Browse Prior Art Database

Redirector Multimedia Streaming Using Asynchronous Read Ahead

IP.com Disclosure Number: IPCOM000112368D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 166K

Publishing Venue

IBM

Related People

Baugher, M: AUTHOR [+4]

Abstract

Disclosed is a mechanism for improving multimedia file access across a network through an improved client bufferring strategy. Multimedia file access often requires hundreds of kilobytes per second rates of guaranteed throughput. DOS clients which perform synchronous READ operations, and multimedia client applications which perform software video decode cannot tolerate the delays incurred when reading file elements from a remote file server, especially when these READs entail disk access, as well as network access delays. But since multimedia file access is periodic and sequential, a client buffering scheme coupled with asynchronous I/O in the Redirector and Server will permit standalone multimedia applications to transparently access remote files.

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Redirector Multimedia Streaming Using Asynchronous Read Ahead

      Disclosed is a mechanism for improving multimedia file access
across a network through an improved client bufferring strategy.
Multimedia file access often requires hundreds of kilobytes per
second rates of guaranteed throughput.  DOS clients which perform
synchronous READ operations, and multimedia client applications which
perform software video decode cannot tolerate the delays incurred
when reading file elements from a remote file server, especially when
these READs entail disk access, as well as network access delays.
But since multimedia file access is periodic and sequential, a client
buffering scheme coupled with asynchronous I/O in the Redirector and
Server will permit standalone multimedia applications to
transparently access remote files.

      Multimedia file access usually entails periodic and sequential
transfers of file elements at a high rate such as 150 kilobytes per
second or greater for full-motion video.  Traditional file system
strategies such as cache and small READ operations are ill-suited to
supporting multimedia flows.  When a client READ request requires
that the request be satisfied from the server's memory (server cache)
or disk, the transfer time may be too great to prevent disruption of
sound, voice or video on the client workstation.  In DOS* or
Windows*, this problem is easily demonstratable when adaptive
applications, like Microsoft Video for Windows*, attempt to scale
back video quality by displaying only a subset of the video frames.
This adaption strategy can produce choppy video, which becomes
noticeably worse when i/o is delayed due to variation in the network
read response time.  Since DOS and Windows can not implement
asynchronous i/o, and multithreading in these environments is often
unrealistic, many multimedia applications have serious problems
handling the delay variation inherent in network operations.

      The invention described in this article makes it possible to
"Read Ahead" in a file and to always ensure that file elements are in
client memory prior to a request from the multimedia application.
This allows a form of parallelism to occur on the client that DOS and
Windows do not provide natively.  In effect, reading video frames and
decoding video frames is occurring in parallel.  To accomplish this,
the client Redirector must maintain dedicated memory buffers to store
read ahead data for large video files.  The Redirector will fill and
re-fill these buffers based upon the state of the buffers - when
enough memory has been freed by client application transfers from the
buffer, the Redirector will fill the buffers without being explicitly
requested to do so by the client application.

      This function is configurable so the Redirector can identify
which files can be allocated dedicated memory (called "MM BUFS" or
multi-media buffers) and which should be treated like standard
network files.  The...