[rohc] Comments on RFC 4997

["Lee, Jiwoong" <[e-mail]>]

Dear ROHC WG,

I hope this comment was not discussed before. At least my quick search did not find the related thread.

These are some questions and comments about RFC 4997.


1.       Definition of Single quotes



According to pp 26 of the same document,  a discriminator is defined
     discriminator     =:=   '01101';
as equivalent to
     discriminator     =:=   compressed_value(5, 13);

In pp 36 the last paragraph, COMPRESSED format3 was defined with
field_4 =:= '1010';            // set ULENGTH to zero

Here unless one do not impose different interpretation of the single
quotes for the /field/ and the /discriminator/, wouldn't it be better
to change this into the following?
field_4 =:= '1010';            // set ULENGTH to 4



2.       Possible error in the Worked Example



I suspected in Appendix B.7 pp. 56 "COMPRESSED flags_set" format,

abc_flag_bits =:= uncompressed_value(3, 7) [0];

shoud be corrected to

abc_flag_bits =:= irregular(3) [3];



Accordingly, subsequent examples till Appendix B.8 should be corrected.





3.       Encoding function naming issue.



To my impression, the ROHC documents are using the notion and the term "compression" to mean both of compression and encoding, as if they are the same. I believe it is not.



To single out a case, the same document is defining encoding functions

"uncompressed_value( ., . )" and "compressed_value( ., .)"



These functions are indeed for inference functions. That is, it says "the field value can be computed by using other explicit field values".  Above naming does not carry this descriptive understanding at all. I understand the author's original idea of that naming - which is possibly derived from the fact that the associated field is/is not defined in UNCOMPRESSED/COMPRESSED format, or so, which is less crucial in catching the notion of "inference" encoding.





I will appreciate your inputs.

Many thanks,



Jwoong