Consider the packet trace shown below which is from part of an HTTP session. The

Question

Consider the packet trace shown below which is from part of an HTTP session.
The source (“Src”) and the destination (“Dst”) columns indicate “C” for the client and “S” for
the server. The values for “Time” are given in seconds.
No Time Src Dst Prot Info
1 0.000000 C S TCP 1686 > http [SYN] Seq=592488238 Ack=0 Win=16384 Len=0
2 0.001388 S C TCP http > 1686 [SYN, ACK] Seq=2589966238 Ack=592488239 Win=24820
Len=0
3 0.001470 C S TCP 1686 > http [ACK] Seq=592488239 Ack=2589966239 Win=17520 Len=0
4 0.002160 C S HTTP POST /bin/common/dropbox.pl HTTP/1.1
5 0.004029 S C TCP http > 1686 [ACK] Seq=2589966239 Ack=592489053 Win=24820 Len=0
6 0.007943 C S HTTP Continuation
7 0.007986 C S HTTP Continuation
8 0.008015 C S HTTP Continuation
9 0.030065 S C TCP http > 1686 [ACK] Seq=2589966239 Ack=592490513 Win=24820 Len=0
10 0.030135 S C TCP http > 1686 [ACK] Seq=2589966239 Ack=592493433 Win=24820 Len=0
a. How much time is required to establish the TCP connection?
b. Considering TCP’s flow control mechanism (but ignoring congestion control), what is the
range of bytes, specified as sequence numbers, that can be sent from the client to the
server after the client receives packet 2 and sends packet 3?
c. What is the meaning of packet 4 with respect to the HTTP application layer protocol?
d. What is in packets 6, 7, and 8?
e. Why is the value of “Seq” the same in packets 9 and 10?
f. When packet 10 is received at the client, how many bytes sent from the client to the
server have been acknowledged by the server?
g. What port is used at the client for the connection to the HTTP server?
h. Which version of HTTP is supported by the client?

Explanation / Answer

a)

1st ,2nd and 3rd packets are used to create TCP three way hand shaking.

Time in 1st packet is 0.000000 seconds and time in 3rd packet is 0.001388 seconds.

Thus, the connection is established in 0.001388 seconds

b)

Since the window size of the client is 16384, the client can send 16384 bytes to the server.

That is, the range of bytes, specified as sequence numbers, is 592488240-592504623.

c)

Given 4th packet is 4 0.002160 C S HTTP POST /bin/common/dropbox.pl HTTP/1.1.

GET and POST are the HTTP request methods.

Where, HTTP POST uploads or submits the data or file to a resource to process or to store.

In the given example, HTTP POST in the 4th packet requests the server to accept and store a file.

d)

Http continuation is used to tell the server the data is the continuation for the previous. If the data is not fit into a packet, it sends by breaking the data.

e)

Observe the packet 9 and 10. Both are acknowledgments form the server. Acknowledgement does not consume the sequence number. And moreover, the client does not send any packet between packet 9 and 10.

f)

592493433-592490513= 2920 bytes

g)

Client port number is 1686.

h)

http version that is supported by the client is HTTP/1.1

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