The recent advent of the Internet Multicast service has enabled a number of
successful real-time multimedia applications,
yet the scalability of these applications remains challenged
by the inherent heterogeneity of the underlying Internet.
One promising approach for taming this heterogeneity
is to encode each media flow as a layered signal
that is striped across multiple multicast groups,
thereby allowing a receiver to tune its individual
reception rate by modulating its subscription to
multicast groups.
Though significant
progress had been made on media transport protocols
and congestion control strategies for adjusting multicast
groups in this fashion, comparatively little
work has been devoted to extending the session directory
service and address allocation architecture to meet the
needs and requirements of layered media.
Moreover, the large-scale deployment of layered media formats
is hindered by the lack of support for layered formats
in existing session directory tools.
To overcome these limitations, we propose a new architecture
for session advertisement and caching that exploits
multicast ``administrative scope'' through protocol proxies
to admit
layered media formats and reduce the start-up latency
of a directory-service client by an order of magnitude or more.
Our architecture is fully compatible with the existing
directory service allowing our implementation, which is split
across a new session directory tool and network proxy,
to be incrementally deployed within the current Internet
multimedia conferencing architecture.