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Pataasin ang iyong marka sa homework at exams ngayon gamit ang Quizwiz!

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."

Match the names of the principal router components (A,B,C,D below) with their function and whether they are in the network-layer data plane or control plane.

(A) are ... - input ports, operating primarily in the data plane. (B) is ... - the switching fabric, operating primarily in the data plane. (C) are ... - output ports, operating primarily in the data plane. (D) is ... - the routing processor, operating primarily in the control plane.

Which of the following statements about a DHCP request message are true (check all that are true). Hint: check out Figure 4.24 in the 7th and 8th edition of our textbook.

- A DHCP request message is sent broadcast, using the 255.255.255.255 IP destination address. - A DHCP request message may contain the IP address that the client will use. - The transaction ID in a DHCP request message will be used to associate this message with future DHCP messages sent from, or to, this client.

Consider the travel analogy discussed in the textbook - some actions we take on a trip correspond to forwarding and other actions we take on a trip correspond to routing. Which of the following travel actions below correspond to forwarding? The other travel actions that you don't select below then correspond to routing.

- A car waits at light and then turns left at the intersection. - A car stops at an intersection to "gas-up" and take a "bathroom break" - A car takes the 3rd exit from a roundabout.

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 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 receiverknows that one of the bits in the received packet has been changed during transmission from sender to receiver. - The sender-computed checksum value is often included in a checksum field within a packet header.

Which of the following descriptions below correspond to a "nuts-and-bolts" view of the Internet? Select one or more of the answers below that are correct. [Hint: more than one of answers below are correct].

- 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 collection of billions of computing devices, and packet switches interconnected by links. - A "network of networks".

Which of the following actions are associated with end-end congestion control (say versus network-assisted congestion control). Check all that apply.

- A datagram experiences delay at a congested network router, which is then measured by the sender and used to decrease the sending rate. - A sender decreases its sending rate in response to packet loss detected via its transport-layer ACKing. - The transport-layer sender decreases its sending rate in response to a measured increase in the RTT. - A router drops a packet at a congested router, which causes the transport-layer sender to infer that there is congestion due to the missing ACK for the lost packet.

What information does the type "A" resource record hold in the DNS database? Check all that apply.

- A hostname and an IP address.

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.

Which of the following descriptions below correspond to a "services" view of the Internet? Select one or more of the answers below below that are correct below that are correct. [Hint: more than one of answers below are correct].

- A place I go for information, entertainment, and to communicate with people. - A platform for building network applications.

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.

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

Which of the following actions are used in network-assisted congestion control (say versus end-end congestion control) to signal congestion. Check all that apply.

- A router marks a field in the datagram header at a congested router. - A router sends an ICMP message to a host telling it to slow down its sending rate.

Which of the following statements are true about a self learning switch?

- A self-learning switch frees a network manager from a least one configuration task that might be associated with managing a switch - A self learning switch associates the source MAC address on an incoming frame with the port on which it arrived, and stores this matching in a table. The switch has now learned the port that leads to that MAC address. - A self-learning switch will age-out (forget) a self-learned association of a MAC address x and switch port y if it doesn't see a frame with MAC address x incoming on switch port y after some amount of time.

What is meant by an IP subnet? (Check zero, one or more of the following characteristics of an IP subnet).

- A set of device interfaces that can physically reach each other without passing through an intervening router. - A set of devices that have a common set of leading high order bits in their IP address.

Consider the five images below. Indicate which of these images suggest the need for flow control (the others would suggest the need for congestion control).

- A talking head - A glass overflowing

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.

Consider the simple star-connected Ethernet LAN shown below, and suppose the switch table contains entries for each of the 6 hosts. How will those entries be removed from the switch table?

- An entry for a hostwill be removed if that host doesn't transmit any frames for a certain amount of time (that is, table entries will timeout).

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.

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.

Which of the following services may be implemented in a link-layer protocol? Select one or more statements.

- Coordinated access to a shared physical medium. - Multiplexing down from / multiplexing up to a network-layer protocol. - Reliable data transfer between directly connected nodes. - Bit-level error detection and correction. - Flow control between directly connected nodes.

Use the pulldown menus below to match the name of the field with the function/purpose of a field within an Ethernet frame.

- Cyclic redundancy check (CRC) field Answer: Used to detect and possibly correct bit-level errors in the frame. - Source address field Answer: 48-bit MAC address of the sending node. - Data (payload) field Answer: The contents of this field is typically (bit not always) a network-layer IP datagram. - Type field. Answer: Used to demultiplex the payload up to a higher level protocol at the receiver. - Sequence number field Answer: This field does not exist in the Ethernet frame

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 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/secWhat is the propagation delay at (along) link 2?

.0033 secs

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?

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), lambdaout, is equal to 0.8 * lambdain'. What fraction of the packets transmitted at the sender are retransmissions?

.20

Consider the circuit-switched network shown in the figure below, with circuit switches A, B, C, and D. Suppose there are 13 circuits between A and B, 13 circuits between B and C, 20 circuits between C and D, and 16 circuits between D and A. 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 is the maximum number of connections that can be ongoing in the network at any one time?

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. - Chunk A file containing the location and encoding rate of files corresponding to video segments in a video. - Manifest An approach that allows a client to adapt the encoding rate of retrieved video to network congestion conditions. - DASH A CDN approach that stores content in access networks, close to clients. - Enter deep

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

Suppose now the server sends the following HTTP response message the 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/htmlWill 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.

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.

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 - Link layer Header H2 - Network Layer Header H3 - Transport layer

Consider routers 2c and 2d in Autonomous System AS2 in the figure below. Indicate the flavor of BGP and the router from which each of 2c and 2d learns about the path to destination x.

How does router 2c learn of the path AS3, X to destination network X? - From 3a via eBGP. How does router 2d learn of the path AS3, X to destination network X? - From 2c via iBGP.

