The port addresses in TCP and UDP segment structures are 16 bits, and can have port numbers in the range of 0-65535. For these 65536 port numbers, there are the following usage rules:

(1) Port numbers less than 256 are defined as public ports, and servers are generally identified by public port numbers. Services provided by any TCP/IP implementation use port numbers between 1- 1023, which are managed by ICANN;

(2) The client only needs to ensure that the port number is unique on this machine. Customer port number is also called temporary port number because of its short existence time;

(3) Most TCP/IP implementations allocate temporary port numbers between 1024-5000. Port numbers greater than 5000 are reserved for other servers.