P9 (a) The average time required to send an object over the access link is ∆ =( 850000 bits )/( 15000000 bits / s )= 0.057 s the arrival rate of objects to the access link is β = 16 requests/s, So ∆ β = 0.057 ∗ 16 = 0.907 the average access delay is ∆ /( 1 − ∆ β )=( 0.057 s )/( 1 − 0.907 )= 0.61 s Thus, the total average response time is the sum of the access delay and the Internet delay, which is, 0.61 s + 3 s = 3.61 s (b) Since the miss rate is 0.4, the traffic intensity on the access link is 0.4* ∆ β = 0.4 ∗ 0.907 = 0.363 the average access delay is ∆ /( 1 − ∆ β )= 0.057 s /( 1 − 0.363 )= 0.089 s the average response time needed with the origin servers is 0.089 s + 3 s = 3.089 s and the average response time needed by the cache is within 0.01s. Since the miss rate is 0.4 for the cache, the total response time is 0.4 ∗ 3.089 s + 0.6 ∗ 0.01 s = 1.24 s (a) Yes. Because with parallel instances of non-persistent HTTP, Bob has more connections, he has larger link bandwidth than four other users, and this improves the HTTP response time. (b) Yes. Bob’s parallel connections would still be beneficial because Bob still uses parallel instances of non-persistent HTTP with parallel downloads, otherwise he will get less bandwidth share than four other users.
P12 The program can be like this: from socket import * serverPort = 12000 serverSocket = socket(AF_INET, SOCK_STREAM) serverSocket.bind((‘’, serverPort)) serverSocket.listen(1) while 1: connectionSocket, addr = serverSocket.accept() clientSentence = connectionSocket.recv(1024) serverSentence = clientSentence.upper() connectionSocket.send(serverSentence) print ‘From Server:’, serverSentence, ‘\n’ connectionSocket.close() serverSocket.close() P13 The command MAIL FROM: in SMTP is part of the SMTP handshaking protocol, it is a SMTP message from the SMTP client to the server, which is used for identifying the sender. From: in the mail message is part of the mail message itself, it is just a line contained in the mail message, it is not a SMTP message. (a) A whois database is a database that stores the registered users or assignees of Internet resource, such as domain name, IP address, and it has the query and response protocol for locating the corresponding DNS server, whois server and so on for a given resource such as IP address or domain name.
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- Spring '17
- IP address, Domain Name System