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.

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

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.

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.

In the US, which of the following services has been regulated by the Federal Communications Commission (FCC) going back into the 20th century?

Telecommunication services.

In 2021, the International Telecommunications Union (ITU) reported that 61.6% of the worlds's population are "Internet users". What does it mean to be an "Internet user" according to the ITU? To answer this question you'll need to watch the chapter 1 supplemental video on "Who Uses the Internet?"

That someone has used the Internet at least once in the last three months.

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.

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.

What is meant when it is said that the Internet has an "hourglass" architecture? See the picture below if you are unfamiliar with an "hourglass".

The Internet protocol stack has a "thin waist" in the middle, like an hourglass. The Internet Protocol (IP) is the only network-layer protocol in the middle layer of the stack. Every other layer has multiple protocols at that layer.

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.

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.

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 - This should never happen. The currently measured throughput is equal to or a bit less than than cwnd/RTTmin - increase the sending rate The currently measured throughput is much less that than cwnd/RTTmin - decrease the sending rate

Between 2010 and 2018, which of the following digital divides has changed the least in the US? To answer this question you'll need to watch the chapter 1 supplemental video on "Who Uses the Internet?" To answer this question you'll need to watch the chapter 1 supplemental video on "Who Uses the Internet?"

The gap in Internet use between Black and Hispanic populations versus White populations in the US.

Suppose a datagram is switched through the switching fabric and arrives to its appropriate output to find that there are no free buffers. In this case:

The packet will either be dropped or another packet will be removed (lost) from the buffer to make room for this packet, depending on policy. But the packet will definitely not be be sent back to the input port.

[This question is the same as an earlier question, except for the question statement at the very end.] 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 or 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 add

The request at t=10.

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. Answer: Processing delay Time spent waiting in packet buffers for link transmission. Answer: Queueing delay Time spent transmitting packets bits into the link. Answer: Transmission delay Time need for bits to physically propagate through the transmission medium from end one of a link to the other. Answer: Propagation delay

For the given function of a field in the TCP segment, select the name of that field from the pull-down list.

This field contains the port number associated with the sending socket for this TCP segment. - Source port number This field contains application data that was written into a socket by the sender of this TCP segment. - Data (or payload). 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. - Sequence number This field contains the index in the byte stream of the next in-order byte expected at the receiver - ACK number field 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. - ACK bit This field contains the number of available bytes in the TCP receiver's buffer. - Receiver advertised window This field contains the Internet checksum of the TCP segment and selected fields in the IP datagram header. - Checksum This field contains the number of bytes in the TCP header. - Header length field

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: 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

True or False: The transport layer provides for host-to-host delivery service?

True.

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/htmlWill the web server close the TCP connection after sending this message?

Yes, because this is HTTP 1.0

Again, 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 (same as in previous problem): 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/535.11Does the client have a cached copy of the object being requested?

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

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/535.11Does 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 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 provide

transition x1 - R1 transition x2 - S2 transition x3 - R3 transition x4 - S3 transition x5 - R4

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

transition x1 - R1 transition x2 - S3 transition x3 - R4 transition x4 - S6

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

transition x1 - R6 transition x2 - S2 transition x3 - R1 transition x4 - S3 transition x5 - R4

Which of the following match+actions can be taken in the generalized OpenFlow 1.0 match+action paradigm that we studied in Section 4.4? Check all that apply.

- ... after matching on the port number in the segment's header, the action taken is to forward the datagram to the output port associated with that destination IP address. - ... after matching on the port number in the segment's header, the action taken is to decide whether or not to drop that datagram containing that segment. - ... after matching on the source and destination IP address in the datagram header, the action taken is to forward the datagram to the output port associated with that source and destination IP address pair. - ... after matching on the destination IP address in the datagram header, the action taken is to forward the datagram to the output port associated with that destination IP address. - ... after matching on the 48-bit link-layer destination MAC address, the action taken is to forward the datagram to the output port associated with that link-layer address. - ... after matching on the destination IP address in the datagram header, the action taken is to decide whether or not to drop that datagram.

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).

Consider the Cyclic Redundancy Check (CRC) algorithm discussed in Section 6.2.3 of the text. Suppose that the 4-bit generator (G) is 1001, that the data payload (D) is 10011001 and that r = 3. What are the CRC bits (R) associated with the data payload D, given that r = 3?

- 000

Consider the Cyclic Redundancy Check (CRC) algorithm discussed in Section 6.2.3 of the text. Suppose that the 4-bit generator (G) is 1001, that the data payload (D) is 10011000 and that r = 3. What are the CRC bits (R) associated with the data payload D, given that r = 3?

- 001

Consider the Cyclic Redundancy Check (CRC) algorithm discussed in Section 6.2.3 of the text. Suppose that the 4-bit generator (G) is 1001, that the data payload (D) is 10011010 and that r = 3. What are the CRC bits (R) associated with the data payload D, given that r = 3?

- 0011

Consider the Cyclic Redundancy Check (CRC) algorithm discussed in Section 6.2.3 of the text. Suppose that the 4-bit generator (G) is 1001, that the data payload (D) is 10011011 and that r = 3. What are the CRC bits (R) associated with the data payload D, given that r = 3?

- 010

Consider the simple star-connected Ethernet LAN shown below, and suppose the Ethernet switch is a learning switch, and that the switch table is initially empty. Suppose C sends an Ethernet frame address to C' and C ' replies back to C. How many of these two frames are also received at B's interface?

- 1

Consider the Cyclic Redundancy Check (CRC) algorithm discussed in Section 6.2.3 of the text. Suppose that the 4-bit generator (G) is 1001, that the data payload (D) is 10011101 and that r = 3. What are the CRC bits (R) associated with the data payload D, given that r = 3?

