wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

PROFINET 40-9
31.25 μs ≤ Tsend_cycle ≤ 4 ms
Max 60% of Tsend_cycle
RT_CLASS_3
RED
(optional)
RT_CLASS_2
ORANGE
(optional)
Prio
7
Prio 6
RT_CLASS_2/1
Prio
6
Prio
5
Green (mandatory)
...
Prio
0
Yellow
(optional)
Reserved interval
Open interval
FIGURE 40.3
Bus cycle of PROFINET IO with IRT communication.
The division of the cycle is shown in Figure 40.3.
The following intervals are defined along with their properties in PROFINET:
Red interval: Only RT_CLASS_3 frames may be forwarded through switches in this interval. The forwarding
rules defined in IEEE 802.1D do not apply here. Instead, the forwarding rules defined in IEC 61158
are used. The start time of the red interval is constantly synchronized. The chronological sequence of all
RT_CLASS_3 frames is defined during engineering. If UDP/IP frames arrive or are generated (because
the application is not IRT-capable) during a “red interval,” they are temporarily saved in an IRT-capable
switch and are sent only after completion of the “reserved interval.” The frame IDs used to identify the different
frames is specified during plant configuration in the engineering tool. The receipt of the cyclic data
is timed exactly such that the synchronous application can be started directly without delays.
Orange interval: Only RT_CLASS_2 frames may be forwarded through switches in this interval. The
forwarding rules defined in IEEE 802.1D are used here. The “orange interval” starts (if present) immediately
at the start of a “send clock” or after the “red interval.” RT_CLASS_2 frames require no prior
planning. As a result, the available band width is not optimally used. Receipt of the cyclic data is not
timed exactly. A safety reserve must therefore be included.
Green interval: For forwarding of data frames in switches, the rules defined in IEEE 802.1D apply.
Prioritization can occur based on IEEE 802.1Q (VLAN tag). If IRT frames arrive during the “green
interval,” they are destroyed and an alarm message is generated. The important thing is that no jobs are
still active at the end so that the reserved interval can start unhindered. A “green interval” does not have
to exist within a phase.
Yellow interval: The transition from the “green interval” to the “red interval” is preceded by a “yellow
interval” in which an IRT-suitable switch accepts only jobs that can be completely transported before
the start of the next “red interval.”
For forwarding data frames in switches, the rules defined in IEEE 802.1D may be disabled to ensure
the start of the next reserved phase. Prioritization can occur based on IEEE 802.1Q (VLAN tag). If the
forwarding of these frames before the start of the next reserved interval is not assured, these frames are
stored temporarily and sent in the next “green interval.”
40.3.1 Flexible Communication Based on RT_CLASS_2 (Orange Interval)
For communication during the “orange interval” in “switched Ethernet networks,” the configuration of end
nodes is sufficient. During the power-up phase, all network components (switches) in between set up address
tables can be used to forward the received frames to their appropriate destinations. The communication is
trained in a quasi manner using “source and destination MAC addresses.” The rules defined in IEEE 802.1D
are used here. In the “orange interval,” data must always be exchanged in conjunction with bus synchronization
(synchronized RT_CLASS_2). Frames are transmitted within one Send clock in the “orange interval,” in
© 2011 by Taylor and Francis Group, LLC