Image Processing Reference
In-Depth Information
TABLE .
Performance Indicators for Ethernet/IP
Performance Indicator
Profile /
Profile /.
Delivery time
µs to . ms
- µs
Number of end-stations
-
-
Number of switches between end-stations
-
-
Throughput RTE
-. M octets/s
-. M octets/s
Non-RTEbandwidth
%to%
%to%
Time synchronization accuracy
—
≤
µs
Non-time-based synchronization accuracy
—
—
Redundancy recovery time
—
—
transmission of an Ethernet frame. his may lead to nondeterministic delays which are not suitable
for RT applications. To reduce these delays, a priority mechanism is defined in IEEE . which
allows the sender of a frame to assign a priority to an Ethernet frame. A virtual bridged local area
network (VLAN) tag is added into the Ethernet frame containing a VLAN-ID and a priority level
to of the message. he Ethernet/IP RT messages get the highest priority and are transmitted by the
switches before other NRT frames which results in better accuracy for the RT constraints.
In the CIPsync extensions, the clocks of the devices are synchronized with the IEEE [] pro-
tocol (accuracy of . is he only problem is that delays may be introduced in the software protocol
stack. Based on this time synchronization, the actions in the distributed system are executed based
on the planned timing, e.g., a device sets its outputs to a defined value not based on the moment a
message is received, but on the scheduled time. With this principle, the timing of the application is
independent of the delay introduced in the communication network and relies only on the accuracy
of the time synchronization. his is defined as profile /.. When these guidelines are strictly applied,
Ethernet/IP is an RT solution usable even for the most demanding classes of applications—compare
the range of values in Table .—but it is still not deterministic as a communication network.
CIP defines objects
∗
to transport control-oriented data associated with I/O devices and other
information which are related to the system being controlled, such as configuration parameters and
diagnostics. he CIP communication objects and application objects are grouped in classes. Profiles
for different types of applications define the objects to be implemented and their relations.
21.4.1.3 P-NET (Profile 4/3)
heP-NETonIPspeciicationhasbeenproposedbytheDanishnationalcommitteeandisdesigned
for use in an IP-environment as profile /. P-NET on IP enables use of P-NET (type in IEC )
RT communication wrapped into UDP/IP packages.
P-NET packages can be routed through IP-networks in exactly the same way as they can be routed
through non-IP-networks. Routing can be through any type of P-NET network and in any order.
A P-NET frame has always two P-NET-route elements constructed as a table of destination and
source addresses. In the simple case of a fieldbus solution, these two addresses are the node addresses
of the fieldbus network. To allow routing over IP-based networks, these P-NET-route tables are now
extended to include also IP addresses in the P-NET-route element. For a fieldbus-based P-NET node,
these IP addresses are just another format of addresses. his means that any P-NET client can access
servers on an IP-network without knowing anything about IP-addresses.
In fact, the P-NET on IP specification just defines how the existing P-NET package is tunneled over
UDP/IP networks without any special measures to ensure RT behavior on the Ethernet network. he
performance indicators are listed in Table ..
∗
An object in CIP provides an abstract representation of a particular component within a device.
