Sharif University of technology
Computer Engineering Department
CE 443: Computer Networks
Homework V
Zeinab Movahedi
15 Khordad 1391
Question 1
We want to transfer a file index.html from a server S to a client C according to the FTP
application protocol. Assume that: a FTP client program is executed on C, the FTP server
program is launched on S, and the file is available in the user directory of S with alice as the
username and hfsdk as password.
1. Draw a general schema and precise the used ports:
2. Represent the application exchanges for the FTP session recovering the file named index.html
(you do not need to specify the exact names of commands or response codes):
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3. Draw the timing diagram of exchanges happened in the transport layer:
Question 2
Consider an unlimited file transfer on a classical TCP connection (without fast retransmit). The
Maximum Segment Size (MSS) is 200 bytes. The transmission starts. Hereafter, you find the
timeline diagram: complete the parameters associated to each segment (sequence N°,
acknowledgement N°, flags and data size)
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Ack
loss
After completing the above schema, answer to following questions:
1. What is the impact of the first loss on the next acks?
2. How the first loss is detected and how it is covered?
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Data Size
3. How the second loss of data segement is detected and how it is covered?
4. Does the slow start help for limiting the retransmissions?
5. Are there any unnecessary retransmissions?
Question 3
Here is the screenshot in hexadecimal representation of an Ethernet frame without preamble
Please delineate the different protocol structures directly on the track below. Then answer the
questions overleaf.
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1. What are the protocols existing in this frame?
2. At what stage of the exchange application is this frame?
3. What applicative information exists in this frame?
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