Re: [rohc] Clarification regarding the ESP SN Encoding

[Klaus Warnke <[e-mail]>]

Hello Anil,

if I remember correct, RoHCv1 requires, that the link layer delivers
all packets in order (RoHCv2 not).

For p see 5.12.:

  The interpretation interval (value of p) for the ESP-based SN is as
  with ROHC RTP (profile 0x0001).

Therefore p is as 5.7.:

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

Regards, Klaus

At Wed, 16 Jun 2010 12:32:18 +0530,
Anil Maguluri wrote:
> 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