computer作业代写
computer作业代写 [Adapted from Walrand 2nd edition problems 3.1 and 3.2] Suppose a network with 109hostnames (not including the…
DNS: computer作业代写
- [Adapted from Walrand 2nd edition problems 3.1 and 3.2] Suppose a network with 109hostnames (not including the names of the nameservers themselves) uses non-recursive DNS.
Assume that there is a single root nameserver, multiple local nameservers, and M levels of nameservers in between local nameservers and the root nameserver. (The top level domain (TLD) nameservers are on the highest level of these M levels.)
Each nameserver has N names in its database. For instance, the root nameserver stores the N names of the TLD nameservers, and the local nameservers each store N names of host names.
You may consider all of these nameservers as organized in a tree. The root of the tree is the single name server, and the second level of the tree has N TLD nameservers. The bottom of the tree consists of local nameservers, which collectively store 109 hostnames. For M=1, there is one level of nameservers between local nameservers and the root nameserver. For M=2: there are two levels of nameservers between local nameservers and the root nameserver. For M=3, there are three levels of nameservers between local nameservers and the root nameserver.
(a) If M=1, find N. If M=2, find N. If M=3, find N. [Hint: First, draw the DNS tree for M=1, and make sure you know what entries are in each DNS table.]
(b) Assume that the total of transmission, propagation and queueing delay for each message takes 0.2 seconds. Assume that the processing delay of a single DNS nameserver to respond to a DNS query takes 0.5 log(N) seconds, if the nameserver has N names in its database, where the log is base 10. Compare the time for a query and response for a complete DNS query and response (to all required nameservers) if M=1, M=2, and M=3.
MAC addresses & ARP: computer作业代写
- [Kurose 7th or 8th edition, chapter 6, problem P15] Consider Figure 6.33.
Figure 6.33 Three subnets, interconnected by routers
Now we replace the router between subnets 1 and 2 with a switch S1, and label the router between subnets 2 and 3 as R1.
(a) Consider sending an IP datagram from Host E to Host F. Will Host E ask router R1 to help forward the datagram? Why? In the Ethernet frame containing the IP datagram, what are the source and destination IP and MAC addresses?
(b) Suppose E would like to send an IP datagram to B, and assume that E’s ARP cache does not contain B’s MAC address. Will E perform an ARP query to find B’s MAC address? Why? In the Ethernet frame (containing the IP datagram destined to B) that is delivered to router R1, what are the source and destination IP and MAC addresses?
(C) Suppose Host A would like to send an IP datagram to Host B, and neither A’s ARP cache contains B’s MAC address nor does B’s ARP cache contain A’s MAC address. Further suppose that the switch S1’s forwarding table contains entries for Host B and router R1 only. Thus, A will broadcast an ARP request message. What actions will switch S1 perform once it receives the ARP request message? Will router R1 also receive this ARP request message? If so, will R1 forward the message to Subnet 3? Once Host B receives this ARP request message, it will send back to Host A an ARP response message. But will it send an ARP query message to ask for A’s MAC address? Why? What will switch S1 do once it receives an ARP response message from Host B?
OSPF: computer作业代写
- [Kurose 7th or 8th edition, chapter 5, problem P3] Consider the network in this figure.
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 5.1.
BGP:
- [Kurose 7th or 8th edition, chapter 5, problem P17] In Figure 5.13, consider the path information that reaches stub networks W, X, and Y.
Figure 5.13 A simple BGP policy scenario
The topology view at Y is shown in this figure.
Based on the information available at W and X, what are their respective views of the network topology? Justify your answer.
BGP: computer作业代写
- [Kurose 7th or 8th edition, chapter 5, problem P19] In Figure 5.13, suppose that there is another stub network V that is a customer of ISP A.
Figure 5.13 A simple BGP policy scenario
Suppose that B and C have a peering relationship, and A is a customer of both B and C. Suppose that A would like to have the traffic destined to W to come from B only, and the traffic destined to V from either B or C.
(a) How should A advertise its routes to B and C?
(b) What AS routes does C receive?
ALOHA:
- [Kurose 7th or 8th edition, chapter 6, problem P10] 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 pA is greater than node B’s retransmission probability, pB.
(a) Provide a formula for node A’s average throughput. What is the total efficiency of the protocol with these two nodes?
(b) If pA = 2 pB, is node A’s average throughput twice as large as that of node B? Why or why not? If not, how can you choose pA and pB to make that happen?
(c) In general, suppose there are N nodes, among which node A has retransmission probability 2p and all other nodes have retransmission probability p. Provide expressions to compute the average throughputs of node A and of any other node.
ALOHA: computer作业代写
- [Kurose 7th or 8th edition, chapter 6, problem P11, but with the numbers given here] 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 each slot with probability p. The first slot is numbered slot 1, the second slot is numbered slot 2, and so on.
(a) What is the probability that node A succeeds for the first time in slot 4?
(b) What is the probability that some node (either A, B, C or D) succeeds in slot 5?
(c) What is the probability that the first success occurs in slot 4?
(d) What is the efficiency of this four-node system?
