Req Help with TCP headers

From: Daniel Peters (anon_SPAMTRAP_at_msn.co.uk)
Date: 03/28/04 

Date: Sun, 28 Mar 2004 11:18:13 +0100

Hi all,
I know this will seem very basic to you, but i am really struggling to
understand the TCP headers --> handshake process etc

I understand that the first header must send a SYN to the server which will
add the 1 to the header but i dont understand how 00000000011's etc change /
reverse.

Any help gratefully appreciated as i cant speak to my teacher till after the
holidays, and i feel so lost at the moment i must be missing something basic
/ obvious.

Table 1

0000000000010100 | 0000000001111000
                    0000000000000010
                    0000000000000000
0101|XXXXXX| 0 | 0 | 0 | 0 | 1 | 0 | 0000000000000000
 Xx16 | Xx16

A web page is being opened, which requires a TCP connection to be opened to
the server, table 1 represents the header of a TCP segment in order to allow
the connection.

Note the 6-bit reserved field in the fourth row and the bottom two fields
are not relevant for this question and have been marked X

Also the leading sixteen zeros have been omitted, you should also omit these
in your answer.

Table 2

        enter values | enter values
                0000000000000111
                    enter values
? |XXXXXX| 0 | ? | 0 | 0 | ? | 0 | 0000000000100000
 Xx16 | Xx16

This partially represents the header of the TCP segment returned by the
server in response.

You need to, 1) complete the table enter values + ??, explaining why you
choose the values

2) Work out how many octets can be sent from the users computer to the
server without waiting for an acknowledgement.

Table 3

        enter values | enter values
                0000000000000100
                    enter values
? |XXXXXX| 0 | ? | 0 | 0 | ? | 0 | 0000000001000000
 Xx16 | Xx16

Table 3 represents the header of TCP segment then sent from the users
computer to the server, (i) complete the table giving reasons for your
answers.

(ii) how many octets can be sent form the server to the clients computer
without waiting for a acknowledgement?

Thanks for any replies and help

Dan

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