Image Processing Reference
In-Depth Information
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.