Thesis Presentation

End System Multicast (ESM) is an overlay based architecture to enable multicast in the Internet, and the application-endpoint model of deploying ESM shows tremendous promise because there is no dependence on dedicated infrastructure. However, the presence of Network Address Translators(NAT) and firewalls challenges the deployment of ESM and other such systems because NATs and firewalls impose fundamental connectivity constraints. Although several network level solutions have been proposed, none have been well deployed, therefore there is a need for an application level solution to support NAT and firewall that is immediately deployable by application-endpoint based systems. To achieve this goal in ESM, we have developed a two level solution that first resolves the intricate addressing issues and increases the degree of connectivity between pairs of hosts, and second optimizes performance of the overlay by incorporating NAT-aware enhancements. With this solution, NAT and firewall hosts are able to receive content from and provide content to public hosts.

Through the course of building and evaluating this solution using both controlled testbed emulations and real Internet broadcasts, we have gained valuable experience with supporting NAT and firewall hosts in ESM. The key lesson we have learned is that supporting NAT and firewall is a more important and challenging problem for application-endpoint based systems than we had initially considered because: (i) there exist realistic environments where these hosts consist of a large portion of the participating hosts, close to 70% in our experience, (ii) they may lead to unexpected performance degradation of even non-NAT/firewall hosts and (iii) a solution to support them will likely result in a wide range of changes from the transport layer to the overlay protocol’s key functionalities such as group membership in ESM. With regard to our goal, we have built a complete solution in ESM, where we can sustain a reasonable fraction of NAT/firewall hosts with good performance and have discovered and started incorporating promising mechanisms to improve the solution for more extreme environments.

Thesis Committee:
Hui Zhang, Chair
Srini Seshan
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