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to handle the TCP/IP protocol in RT or the protocol stack must be simplified and reduced
to get these reaction times on simple and cheap resources.
The third and most demanding class is imposed by the requirements of motion control :
To synchronize several axes over a network, a cycle time less than  ms is needed with
a jitter of not more than  µs. This can only be reached with Ethernet network with a
minimal bit rate of  Mbps, if both protocol medium access and hardware structure are
modified.
21.3.2 Performance Indicators of the IEC Standard
The following performance indicators are defined in the CPs for RTE (IEC -):
Delivery time
Number of RTE end-stations
Basic network topology
Number of switches between RTE end-stations
hroughput RTE
Non-RTE bandwidth
Time synchronization accuracy
Non-time-based synchronization accuracy
Redundancy recovery time
Delivery time is the time needed to convey a service data unit (SDU, message payload) from one
node (source) to another node (destination). he delivery time is measured at the application layer
interface. he maximum delivery time shall be stated for the two cases of no transmission errors, and
one lost frame with recovery.
he number of RTE end-stations states the maximum number of RTE end-stations supported
by a CP.
he basic network topology supported by a CP comprises the topologies listed in Table ., or as a
combination of these topologies.
he number of switches between RTE end-stations supported by a CP defines the possible network
layoutandisalsoanimportantindicator.
he throughput RTE is the total amount of application data by octet length on one link received
per second.
Non-RTE bandwidth isthepercentageofbandwidth,whichcanbeusedfornon-RTEcommuni-
cation on one link.
Time synchronization accuracy shall indicate the maximum deviation between any two nodes'
clocks.
Non-time-based synchronization accuracy indicates the maximum jitter of the cyclic behavior of
any two nodes, triggered by periodic events over the network for establishing cyclic behavior.
TABLE . Possible RTE Topologies
Basic Network Topology CP
Hierarchical star CP m/
Ring (loop) CP m/
Daisy-chain CP m/
Note: A real topology could be any combina-
tion of the three basic topologies.
 
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