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12 INTELLIGENT COMMUNICATION SYSTEMS
FIGURE 2.5 Function of OSI protocol.
transmission both ways) or half-duplex transmission. This is done via a session-
level protocol. A presentation-level protocol provides the code conversion for the
message. An application-level protocol provides the file transfer function, job trans-
fer function, or telnet remote access function. These protocols have been standard-
ized, and they are called OSI standard protocol. The TCP/IP protocol is used on the
Internet. The IP protocol corresponds to the OSI network-level protocol. The TCP
protocol corresponds to the OSI transport-level protocol. The TCP/IP protocol is
shown in Figure 2.4. The OSI protocol is presented in Figures 2.4 and 2.5. Further
details of the OSI and TCP/IP protocols are described in later chapters.
