[rohc] Clarification regarding the ESP SN Encoding

[Anil Maguluri <[e-mail]>]

Hi All,

Currently I am working on ROHCv1 Profile-3 (ESP/IP).

Please let me know whether my understanding is right or not regarding the ESP SN Encoding.

As per RFC 3095, 4.5.1, " The parameter p is introduced so that the interpretation interval can be shifted with respect to v_ref.
Choosing a good value for p will yield a more efficient encoding for fields with certain characteristics. Below are some examples:

-          P = -1 if the field value is expected to increase always

-          p = 0 if the field value is constant or increase

-          p = 2^(k-1) - 1, if the field value is expected to deviate slightly from a constant

-          p = 2^(k-2) - 1, if the field value is expected to undergo small negative changes or larger positive changes "

Also RFC 3095, 5.7, " SN: The compressed RTP Sequence Number.
Compressed with W-LSB. The interpretation intervals, see section 4.5.1, are defined as follows:
p = 1 if bits(SN) <= 4
p = 2^(bits(SN)-5) - 1 if bits(SN) > 4 "

As per my understanding,  we should use the below 'p' values at compressor [for SN Encoding]

-          p=-1, if packets are received in-order

-          p=2^(k-2)-1, if packets are received out-of-order
at decompressor

-          p = 1 if bits(SN) <= 4

-          p = 2^(bits(SN)-5) - 1 if bits(SN) > 4


Queries

1.       Is my understanding is right?

2.       What is the value of 'p' for Profile-3 at compressor and decompressor?  Is it same as above?


Thanks for your support.

Regards,
Anil Kumar Maguluri

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