Image Processing Reference
In-Depth Information
Red
RT_Class 3
Orange
RT_Class 2
Green
Class 2/Class 1
Yellow
Non-real-time
FIGURE .
Profinet IO transmission cycle.
The medium access protocol of Profinet IO is based on a time division multiple access (TDMA)
technique. In practice, the traffic is scheduled according to a cycle, which consists of four phases, as
shown in Figure .. he irst phase (RED) is reserved for RT_CLASS  traffic (the most critical) that
takes place over predefined physical links enforced by a special kind of switches purposely developed
for Profinet IO. In the ORANGE phase, only RT_CLASS  frames are exchanged. his is still time-
critical traffic; however, in this case, requirements for physical links are not defined. The GREEN
phase is reserved for both RT_CLASS  and RT_CLASS  frames, either cyclic or acyclic. his is the
only mandatory phase; the access to the physical medium is regulated by the priority assigned to
frames, as specified by the IEEE .Q [] standard. Finally, the YELLOW phase is reserved for
non-real-time traffic.
The application layer protocol of Profinet IO, analogously to other RTE networks encompassed by
the IEC  standard, is based on the definition of communication objects that can be exchanged
over the network via communication relationships established between I/O controllers and I/O
devices.
26.2.2 DeviceNet and EtherNet/IP
DeviceNet and EtherNet/IP (together with ControlNet and CompoNet) are communication solu-
tions that rely on the well-assessed common industrial protocol (CIP) []—formerly known as
“control and information protocol”—which enables a high degree of interoperability among these
kinds of networks. Figure . depicts the protocol stack foreseen by CIP. CIP can be placed on top
of several networks that include (but are not limited to) CAN and Ethernet. Seamless bridging and
routing are natively supported by this protocol, which allows parameterization information and pro-
cess data to be easily exchanged in heterogeneous-distributed systems that rely on both fieldbus and
industrial Ethernet transmission technologies.
DeviceNet adopts the CAN protocol at the low end of its protocol stack (physical and data-link
layers). Despite the plain bus topology and the relatively low speed (from  up to  Kb/s), this
User layer
Device profiles and application objects
Application
layer
CIP (explicit vs. I/O messaging)
Encapsulation protocol
DeviceNet
connection
manager
Transport
layer
TCP/UDP
IP
Data-link
and physical
layers
CAN
ISO 11898
Ethernet
IEEE 802.3
WiFi
IEEE 802.11
FIGURE .
Protocol stack of CIP-based networks.
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