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Scoped
Hybrid Automatic Repeat reQuest with Forward Error Correction (SHARQFEC)
Roger G. Kermode (M.I.T. Media Laboratory)
Reliable multicast protocols scale only as well as their
ability to localize traffic. This is true for repair requests,
repairs, and the session traffic that enables receivers to
suppress extraneous requests and repairs. We propose a
new reliable multicast traffic localization technique
called Scoped Hybrid Automatic Repeat reQuest with
Forward Error Correction (SHARQFEC). SHARQFEC
operates in an end-to-end fashion and localizes traffic
using a hierarchy of administratively scoped regions. Session
traffic is further reduced through the use of a novel
method for indirectly determining the distances between
session members. For large sessions, this mechanism
reduces the amount of session traffic by several orders of
magnitude over non-scoped protocols such as Scalable
Reliable Multicast (SRM). Forward Error Correction is
selectively added to regions which are experiencing
greater loss, thereby reducing the volume of repair traffic
and recovery times. Receivers request additional repairs
as necessary. Simulations show that SHARQFEC out
performs both SRM and non-scoped hybrid Automatic
Repeat reQuest / Forward Error Correction protocols.
Assuming the widespread deployment of administrative
scoping, SHARQFEC could conceivably provide scalable
reliable delivery to tens of millions of receivers without
huge increases in network bandwidth.
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