Computer Networking A Top-Down Approach 5th edition James F. Kurose, Keith W. Ross - Solutions

Consider the TCP procedure for estimating RTT. Suppose that a = 0.1. Let SampleRTT1 be the most recent sample RTT. let SampleRTT2 be the next most recent sample RTT, and so on.a. For a given TCP connection, suppose four acknowledgments have been returned with corresponding sample RTTs SampleRTT4'
UDP and TCP use I s complement for their checksums. Suppose you have the following three 8-bit bytes: 01010011, 01010100, 01110100. What is the 1s complement of the sum of these 8-bit bytes? Show all work. Why is it that UDP takes the 1s complement of the sum; that is, why not just use the sum?
In Section 3.5.3, we discussed TCP's estimation of RTT. Why do you think T P avoids measuring the SampleRTT for retransmitted segments?
What is the relationship between the variable SendBase in Section 3.5.4 and the variable LastByteRcvd in Section 3.5.5?
What is the relationship between the variable LastByteRcvd in Section 3.5.5 and the variable y in Section 3.5.4?
in Section 3.5.4, we saw that TCP waits until it has received three duplicate A Ks before performing a fast retransmit. Why do you think the TCP designers chose not to perform a fast retransmit after the first duplicate ACK for a segment is received')
Compare GBN, SR, and TCP (no delayed ACK). Assume that the timeout value for all three protocols are sufficiently long such that 5 consecutive data segments and their corresponding ACKs can be received (if not lost in the channel) by the receiving host (Host B) and the sending host (Host A)
Consider Figure 3.46(b). If λ′in increases beyond R/2, can λOut increase beyond R/3 ? Explain. Now consider Figure 3.46(c). If λ′in increases beyond R/2, can λOut increase beyond R/4 under the assumption that a packet will be forwarded twice on average from the router to the receiver'?
Consider Figure 3.58.Assuming TCP Reno is the protocol experiencing the behavior shown above, answer the following questions. In all cases, you should provide a short discussion justifying your answer.a. Identify the intervals of time when TCP slow start is operating.b. Identify the intervals of
Refer to Figure 3.56, which illustrates the convergence of TCP's AIMD algorithm. Suppose that instead of a multiplicative decrease, TCP decreased the window size by a constant amount. Would the resulting AIAD algorithm converge to an equal share algorithm? Justify your answer using a diagram
In Section 3.5.4, we discussed the doubling of the timeout interval after a timeout event. This mechanism is a form of congestion control. Why does TCP need a window-based congestion-control mechanism (as studied in Section 3.7) in addition to this doubling-timeout-interval mechanism?
a. Suppose you have the following 2 bytes: 0 10 111 00 and 0101 0 110. What is the 1s complement of the sum of these 2 bytes? b. Suppose you have the following 2 bytes: 110 1 010 and 00110 I 10. What is the 1s complement of the sum of these 2 bytes? c. For the bytes in part (a), give an example
Host A is sending an enormous file to Host B over a TCP connection. Over this connection there is never any packet loss and the timers never expire. Denote the transmission rate of the link connecting Host A to the Internet by R bps. Suppose that the process in Host A is capable of sending data
Consider sending a large file from a host to another over a TCP connection that has no loss. a. Suppose TCP uses AIMD for its congestion control without slow start. Assuming cwnd increases by I MSS every time a batch of ACKs is received and assuming approximately constant round-trip times, how long
Recall the macroscopic description of TCP throughput. In the period of time from when the connection's rate varies from W/(2. RTT) to W/RTT, only one packet is lost (at the very end of the period).a. Show that the loss rate (fraction of packets lost) is equal tob. Use the result above to show that
Consider that only a single TCP (Reno) connection uses one 10Mbps link which does not buffer any data. Suppose that this link is the only congested link between the sending and receiving hosts. Assume that the TCP sender has a huge file to send to the receiver, and the receiver's receive buffer is
Consider the scenario described in the previous problem. Suppose that the 10Mbps link can buffer a finite number of segments. Argue that in order for the link always busy sending data, we would like to choose a buffer size that is at least the product of the link speed C and the two-way propagation
Repeat Problem 43, but replacing the 10 Mbps link with a 10 Gbps link. Note that in your answer to part c, you will realize that it takes a very long time for the congestion window size to reach its maximum window size after recovering from a packet loss. Sketch a solution to solve this
Let T (measured by RTT) denote the time interval that a TCP connection takes to increase its congestion window size from W/2 to W, where W is the maximum congestion window size. Argue that T is a function of TCP's average throughput.
Consider a simplified TCP's ALMD algorithm where the congestion window size is measured in number of segments, not in bytes. In additive increase, the congestion window size increases by one segment in each RTT. In multiplicative decrease, the congestion window size decreases by half (if the result
Consider the network described in the previous problem. Now suppose that the two TCP connections, C I and C2, have the same RTT of 100 msec. Suppose that at time t0, CI's congestion window size is 15 segments but C2's congestion window size is 10 segments. a. What are their congestion window sizes
Consider a modification to TCP's congestion control algorithm. Instead of additive increase, we can use multiplicative increase. A TCP sender increases its window size by a small positive constant α (0 < a < 1) whenever receives a valid ACK. Find the functional relationship between loss rate L and
Suppose that the UDP receiver computes the Internet checksum for the received UDP segment and finds that it matches the value carried in the checksum field. Can the receiver be absolutely certain that no bit errors have occurred? Explain.
In our discussion of TCP futures in Section 3.7, we noted that to achieve a throughput of 10 Gbps, TCP could only tolerate a segment loss probability of 2· 10-)10 (or equivalently, one loss event for every 5,000,000,000 segments). Show the derivation for the values of 2. 10-10 1-out-of-5,000,000
In our discussion of TCP congestion control in Section 3.7, we implicitly assumed that the TCP sender always had data to send. Consider now the case that the TCP sender sends a large amount of data and then goes idle (since it has no more data to send) at t1. TCP remains idle for a relatively long
In this problem we investigate whether either UDP or TCP provides a degree of end-point authentication. a. Consider a server that receives a request within a UDP packet and responds to that request within a UDP packet (for example, as done by a DNS server). If a client with IP address X spoofs its
In this problem. we consider the delay introduced by the TCP slow-start phase. Consider a client and a Web server directly connected by one link of rate R. Suppose the client wants to retrieve an object whose size is exactly equal to 15 S, where S is the maximum segment size (MSS). Denote the
Consider our motivation for correcting protocol rdt2.1. Show that the receiver, shown in Figure 3.57, when operating with the sender shown in Figure 3.11, can lead the sender and receiver to enter into a deadlock !Slate, where each is waiting for an event that will never occur.
In protocol rdt3. 0, the ACK packets flowing from the receiver 10 the sender do not have sequence numbers (although they do have an ACK field that contains the sequence number of the packet they are acknowledging). Why is it that our ACK packets do not require sequence numbers?
Draw the FSM for the receiver side of protocol rdt3. 0.
Give a trace of the operation of protocol rdt3. 0 when data packets and acknowledgment packets are garbled. Your trace should be similar to that used in Figure 3.16.
Let's review some of the terminology used in this textbook. Recall that the name of a transport-layer packet is segment and that the name of a link-layer packet is frame. What is the name of a network-layer packet? Recall that both routers and link-layer switches are called packet switches. What is
What is HOL blocking? Does it occur in input ports or output ports?
What is the 32-bit binary equivalent of the IP address 223.1.3.27?
Suppose you purchase a wireless router and connect it to your cable modem. Also suppose that your ISP dynamically assigns your connected device (that is, your wireless router) one IP address. Also suppose that you have five PCs at home that use 802.11 to wirelessly connect to your wireless router.
Compare and contrast link-state and distance-vector routing algorithms.
Discuss how a hierarchical organization of the Internet has made it possible to scale to millions of users.
Consider Figure 4.37. Starting with the original table in D, suppose that D receives from A the following advertisement:Will the table in D change? If so how?
Compare and contrast the advertisements used by RIP and OSPF.
Why are policy considerations as important for intra-AS protocols, such as OSPF and Rrp, as they are for an inter-AS routing protocol like BGP?
