Shared Content Addressing Protocol (SCAP): Optimizing multimedia content distribution at the transport layer

In recent years, the networking community has put huge research effort in identifying new ways to distribute content to multiple users in a better-than-unicast manner. At the application layer, a wide variety of solutions exist that share the assumption that content transport has to be done on top of the established transport protocol suite. In this paper, we present SCAP (Shared Content Addressing Protocol), an experimental transport protocol that handles existing content delivery challenges at the transport layer. In a layer 3 IP network SCAP behaves as a reliable end-to-end unicast protocol, but by uniquely identifying content and adding deadline information, it enables deployment of autonomous and transparent optimization functions in the network. Intermediate nodes can easily perform optimizations such as request combination, content duplication, deadline-aware scheduling, long-term buffering and caching. Since SCAP is further down the network stack than application layer solutions, these optimizations can be implemented more efficiently. SCAP allows packet level processing and facilitates dedicated hardware acceleration. We have evaluated the SCAP protocol using both simulation and a prototype implementation. The results presented in this paper show major improvements compared to state-of-the-art segment-based content delivery over HTTP.