Browse Prior Art Database

Controlling Jitter Of Multimedia Data through Hardware Threshholding

IP.com Disclosure Number: IPCOM000112930D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Graziano, M: AUTHOR [+3]

Abstract

Data delivered across an asynchronous backplane (such as the Micro Channel*) experiences variable delay (jitter) due to uncertain bus acquisition delays. These delays are caused by other participants within the system utilizing the backplane resource. This jitter is particularly undesirable when transferring Multimedia data (such as audio, video, or real time data) across the backplane. One such application would be the communication of Multimedia data between a CODEC and a LAN adaptor (such as Harmony).

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Controlling Jitter Of Multimedia Data through Hardware Threshholding

      Data delivered across an asynchronous backplane (such as the
Micro Channel*) experiences variable delay (jitter) due to uncertain
bus acquisition delays.  These delays are caused by other
participants within the system utilizing the backplane resource.
This jitter is particularly undesirable when transferring Multimedia
data (such as audio, video, or real time data) across the backplane.
One such application would be the communication of Multimedia data
between a CODEC and a LAN adaptor (such as Harmony).

      The Harmony adaptor utilizes a hardware threshholding algorithm
to smooth jitter introduced from the backplane.  A threshhold is set
within the Combine chip (one of the chips developed for the Harmony
adaptor) that allows a programmable amount of data to be accumulated
from the media into adaptor storage before delivery to the backplane.
After the initial delivery of data the threshhold is divided in half.
Thus subsequent delivery to the backplane occurs after threshhold/2
bytes of data have been accumulated.

      By dividing the threshhold in half the Harmony adaptor will
provide a buffer of data at the destination (across the backplane) of
threshold/2 bytes.  Thus if the source device (Harmony) experiences a
delay in obtaining the backplane the destination still has data to
work with.  An example may help show this:

      For this example the source adaptor will receive audio data
from the media at a constant rate of 1 byte every 125 microseconds.
The initial threshhold is set at 4 bytes and the worst case delay in
obtaining access to the backplane is 125 microseconds.  When the
source adaptor accumulates data from the media equal to the
threshhold it will deliver it across the backplane to the destination
device.  The following table shows the number of bytes on the media,
bytes stored at the source, bytes stored at the destination, and
threshhold.  Each row represents 125 microseconds of time.

      At cycle E the source device has received threshhold bytes of
data from the media and delivers it to the destination across the
backplane at cycle F. The source also divides the threshhold in half.
The destination can now begin to consume its data at a rate of 1 byte
every 125 microseconds.

+------------------------------------------------------------------------+
| Cycle    | Media     | Source   | Backplane | Destination | Threshhold |
|------------------------------------------------------------------------|
| A        | 1         |          |           |             | 4          |
|---------...