A mobile ad hoc network (MANET) comprises a group of randomly
wandering wireless-enabled portable computing devices that in the
absence of a centralized base station and limited transmission range
communicate with distant nodes through multihop paths. Random node
mobility and the unpredictable characteristics of the wireless
medium make application desired QoS provisioning in MANETs very
difficult. Hence instead of satisfying QoS requirements on an
absolute basis, it is viable to provide QoS on a best effort basis
with additional protocol support for gradual QoS adaptations to
unpredictable MANET dynamics. Our proposal identifies this design
philosophy and implements it over a popular tree-based multicast
protocol (MAODV) for MANETs.
In a tree-based multicast, the core is always a flashpoint for
almost all the traffic that flows in the network. The relative
placement of the core with respect to the group members affects the
delay experienced by leaves of the tree thereby influencing the
performance of the multicast. Our protocol therefore seeks to
conduct an optimal core selection by having the core record the
history of delays to group members in terms of the relative time
difference between sending the multicast packets and receiving
corresponding acknowledgments from the respective subtree branches.
If the average delay exceeds the QoS requirement by a given
threshold, the core selects a better core candidate from nearby
members to reduce migration overhead. In this way, the core migrates
on a hop-by-hop basis continuously adapting to the network dynamics;
and whenever the topology remains constant for a sufficient
duration, the core reaches an optimal position corresponding to the
desired QoS.
Keywords: MANETs, QoS, tree-based multicast (MAODV), packet delay history,
delay threshold, and group-leader (core) migration.
on
Oct-14-2004