Define and contrast the following terms: subnet, prefix, and BG? route.
How does BGP use the NEXT-HOP attribute? How does it use the AS-PATH attribute?
Describe how a network administrator of an upper-tier ISP can implement policy when configuring BGP.
What is an important difference between implementing the broadacst abstraction via multiple unicasts, and a single network- (router-) supported broadcast?
For each of the three general approaches we studied for broadcast communication (uncontrolled flooding, controlled flooding, and spanning-tree broadcast), are the following statements true or false? You may assume that no packets are lost due to buffer overflow and all packets are delivered on a
What are the roles played by the IGMP protocol and a wide-area multicast routing protocol?
What is the difference between a group-shared tree and a source-based tree in the context of multicast routing?
Describe some hypothetical services that the network layer can provide to a single packet. Do the same for a flow of packets. Are any of your hypothetical services provided by the Internet's network layer? Are any provided by ATM's CBR service model? Are any provided by ATM's ABR service model?
Discuss why each input port in a high-speed router stores a shadow copy of the forwarding table.
Describe how packet loss can occur at input ports. Describe how packet loss at input ports can be eliminated (without using infinite buffers).
In this question, we consider some of the pros and cons of virtual-circuit and datagram networks. a. Suppose that routers were subjected to conditions that might cause them to fail fairly often. Would this argue in favor of a VC or datagram architecture? Why? b. Suppose that a source node and a
Consider a datagram network using 8-bit host addresses. Suppose a router uses longest prefix matching and has the following forwarding table: Prefix Match Interface 00................... 0 010................... 1 011................... 2 10...................
Consider a datagram network using 8-bit host addresses. Suppose a router uses longest prefix matching and has the following forwarding table: Prefix Match Interface 1............................ 0 10........................... 1 111......................... 2 otherwise.................. 3 For
Consider a router that interconnects three subnets: Subnet I, Subnet 2, and Subnet 3. Suppose all of the interfaces in each of these three subnets are required to have the prefix 223.1 .17/24. Also suppose that Subnet I is required to support up to 63 interfaces, Subnet 2 is to support up to 95
In Section 4.2.2 an example forwarding table (using longest prefix matching) is given. Rewrite this forwarding table using the a.b.c.d/x notation instead of the binary string notation.
In Problem P9 you are asked to provide a forwarding table (using longest prefix matching). Rewrite this forwarding table using the a.b.c.d/x notation instead of the binary string notation.
Consider a subnet with prefix 128.119.40.128/26. Give an example of one IP address (of form xxx. xxx. xxx. xxx) that can be assigned to this network. Suppose an ISP owns the block of addresses of the form 128.119.40.64/25. Suppose it wants to create four subnets from this block, with each block
Consider the topology shown in Figure 4.17. Denote the three subnets with hosts (starting clockwise at 12:00) as Networks A, B, and C. Denote the subnets without hosts as Networks D, E, and F.a) Assign network addresses to each of these six subnets, with the following constraints: All addresses
Consider sending a 2400-byte datagram into a link that has an MTU of 700 bytes. Suppose the original datagram is stamped with the identification number 422. How many fragments are generated? What are the values in the various fields in the IP datagram(s) generated related to fragmentation?
Suppose datagrams are limited to 1,500 bytes (including header) between source Host A and destination Host B. Assuming a 20-byte IP header, how many datagrams would be required to senti an MP3 consisting of 5 million bytes? Explain how you computed your answer.