- 100

Consider the Cyclic Redundancy Check (CRC) algorithm discussed in Section 6.2.3 of the text. Suppose that the 4-bit generator (G) is 1001, that the data payload (D) is 10011100 and that r = 3. What are the CRC bits (R) associated with the data payload D, given that r = 3?

- 101

Consider the Cyclic Redundancy Check (CRC) algorithm discussed in Section 6.2.3 of the text. Suppose that the 4-bit generator (G) is 1001, that the data payload (D) is 10011111 and that r = 3. What are the CRC bits (R) associated with the data payload D, given that r = 3?

- 110

Which of the following fields occur ONLY in the IPv6 datagram header (i.e., appear in the IPv6 header but not in the IPv4 header)? Check all that apply.

- 128-bit source and destination IP addresses. - The flow label field.

Consider the three subnets in the diagram below. Which of the following addresses can not be used by an interface in the 223.1.3/29 network? Check all that apply.

- 223.1.3.16 - 223.1.3.28 - 223.1.2.6

Which of the following statements is true about a two-dimensional parity check (2D-parity) computed over a payload?

- 2D-parity can detect and correct any case of a single bit flip in the payload. - 2D-parity can detect any case of two bit flips in the payload. - 2D-parity can detect any case of a single bit flip in the payload.

Which of the following physical layer technologies has the highest transmission rate and lowest bit error rate in practice?

- Fiber optic cable

Suppose an Ethernet frame arrives to an Ethernet switch, and the Ethernet switch does not know which of its switch ports leads to the node with the given destination MAC address? In this case, what does the switch do?

- Flood the frame on all ports except the port on which the frame arrived.

Which of the following statements are true about MAC (link-layer) addresses? Select one or more statements below.

- Generally stays unchanged as a device moves from one network to another. - Has 48 bits. - Generally does not change, and is associated with a device when it is

Which of the following network devices can be thought of as a "middlebox"? Check all that apply.

- HTTP cache - Network Address Translation box - HTTP load balancer

We learned that in HTTP web browser caching, HTTP local web server caching, and in local DNS caching, that a user benefits (e.g., shorter delays over the case of no caching) from finding a local/nearby copy of a requested item. In which of the following forms of caching does a user benefit from its not only from its own recent requests (and cached replies) but also from recent requests made from other users?

- HTTP local web caching - Local DNS server caching

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.

Which of the following characteristics apply to both HTTP and SMTP? Note: check one or more of the characteristics below.

- Has ASCII command/response interaction, status codes. - Is able to use a persistent TCP connection to transfer multiple objects.

What protocol (or protocols) constitutes the "thin waist" of the Internet protocol stack? Check all that apply.

- IP

Which of the following fields in the frame/datagram/segment/application-layer message can be matched in OpenFlow 1.0? Check all that apply.

- IP type-of-service field - IP destination address - IP source address - Source and/or destination port number - Upper layer protocol field

Which of the following statements is true regarding an IP address? (Zero, one or more of the following statements is true).

- If a router has more than one interface, then it has more that one IP address at which it can be reached. - If a host has more than one interface, then it has more that one IP address at which it can be reached. - An IP address is associated with an interface.

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 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. - 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.

Consider the network below. We want to specify the match+action rules at s3 so that s3 acts only as a relay for traffic between 137.220/16 and 67.56/16. In particular s3 should not accept/forward and traffic to/from 128.119/16. From the list of match+action rules below, select the rules to include in s3's flow table to implement this forwarding behavior. Assume that if a packet arrives and finds no matching rule, it is dropped.

- Input port: 2; Dest: 67.56/16 Action: forward(3) - Input port: 3; Dest: 137.220/16 Action: forward(2)

Consider the network below. We want to specify the match+action rules at s3 so that only the following network-wide behavior is allowed: traffic from 128.119/16 and destined to 137.220/16 is forwarded on the direct link from s3 to s1; traffic from 128.119/16 and destined to 67.56/16 is forwarded on the direct link from s3 to s2; incoming traffic via port 2 or 3, and destined to 128.119/16 is forwarded to 128.119/16 via local port 1. No other forwarding should be allowed. In particular s3 should not forward traffic arriving from 137.220/16 and destined for 67.56/16 and vice versa. From the list of match+action rules below, select the rules to include in s3's flow table to implement this forwarding behavior. Assume that if a packet arrives and finds no matching rule, it is dropped.

- Input port: 3; Dest: 128.119/16 Action: forward(1) - Input port: 1; Dest: 67.56/16 Action: forward(3) - Input port:1 ; Dest: 137.220/16 Action: forward(2) - Input port: 2; Dest: 128.119/16 Action: forward(1)

Consider the OSPF routing protocol. Which of the following characteristics are associated with OSPF (as opposed to BGP)?

- Is an intra-domain routing protocol. - Finds a least cost path from source to destination. - Floods link state control information.

For each of the actions below, select those actions below that are primarily in the network-layer data plane. The other actions that you don't select below then correspond to control-plane actions.

- Looking up address bits in an arriving datagram header in the forwarding table. - Moving an arriving datagram from a router's input port to output port - Dropping a datagram due to a congested (full) output buffer.

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. - Flow Control. The provided service will ensure that the sender does not send so fast as to overflow receiver buffers. - Congestion control. The service will control senders so that the senders do not collectively send more data than links in the network can handle.

Which of the following statements about the characteristics of wireless links are true?

- 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. - The bit error rate (BER) of a wireless channel decreases as the signal-to-noise ratio (SNR) increases. - Path loss refers to the decrease in the strength of a radio signal as it propagates through space. - 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.

Which of the functions below belong in the controller layer labeled "Interface, abstractions for network control apps"? Check all below that apply.

- Network graph - Intent

Check the one or more of the following statements about the OSPF protocol that are true.

- OSPF implements hierarchical routing - OSPF is an intra-domain routing protocol. - OSFP uses a Dijkstra-like algorithm to implement least cost path routing.

