Subject: [rohc] Regarding State Creation by Compressor in Sig-comp

From: "Baratam Govinda Rao" <[email-masked]>
Date: Mon, 18 Nov 2002 18:23:08 +0530

Hi,

I am trying to implement a SigComp Compressor based on Simplified LZSS
Algorithm which is given in the Users Guide. The Simplified LZSS makes use
of a static dictionary containing ASCII from 0 to 255.

Its mentioned in the SigComp draft that creating of new state items after
establishing a peer to peer SigComp session can increase the Compression
ratio. In this context, I would like to know on what basis should my
Compressor (based on simplified  LZSS) decide that a new state item can be
created to increase the Compression ratio ?

Thanks and Regards,
Govind

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From: "Price, Richard" <[email-masked]>
Date: Mon, 25 Nov 2002 11:11:47 -0000

Hi,

I'd recommend creating a new state item after decompressing every
message in a flow, as this allows the Simplified LZ77 algorithm to
reference text strings from any of the previous messages in the flow.
This means that later messages will be compressed more aggressively
than earlier messages. It also avoids needing to upload the bytecode
for LZ77 itself more than once.

In fact the bytecode for Simplified LZ77 in the User Guide already
creates a state item after decompressing each message. Basically it
just saves a copy of the entire UDVM memory, which can then be
accessed by sending the correct state identifier as explained in
Section 5.1 of the User Guide.

Note that if you're running over an unreliable transport such as UDP
then an acknowledgement scheme will also be needed to make sure that
the state items have been correctly saved. Some bytecode for a simple
acknowledgement scheme can be found in Section 6.1 of the User Guide.

Regards,

Richard

> -----Original Message-----
> From: Baratam Govinda Rao [mailto:[email-masked]]
> Sent: Monday, November 18, 2002 12:53 PM
> To: [email-masked]
> Subject: [rohc] Regarding State Creation by Compressor in Sig-comp
> 
> 
> Hi,
>