RTTs are 330 msec and 240 msec respectively. We want to calculate TCP's RTT estimate, and the value of TCP's timeout interval. Note that given a new measured RTT, you should first compute devRTT, then estimatedRTT (the textbook incorrectly reverses those computations), and then (lastly) the timeout interval. Use the values of α = 0.125, β = 0.25.

373

2.2-3 HTTP 1.1 GET with an embedded object. Suppose an HTTP client makes a request to the gaia.cs.umass.edu web server. The client has never before requested a given base object, nor has it communicated recently with the gaia.cs.umass.edu server. You can assume, however, that the client host knows the IP address of gaia.cs.umass.edu. Suppose also that after downloading the base file, the browser encounters a jpeg object in the base html file that is stored on gaia.cs.umass.edu, and therefore makes another GET request to gaia.cs.umass.edu for that referenced jpeg object.

4 RTT

3.07-6 TCP RTT estimation and timeout value (f). Suppose that TCP's current estimated values for the round trip time (estimatedRTT) and deviation in the RTT (DevRTT) are 300 msec and 13 msec, respectively. Suppose that the next two measured RTTs are 330 msec and 240 msec respectively. We want to calculate TCP's RTT estimate, and the value of TCP's timeout interval. Note that given a new measured RTT, you should first compute devRTT, then estimatedRTT (the textbook incorrectly reverses those computations), and then (lastly) the timeout interval. Use the values of α = 0.125, β = 0.25.

411

7.4-5. Connecting 4G cellular networks together. Which of the following statements is true about how 4G cellular networks (operated by different carriers/companies) connect together?

4G networks are generally all-IP, and so cellular networks interconnect (peer) directly to each other, or peer at the cellular equivalents of the Internet Exchange Points that we saw used for interconnecting wired networks in the public Internet.

7.1-1. How fast is that wireless technology? Use the pulldown menus below to match the approximate transmission rate with the the wireless technology that achieves that rate. Of course, sender/receiver distance, noise and other factors determine actual transmission speed, so "your mileage may vary" (YMMV).

802.11 ax - 14 Gbps 5G celluar - 10 Gbps 802.11 ac - 3.5 Gbps 4G LTE - hundreds of Mbps 802.11 g - 54 Mbps Bluetooth - 2 Mbps

7.4-2. IMSI. In 4G LTE cellular systems, what is an International Mobile SubscriberIdentity (IMSI)?

A 64-bit identifier stored on a cellular SIM (Subscriber Identity Module) card that identifies the subscriber in the worldwide cellular carrier network system.

2.2-1 "HTTP is stateless." 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.

2.2-9 HTTP/2 versus HTTP/1.1: object download delays. Consider a client and a server, separated by an RTT of 4 time units. The client makes a request for 4 objects at t=0. O1 consists of 10 frames, O2 and O4 each consist of 1 frame, and O3 consists of 2 frames. In the HTTP/2 example shown below, the server is transmitting frames to the client in the order O1, O2, O3, O4 (as long as there are frames of type i to transmit, and when not the server just moves on to a frame from object i+1 mod 4). Each frame takes 1 time unit to transmit.

Average object download delay under HTTP/1.1: 16.0, under HTTP/2: 10.5

7.3-3. Why three addresses? Why does the WiFi (802.11) link-layer frame have three addresses? [Note: WiFi actually has four MAC addresses in the frame, but we're only focusing here on the three widely used ones].

Because both the access point that will relay this frame to the intended link-layer receiving host or router interface, as well as that intended destination host or router interface need to be specified.

3.3-3 UDP segment length field. 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.

3.5-3 TCP sequence numbers and ACKs (1). 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.

2.1-3 UDP service. 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.

7.3-6. Bluetooth. Which of the following statement are true about the Bluetooth protocol?

Bluetooth uses TDM, FDM, polling, error detection and correction, and has sleep modes to conserve device power. Pretty sophisticated for a consumer technology!

7.4-6. Reliable data transfer at the link layer. Which of the following statements is true about the link-level service of reliable data transfer (using ACKs) in WiFi (802.11) networks and in 4G cellular networks?

Both WiFi and LTE provide link-level reliable data transfer.

