Title: Scalability of Multicast Delivery for Non-sequential Streaming Access
Author: Shudong Jin and Azer Bestavros
Date: October 30, 2001

Abstract: 

Multicast is considered a panacea for scalable streaming media
delivery over the Internet. To enable asynchronous service over a
multicast infrastructure, two categories of techniques have been
proposed: stream merging and periodic broadcasting. The scalability of
these techniques stems from the fact that for sequential streaming
access, the required server bandwidth grows {\em logarithmically} with
request arrival rates for stream merging techniques, and {\em
logarithmically} with the inverse of start-up delay for periodic
multicasting techniques. Recent studies raise doubts as to the
appropriateness of the sequential access model (in which access to a
stream proceeds uninterrupted from beginning to end). A non-sequential
access model (allowing access to start at random points in the stream)
is more accurate as it allows the modeling of partial access and
client inter-activity.  In this paper, we analytically and
experimentally (re-)evaluate the scalability of multicast delivery
under a non-sequential access model. We show that under such a
realistic model, the required server bandwidth for any protocol
providing immediate service grows at least as fast as the {\em square
root} of the request arrival rate, and that the required server
bandwidth for any protocol providing delayed service grows {\em
linearly} with the inverse of the start-up delay. We also investigate
the impact of limited client bandwidth on scalability.  We present
practical protocols, which provide immediate service to non-sequential
requests (subject to limited client bandwidth), and which are
near-optimal in that the required server bandwidth is very close to
its lower bound.