
Active Components and Topologies
6-7
SIMATIC NET Tw isted-Pair and Fiber-Optic Networks
C79000-G8976-C125-02
Jabber Lockup Protection
The network can be tied up continuously with data, for example due to a defective
transceiver or LAN controller. To protect the network from this situation, the
OLM/ELM stops reception as follows:
-- At the ITP or AUI port affected after 5.5 ms.
The interruption is canceled after an idle phase of 9.6 µs.
-- At the fiber-optic port affected after 3.9 ms.
The interruption is canceled after 420 ms of problem-free operation.
6.1.3.2 Functions Specific to the ITP Interface
Link Control
The OLM/ELM monitors the connected ITP line segments for short-circuits or
breaks using regular link test pulses complying with the IEEE 802.3 10BASE-T
standard. The OLM/ELM does not send data to an ITP segment from which it does
not receive a link test pulse.
Note
An unused port is evaluated as a line break. The ITP link to a DTE that is turned
off is also evaluated as a line break since the transceiver cannot send link test
pulses without a power supply.
Auto Polarity Exchange
If the pair of receive lines is connected incorrectly (RD+ and RD-- swapped over),
the polarity is reversed automatically.
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