Discrete Cosine Transform (DCT)
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References 1. International Telecommunication Union, Telecommunication Standardization Sector H.323 Recommendation - Packet-based multimedia communications systems, July 2003. 2. International Telecommunication Union, Telecommunication Standardization Sector T.120 Recommendation - Data protocols for multimedia conferencing, July 1996,
DATA DISCOVERY, ROUTING AND TRAFFIC PATTERNS Definition: Resource discovery and rendezvous mechanisms are necessary to dynamically locate media servers (e.g., the nearest or best servers), data storages, membership servers (for multicast sessions), or peers (e.g., other users) for direct connections. In general, the resource discovery module of CHaMeLeoN can be categorized as either 'location-aware' or "location-free". Location-aware architectures require availability of location information. They typically use geographic or trajectory routing to forward the updates or queries and include geographic rendezvous mechanisms (such as GLS [1],
140 D Rendezvous Regions [2], and GHT [3]) and trajectory advertisement schemes (such as TBF [4]). In location-aware networks, geographic-based distributed hash tables [2, 3] are utilized to efficiently establish content based routing schemes. In earlier work [2], we designed a geographic rendezvous mechanism based on rendezvous regions. In this architecture, the network is divided into regions, and the resource key space (e.g., file space) is divided into prefixes. Each resource prefixes maps into a region. The mapping can be discovered dynamically using a bootstrap mechanism. We have shown that using regions (instead of locations as in GHT [3]) is robust to mobility and location inaccuracy effects. Furthermore, the performance of the rendezvous architecture depends on the data semantics and access pattern. For example, for media servers, where there is a high lookup-to-insertion ratio (meaning the media is accessed many times per storage), the Rendezvous Regions scheme produces far fewer messages (over 80% less) when compared with GHT, and achieves near perfect success rate. Hence, it is important to tailor the rendezvous mechanism to the application characteristics (e.g., lookup-to-insertion ratio). Characterizing applications, data semantics and access patterns is of key interest. Matching rendezvous architectures to application classes, and designing new (adaptive) rendezvous mechanisms are additional challenges that need to be addressed in future work. Location-free discovery architectures do not use location information [5]. Some of the main approaches include flooding-based techniques, on-demand routing with caching, hierarchical and hybrid routing. Flooding techniques include simple flooding (or expanding ring search), scoped flooding, and efficient reduced broadcast. Hierarchical routing includes cluster-based, landmark, and dominating set approaches. Hybrid routing includes zone routing and contact-based architectures. We have extensively studied these techniques. Our studies show that a loose hierarchy (using zones) coupled with 'conta
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