Subject: [rohc] Doubt in W-LSB Encoding

From: "Gangadharan G, TLS-Chennai" <[email-masked]>
Date: Tue, 4 Sep 2007 17:06:50 +0530

Hi All,

I am new to the ROHC technology.

Please, can anyone clarify my below doubt.

RFC 3905 Section 5.7 (page 75) states that,

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 stated above, the value of P (constant integer of LSB encoding) is
depends on bits(SN).

Here, the bits(SN) denote the no. of bits for the SN field in the ROHC
packet.

But the value of bits(SN) can be derived only from the value of K
(output of the LSB Encoding algorithm).

How the Input value of the LSB Encoding (P) can depend on the Output
value of the LSB Encoding (K)?

Please forgive me if I am ignorant on anything.

Thanks in Advance,

Gangadharan

DISCLAIMER:
-----------------------------------------------------------------------------------------------------------------------

The contents of this e-mail and any attachment(s) are confidential and intended for the named recipient(s) only.
It shall not attach any liability on the originator or HCL or its affiliates. Any views or opinions presented in 
this email are solely those of the author and may not necessarily reflect the opinions of HCL or its affiliates.
Any form of reproduction, dissemination, copying, disclosure, modification, distribution and / or publication of 
this message without the prior written consent of the author of this e-mail is strictly prohibited. If you have 
received this email in error please delete it and notify the sender immediately. Before opening any mail and 
attachments please check them for viruses and defect.

-----------------------------------------------------------------------------------------------------------------------

_______________________________________________
Rohc mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/rohc

---

From: Biplab Sarkar <[email-masked]>
Date: Tue, 04 Sep 2007 18:08:02 +0530

Gangadharan,

At the decompressor, the value of 'K'  is the number of bits that can
fit in the particular ROHC packet. So given a ROHC packet, the value of
'K' is fixed. The problem now melts down to find out which is the value
in this range of 2^K numbers that is really being transmitted.

At the compressor, the problem is to first find out what would be the
optimal value of 'K' that is good enough to carry the desired number of
bits with a particular value of reordering 'p'. So at the compressor
once the value of 'K' is chosen depending upon the number of bits to be
sent, the value of 'p' also gets set.

Thanks
Biplab

On Tue, 2007-09-04 at 17:06 +0530, Gangadharan G, TLS-Chennai wrote:
> The contents of this e-mail and any attachment(s) are confidential and
> intended for the named recipient(s) only.
> It shall not attach any liability on the originator or HCL or its
> affiliates. Any views or opinions presented in 
> this email are solely those of the author and may not necessarily
> reflect the opinions of HCL or its affiliates.
> Any form of reproduction, dissemination, copying, disclosure,
> modification, distribution and / or publication of 
> this message without the prior written consent of the author of this
> e-mail is strictly prohibited. If you have

---

From: "Gangadharan G, TLS-Chennai" <[email-masked]>
Date: Tue, 4 Sep 2007 19:16:20 +0530

Hi Biplab,

________________________________

From: Biplab Sarkar [mailto:[email-masked]] 
Sent: Tuesday, September 04, 2007 6:08 PM
To: Gangadharan G, TLS-Chennai
Cc: [email-masked]
Subject: Re: [rohc] Doubt in W-LSB Encoding

Gangadharan,

How to choose that optimal value of K?

Is it any of the below method?

(1) Actual no. of bits required to represent the [Current value (v) -
v_ref]

(2) The above value(1) round off to a nearer possible that can be
represented in the Rohc packet (4 for UO-0, 6 for UOR-2, etc.)

(3) Any constant value (common to all v values)

Thanks,

Gangadharan

Thanks
Biplab

Hi All,

            p = 1                   if bits(SN) <= 4

 

Thanks in Advance,

Gangadharan

DISCLAIMER:
------------------------------------------------------------------------
-----------------------------------------------

received this email in error please delete it and notify the sender
immediately. Before opening any mail and 

------------------------------------------------------------------------
-----------------------------------------------

---

From: Biplab Sarkar <[email-masked]>
Date: Tue, 04 Sep 2007 19:44:17 +0530

Option [2] will do. 

Thanks
Biplab

On Tue, 2007-09-04 at 19:16 +0530, Gangadharan G, TLS-Chennai wrote:
> Hi Biplab,
> 
>  
> 
> 
>                                    
> ______________________________________________________________________
> 
> fit in the particular ROHC packet. So given a ROHC packet, the value
> of 'K' is fixed. The problem now melts down to find out which is the
> value in this range of 2^K numbers that is really being transmitted.
> 
> optimal value of 'K' that is good enough to carry the desired number
> of bits with a particular value of reordering 'p'. So at the
> compressor once the value of 'K' is chosen depending upon the number
> of bits to be sent, the value of 'p' also gets set.
> 
>  
> 
> (1) Actual no. of bits required to represent the [Current value (v) –
> v_ref]
> 
> > The contents of this e-mail and any attachment(s) are confidential
> > and intended for the named recipient(s) only.