3 Operation Theory
PCS-9785 Satellite-Synchronized Clock
3-3
Date: 2019-07-05
3.3.1.2 Receiving and Transmitting
Each node has two ports that operate in parallel and that are attached to the same upper layers of
the communication stack through the Link Redundancy Entity (LRE). For the basic communication,
the LRE presents toward its upper layers the same interface as a non-redundant network adapter,
so the upper layers are unaware of redundancy.
When receiving a frame from the node’s upper layers, the LRE appends to the frame a
Redundancy Check Trailer (RCT) containing a sequence number and sends the frame through
both its ports at nearly the same time. The two frames are nearly identical except for the LAN
identifier (and the checksum).
When receiving frames from the network, the LRE forwards the first received frame of a pair to its
node’s upper layers and discards the duplicate frame (if it arrives). It removes the RCT if required.
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