5.6 Handling node Movement
In order to handle node mobility in ad hoc networks, SARM uses periodical messages
discussed before. These messages take the responsibility to detect any changes in the
multicast tree because of node movement.
SARM protocol uses a set of operations to guarantee the mobility feature. These
operations are:-
■ Each BNR sends a periodical BNR_Down message to its next BNRs stored in its
MFT table. The time interval between messages is defined by
BNR_Down_refresh value.
■ Each BNR sends BNR_UP message to its previous BNR stored in its MFT table.
This message is sent periodically every BNR_UP_refresh period of time.
■ Each LMR exchanges a periodical member refresh message with its BNR. This
message will guarantee the connection of LMRs to their BNRs. Whereas, the first
two messages will guarantee the multicast tree session connectivity.
By performing the previous operations the multicast group session will stay connected to
each other.
If any of BNRs, for example X, does not receive any of the periodical messages
(BNR_UP,BNR_Down) in a predefined time interval, it assumes that a link failure has
happened upstream or downstream, respectively.
According to node mobility management, link failure happens if either the upstream node
does not receive a BNR_UP message from its downstream BNRs and LMRs (case1) or
the downstream BNR node does not receive a BNR_Down from its upstream BNR
(case2). Next each case will be discussed in details.
111
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