What are the principal components of the IPv4 protocol (check all that apply)?

- Packet handling conventions at routers (e.g., segmentation/reassembly) - IPv4 addressing conventions. - IPv4 datagram format.

Which of the following statements is true about both Pure Aloha, and CSMA (both with and without collision detection?

- Pure Aloha and CSMA can achieve 100% utilization, in the case that there is only one node that always has frames to send - There can be simultaneous transmissions resulting in collisions.

What are advantages of implementing transport-layer functionality in QUIC at the application layer? Select all that apply.

- QUIC can establish all connection parameters (security, reliability, flow and congestion control)in just one handshake rather than separately in two. - As an application-layer protocol, QUIC can be updated/modified at "app frequency" rather than at the frequency of operating system updates.

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].

- RTC/CTS frames helps nodes in a wireless network mitigate the effects of the hidden terminal problem. - 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.

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 congestion control service to ensure that multiple senders do not overload network links. - A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender.

We've seen that there are two approaches towards implementing the network control plane - a per-router control-plane approach and a software-defined networking (SDN) control-plane approach. Which of the following actions occur in a per-router control-plane approach? The other actions that you don't select below then correspond to actions in an SDN control plane.

- Routers send information about their incoming and outgoing links to other routers in the network. - A router exchanges messages with another router, indicating the cost for it (the sending router) to reach a destination host.

Which of the following statements correctly identify the differences between routing and forwarding. Select one or more statements.

- Routing refers to determining the route taken by packets from source to destination, and is implemented in the control plane. - Forwarding refers to moving packets from a router's input to appropriate router output, and is implemented in the data plane.

Consider the rdt 2.0 sender and receiver shown below, with FSM transitions at the sender labeled S1, S2, and S3; and receiver transitions labeled R1 and R2.Which of the following sequences of transitions could possibly occur as a result of an initial rdt_send() call at the sender, and possible later message corruption and subsequent error recovery.

- S1, R2, S3 - S1, R1, S2 - S1, R1, S2, R2,S3

Which of the fields below are in a UDP segment header? [Hint: note the use of the word "header" in this question statement.]

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

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

Which of the functions below belong in the controller layer labeled "Network-wide distributed, robust state management"? Check all below that apply.

- Switch information - Host information - Statistics - Flow tables - Link-state information

Consider the following multiple access protocols that we've studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. For which of these protocols is the maximum channel utilization 1 (or very close to 1)?

- TDMA and FDMA - Polling

Consider the following multiple access protocols that we've studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. For which of these protocols is there a maximum amount of time that a node knows that it will have to wait until it can successfully gain access to the channel?

- TDMA and FDMA - Polling

Consider the following multiple access protocols that we've studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. Which of these protocols are collision-free (e.g., collisions will never happen)?

- TDMA and FDMA - Polling

Consider the following multiple access protocols that we've studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. Which of these protocols requires some form of centralized control to mediate channel access?

- TDMA and FDMA - Polling

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.

Which of the statements below about ICMP are true?

- The TTL-expired message type in ICMP is used by the traceroute program. - ICMP is used by hosts and routers to communicate network-level information. - ICMP messages are carried directly in IP datagrams rather than as payload in UDP or TCP segments.

Which of the statements below are true statements regarding the "end-to-end principle"? Check all that apply.

- The end-to-end argument allows that some redundant functionality might be placed both in-network and at the network edge in order to enhance performance. - The end-to-end argument advocates placing functionality at the network edge because some functionality cannot be completely and correctly implemented in the network, and so needs to be placed at the edge in any case, making in-network implementation redundant.

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.

Check all of the statements below about where (in the network) the network layer is implemented that are true.

- The network layer is implemented in hosts at the network's edge. - The network layer is implemented in routers in the network core.

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? [Note: you can find more problems like this one here.]

.000096 secs

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 or 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

- The request at t=0. - The request at t=30. - The request at t=1.

- The request at t=12. - The request at t=5.

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 sender will resend that packet in any case. - The implementation at the receiver is simpler.

Consider Dijkstra's link-state routing algorithm that is computing a least-cost path from node a to other nodes b, c, d, e, f. Which of the following statements is true. (Refer to Section 5.2 in the text for notation.)

- The values computed in the vector D(v), the currently known least cost of a path from a to any node v, will never increase following an iteration. - Suppose nodes b, c, and d are in the set N'. These nodes will remain in N' for the rest of the algorithm, since the least-cost paths from a to b, c, and d are known. - In the initialization step, the initial cost from a to each of these destinations is initialized to either the cost of a link directly connecting a to a direct neighbor, or infinity otherwise.

Which of the following statements is true about channel partitioning protocols?

- There can be times when the channel is idle, when a node has a frame to send, but is prevented from doing so by the medium access protocol. - Channel partitioning protocols can achieve 100% channel utilization, in the case that all nodes always have frames to send.

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.

Which of the following statements is true about polling and token-passing protocols?

- These protocol can achieve close 100% utilization, in the case that there is only one node that always has frames to send (the fact that the utilization is close to, but not exactly, 100% is due to a small amount of medium access overhead but not due to collisions) - These protocol can achieve close to 100% channel utilization, in the case that all nodes always have frames to send (the fact that the utilization is close to, but not exactly, 100% is due to a small amount of medium access overhead but not due to collisions)

We've now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is only a property of IPv4 addresses (and therefore is not a property of MAC addresses - careful!).

- This address is allocated by DHCP. - This is a 32-bit address. - This is a network-layer address.

We've now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is a property of both IPv4 addresses and MAC addresses.

- This address must be unique among all hosts in a subnet.

We've now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is only a property of MAC addresses (and therefore is not a property of IPv4 addresses - careful!).

- This is a link-layer address. - This is a 48-bit address. - This address remains the same as a host moves from one network to another.

