Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-11-14
2001-05-15
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S512000, C348S423100, C348S512000, C375S368000, C375S376000
Reexamination Certificate
active
06233238
ABSTRACT:
FIELD OF THE INVENTION
The invention is based on a method for updating of clock references in a digital data stream as well as on a remultiplexer operating by this method according to the category of the independent claims.
According to MPEG2 specifications, IEC 13818-1, 1994, page 24 ff, it is known that each information data program stream coded according to this method has assigned to it a program clock reference (PCR) data field. This PCR contains an individual clock reference that is specific to a certain information data packet or program. The MPEG data stream is transmitted from the data source to the data sink together with the clock references. The clock references are used on the receiver side for time recovery and pulse synchronization. An update of the PCR is necessary at every action upon the data stream, whether due to change of data rate or a change in the data packet sequence on the way from data source to data sink. In a data stream, a multiple program transport stream (MPTS), any number of PCRs assigned to them may also be present.
DESCRIPTION OF THE PRIOR ART
PCRs in remultiplexers known to date are updated by means of a system clock for each individual PCR. These clocks must be synchronized with each other over a phase locked loop (PLL) and be adjustable. The cost for updating the PCR units for each program is high and it greatly limits flexibility as regards the number of programs.
SUMMARY OF THE INVENTION
The method according to the invention has, on the other hand, the advantage that all clock references present in the data stream can be updated by means of a single time pulse of a single system clock. It is advantageous that in this method no subsequent adjustment is needed, and a PLL circuit is unnecessary.
Other steps described herein allow for advantageous further embodiments and improvements of the method for updating of clock references.
It is of advantage that, in time recovery, the clock reference is read out and the read-out out time is compared to the time in the system clock. In an advantageous manner the difference of the two times is stamped into, i.e., written over, the field of the previously read clock reference.
In the further execution of the method, after the remultiplexing of the data stream, the clock reference in the stamp unit which was updated in a first step is read and compared to the system clock time which time is shifted by a delay time d. The result of this comparison contains a time shifted by a delay time d which is stamped into the clock reference field.
The remultiplexer according to the invention has the advantage that every time pulse recovery and every time stamp unit has a connection to a single system clock. This removes unnecessary circuits and connections to individual clocks which update the clock references in the program stream.
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Romanowski Alexander
Vogt Wilhelm
Fulbright & Jaworski LLP
Ho Duc
Hsu Alpus H.
Robert & Bosch GmbH
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