Assignment1
Questions: (50 points)
1, (6 points) Suppose there are exactly two packet switches (switch1 and switch2)
between a sending host and a receiving host. The transmission rate between the sending
host and switch1 is R1, 200Mbps.
The transmissions rate between switch1 and switch2 and between switch2 and the receiving host are R2, 400Mbps and R3, 500Mbps, respectively. Assuming that the switches use store–and–forward packet switching, what is the total end–to–end delay to send a packet of length L, 1000 bytes? (Ignore queuing, propagation delay, and processing delay.)
2, (8 points)
(a) In general, how long does it take a packet of length L to be delivered from the
sending host to the receiving host over a link of distance d, propagating speed s,
and transmission rate R bps (consider both transmission delay and propagation
delay)?
(b) How many milliseconds (ms) does it take for a packet of length 1,000 bytes to be
delivered from the sending host to the receiving host over a link of distance 2,000
km, propagation speed 2.5x108 m/s, and transmission rate 50Mbps (consider both
transmission delay and propagation delay)?
(c) How many milliseconds does it take for the first bit of the packet to arrive at the
receiving host (start to count the time when the sending host starts to transmit the
first bit of the packet)?
(d) How many milliseconds does it take for the whole packet to be put on the link
(start to count the time when the sending host starts to transmit the first bit of the
packet)?
3, (6 points) Suppose Host A wants to send a large file to Host B. The path from Host A
to Host B has three links, of rate R1=100Mbps, R2=500Mbps, and R3=200Mbps.
(a) Assume no other traffic in the network, what is the throughput for the file transfer?
(b) Suppose the file is 500MB (Assume 1MB= 106 bytes). Dividing the file size by
the throughput, roughly how long will it take to transfer the file to Host B?
4, (4 points) What information is used by a process running on one host to identify a
process running on another remote host? For a communication between a pair of
processes, which process is the client and which is the server?
5, (8 points) True or false? Why?
a, A user requests a Web page that consists of some text and two images. For this page,
the client will send one request message and receive one response message.
b, Two distinct Web pages (for example, www.nova.edu/resources/current_students.html
and www.nova.edu/resources/faculty_staff.html ) can be sent over the same persistent
connection.
c, With persistent connections between browser and origin server, it is possible for a
single TCP segment to carry two distinct HTTP request messages.
d, The Date: header in the HTTP response message indicates the time and date when the
HTTP response was last modified.
6, (8 points) What is an application–layer message? A transport–layer segment? A
network–layer datagram? A link–layer frame?
7, (2 points) Consider a TCP connection between Host A and Host B. Suppose that the
TCP segments traveling from Host A to Host B have source port number 10408 and
destination port number 80. What are the source and destination port numbers for
segments traveling from Host B to Host A on the same TCP connection?
8, (4 points) Suppose a process in Host C has a UDP socket with port number 8880,
Suppose Host A and Host B each sends a UDP segment to Host C with destination port
number 8880. Will both of these two segments be directed to the same socket at Host C?
If so, how will the process at Host C know that these two segments originated from two
different hosts?
9, (4 points) Suppose that a Web server runs in Host C on port 80. Suppose this Web
server uses persistent connections, and is currently receiving requests from two different
Hosts, A and B. Are all of the HTTP requests from Host A and B being sent through the
same socket at Host C? If they are being passing through different sockets, do both of the
sockets have port 80? Discuss and explain