Which of the characteristics below are associated with the technique of packet switching? Select all correct answers. [Hint: more than one of the answers is correct].

- This technique is used in the Internet. - Resources are used on demand, not reserved in advance. - Congestion loss and variable end-end delays are possible with this technique. - Data may be queued before being transmitted due to other user's data that's also queueing for transmission.

Which of the characteristics below are associated with the technique of circuit switching? Select all correct answers. [Hint: more than one of the answers is correct].

- This technique was the basis for the telephone call switching during the 20th century and into the beginning of this current century. - Reserves resources needed for a call from source to destination. - Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two approaches for implementing this technique.

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")? Select one or more answers below that are correct. Hint: more than one of answers below are correct.

- 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 characteristics apply to HTTP only (and do not apply to SMTP)? Note: check one or more of the characteristics below.

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

Among the following protocols, terminology or considerations, indicate those that are associated with "routing within a single network (typically owned and operated by one organization)."

- intra-domain routing - Driven more by performance than by routing policy - intra-AS routing - OSPF

Which of the following characteristics below are associated with a UDP socket? Check one or more that apply.

- the application must explicitly specify the IP destination address and port number for each group of bytes written into a socket - provides unreliable transfer of a groups of bytes ("a datagram"), from client to server - data from different clients can be received on the same socket - socket(AF_INET, SOCK_DGRAM) creates this type of socket

Which of the following characteristics below are associated with a TCP socket? Check one or more that apply.

- when contacted, the server will create a new server-side socket to communicate with that client - socket(AF_INET, SOCK_STREAM) creates this type of socket - provides reliable, in-order byte-stream transfer (a "pipe"), from client to server - a server can perform an accept() on this type of socket

Suppose a provider network only wants to carry traffic to/from its customer networks (i.e., to provide no transit service), and customer networks only want to carry traffic to/from itself. Consider the figure below. To implement this policy, to which of the following networks would network C advertise the path Cy?

- x - A - B

Destination-based forwarding, which we studied in section 4.2, is a specific instance of match+action and generalized forwarding. Select the phrase below which best completes the following sentence: "In destination-based forwarding, ..."

... after matching on the destination IP address in the datagram header, the action taken is to forward the datagram to the output port associated with that destination IP address.

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.

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? [Note: you can find more problems like this one here.]

.000012 secs

Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 300 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 50 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 90 Mbps. Assuming that the servers are all sending at their maximum rate possible, what are the link utilizations of the client links (with transmission capacity RC)? Enter your answer in a decimal form of 1.00 (if the utilization is 1) or 0.xx (if the utilization is less than 1, rounded to the closest xx). Your answer: The utilization of client link is: [A]

0.56

Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 300 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 50 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 90 Mbps.Assuming that the servers are all sending at their maximum rate possible, what are the link utilizations of the shared link (with transmission capacity R)? Enter your answer in a decimal form of 1.00 (if the utilization is 1) or 0.xx (if the utilization is less than 1, rounded to the closest xx). Your answer: The utilization of shared link is: [A]

0.67

Compute the Internet checksum value for these two 16-bit words: 11110101 11010011 and 10110011 01000100

01010110 11100111

Consider the pattern of red and green packet arrivals to a router's output port queue, shown below. Suppose each packet takes one time slot to be transmitted, and can only begin transmission at the beginning of a time slot after its arrival. Indicate the sequence of departing packet numbers (at t = 1, 2, 3, 4, 5, 7, 8) under FCFS scheduling. Give your answer as 7 ordered digits (each corresponding to the packet number of a departing packet), with a single space between each digit, and no spaces before the first or after the last digit, e.g., in a form like 7 6 5 4 3 2 1).

1 2 3 4 5 6 7

Consider the pattern of red and green packet arrivals to a router's output port queue, shown below. Suppose each packet takes one time slot to be transmitted, and can only begin transmission at the beginning of a time slot after its arrival. Indicate the sequence of departing packet numbers (at t = 1, 2, 3, 4, 5, 7, 8) under priority scheduling, where red packets have higher priority. Give your answer as 7 ordered digits (each corresponding to the packet number of a departing packet), with a single space between each digit, and no spaces before the first or after the last digit, e.g., in a form like 7 6 5 4 3 2 1).

1 2 3 5 4 7 6

Consider the pattern of red and green packet arrivals to a router's output port queue, shown below. Suppose each packet takes one time slot to be transmitted, and can only begin transmission at the beginning of a time slot after its arrival. Indicate the sequence of departing packet numbers (at t = 1, 2, 3, 4, 5, 7, 8) under priority scheduling, where red packets have higher priority. Give your answer as 7 ordered digits (each corresponding to the packet number of a departing packet), with a single space between each digit, and no spaces before the first or after the last digit, e.g., in a form like 7 6 5 4 3 2 1).

1 2 4 3 5 6 7

Consider the pattern of red and green packet arrivals to a router's output port queue, shown below. Suppose each packet takes one time slot to be transmitted, and can only begin transmission at the beginning of a time slot after its arrival. Indicate the sequence of departing packet numbers (at t = 1, 2, 3, 4, 5, 7, 8) under round robin scheduling, where red starts a round if there are both red and green packets ready to transmit after an empty slot. Give your answer as 7 ordered digits (each corresponding to the packet number of a departing packet), with a single space between each digit, and no spaces before the first or after the last digit, e.g., in a form like 7 6 5 4 3 2 1).

1 2 4 3 5 6 7

Consider the pattern of red and green packet arrivals to a router's output port queue, shown below. Suppose each packet takes one time slot to be transmitted, and can only begin transmission at the beginning of a time slot after its arrival. Indicate the sequence of departing packet numbers (at t = 1, 2, 3, 4, 5, 7, 8) under round robin scheduling, where red starts a round if there are both red and green packets ready to transmit after an empty slot. Give your answer as 7 ordered digits (each corresponding to the packet number of a departing packet), with a single space between each digit, and no spaces before the first or after the last digit, e.g., in a form like 7 6 5 4 3 2 1).

