Subject: [rohc] sdvl() in *-rohcv2-profiles-00.txt (fwd)

From: Carl Knutsson <[email-masked]>
Date: Thu, 14 Dec 2006 13:58:10 +0100 (MET)

Kristofer, Ghyslain, rohcers,

The svdl encoding method uses reference based lsb encoding. Not all of
the encoding methods that use sdvl encoding needs to be lsb-encoded using
the context as a reference. For example optional_stride uses sdvl. This
may be okey in compressed packets, but I don't like the idea to compress
the ts_stride using the context ts_stride as reference when decompressing
a dynamic chain.

1. I suggest to always use zero as reference and a p-value of 0 for
lsb-encoding the ts_stride. (the ts_stride is always positive?). I
think we need to add a new encoding method for this.

2. My second proposal is to remove the lsb-encoding from the sdvl
encoding method or to have an argument for p value (none, quarter, half,
three quarters). To enable fields to be sdvl-encoded with different p
values.

3. The p-values needs to be changed in the sdvl-encoding method. At least
the compressed format lsb7 (field =:= lsb(14, 16383)), since it can only
encode the field to smaller values than the current reference. Compressed
formats lsb21 and lsb29 use the same p-value. If my suggestion 2 is not
accepted I propose a change use 2^k/-1 for all p-values.

field =:= lsb(7, 63)  [ 7 ];
field =:= lsb(14, 8191) [ 14 ];
field =:= lsb(21, 1048575) [ 21 ];
field =:= lsb(29, 268435456) [ 29 ];

*-profiles-00.txt (old values):
field =:= lsb(7, 63)  [ 7 ];
field =:= lsb(14, 16383) [ 14 ];
field =:= lsb(21, 65535) [ 21 ];
field =:= lsb(29, 65535) [ 29 ];

rgds,
/Carl Knutsson

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