The link quality mechanism of the Mobile Ad Hoc Network (MANET)
Neighborhood Discovery Protocol (NHDP) enables "ignoring" some 1-hop
neighbors if the measured link quality from that 1-hop neighbor is
below an acceptable threshold while still retaining the corresponding
link information as acquired from the HELLO message exchange. This
allows immediate reinstatement of the 1-hop neighbor if the link
quality later improves sufficiently. NHDP also collects information
about symmetric 2-hop neighbors. However, it specifies that if a link
from a symmetric 1-hop neighbor ceases being symmetric, including
while "ignored" (as described above), then corresponding symmetric
2-hop neighbors are removed. This may lead to symmetric 2-hop
neighborhood information being permanently removed (until further
HELLO messages are received) if the link quality of a symmetric 1-hop
neighbor drops below the acceptable threshold, even if only for a
moment. This specification updates RFC 6130 "Mobile Ad Hoc Network
(MANET) Neighborhood Discovery Protocol (NHDP)" and RFC 7181 "The
Optimized Link State Routing Protocol Version 2 (OLSRv2)" to permit,
as an option, retaining, but ignoring, symmetric 2-hop information
when the link quality from the corresponding 1-hop neighbor drops
below the acceptable threshold. This allows immediate reinstatement of
the symmetric 2-hop neighbor if the link quality later improves
sufficiently, thus making the symmetric 2-hop neighborhood more
"robust".
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