1 3 2 4 5 7 6

What is meant by Head of the Line (HOL) blocking?

A queued datagram waiting for service at the front of a queue prevents other datagrams in queue from moving forward in the queue.

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

Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 300 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 50 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 90 Mbps.Assuming that the servers are all sending at their maximum rate possible, what are the link utilizations for the server links (with transmission capacity RS)? Enter your answer in a decimal form of 1.00 (if the utilization is 1) or 0.xx (if the utilization is less than 1, rounded to the closest xx). Your answer: The utilization of the server links is: [A]

1.00

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/535.11What version of HTTP is the client using?

1.1

What is the maximum throughput achievable between sender and receiver in the scenario shown below?

1.5 Mbps

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?

Compute the Internet checksum value for these two 16-bit words: 01000001 11000100 and 00100000 00101011

10011110 00010000

Where in a router is the destination IP address looked up in a forwarding table to determine the appropriate output port to which the datagram should be directed?

At the input port where a packet arrives.

Consider the following forwarding table below. Indicate the output to link interface to which a datagram with the destination addresses below will be forwarded under longest prefix matching. (Note: The list of addresses is ordered below. If two addresses map to the same output link interface, map the first of these two addresses to the first instance of that link interface.) [Note: You can find more examples of problems similar to this here.]

11001000 00010111 00010010 10101101 - This is the first destination address in the list that maps to output port 0. 11001000 00010111 00011000 00001101 - This is the first destination address in the list that maps to output port 1. 11001000 00010111 00011001 11001101 - This is the first destination address in the list that maps to output port 2. 10001000 11100000 00011000 00001101 - This is the first destination address in the list that maps to output port 3. 11001000 00010111 00011000 11001111 - This is the second destination address in the list that maps to output port 1. 11001000 00010111 00010001 01010101 - This is the second destination address in the list that maps to output port 0. 11001000 00010111 00011101 01101101 - This is the second destination address in the list that maps to output port 2.

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.

Consider the three subnets in the diagram below. What is the maximum # of interfaces in the 223.1.2/24 network?

256

Consider the circuit-switched network shown in the figure below, with circuit switches A, B, C, and D. Suppose there are 11 circuits between A and B, 14 circuits between B and C, 16 circuits between C and D, and 12 circuits between D and A. 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 is the maximum number of connections that can be ongoing in the network at any one time?

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? Recall the figure below from our class notes: Link: https://gaia.cs.umass.edu/kurose_ross/knowledgechecks/problem.php?c=2&s=3 Q1

Consider the graph shown below and the use of Dijkstra's algorithm to compute a least cost path from a to all destinations. Suppose that nodes b and d have already been added to N'. What is the path cost to the next node to be added to N' (refer to the text for an explanation of notation).

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.

Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 300 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 50 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 90 Mbps.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? Your answer: [A] Mbps

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?

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?

Consider the three subnets in the diagram below. What is the maximum # of interfaces in the 223.1.3/29 network?

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? [Note: you can find more problems like this one here.]

8 x 10^(-5) secs

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

In 4G LTE cellular systems, what is an International Mobile Subscriber

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

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.

Where in a router does "match plus action" happen to determine the appropriate output port to which the arriving datagram should be directed?

At the input port where a packet arrives.

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.

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.

Match the description of a TCP connection management message with the name of the message used to accomplish that function.

A message from client to server initiating a connection request. - SYN mesage 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. - SYNACK message A message indicating that the sending side is initiating the protocol to terminate a connection. - FIN message 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 - FINACK message 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. - RESET message

Suppose that as shown in the figure below, a TCP sender is sending segments with 100 bytes of payload. The TCP sender sends five segments with sequence numbers 100, 200, 300, 400, and 500. Suppose that the segment with sequence number 300 is lost. The TCP receiver will buffer correctly-received but not-yet-in-order segments for later delivery to the application layer (once missing segments are later received).

After receiving segment 100, the receiver responds with an ACK with value: - 200 After receiving segment 200, the receiver responds with an ACK with value: - 300 After receiving segment 500, the receiver responds with an ACK with value: - 300, a duplicate ACK After receiving the retransmitted segment 300, the receiver responds with an ACK with value: - 600 The TCP receiver does not respond in the example, with an ACK with value: - 400

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.

What is meant by generalized forwarding (as opposed to destination-based forwarding) in a router or switch?

Any of several actions (including drop (block), forward to a given interface, or duplicate-and-forward) can be made based on the contents of one or more packet header fields.

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.

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 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!

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.

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.

Match the name of a general approach to routing with characteristics of that approach.

Centralized, global routing. - All routers have complete topology, and link cost information. Decentralized routing. - An iterative process of computation, exchange of informatoin with neighbors. Routers may initially only know link costs to directly-attached neighbors. Static routing. - Routes change slowly over time. Dynamic routing. - Routing changes quickly over time.

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 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).

Match the networking event with the time frame when the event occurred.

Early studies of packet switching by Baran, Davies, Kleinrock. - Early 1960's First ARPAnet node operational. - Late 1960's Internetting: DARPA researchers connect three networks together. - 1970's The Internet Protocol (IP) is standardized in RFC 791. - Early 1980's Congestion control is added to the TCP protocol. - Late 1980's The WWW starts up (note: the WWW design started at the end of previous decade). - 1990's Software-defined networking begins. - 2000-2010 The number wireless Internet-connected devices surpasses the number of connected wired devices. - 2010 - 2020

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: Wired. Up to 100's Gbps per link. 802.11 WiFi: Wireless. 10's to 100's of Mbps per device. Cable access network: Wired. Up to 10's to 100's of Mbps downstream per user. Digital Subscriber Line: Wired. Up to 10's of Mbps downstream per user. 4G cellular LTE: Wireless. Up to 10's Mbps per device.

