This chapter structure:
1.TCP protocol describes
2.TCP packet format
3.TCP three-way handshake
4.TCP four waved
5.UDP protocol describes
6. The common protocols and ports
1.
the TCP (Transmission Control Protocol) is connection-oriented, reliable process to process communication protocol;
the TCP provides full-duplex service, i.e., two-way transmission of data at the same time;
the TCP segment:
a.TCP the plurality of word section constituting one packet, called the segment (segment);
b.TCP segment encapsulated in an IP datagram. 
2. The 
source port number: source port address;
destination port number: destination port address;
ID: transmitting end for each byte number for the convenience of recombinant correctly;
acknowledgment number: acknowledgment information for the transmitting side;
window size: with in that the local number of data segments may be received, the window size is variable;
header length: length of the data segment header;
the URG: urgent pointer bits. 1: Open; 0: off (without caching submitted directly to each other)
PSH: receiving transmitted quickly to the application layer. 1: Open; 0: off (subject to the cache, and a number of segments in place, the application layer is directly transmitted)
the SYN: connection establishment request flag (labeled 1)
the FIN: connection request flag is turned off (labeled 1 )
the ACK: acknowledgment bit (labeled confirmed. 1)
the RST: reconnecting transmission, corresponding to the reset
checksum: checksum formats, error check
options: dispensable
3. 
PC1 wants to establish a connection with pc2, pc1 first terminal sends a request to establish a data connection to pc2, pc2 receipt will then transmit the request to receive data pc1, while confirming the connection pc1 and the last received data pc1 and sending acknowledgment data to pc2. Such pc1 and pc2 both ends of the connection established two-way communication.
4. 
PC1 wants to disconnect pc2, pc1 first terminal sends a disconnect request data to pc2, pc2 confirming and disconnected, first confirm receipt pc2, thus, TCP half-closed ( pc1 can not send data to pc2, but you can still send data to pc2 pc1). Pc2 then sends the data to pc1 disconnected, while confirming pc1 and disconnected. Finally pc1 receives the data and sends the data to confirm pc2. Such two-way communication pc1 and pc2 is then disconnected.
5. The
A.UDP: User Datagram Protocol 
UDP length: to indicate the total length of the UDP, headed portion plus data
Checksum: The only reliable UDP protocol provides a mechanism for the completion of error check data for UDP, which is
6. The
A. common TCP port, and protocol functions:
Port --- ---- protocol function
20 --- FTP --- data connection
21 --- FTP --- control connection
23 --- TELNET- - means for remote login, remote control management target computer (plaintext)
22 is used for remote login --- --- SSH, can be managed remotely control the target computer (ciphertext)
25 --- --- for transmitting the SMTP message
80 --- HTTP --- hypertext transfer protocol
443 --- https --- hypertext transfer protocol server
110 --- POP3 --- for incoming mail
B. common UDP port numbers and their functions: