IBM CTI 2572 manual TCP/IP Overview, TCP/IP Components

CHAPTER 5. TCP/IP OVERVIEW

5.1 TCP/IP Components

TCP/IP consists of a hierarchy of related protocols. Upper level protocols are encapsulated in the data structure of lower level protocols.

Figure 11 TCP/IP Data Encapsulation

In a typical application using the 2572, the host computer application sends PLC commands via either TCP (Transmission Control Protocol) or UDP (User Datagram Protocol) services. TCP is used if connection-oriented communications is desired; UDP is used for connectionless communications. The TCP segment or UDP datagram is placed in an IP (Internet Protocol) datagram which is then sent to a 2572 over the network. The receiving 2572 removes the TCP (or UDP) packet from the IP datagram, removes the PLC command from the TCP (or UDP) packet, and transfers the PLC command to the PLC processor. Responses from the PLC are processed in a similar manner.

CTI 2572 Technical Overview Manual 21