Match the terms "interdomain routing" and intradomain routing" with their definitions. Recall that in Internet parlance, an "AS" refers to "Autonomous System" - a network under the control of a single organization.

Interdomain routing. - Routing among different ASes ("networks"). Intradomain routing. - Routing among routers within same AS ("network").

Match an organization name below with the role of the organization in Internet governance. To answer this question you'll need to watch the Chapter 1 supplemental video on "Who Controls the Internet?".

Internet Governance Forum (IGF) - A multistakeholder deliberation body, convened by the United Nations, that does not make decisions but informs and inspires those who do. Internet Engineering Task Force (IETF) - Sets the technical standards for Internet infrastructure -- particularly protocols, device requirements, and data formats -- in more than 9000 Request for Comments (RFCs). 3rd Generation Partnership Project (3GPP). - Sets the technical standards for 3G, 4G, and 5G mobile cellular system. Internet Corporation for Assigned Names and Numbers (ICANN) - Handles (assigns, adjudicates) Internet names, and manages the root level of the DNS. Institute for Electrical and Electronics Engineers - Sets the technical standard for Ethernet and WiFi link-layer standards.

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.

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. - NAK Used by sender or receiver to detect bits flipped during a packet's transmission. - Checksum Allows for duplicate detection at receiver. - Sequence numbers Lets the sender know that a packet was received correctly at the receiver. - ACK Allows the receiver to eventually receive a packet that was corrupted or lost in an earlier transmission. - Retransmission

Match the function of an element in the 4G LTE architecture with its name, using the pulldown menus.

Located in a mobile device's home network, this element provides authentication, access privileges in home and visited networks. - Home Subscriber Server (HSS) This router in a cellular carrier's network, coordinates packet forwarding and routing to outside the carrier's network. - Serving Gateway (S-GW) This element coordinates mobile device services - authentication, mobility management - for a mobile resident in that network. - Mobility Management Entity (MME) This element is on the network side of wireless link into the LTE network. - Base Station (eNode-B) This element is the wireless link between mobile device and a base station - Radio Access Network (RAN)

Consider the circuit-switched network shown in the figure below, with circuit switches A, B, C, and D. Suppose there are 11 circuits between A and B, 14 circuits between B and C, 16 circuits between C and D, and 12 circuits between D and A. Suppose that 13 connections are needed from A to C, and 15 connections are needed from B to D. Can we route these calls through the four links to accommodate all 28 connections? Answer Yes or No

Consider the circuit-switched network shown in the figure below, with circuit switches A, B, C, and D. Suppose there are 11 circuits between A and B, 14 circuits between B and C, 16 circuits between C and D, and 12 circuits between D and A. Suppose that these maximum number of connections are all ongoing. What happens when another call connection request arrives to the network, will it be accepted? Answer Yes or No

Consider the circuit-switched network shown in the figure below, with circuit switches A, B, C, and D. Suppose there are 13 circuits between A and B, 13 circuits between B and C, 20 circuits between C and D, and 16 circuits between D and A. Suppose that these maximum number of connections are all ongoing. What happens when another call connection request arrives to the network, will it be accepted? Answer Yes or No

What is meant by saying that DHCP is a "plug and play" protocol?

No manual configuration is needed for the host to join the network.

Which of the following quality-of-service guarantees are part of the Internet's best-effort service model? Check all that apply.

None of the other services listed here are part of the best-effort service model. Evidently, best-effort service really means no guarantees at all!

Again, suppose a provider network only wants to carry traffic to/from its customer networks (i.e., to provide no transit service), and customer networks only want to carry traffic to/from itself. Suppose C has advertised path Cy to x. To implement this policy, to which of the following networks would network x advertise the path xCy?

None of these other networks

Which of the functions below belong in the controller layer labeled "Communication to/from controlled device"? Check all below that apply.

OpenFlow protocol

Match the name of the approach towards implementing a control plane with a description of how this approach works.

Per-router control plane. - Individual routing algorithm components - with a component operating in each and every router - interact with each other in the control plane. The individual routing algorithm component executing in a given router computes the local fowarding table fir that router. Software-defined networking (SDN). - A (typically) remote controller gathers information from routers, and then computes and installs the forwarding tables in routers.

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.

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. - Authoritative DNS server Replies to DNS query by local host, by contacting other DNS servers to answer the query. - Local DNS server Responsible for a domain (e.g., *.com, *.edu); knows how to contact authoritative name servers. - Top Level Domain (TLD) servers Highest level of the DNS hierarchy, knows how to reach servers responsible for a given domain (e.g., *.com, *.edu). - DNS root servers

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. - SMTP Pulls mail from one mail server to another mail server. - Neither SMTP nor IMAP does this. Pulls email to a mail client from a mail server. - IMAP

Match the name of an Internet layer with unit of data that is exchanged among protocol entities at that layer, using the pulldown menu.

Q1: Application layer Answer: Message Q2: Transport layer Answer: Segment Q3: Network layer Answer: Datagram Q4: Link layer Answer: Frame Q5: Physical layer Answer: Bit

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.

