Questions and Answers of Computer Network

Consider a datagram network using 32-bit host addresses. Suppose a router has four links, numbered 0 through 3, and packets are to be forwarded to the link intelfaces as follows: Destination Address
Why is an ARP query sent within a broadcast frame? Why is an ARP response sent within a frame with a specific destination MAC address?
Suppose that N switches supporting K VLAN groups are to be connected via a trunking protocol. How many ports are needed to connect the switches? Justify your answer.
If all the links in the Internet were to provide reliable delivery service, would the TCP reliable delivery service be redundant? Why or why not?
What are some of the possible services that a link-layer protocol can offer to the network layer? Which of these link-layer services have corresponding services in IP? In TCp?
Describe polling and token-passing protocols using the analogy of cocktail party interactions.
Why would the token-ring protocol be inefficient if a LAN had a very large perimeter?
Suppose nodes A, B, and C each attach to the same broadcast LAN (through their adapters).If A sends thousands of IP datagrams to B with each encapsulating frame addressed to the MAC address of B,
Suppose the information content of a packet is the bit pattern 1110 10 II 100 I 1101 and an even parity scheme is being used, What would the value of the field containing the parity bits be for the
Consider two nodes, A and B, that use the slotted ALOHA protocol to contend for a channel. Suppose node A has more data to transmit than node B. and node A's retransmission probability PAis greater
Suppose four active nodes-nodes A, B, C and D-are competing for access to a channel using slotted ALOHA. Assume each node has an infinite number of packets to send. Each node attempts to transmit in
Graph the efficiency of slotted ALOHA and pure ALOHA as a function p for the following values of N: a. N=15. b. N=20. c. N=30.
Consider a broadcast channel with N nodes and a transmission rate of R bps. Suppose the broadcast channel uses polling (with an additional polling node) for multiple access. Suppose the amount of
Consider three LANs interconnected by two routers, as shown in Figure 5JX.a. Assign IP addresses to all of the interfaces. For Subnet I use addresses of the form 192.168. I .xxx; for Subnet 2 uses
Consider Figure 5.38. Now we replace the router between subnets I and 2 with a switch S l, and label the router between subnets 2 and 3 as R l. a. Consider sending an IP datagram from Host E to Host
Consider the previous problem, but suppose now that the router between subnets 2 and 3 is replaced by a switch. Answer questions (a)-(c) in the previous problem in this new context.
Recall that with the CSMA/CD protocol, the adapter waits K· 512 bit times after a collision, where K is drawn randomly. For K = 100, how long does the adapter wait until returning to Step 2 for a 10
Suppose nodes A and B are on the same 10 Mbps Ethernet bus, and the propagation delay between the two nodes is 325 bit times. Suppose node A begins transmitting a frame and, before it finishes, node
Explain why a minimum frame size is required for Ethernet. For example, I OBase Ethernet imposes a minimum frame size constraint of 64 bytes. (If you have done the previous problem, you might have
Show (give an example other than the one in Figure 5,6) that two-dimensional parity checks can correct and detect a single bit error. Show (give an example) of a double-bit error that can be detected
Suppose that you would like to increase the link speed of your Ethernet cable, how would this upgrade affect the minimum required packet sizes? If you upgrade your cable to a higher speed and realize
Suppose nodes A and B are on the same 10 Mbps Ethernet bus, and the propagation delay between the two nodes is 245 bit times. Suppose A and B send frames at the same time, the frames collide, and
Consider a 100 Mbps 100BASE-T Ethernet with all nodes directly connected to a hub. To have an efficiency of 0.50, what should be the maximum distance between a node and the hub? Assume a frame length
Suppose four nodes, A, B, C, and D, are all connected to a hub via 10Mbps Ethernet cables. The distances between the hub and the 'e four nodes are 300m, 400111, 500m, and 700m, respectively. Recall
[n this problem you will derive the efficiency of a CSMNCD-like multiple access protocol. [n this protocol, time is slotted and all adapters are synchronized to the slots. Unlike slotted ALOHA,
Suppose two nodes, A and B, are attached to opposite ends of an 800 m cable, and that they each have one frame of I,SOO bits (including all headers and preambles) to send to each other. Both nodes
In the Ethernet standard, a sender pauses 96 bit times between sending consecutive frames. This pausing time is referred to as inter-frame gap, and it is used to allow a receiving device to complete
Consider Figure S.38 in problem P14. Provide MAC addresses and IP addresses for the interfaces at Host A, both routers, and Host F. Suppose Host A sends a datagram to Host F. Give the source and
Suppose now that the leftmost router in Figure S.38 is replaced by a switch. Hosts A, B, C, and D and the right router are all star-connected into this switch. Give the source and destination MAC
Suppose the information portion of a packet (D in Figure SA) contains 10 bytes consisting of the 8-bit unsigned binary ASCII representation of string "Link Layer." Compute the Internet checksum for
Suppose the three departmental switches in Figure 5.26 All links are 100 Mbps. Now answer the questions posed in problem P29.
