<TCP header>
| Field | Description |
| Source port Destination port | The port number. |
| SEQ(Sequence number) ACK(Acknowledgement number) | The value for arranging the segments. It implements reliable data transmission.
* First SEQ = arbitrary value.
* SEQ = received ACK
* ACK = received SEQ + received data size(If data is 0, +1)
|
| Header length | Header length divided by 4.
* Generally 5.
|
| TCP flags | The property of a segment.
* N(NS. Nonce Sume) : The flag to protect CWR, ECE field from concealment.
* C(CWR. Congestion Window Reduced) : The flag notify that the sender has received an ECE flag. It reduce the window size of the sender.
* E(ECE. ECN-Echo) : (SYN=0)The flag to request reducing the window size of sender due to network congestion. (SYN=1)The flag to notify the fact that the receiver use ECN.
* U(URG) : The flag to notify urgent Data.
* A(ACK) : The flag to notify data reception.
* P(PSH) : The flag notify that transmission data will be transmitted immediately without storing in the buffer.
* R(RST) : The flags requesting connection re-establishment.
* S(SYN) : The flag to notify connection establishment.
* F(FIN) : The flag to notify disconnection.
|
| Window size | The buffer size that the system can send/receive. It is related to flow control congestion control.
* Flow control : control considering the buffer size notified by the sender.
* Congestion control : control considering network congestion.
|
| Checksum | The checksum value for checking error of TCP header and the payload. |
| Urgent pointer | The value that indicates the starting point of the emergency data.
* The urgent pointer is needed, because the emergency data is mixed with ordinary data.
|
<UDP header>
| Field | Description |
| Source port Destination port | The port number. |
| Length | Whole segment size. UDP header size + Payload size. |
| Checksum | The checksum value for checking error of UDP header and the payload. |