Consider the network setup in Figure 4.22. Suppose that the ISP instead assigns the router the address 24.34.112.235 and that the network address of the home network is 192.168. 1124. a) Assign addresses to all interfaces in the home network. b) Suppose each host has two ongoing TCP connections,
Consider a virtual-circuit network. Suppose the VC number is a 8-bit field. a) What is the maximum number of virtual circuits that can be carried over a link? b) Suppose a central node determines paths and VC numbers at connection setup. Suppose the same VC number is used on each link along the
Suppose you are interested in detecting the number of hosts behind a NAT. You observe that the IP layer stamps an identification number sequentially on each IP packet. The identification number of the first IP packet generated by a host is a random number, and the identification numbers of the
[n this problem we'll explore the impact of NATs on P2P applications. Suppose a peer with username Arnold discovers through querying that a peer with username Bernard has a file it wants to download. Also suppose that Bernard and Arnold are both behind a NAT. Try to devise a technique that will
Looking at Figure 4.27, enumerate the paths from y to u that do not contain any loops.Figure 4.27. Abstract graph model of a computer network
Repeat Problem P22 for paths from x to Z, Z to u, and z to w.In Problem P22Looking at Figure 4.27, enumerate the paths from y to u that do not contain any loops.Figure 4.27. Abstract graph model of a computer network
Consider the following network. With the indicated link costs, use Dijkstra's shortest-path algorithm to compute the shortest path from x to all network nodes. Show how the algorithm works by computing a table similar to Table 4.3.
Consider the network shown in Problem P24. Using Dijkstra's algorithm, and showing your work using a table similar to Table 4.3, do the following:a. Compute the shortest path from t to all network nodes.b. Compute the shortest path from u to all network nodes.c. Compute the shortest path from v to
Consider the network shown below, and assume that each node initially knows the costs to each of its neighbors. Consider the distance-vector algorithm and show the distance table entries at node z.
Consider a general topology (that is, not the specific network shown above) and a synchronous version of the distance-vector algorithm. Suppose that at each Iteration, a node exchanges its distance vectors with its neighbors and receives their distance vectors. Assuming that the algorithm begins
Consider the network fragment shown below. x has only two attached neighbors, wand y. w has a minimum-cost path to destination u (not shown) of 5, and y has a minimum-cost path to u of 6. The complete paths from wand y to II (and between wand y) are not shown. All link costs in the network have
Consider the three-node topology shown in Figure 4.30. Rather than having the link costs shown in Figure 4.30, the link costs are c(x, y) =3, c(y, z) = 6, c(z. x) = 4. Compute the distance tables after the initialization step and after each iteration of a synchronous version of the distance-vector
A bare-bones forwarding table in a VC network has four columns. What is the meaning of the values in each of these columns'? A bare-bones forwarding table in a datagram network has two columns. What is the meaning of the values in each of these columns'?
Consider the count-to-infinity problem in the distance vector routing. Will the count-to-infinity problem occur if we decrease the cost of a link? Why? How about if we connect two nodes which do not have a link?
Argue that for the distance-vector algorithm in Fig. 4.30, each value in the distance vector D(x) is non-increasing and will eventually stabilize in a finite number of steps.
Consider Figure 4.31. Suppose there is another router w, connected to router y and z. The costs of all links are given as follows: c(x, y) = 4, c(x, z) = 50, c(y, w) = 1, e(2, w) = I, c(y, z) = 3. Suppose that poisoned reverse is used in the distance- vector routing algorithm.a) When the distance
Describe how loops in paths can be detected in BGP.
Will a BGP router always choose the loop-free route with the shortest AS-path length? Justify your answer.
Consider the network shown below. Suppose AS3 and AS2 are running OSPF for their intra-AS routing protocol. Suppose AS 1 and AS4 are running RIP might for their intra-AS routing protocol. Suppose eBGP and iBGP are used for the peering inter-AS routing protocol. Initially suppose there is no
Referring to the previous problem, once router I d learns about x it will put an entry (x, f) in its forwarding table. a) Will I be equal to I1 or 12 for this entry? Explain why in one sentence. b) Now suppose that there is a physical link between AS2 and AS4, shown by the dotted line. Suppose
Consider the following network. ISP B provides national backbone service to regional ISP A. ISP C provides national backbone service to regional ISP D. Each ISP consists of one AS. Band C peer with each other in two places using BGP. Consider traffic going from A to O. B would prefer to hand that
In Figure 4.42, consider the path information that reaches stub networks W, X, and Y. Based on the information available at Wand X, what are their respective views of the network topology? Justify your answer. The topology view at Y is shown below.