Suppose that all the Switches In FIgure S .16 are replaced by hubs. All links are 100 Mbps. Now answer the questions posed in problem P29.
Let's consider the operation of a learning switch in the context of Figure 5.24. Suppose that (i) B sends a frame to E, (ii) E replies with a frame to B, (iii) A sends a frame to B, (iv) B replies
In this problem, we ex.plore the use of small packets for Voice-over IP applications. One of the drawbacks of a small packet size is that a large fraction of link bandwidth is consumed by overhead
Consider the single switch VLAN in Figure 5.30, and assume an external router is connected to switch port 1. Assign IP addresses to the EE and CS hosts and router interface. Trace the steps taken at
Consider the MPLS network shown in Figure 5.36, and suppose that routers R5 and R6 are now MPLS enabled. Suppose that we want to perform traffic engineering so that packets from R6 destined for A are
Consider again the same scenario as in the previous problem, but suppose that packets from R6 destined for 0 are switched via R6-R4-R3, while packects from R5 destined to D are switched via
In this problem, you will put together much of what you have learned about Internet protocols. Suppose you walk into a room, connect to Ethernet, and want to download a web page. What are all the
Consider the previous problem, but instead of containing the binary of the numbers 0 through 9 suppose these 10 bytes contain a, the binary representation of the numbers I through 10, b, the ASCII
Consider the previous problem, but suppose that D has the value a. 1001000101. b. 1010001111 . c. 0101010101.
In this problem, we explore some of the properties of the CRC. For the generator G (=1001) given in Section 5.2.3, answer the following questions. a. Why can it detect any single bit error in data
In Section 5.3, we provided an outline of the derivation of the efficiency of slotted ALOHA, in this problem we'll complete the derivation, a, Recall that when there are N active nodes, the
Show that the maximum efficiency of pure ALOHA is 1/(2e). Note: This problem is easy if you have completed the problem above!
What does it mean for a wireless network to be operating in "infrastructure mode"? If the network is not ill infrastructure mode, what mode of operation is it in, and what is the different between
Suppose the IEEE 802.11 RTS and CTS frames were as long as the standard DATA and ACK frames. Would there be any advantage to using the CTS and RTS frames? Why or why not')
Section 6.3.4 discusses 802.11 mobility, in which a wireless station moves from one BSS to another within the same subnet. When the APs are interconnected with a switch, an AP may need to send a
What is meant by "opportunistic scheduling" in WiMAX?
If a node has a wireless connection to the Internet, does that node have to be mobile? Explain. Suppose that a user with a laptop walks around her house with her laptop, and always accesses the
What is the difference between a permanent address and a care-of address'? Who assigns a care-of address?
What are the purposes of the HLR and VLR in GSM networks? What elements of mobile IP are similar to the HLR and VLR?
What are the four type of wireless networks identified in our taxonomy in Section 6.1 Which of these types of wireless networks have you used?
What are three approaches that can be taken to avoid having a single wireless link degrade the performance of an end-end transport-layer TCP connection?
What are the differences between the following types of wireless channel impairments: path loss, multi path propagation, interference from other sources?
Describe how the RTS threshold works.
Consider the following idealized WiMAX scenario. The downstream sub-frame (see Figure 6.17) is slotted in time, with N downstream slots per sub-frame, with all time slots of equal length in time.
In Section 6.5, one proposed solution that allowed mobile users to maintain their IP addresses as they moved among foreign networks was to have a foreign network advertise a highly specific route to
Suppose the correspondent in Figure 6.22 were mobile. Sketch the additional network-layer infrastructure that would be needed to route the datagram from the original mobile user to the (now mobile)
In mobile IP, what effect will mobility have on end-to-end delays of data-grams between the source and destination?
Consider the chaining example discussed at the end of Section 6.7.2. Suppose a mobile user visits foreign networks A, B, and C, and that a correspondent begins a connection to the mobile user when it
Consider two mobile nodes in a foreign network having a foreign agent. Is it possible for the two mobile nodes to use the same care-of address in mobile IP? Explain your answer.
In our discussion of how the VLR updated the HLR with information about the mobile s current location, what are the advantages and disadvantages of providing the MSRN as opposed to the address of the
Suppose that the receiver in Figure 6.6 wanted to receive the data being sent by sender 2. Show (by calculation) that the receiver is indeed able to recover sender 2's data from the aggregate channel
Suppose there are two ISPs providing WiFi access in a particular cafe, with each ISP operating its own AP and having its own IP address block. a. Further suppose that by accident, each ISP has
In step 4 of the CSMA/CA protocol, a station that successfully transmits a frame begins the CSMAJCA protocol for a second frame at step 2, rather than at step 1. What rationale might the designers of
Suppose an 802.11 b station is configured to always reserve the channel with the RTS/CTS sequence. Suppose this station suddenly wants to transmit 1,000 bytes of data, and all other stations are idle
Consider the scenario shown in Figure 6.33, in which there are four wireless nodes, A, B, C, and D. The radio coverage of the four nodes is shown via the shaded ovals; all nodes share the same
Three RTCP packet types are described in Section 7.4. Briefly summarize the information contained in each of these packet types.