Q1: Each user generates traffic at an average rate of 2.1 Mbps, generating traffic at a rate of 15 Mbps when transmitting Answer: Neither works well in this overload scenario Q2: Each user generates traffic at an average rate of 2 Mbps, generating traffic at a rate of 2 Mbps when transmitting Answer: Circuit switching Q3: Each user generates traffic at an average rate of 0.21 Mbps, generating traffic at a rate of 15 Mbps when transmitting Answer: Packet switching

ERROR DETECTION AND CORRECTION: TWO DIMENSIONAL PARITY Suppose that a packet's payload consists of 10 eight-bit values (e.g., representing ten ASCII-encoded characters) shown below. (Here, we have arranged the ten eight-bit values as five sixteen-bit values): 01100111 10100110 00010101 01010111 00001000 11010010 10000010 11001000 00011011 11110110 Both the payload and parity bits are shown. One of these bits is flipped. 00010110 01111000 1 11011000 10000111 0 00110100 00000001 0 11100101 00101101 1 11100100 00011011 1 11011011 11001000 1 Both the payload and parity bits are shown; Either one or two of the bits have been flipped. 10111111 10111100 0 11010001 10101110 0 10110011 10111100 0 10001010 01011000 0 01011101 11110110 1 00001010 00100000 1

Q1: For figure 1, compute the two-dimensional parity bits for the 16 columns. Combine the bits into one string Answer: 1110001100011101 Q2: For figure 1, compute the two-dimensional parity bits for the 5 rows (starting from the top). Combine the bits into one string Answer: 10110 Q3: For figure 1, compute the parity bit for the parity bit row from question 1. Assume that the result should be even. Answer: 1 Q4: For figure 2, indicate the row and column with the flipped bit (format as: x,y), assuming the top-left bit is 0,0 Answer: 2,4 Q5: For figure 3, is it possible to detect and correct the bit flips? Yes or No Answer: Yes

Match the function of a layer in the Internet protocol stack to its its name in the pulldown menu.

Q1: Protocols that are part of a distributed network application. Answer: Application Layer Q2: Transfer of data between one process and another process (typically on different hosts). Answer: Transport layer Q3: Delivery of datagrams from a source host to a destination host (typically). Answer: Network layer Q4: Transfer of data between neighboring network devices. Answer: Link layer Q5: Transfer of a bit into and out of a transmission media. Answer: Physical layer

What is the definition of a "good" path for a routing protocol? Chose the best single answer.

Routing algorithms typically work with abstract link weights that could represent any of, or combinations of, all of the other answers.

Consider the SDN layering shown below. Match each layer name below with a layer label (a), (b) or (c) as shown in the diagram.

SDN Controller (network operating system) - (b) SDN-controlled switches - (c) Network-control applications - (a)

Consider the figure below that shows the generalized forwarding table in a router. Recall that a * represents a wildcard value. Now consider an arriving datagram with the IP source and destination address fields indicated below. For each source/destination IP address pair, indicate which rule is matched. Note: assume that a rule that is earlier in the table takes priority over a rule that is later in the table and that a datagram that matches none of the table entries is dropped.

Source: 1.2.56.32 Destination:128.116.40.186 - Rule 2, with action drop Source: 65.92.15.27 Destination: 3.4.65.76 - Rule 1, with action forward(2) Source: 10.1.2.3 Destination: 7.8.9.2 - Rule 3, with action send to controller Source: 10.1.34.56 Destination: 54.72.29.90 - No match to any rule.

Match the description of a security defense with its name.

Specialized "middleboxes" filtering or blocking traffic, inspecting packet contents inspections - Firewall Provides confidentiality by encoding contents - Encryption Used to detect tampering/changing of message contents, and to identify the originator of a message. - Digital signatures Limiting use of resources or capabilities to given users. - Access control Proving you are who you say you are. - Authentication

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. - end-end 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. - network-assisted The sender measures RTTs and uses the current RTT measurement to infer the level of congestion. - delay-based

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

The source port number of the UDP segment (B) sent in reply is: - 3546 The source IP address of the IP datagram containing the UDP segment (B) sent in reply is: - 128.119.40.186 The destination port number of the UDP segment (B) sent in reply is: - 4829 The destination IP address of the IP datagram containing the UDP segment (B) sent in reply is: - 60.54.75.24

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.

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

What is the purpose of the Dynamic Host Configuration Protocol?

To obtain an IP address for a host attaching to an IP network.

Where is transport-layer functionality primarily implemented?

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

Again, suppose a client is sending an HTTP GET request message to a web server, gaia.cs.umass.edu. The client-to-server HTTP GET message is the following (same as in previous problem): 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/535.11What is the language in which the client would least prefer to get a response? [You may have to search around the Web a bit to answer this.]

United Kingdom English

Match each of the following fields in the IP header with its description, function or use.

Version field - This field contains the IP protocol version number. Type-of-service field - This field contains ECN and differentiated service bits. Fragmentation offset field - This field is used for datagram fragmentation/reassembly. Time-to-live field - The value in this field is decremented at each router; when it reaches zero, the packet must be dropped. Header checksum field - This field contains the Internet checksum of this datagram's header fields. Upper layer field - This field contains the "protocol number" for the transport-layer protocol to which this datagram's payload will be demultiplexed - UDP or TCP, for example. Payload/data field - This field contains a UDP or TCP segment, for example. Datagram length field. - This field indicates the total number of bytes in datagram.

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.

Consider the circuit-switched network shown in the figure below, with circuit switches A, B, C, and D. Suppose there are 13 circuits between A and B, 13 circuits between B and C, 20 circuits between C and D, and 16 circuits between D and A. Suppose that 12 connections are needed from A to C, and 17 connections are needed from B to D. Can we route these calls through the four links to accommodate all 29 connections? Answer Yes or No

Yes

Consider the graph shown below and the use of Dijkstra's algorithm to compute a least cost path from a to all destinations. Suppose that nodes b and d have already been added to N'. What is the next node to be added to N' (refer to the text for an explanation of notation).

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 Note: Routing may change, so the answer here may not be correct anymore. Also, if you are a Verizon user, there are known problems using traceroute with Verizon - if traceroute shows you two hops only to gaia.cs.umass.edu or any destination, skip this question.

nscs1bbs1

Again, suppose a provider network only wants to carry traffic to/from its customer networks (i.e., to provide no transit service), and customer networks only want to carry traffic to/from itself. Suppose C has advertised path Cy to A. To implement this policy, to which of the following networks would network A advertise the path ACy?

clgna

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