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Motorola patent 5,130,993 on checksum of encoded data
We have been having a problem which arose in the PPP WG, where a draft
for the compression over PPP has been held up due to Motorola sending
a letter to the Secretariat last winter.
A member of the PPP WG recently typed in the text of the patent claims.
This one covers the DES CBCC concept. Do we have art prior to December
1989?
> From: Paul Mackerras <Paul.Mackerras@cs.anu.edu.au>
> I have obtained a copy of the Motorola patent which covers the CCP
> reset req/ack mechanism. (Specifically, I have a copy of Australian
> patent 73296/91, which corresponds to US patent 5,130,993.)
> I have reproduced the claims section below (including their spelling
> mistakes :-).
>
> A few notes:
>
> - The patent acknowledges as prior art the configuration where the
> compressor/decompressor are connected using a link which uses error
> detection and retransmission to provide a reliable link. Using CCP
> over V.42 modems would seem to me to fall into this category.
>
> - The 1st paragraph of the "Summary of the Invention" section reads:
> "In general, the invention features transmitting encoded (e.g., compressed
> or encrypted) data over an unreliable network, by checking for
> transmission errors after decoding, and resetting the encoder if
> an error is detected. Synchronization of encoding and decoding can
> thereby be maintained."
>
> I know that this isn't legally a claim, but I think it gives some idea
> of the range of implementations which Motorola would like to think
> the patent covers.
>
> CLAIMS:
>
> 1. A method for transmitting encoded data across unreliable
> networks, said encoding being of the type in which encoding and
> decoding are synchronized, said method comprising the steps of:
> encoding said data;
> transmitting said encoded data across said unreliable network;
> receiving and decoding said data;
> subsequently detecting any errors introduced by said
> unreliable network; and
> resetting said encoding method upon said detection of errors.
>
> 2. The method of claim 1 wherein error detection information
> is added to said data prior to encoding said data, and said error
> detection information is used, following decoding, to detect any
> errors introduced by said unreliable network.
>
> 3. The method of claim 2 wherein said error correction
> information is a code sequence inserted into said data prior to
> encoding.
>
> 4. The method of claim 3 wherein said code sequence is a
> cyclic redundancy check (CRC).
>
> 5. The method of claim 1 wherein said unreliable network
> includes a plurality of nodes so arranged that a plurality of paths
> exist between at least some nodes between which said method is
> practiced.
>
> 6. The method of claim 5 wherein at least one node may
> communicate with more than one node at a time.
>
> 7. The method of claim 1 wherein said data encoding comprises
> data compression.
>
> 8. The method of claim 1 wherein said data encoding comprises
> encryption.
>
> 9. The method of claim 1 wherein said step of resetting said
> encoding method further includes
> transmitting a reset request code sequence over a reverse
> channel upon said detection of errors; and
> transmitting a request acknowledgement code sequence over said
> unreliable network to acknowledge reception of said reset request code
> sequence.
>
> 10. The method of claim 9 wherein
> the reset request code sequence initiates the resetting of the
> encoder; and
> the reset acknowledgement code sequence initiates the
> resetting of the decoder.
>
> 11. The moethod of claim 10 wherein said step of resetting
> said encoder further includes
> starting a timer upon said detection of errors;
> transmitting a second reset request code sequence over said
> reverse channel upon failure to receive said request acknowledgement
> code sequence upon the expiration of said timer.
>
> 12. The method of claim 11 wherein
> said unreliable network further includes a plurality of nodes
> so arranged that a plurality of paths exist between at least some
> nodes between which said method is practiced; and wherein
> at least one node may communicate with more than one node at a
> time using different encoding methods to communicate with at least two
> different nodes; and wherein said timer is shared by said different
> encoding methods.
>
> 13. The method of claim 1 wherein
> said data encoding comprises data compression; and wherein
> said step of resetting said data encoding includes
> resynchronizating the encoder and decoder of said data compression.
>
> 14. The method of claim 13 wherein said error detection
> information is added to said data prior to encoding said data, and
> said error detection infofmation is used, following decoding of said
> data, to detect any errors introduced by said unreliable network.
>
> 15. The method of claim 13 wherein said unreliable network
> includes a plurality of nodes so arranged that a plurality of paths
> exist between at least some nodes between which said method is
> practiced.
>
> -----------------------------------------------------------------------------
> Paul Mackerras paulus@cs.anu.edu.au
> Dept. of Computer Science
> Australian National University
>
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