Siemens SIMATIC NET Instrucciones de operaciones Pagina 122

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Active Components and Topologies
6-6
SIMATIC NET Tw isted-Pair and Fiber-Optic Networks
C79000-G8976-C125-02
Handling Collisions
If the OLM/ELM detects a data collision, it stops transmission. During the collision,
the data packet that has collided is replaced by a jam signal (0/1 bit pattern) to
ensure that the DTEs recognize the collision.
Auto Partitioning
A breakdown on the network can be caused by jabber lockup, wire breaks, missing
terminating resistors, damaged cable insulation, and frequent collisions due to
electromagnetic interference. To protect the network from these breakdowns, the
OLM disconnects the segment from the remainder of the network in the receive
direction.
On the OLM/ELM, this partitioning function operates separately for each port. You
can continue to operate other ports without any problems if one of the ports has
been partitioned. When a segment has been partitioned, the module continues to
transmit to the ITP segment or to the optical fiber cable but reception at this port is
disabled.
On twisted pair, the partitioning is active in the following situations:
-- When a data collision lasts longer than 105 µsor
-- more than 64 data collisions occur in succession.
On optical fiber cable, the partitioning is active in the following situations
-- When a data collision lasts longer than 1.5 ms (normal mode) or 0.2 ms
(redundant mode) or
-- When more than 64 (normal mode) or 16 (redundant mode) data collisions
occur in succession.
Reconnection
The segment is reconnected to the network as soon as a packet with the minimum
length of 51 µs is received at the port where collisions were occurring; in other
words when the segment is operating correctly again.
With the OLM version 2.0 in the redundant mode, packets longer than 51 µs sent
without a collision occurring also lead to reconnection.
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