| Summary: | 博士 === 國立交通大學 === 資訊工程系 === 89 === Multicast is a communication paradigm widely used for
information dissemination, and is one of the most important
facilities for constructing reliable, distributed cooperative
applications. The current trend towards ubiquitous computing
has resulted in the development of wireless Internet, aiming
to provide users with convenient anytime and anywhere accesses
to the network. The introduction of host mobility, however,
challenges the deployment of multicast in this environment.
For example, since a multicast delivery path locates all the
participants in a given group, the path can become obsolete
upon members'' movements. Migrant hosts may therefore experience
substantial data loss. As a consequence, this can overwhelm
the protocols that require reliable ordered message delivery,
due to repeatedly performing error recovery and handling
out-of-order message arrivals. On the other hand, if we
restructure multicast delivery paths in the system along with
host migrations, prohibitive cost could result.
In this thesis, we present approaches to the above problems.
First of all, two cost-effective schemes, both sharing the
same routing efficiency, provide leverages to adjusting
multicast delivery paths to mobile host locations. To save
the overhead of dynamically modifying the paths, one way is
to exploit the locality in host movement patterns and keep
active the networks that mobile members visited most recently.
Therefore as long as hosts of the same group migrate within
these active networks, the established paths need not change
in the event of users'' mobility. Alternatively, we can
partition the mobile environment into non-overlapping regions,
so that changes in multicast routes upon participant
intra-region movements are localized within the region. In
this manner, topology alterations are mostly hidden from other
regions.
The afore-mentioned solutions prove to be promising. Despite
this, we still need to tackle some issues other than host
mobility to support Internet multicast. These issues mainly
stem from that conventional protocols do not take into account
important characteristics of a mobile system, such as tight
resource constraints on mobile hosts and lossy communication
links. In particular, here we are concerned with an essential
transport service that orders multicast messages in light of
a potential causality relation. Given this support, group
members can observe consistent ordering of events affecting
the group as a whole. Otherwise multicast messages may be
misinterpreted. To this end, we propose two scalable
protocols by organizing the system into a client-server model.
Causally ordered delivery results from serializing messages
by mobile clients within the administrative realm of each
switching station and using these stations to maintain
server-level causal order. These proposals are effective to
accommodate the explosive growth of mobile users in the future,
and exhibit lower complexity than counterpart protocols.
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