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Design Architecture for MPEG2 Transport Demultiplexor Assist Disclosure Number: IPCOM000117655D
Original Publication Date: 1996-Apr-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 152K

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Abdulhafiz, J: AUTHOR [+3]


The MTDA consists of four functional elements: a Packet Framer, a Packet ID (PID) Filter, a Program Clock Reference (PCR) Comparator, and a System Interface as shown in Fig. 1.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 43% of the total text.

Design Architecture for MPEG2 Transport Demultiplexor Assist

      The MTDA consists of four functional elements:  a Packet
Framer, a Packet ID (PID) Filter, a Program Clock Reference (PCR)
Comparator, and a System Interface as shown in Fig. 1.

      Disclosed is dedicated hardware, referred to as MPEG2 Transport
Demultiplexor Assist (MTDA), that provides realtime preprocessing of
MPEG2 Transport Streams for further demultiplexing by a host

      MPEG2 Transport Streams carry timing information that must be
handled with a predictable and constant delay.  In addition,
Transport Streams may contain multiple programs requiring large
amounts of system bandwidth.  The MTDA function reduces bandwidth
demands on the system by passing only the packet types of interest,
and extracts time references after a fixed delay.  The MTDA function
also minimizes the load on the processor for clock recovery functions
by performing the repetitive comparison calculations and only
notifying the system host when action is required.

      The Packet Framer establishes packet boundaries on an incoming
Transport Stream.  It searches for an initial predefined
synchronization character (x47) in the incoming stream, and then
verifies that the character is repeated every 188 bytes (one packet
length) before considering the stream fully synchronized.  The Packet
Framer then continuously monitors for synchronization characters
occurring every 188 bytes to determine if the stream is no longer
aligned correctly.

      Correct packet alignment is required by the other functional
blocks of the MTDA in order to properly identify the various fields
contained in the Transport Stream.

      The PID Filter removes packets that are not required by the
system.  It compares incoming packets against two fixed PID values
(predefined for MPEG2 Transport Streams) and several programmable PID
values.  As Transport packets arrive, the PID for each packet is
compared against the values listed in the PID Filter.  If the packet
PID matches any of the Filter values, the packet is passed on through
the system.  If it does not match, the packet is discarded.  In
addition, any packets with a PID matching the predefined value
indicating a Null Packet are also discarded.

      Fig. 2 illustrates how the MTDA is used in an MPEG2 System
Decoder.  Data arrives at the Network Interface.  Network specific
information is removed yielding a Transport Stream which is sent to
the MTDA.

      On an exception basis (controlled by the host processor), the
PID Filter may be overridden and all packets passed, or Null Packets
may be passed (along with all valid PID values).

      By reducing the number of packets entering the system through
the PID Filter, the bandwidth requirements are reduced.

      Program Clock Reference (PCR) Comparator - MPEG2 Transport
Streams contain timing information that must be extracted in order to
establish corre...