Installation guide

Network Infrastructure for EtherNet/IP™
Understanding the Basics of Network Protocols
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2.1 The TCP/IP Suite
EtherNet/IP incorporates the TCP/IP suite, utilizing TCP for explicit messaging and UDP for implicit or
I/O messaging. These widely adopted protocols are implemented at the network layer (IP) and the
transport layer (UDP and TCP) of the OSI Model, and are the basic networking technology for
EtherNet/IP.
Transmission Control Protocol (TCP)
Transmission Control Protocol (TCP) is a connection-oriented transport protocol that
sends data as an unstructured stream of bytes. By using sequence numbers and
acknowledgment messages, TCP can provide a sending node with delivery information about
packets transmitted to a destination node. EtherNet/IP uses TCP for explicit messaging (i.e., device
configuration).
TCP’s multiplexing allows simultaneous upper-layer conversations to be multiplexed over a single
connection. TCP provides connection-oriented, end-to-end reliable packet delivery by sequencing bytes
with a forwarding acknowledgment number that indicates to the destination the next byte the source
expects to receive. Bytes not acknowledged within a specified time period are retransmitted. The
reliability mechanism of TCP allows devices to deal with lost, delayed, duplicate, or misread packets.
For example, if data is lost in transit from source to destination, TCP can retransmit the data until either a
timeout condition is reached or successful delivery is achieved. TCP can also recognize duplicate
messages and appropriately discard them. If the sending computer is transmitting too fast for the receiving
computer, TCP can employ flow control mechanisms to slow data transfer. TCP can also communicate
delivery information to upper-layer protocols and applications. Figure 2-2 shows the TCP packet fields.
Figure 2-2 TCP Packet Fields.