Subject: [rohc] Encoding Methods in ROHC

From: umair afzal <[email-masked]>
Date: Tue, 5 Nov 2002 11:21:26 +0500

Hello All

I have some confusions in understanding the Encoding Methods (section 4.5)
of ROHC - RFC 3095. 

1. Can some one plz send me some useful material on LSB Encoding and
Window-based LSB Encoding? What is this v_ref, when and how is it sent, and
what/why is this interpretation interval?

2. Is value of v_ref updated on every packet transmitted and received
(v_ref_c and v_ref_d), or is updated on some special packets?.

3. What r these "k bits"? How r the determined?

Thanks in Advance.

Regards
Umair

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From: "Lars-Erik Jonsson (EAB)" <[email-masked]>
Date: Tue, 5 Nov 2002 09:31:18 +0100

Umair,

> I have some confusions in understanding the Encoding Methods 
> (section 4.5) of ROHC - RFC 3095. 
> 
> Window-based LSB Encoding? What is this v_ref, when and how 
> is it sent, and what/why is this interpretation interval?

This is explained in section 4.5.1. The parameter v_ref is a
previously received value in absolute form, which is used as
a reference when interpreting a new received value in LSB form.
The new value is then assumed to belong in an interpretation
interval, based on v_ref (as shown on page 26).

> 2. Is value of v_ref updated on every packet transmitted and
> received (v_ref_c and v_ref_d), or is updated on some special
> packets?.

Chapter 5 defines all the rules related to which packet formats
update what in which mode. A value included in the context is
used as v_ref. Note that the LSB encoding normally used is
W-LSB.

> 3. What r these "k bits"? How r the determined?

k represents the number of bits used for LSB encoding. For example,
with packet format UO-0, k for SN is 4 (bits). How it is determined
is described in 4.5.1 and 4.5.2.

/L-E