Ad Hoc Networks : Technologies and Protocols - University of ...

112 Multicasting in Ad Hoc Networks
information such as k-hop neighborhood information. This selection process
can be proactive (i.e., “up-to-date”) or reactive (i.e., “on-the-fly”). Several existing
proposals on broadcasting in ad hoc networks can be viewed as special
cases of the coverage conditions with k-hop neighborhood information. Based
on this proposed framework, the authors further propose new algorithms that
combine features of previous works and show better performance.
4.5 Protocol Comparisons
It is difficult to make a quantitative, side-by-side comparison of all existing ad
hoc multicast protocols due to the lack of such kind of performance evaluation
results. In the context of ad hoc broadcasting, a good comparison can be found
in [24]. For ad hoc multicasting, however, different research group have used
different simulation environments and parameters, which greatly diminishes
the comparability of the simulation result. We believe it is more practical
to compare protocols qualitatively in the sense that which protocol(s) benefit
most in what kind(s) of application scenarios. In other words, we believe it
is difficult to make distinct statement that which multicast protocol is the best
in existing literature due to the dynamic nature of ad hoc networks and the
diversity of potential applications. It is more reasonable to believe that each of
the protocols may fit in only some, not all, specific application scenarios.
In this section, we mainly consider three factors, namely, network size, network
mobility, and multicast group size. We discuss how each of these factors
may affect the performance of an ad hoc multicast protocol, and which class of
existing protocols are most suited in these conditions.
4.5.1 Network Size
Due to different application scenarios, network size may vary in a vast range,
from a small network with tens of nodes, to a large scale network with tens of
thousands of nodes. Large scale network surely raises more challenges than a
small network. If traffic locality is dominant, network size may not impose much
difficulty in multicasting, and mesh-based protocols are more suited because
group members are within proximity of one another and thus the overhead due
to in-mesh flooding is reduced. However, in the cases where there is little traffic
locality, multihop transmission is inevitable since most pairs of group members
are multihop away.
In the case of large network size and small group size, if group members are
scattered sparsely in the network area, stateless multicast and overlay multicast
are more suited, while tree-based or mesh-based may incur too much overhead
in route maintenance and redundant transmission. In the cases where both
network size and group size are large, especially in cases where group members