PET - A New, Robust and Efficient Message Broadcast Technology *)

Background:

     Many current and proposed telecommunication  based  applica-
tions  rely  on broadcast of multi-media information over packet-
switched networks.  Priority Encoding Transmission, or PET, helps
overcome two major problems encountered by such applications:

1. The  unavoidable  packet  loss  due  to  it's  irregular  and
   unpredictable nature.

2. The limits imposed by the widely varying capacity of  networks
   and processing power of receivers.

What PET does:

     PET can be used with any packet-switched-network hardware or
protocol.  It operates as a layer above the transmission of pack-
ets (ATM cells, etc.).  Using advanced coding techniques, PET im-
proves the quality of transmission over packet networks that have
unpredictable losses.  PET  uses  a  unique  multilevel  forward-
error-correction  scheme  which  introduces a minimum increase in
the transmission rate.

     PET makes possible  MPEG  transmission  over  the  INTERNET,
which  has not been practical due to bursty losses. The data com-
munication industry has been forced to  broadcast  video  in  the
form  of motion JPEG, which requires eight times the transmission
speed of MPEG.

     An implemented example  of  PET  has  been  applied  to  the
transmission  of  video over the INTERNET. A side-by-side display
compares transmission using the standard MPEG1 encoding with  and
without  PET  showing the dramatic improvement of picture quality
due to PET, using only 24% redundancy on top of the standard MPEG
data.  This  represents  a  more  than  five  fold  reduction  in
transmission rate over the JPEG mode to achieve comparable quali-
ty.

     PET also makes it possible  to  broadcast  to  heterogeneous
networks and to receivers of widely different capabilities.  This
allows the network and receiving workstations  to  discard  arbi-
trary packets which cannot be handled due to limited bandwidth or
processing power.

How PET works:

     The key idea is an encoding scheme  that  will  recover  the
most  important  information of a message no matter which packets
are lost or intentionally deleted in a transmission. By the judi-
cious  application  of  erasure  coding, PET achieves greatly im-
proved performance by enabling statistical multiplexing of  video
images.  This  is done without adding excessive overhead in terms
of  network  capacity  or  delay,  thus  effectively   decreasing
transmission cost per channel.

     While  PET   can   take   advantage   of   special   purpose
encoding/decoding  hardware, the implemented examples, e.g. real-
time video transmission, have  demonstrated  effective  operation
without  such  hardware, i.e. with software implementations using
conventional computers.

     For more information contact:  petinfo@icsi.berkeley.edu  or
tune in the World Wide Web at URL //http:www.icsi.berkeley.edu/PET

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*) Patent application pending.