``Designs of high quality streaming systems"

Songqing Chen, Bo Shen, Susie Wee, and Xiaodong Zhang

Proceedings of IEEE INFOCOM'04, Hong Kong, March 7-11, 2004.


Segment-based proxy caching strategies are commonly used to deliver
streaming media by partially caching media objects. The existing
strategies normally only considers increasing the byte hit ratio and/or
reducing the client startup latency (denoted by the metric delayed
startup ratio).  However, these efforts do not guarantee the continuous
media delivery because the to-be-viewed object segments may not be cached
in the proxy when they are demanded. The potential consequence is the
playback jitter at the client side due to the proxy delay in fetching
the uncached segments, which we call as proxy jitter. Thus, for the best
interests of clients, a correct model for media proxy cache design should
aim to minimize the proxy jitter subject to reducing the delayed startup
ratio and increasing the byte hit ratio. However, we have observed two
major pairs of conflicting interests inherent in this model: (1) one
between improving the byte hit ratio and reducing the proxy jitter,
and (2) the other between improving the byte hit ratio and reducing
the delayed startup ratio.  In this study, first, we propose an active
prefetching method for the in-time prefetching of uncached segments,
which provides insights into the first pair of conflicting interests.
Second, we have further improved our lazy-segmentation scheme which
effectively addresses the second pair of the conflicting interests.
Finally, considering our main objective of minimizing proxy jitter
and the two trade-offs, we propose a new media proxy caching system
called Hyper Proxy by effectively coordinating both prefetching and
segmentation techniques.  Synthetic and real workloads are used to
systematically evaluate our system.  The performance results show that
the Hyper Proxy system generates the minimum proxy jitter to the client
with a low delayed startup ratio and a small decrease of byte hit ratio
compared with existing schemes.