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Thursday Oct 21th, 2004 - 4:30pm
Computer Laboratory > Research > Systems Research Group > NetOS > Seminars > Thursday Oct 21th, 2004 - 4:30pm

Towards a joint source-channel coding architecture for packet based multimedia streaming over 2.5G and 3G networks

Julian Chesterfield
As third generation cellular technologies are increasingly being more widely deployed, mobile data users are beginning to experience truly ubiquitous global network access across a variety of 2.5 and 3G technologies. Such provision of higher bandwidth in mobile environments promises greater access to rich multimedia content delivered to handheld or mobile devices such as cellphones and PDAs. Providing seamless performance over IP however in the highly variable wide area mobile cellular environment to ensure a high level of end-user quality for real-time multimedia streams is challenging. Whilst the impact of signal degradation on traditional audio/video broadcasts in the wireless domain is well understood, for packet based communication, the impact can be highly variable. Physical data loss can be masked in a variety of ways, typically comprising a combination of Forward Error Correction, ARQ retransmission and/or application based recovery, the effectiveness of which depends upon the media encoding and the interactivity constraints of the application.

I will present detailed Wide Area Wireless performance measurements, focusing in particular on the impact for real-time multimedia streams. In response to certain interactive streaming criteria, I will further present a general source-channel coding architecture for providing Unequal Error Protection of IP packet based media in the wide area wireless domain.


Pervasive Debugging With Xen

Alex Ho
Building distributed grid applications is notoriously difficult: the complex interactions between concurrently running processes, middleware, operating systems, underlying devices, and interconnecting networks can lead to unpredictable and difficult to analyze errors. Yet debugging support for such systems is woefully inadequate; typically a central user interface coordinates a set of conventional debuggers. This structure leads to synchronization problems and is limited to debugging user-mode applications.

In this paper we present the design and implementation of pdb, a pervasive debugger which executes in a virtualization layer underneath the entire distributed system. By running each node of a distributed application in a separate virtual environment atop the debugger, pdb can exercise full control over the entire execution environment.