7.4-4. Power conserving "sleep modes". Which of the following statements is true about "sleep modes" that allow a wireless device to "sleep" and occasionally "wake up" as a technique for saving battery life?

Both WiFi and LTE provide sleep modes

3.7-2 TCP's AIMD algorithm (2). 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.

3.5-6 TCP timer management. 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

3.1-5 Network-layer functionality. 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:

Correct! The network layer's best effort service doesn't really provide much service at all, does it?

7.1-2. Infrastructure Mode. What is meant when we say that a network of devices is operating in "infrastructure mode"?

Devices communicate with each other and to the larger outside world via a base station (also known as an access point).

3.2-4 Multiplexing/Demultiplexing: TCP port numbers. 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

3.3-8 UDP Checksum: how good is it? 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

3.5-1 TCP reliability semantics. 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

2.6-3 Netflix Streaming. Which of the following (one or more) statements are true about Netflix streaming (check all that are true) or video streaming services in general.

In many video streaming services, the client requests chunks of video from a server using the HTTP protocol.

2.4-8 The DNS authoritative name server. 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.

2.4-7 DNS local caches. We saw that a local DNS cache will respond immediately to a client when the local DNS has the name-to-address translation in its local cache. There are millions of such local DNS caches across the Internet. For a given Internet name, will the name-to-address translation pair stored in these local caches always be the same (i.e., are the contents of the local caches synchronized)?

No. The caches are not always synchronized. An entry in a local cache will eventually time out, and the local cache will again eventually go to the DNS hierarchy to get the name-to-address translation pair for this name. So if the name-to-address mapping changes in the DNS hierarchy, the new mapping will eventually (but not immediately) make its way into the local cache. Therefore not all local caches may have the same value for name-to-address translation pair.

HTTP/3: QUIC connection establishment. How many RTTs are needed to establish an HTTP/3 connection (i.e., before data can begin to flow between client and server) using QUIC?

One RTT. Reliability, congestion control, flow control, and security parameters are established in the first two parts of the setup handshake, which takes one RTT.

3.2-1 Transport-layer demultiplexing. 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.

3.02-3 TCP multiplexing and demultiplexing (c). Which of the following datagram and segment header fields are used, when demultiplexing data up to a TCP socket?

Source and destination IP addresses, and source and destination port numbers.

2.6-1 CDNs. 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.

3.2-2 Transport-layer multiplexing. 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.

7.3-5. The 802.11 Media Access Control protocol. Which of the following statement are true about the 802.11 (WiFi) MAC protocol?

The 802.11 MAC protocol performs collision avoidance. That is, an 802.11 sender and receiver can use approaches such as RTS/CTS, inter-frame spacing, and explicit acknowledgments to try avoid, rather than detect, colliding transmissions from another node.

2.2-3 The HTTP GET. 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.

2.7-3 Server reply (UDP). 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.

2.2-13 Cookies. 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.

3.3-4 Internet checksum and UDP. 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

3.3.10 How "good" are checksums? Suppose a sender computes a checksum (Internet checksum or some other checksum, which is essentially a sum of the bytes in a segment), puts the checksum in the segment header, and sends the segment to the receiver. The receiver receives the segment (with the checksum in the header). The receiver computes the checksum itself (i.e., performs the same calculation as the sender, but over the received data) and compares the checksum it has computed to the checksum it received in the header. It finds that its computed checksum and received checksum in the header are identical. Which of the following statements is true?

The receiver can't tell for certain whether errors (bit flips) have occurred in the received data in the segment, but can be relatively confident that no errors have occurred.

3.5-7 TCP Flow Control. 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

2.2-4 Conditional HTTP GET. 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.

2.2-12 If-Modified-Since. 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.

2.6-4 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

3.1-1 Location of transport-layer functionality. Where is transport-layer functionality primarily implemented?

Transport layer functions are implemented primarily at the hosts at the "edge" of the network.

3.1-2 Transport-layer functionality. True or False: The transport layer provides for host-to-host delivery service?

True

3.2-3 Multiplexing/Demultiplexing: UDP port numbers. 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

3.2-5 Multiplexing UDP with identical port numbers. 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

3.2-6 Multiplexing TCP with identical port numbers. 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

3.3-1 Does UDP preserve application-layer message boundaries? 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

3.3-7 UDP Checksum: how good is it? 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