Saturday, February 9, 2008

Header TCP

# Source port [ 16 bit ] - the door number Identifies on the host sender associated to logon TCP.
# Destination port [ 16 bit ] - the door number Identifies on the host adressee associated to logon TCP.
# Sequence number [ 32 bit ] - Number of sequence, indicates the scostamento (expressed in byte) of the beginning of segment TCP to the inside of the complete flow, to leave from the Initial Sequence Number (ISN), negotiates R-all'.apertura of the logon.
# Acknowledgment number [ 32 bit ] - Number of reply, has only meant if flag the ACK is settato to 1, and confirmation the reception of a part of the data traffic in the opposite direction, indicating the value of the next Sequence number that the host sender of segment TCP expects to receive.
# Header Length [ 4 bit ] - bit) of the header Indicates the length (in word from 32 of segment TCP; such length can vary from 5 word (20 byte) to 15 word (60 byte) to second of the presence and the length of the optional field Options.
# Reserved [ 6 bit ] - Bit does not use you and predisposed for future developments of the protocol.
# Flags [ 6 bit ] - Bit uses you for the control of the protocol:

* URG - if settato to 1 indicates that in the flow they are present urgent data to the position (offset) indicated from the Urgent field pointer;
* ACK - if settato to 1 indicates that the Acknowledgment field number is valid;
* PSH - if settato to 1 indicates that the data in arrival do not have to be bufferizzati but passes endured to the advanced levels of the application;
* RST - if settato to 1 restores the logon; it comes used in case of serious error;
* SYN - if settato to 1 indicates that the host sender of the segment wants to open a logon TCP with the specific host adressee and in the Sequence field number the value of the Initial Sequence Number (ISN); it has the scope sincronizzare the numbers of sequence of the two hosts. The host that has sended the SYN must attend from the remote host a package SYN/ACK.
* END - if settato to 1 indicates that the host sender of the segment wants to close logon TCP opened with the host adressee. The sender attends the confirmation from receiving (with a FIN-ACK). To this point the logon is thought sluice for half: the host that has sended END will not be able more to send given, while the other host has the communication channel still available. When also the other host will send the package with set up END the logon, after the relative FIN-ACK, will be considered completely sluice.

# Advertise Window [ 16 bit ] - the dimension of the window of reception of the host Indicates sender, that is the byte number that the sender is in a position to beginning from accepting that specifying from the acknowledgment number.
# Checksum [ 16 bit ] - Field of control used for the verification of the validity of the segment. Obtained E' making the complement to 1 of the sum complement to one to 16 bit of entire header the TCP (with the field checksum put to zero) with the added one of one pseudo header composed gives: IP address sorgente(32bit), IP address destinazione(32bit), a byte of zeri, a byte that the protocol indicates and two byte that indicate the length of package TCP (header + data).
# Urgent pointer [ 16 bit ] - Gunlayer to urgent data, has only meant if flag the URG is settato to 1 and indicates the scostamento in byte to leave from the Sequence number of the byte of urgent data to the inside of the flow.
# Options - Options (optional) for uses of the protocol is left over to you.

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