The Access Grid (AG) provides collaboration environments over the
IP multicast networks by enabling efficient exchange of multimedia
contents among remote users; however, since lots of current
networks are still multicast-disabled, it is not easy to deploy
this multicast-based multi-party AG. For this problem, the AG
provides multicast bridges as a solution by putting a relay server
into the multicast networks. Multicast-disabled clients make UDP
connections with this relay server and receives forwarded
multicast traffics in unicast UDP packets. This solution is facing
several limitations since it requires duplicate forwarding of the
same packet for each unicast peer. Thus, in this paper, we propose
an alternate solution for the multicast connectivity problem of
the AG based on the UMTP (UDP multicast tunneling protocol). By
taking advantage of flexibilities of UMTP, the proposed solution
is designed to improve the efficiency of network and system
utilization, to allow reuse of multicast-based AG applications
without modification, and to partially address the NAT/firewall
traversal issues. To verify the feasibility of proposed solution,
we have implemented a prototype AG connectivity tool based on the
UMTP, named as the AG Connector.
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