Consider Fig 4.42. B would never forward traffic destined to Y via X based on BGP routing. But there are some very popular applications for which data packets go to X first and then flow to Y. Identify one such application, and describe how data packets follow a path not given by BGP routing.
Consider the network below.a) Suppose that this network is a datagram network. Show the forwarding table in router A, such that all traffic destined to host H3 is forwarded through interface 3.b) Suppose that this network is a datagram network. Can you write down a forwarding table in router A,
In Figure 4.42, suppose that there is another stub network V that is a customer of ISP A. Suppose that Band C have a peering relationship, and A is a customer of both Band C. Suppose that A would like to have the traffic destined to W to come from B on ly, and the traffic destined to V from either
Consider the seven-node network (with nodes labeled t to z) in Problem P4. Show the minimal-cost tree rooted at z that includes (as end hosts) nodes II, II, W, and y. Informally argue why your tree is a minimal-cost tree.
Consider the two basic approaches identified for achieving broadcast, unicast emulation and network-layer (i.e., router-assisted) broadcast, and suppose spanning-tree broadcast is used to achive network-layer broadcast. Consider a single sender and 32 receivers. Suppose the sender is connected to
Consider the operation of the reverse path forwarding (RPF) algotithm in Figure 4.44. Using the same topology, find a set of paths from all nodes to the source node A (and indicate these paths in a graph using thicker-shaded lines as in Figure 4.44) such that if these paths were the least-cost
Consider the topology shown in Figure 4.44. Suppose that all links have unit cost and that node E is the broadcast source. Using arrows like those shown in Figure 4.44) indicate links over which packets will be forwarded using RPF, and links over which packets will not be forwarded, given that node
Repeat Problem P44 using the graph from Problem P24. Assume that z in the broadcast source, and that the link costs are as shown in Problem P22.In Problem P44Consider the topology shown in Figure 4.44. Suppose that all links have unit cost and that node E is the broadcast source. Using arrows like
Consider the topology shown in Figure 4.46, and suppose that each link has unit cost. Suppose node C is chosen as the center in a center-based multicast routing algorithm. Assuming that each attached router uses its least-cost path to node C to send join messages to C, draw the resulting
Repeat Problem P46, using the graph from Problem P24. Assume that the center node is v. In Problem P46 Consider the topology shown in Figure 4.46, and suppose that each link has unit cost. Suppose node C is chosen as the center in a center-based multicast routing algorithm. Assuming that each
In Section 4.5.1 we studied Dijkstra's link-state routing algorithm for computing the unicast paths that are individually the least-cost paths from the source to all destinations . The union of these paths might be thought of as forming a least-unicast-cost ,path tree (or a shortest unicast path
Consider a network in which all nodes are connected to three other nodes. In a single time step, a node can receive all transmitted broadcast packets from its neighbors, duplicate the packets, and send them to all of its neighbors (except to the node that sent a given packet). At the next time
Consider a VC network with a 2-bit field for the VC number. Suppose that the network wants to set up a virtual circuit over four links: link A, link B, link C, and link D. Suppose that each of these links is currently carrying two other virtual circuits, and the VC numbers of these other VCs are as
Design (give a pseudocode description of) an application-level protocol that maintains the host addresses of all hosts participating in a multicast group. Specifically identify the network service (unicast or multicast) that is used by your protocol, and indicate whether your protocol is sending
What is the size of the multicast address space? Suppose now that two multicast groups randomly choose a multicast address. What is the probability that they choose the same address? Suppose now that 1,000 multicast groups are ongoing at the same time and choose their multicast group addresses at
In the text we have used the term connection-oriented service to describe a transport-layer service and connection service for a network-layer service. Why the subtle shades in terminology?
In Section 4.3, we noted that there can be no input queuing if the switching fabric is n times faster than the input line rates, assuming n input lines all have the same line rate. Explain (in words) why this should be so.
Consider the switch shown below. Suppose that all datagrams have the same fixed length, that the switch operates in a slotted, synchronous manner, and that in one time slot a datagram can be transferred from an input port to an output port. The switch fabric is a crossbar so that at most one

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Computer Networking A Top-Down Approach 5th edition James F. Kurose, Keith W. Ross - Solutions

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