14 Topology data base
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My topoinfo
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346 Chapter 12
from the specific station, and the ATD and LRTT frames are used exclusively to fill in
additional information regarding each station.
Context Containment Context containment assists in preventing duplication and reordering
of strict mode traffic during topology changes. Context containment is entered
on detection of a passthrough, or when a span status changes.
Context containment is not exited until the topology is determined to be stable and
valid and the local topology database is determined to match those of its reachable
neighbors. Each station calculates a topology checksum, unique to the ring, and uses
the Topology Checksum (TC) frames to make its calculated topology checksum available
to other stations in the ring.
During context containment all strict frames are discarded. Stations receiving strict
frames whose hops count does not match the expected hops counts for a station, as
reflected in the topology data base, discard them.
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