Installation guide

Network Infrastructure for EtherNet/IP™
Understanding the Basics of Network Protocols
2-10
32 Bits
Source Port Destination Port Length Checksum Data
32 Bits
Unlike the TCP, UDP adds no reliability, flow-control, or error-recovery functions to IP. Because of
UDP’s simplicity, UDP headers contain fewer bytes and, therefore, consume less network overhead than
TCP.
UDP is useful in applications where efficiency of data delivery takes precedence over verification of data
delivery, such as in cases where a higher-layer protocol might provide error and flow control.
User Datagram Protocol (UDP)
User Datagram Protocol (UDP) is the transport protocol for several well-known application-layer
protocols, including Network File System (NFS), Simple Network Management Protocol (SNMP),
Domain Name System (DNS), and Trivial File Transfer Protocol (TFTP). EtherNet/IP uses UDP for
implicit (real-time control) messaging.
The UDP packet format contains four fields, as shown in Figure 2-4. These include Source Port,
Destination Port, Length, and Checksum fields.
Figure 2-4 UDP Packet Format.
Source Port and Destination Port fields contain the 16-bit UDP protocol port numbers used to de-
multiplex datagrams for receiving application-layer processes. A Length field specifies the length of the
UDP header and data. Checksum provides an (optional) integrity check on the UDP header and data.
2.3 Data Exchange Models
EtherNet/IP uses the producer-consumer data exchange model. A data exchange model, or
architecture, describes a set of mechanisms by which data is exchanged between application programs
running in two or more computing devices. Each mechanism, depending on its function, uses unicast,
multicast, or broadcast communication or some combination of these. The most popular data exchange
models today are point-to-point, client-server, publisher-subscriber, and producer-consumer.
Since present networks support a variety of multimedia information services, it is sometimes difficult to
determine whether a particular device supports more than one data exchange model or if one model is a
special case of the other one. EtherNet/IP has the flexibility to support these different types of data
exchanges to meet application needs that may arise.
Point-to-point communication is the simplest data exchange model. Classical examples of point-to-
point connections are communication between two people over a phone and two computers over a TCP/IP
connection.
Client-server communication implies a central server connected to many clients. This is a one-to-many
model. One could argue that a client-server system is actually a collection of point-to-point connections.
Client-server communication (or client-server computing) is popular in office networks and transaction