Transport packet parser

Details Transport packet parser Transport packet parser

1999-07-06

2003-09-16

Yao, Kwang Bin (Department: 2664)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

Reexamination Certificate

active

06621817

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates in general to digital communications and, more particularly, to a transport packet parser.
2. Description of the Related Art
Over the past few years, digital transmission has become a significant technology in communicating audio and video information. Digital transmission is used in digital satellite systems high definition television (HDTV), and in DVD (digital versatile disks) to carry audio and video information.
The MPEG-2 (Motion Picture Experts Group) protocol is the most common protocol used in digital audio/video transmission. MPEG-2 compresses video information and provides the transport protocol for communicating the compressed information.
FIG. 1
illustrates a simplified diagram showing the formation of an MPEG-2 transport stream. Audio information is encoded in by audio encoder
10
and video information is encoded by video encoder
12
. The output of the audio encoder
10
is digitized audio information and the output of video encoder
12
is digitized video information. The audio encoder
10
and video encoder
12
may compress and modify the information.
The outputs of the audio and video encoders
10
and
12
are coupled to packetizers
14
and
16
which arrange digitized audio and video information into packets for transmission The audio and video packets may be combined with packets containing data and PSI (Program Specific Information) to form the transport stream. The PSI includes data transmitted for use by the demultiplexer in the receiver; The transport stream may by modulated for transmission via satellites or by local television digital broadcast.
Packets
18
in the transport stream are shown in FIG.
2
. Each packet include a header
20
and a payload
22
. For MPEG-2 the header is a 32-bit field and the payload is a 184-byte field.
The packet header
20
is shown in greater detail in FIG.
3
. The header
20
comprises a number of fields: an 8-bit sync field
24
, a 1-bit transport error field
26
, a 1-bit payload unit star indicator field
28
, a 1-bit transport priority field
30
, a 13-bit PID (packet identifier) field
32
, a 2-bit transport scrambling controlled field
34
, a 2-bit adaptation field control field
36
and a 4-bit continuity counter (CC) field
38
. Of particular interest is the PID which is used to identify packets associated with a common stream (i.e., an audio stream or a video stream) and the CC which identifies a position for the packet within the stream identified by the PID.
The transport stream is decoded by a transport demultiplexer (after demodulation if necessary). The MPEG-2 transport demultiplexer receives the MPEG transport stream and separates the video, audio and services information packets. After decoding, the audio and video packets are placed in respective memory buffers to form a data stream. An audio decoder decodes the MPEG audio stream and produces an analog audio signal. The video decoder decodes the MPEG video stream and produces the video picture.
A key aspect of demultiplexing the transport stream is identifying which stream a packet is associated with. Packets in a common stream share a PID. The continuity counter (CC) identifies the proper position of the packet in a stream. A CC value which is the same as the previous packet of the same PID indicates a duplication or an adaptation field. A CC value which is equal to the previous CC+1 indicates new packet. Other values may indicate an error in the communication or an allowed discontinuity.
In demultiplexing the transport stream, most systems use a sequential approach to compare the received PID successively with 32 values stored in a PID table. However, due to the high data rate of the MPEG stream,(up to 60 Mbits/s) this method requires high processing frequency and complex logic circuitry.
Therefore a need has arisen for a highspeed method and apparatus to search for PIDs in conjunction with a transport stream.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a transport packet parser. A header decoder identifies a packet identifier and continuity counter for a current packet. An associative memory stores packet identifiers at respective addresses and has a search mode for comparing a current packet identifier and outputting a signal indicating the address at which the packet identifier is stored. A random access memory stores continuity counters associated with a previous packet for each packet identifier stored in the associative memory. Control circuitry coupled the associative memory and the random access memory determines whether the current packet satisfies predetermined criteria.
The present invention provides significant advantages over the prior art. The use of an associative memory speeds the identification of packet identifiers, reducing latencies, logic complexity, and power dissipation associated with sequential approaches.


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