What is the role of a SIP registrar? How is the role of an SIP registrar different from that of a home agent in Mobile IP?
In Section 7.5, we discllssed nonpreemptive priority queuing. What would be preemptive pliority queuing? Does preemptive priority queuing make sense for computer networks?
Three camps were discussed for improving the Internet so that it better supports multimedia applications. Briefly summarize the views of each camp. In which camp do you belong?
What are some typical compression ratios (ratio of the number of bits in an uncompressed object to the number of bits in the compressed version of that object) for image and audio applications, and
Figures 7.1 and 7.2 present two schemes for streaming stored media. What are the advantages and disadvantages of each scheme?
What is the difference between end-to-end delay and packet jitter? What are the causes of packet jitter?
Section 7.3 describes two FEC schemes. Briefly summarize them. Both schemes increase the transmission rate of the stream by adding overhead. Does interleaving also increase the transmission rate?
What is the role of the DNS in a CON? Does the DNS have to be modified to support a CON? What information, if any, must a CON provide to the DNS?
What information is needed to dimension a network so that a given quality of service is achieved?
Consider the figure below (which is similar to Figure 7.5). A sender begins sending packetized audio periodically at f =I. The first packet arrives at the receiver at f =8.a. What are the delays
Consider again the figure in PI 0, showing packet audio transmission and reception times. a. Compute the estimated delay for packets 2 through 8, using the formula for d. from Section 7.3.2. Use a
Recall the two FEC schemes for Internet phone described in Section 7.3. Suppose the first scheme generates a redundant chunk for every four original chunks. Suppose the second scheme uses a low-bit
Given that a CON does not increase the amount of link capacity in a network (assuming the CON uses existing links to distribute its content among CON nodes), how does a CON improve the pert'ormance
Is it possible for a CON to provide worse performance to a host requesting a multimedia object than if the host has requested the object from the distant origin server'? Explain.
How is the interarrival time jitter calculated in the RTCP reception report? (Hint: Read the RTP RFC.)
a. Suppose we send into the Internet two IP datagrams, each carrying a different UOP segment. The first datagram has source IP address AI, destination IP address B, source port PI , and destination
Consider an RTP session consisting of four users, all of which are sending and receiving RTP packets into the same multicast address. Each user sends v ideo at 100 kbps. a. RTCP will limit its
a. How is RTSP similar to HTTP? Does RTSP have methods? Can HTTP be used to request a stream? b. How is RTSP different from HTTP? For example, is HTTP in-band or out-of-band? Does RTSP maiutain state
True or false: a. If stored video is streamed directly from a Web server to a media player, then the application is using TCP as the underlying transport protoco\' b. When using RTP, it is possible
Consider the client buffer shown in Figure 7.3. Suppose that the streaming system uses the third option; that is, the server pllshes the media into the socket as quickly as possible. Suppose the
Suppose that the WFQ scheduling policy is applied to a buffer that supports three classes, and suppose the weights are 0.5, 0.25, and 0.25 for the three classes. a. Suppose that each class has a
Consider the figure on the next page, which is similar to Figures 7.22-7.25. Answer the following questions:a. Assuming FIFO service, indicate the time at which packets 2 through 12 each leave the
Consider again the figure for P21.a. Assume a priority service, with packets 1,4, 5, 6, and 11 being highpriority packets. The remaining packets are low priority. Indicate the slots in which packets
Consider the figure below, which shows a leaky bucket policer being fed by a stream of packets. The token buffer can hold at most two tokens, and is initially full at t =O. New tokens (uTive at a
Repeat P23 but assume that r =2. Assume again that the bucket is initially full.
Consider the leaky-bucket policer (discussed in Section 7.5) that polices the average rate and burst size of a packet flow. We now want to police the peak rate, p , as well. Show how the output of
Show that as long as r l < R w/(∑wj), then d max is indeed the maximum delay that any packet in flow I will ever experience in the WFQ queue.
Are the TCP receive buffer and the media player's client buffer the same thing? If not, how do they interact?
In the Internet phone example in Section 7.3, let h be the total number of header bytes added to each chunk, including UDP and IP header. a. Assuming an IP datagram is emitted every 20 msecs, find
Consider the procedure described in Section 7.3 for estimating average delay di · Suppose that u = 0.1. Let r[ - II be the most recent sample delay, let r2 - f2 be the next most recent sample delay,
Repeat Parts a and b in Question 6 for the estimate of average delay deviation.
For the Internet phone example in Section 7.3, we introduced an online procedure (exponential moving average) for estimating delay. In this problem we will examine an alternative procedure. Let '; be
Compare the procedure described in Section 7.3 for estimating average delay with the procedure in Section 3.5 for estimating round-trip time. What do the procedures have in common? How are they

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