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Re: [rohc] Doubt regarding the Static chain termination for Profile0x004

"Gurushant" <gurushant@tataelxsi.co.in> Wed, 10 March 2010 09:53 UTC

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Subject: Re: [rohc] Doubt regarding the Static chain termination for Profile0x004
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Dear All, 

Can one help on the below issue?

Thanks & Best Regards
Gurushant



Hello Simon,
I have doubt related to static chain termination. The RFC 3843 ,sec 3.1
mentions that "The decompressor must store this indication in the context
for correct decompression of subsequent headers. Note that the IP version
field in decompressed headers must be restored to its original value"

May I request to elaborate more on this reference, i.e. how the subsequent
header version is restored to original value?


Thanks & Best Regards
Gurushant



-----Original Message-----
From: rohc-bounces@ietf.org [mailto:rohc-bounces@ietf.org]On Behalf Of
Simon Laurenz
Sent: Friday, February 12, 2010 12:03 PM
To: Ganesh; rohc@ietf.org
Subject: Re: [rohc] Doubt regarding the Static chain termination for
Profile 0x004


Hi Ganesh

I think you got to things wrong.  First thing is that every change  is
made only in the Version field. This means only in the first 4 bits of
the first byte. There the first  bit is the MSB (Most significance bit).
Thus results in the following replacement:

1. For IPv4:

*
+---+---+---+---+---+---+---+---+
 Version        |  IHL
+---+---+---+---+---+---+---+---+
**
 **MSB     **LSB |
+---+---+---+---+---+---+---+---+
|     0x4         |     0x5         |
+---+---+---+---+---+---+---+---+
*
|     0100       |  0101           |
+---+---+---+---+---+---+---+---+
*

becomes
*
*
+---+---+---+---+---+---+---+---+
 Version        |  IHL
+---+---+---+---+---+---+---+---+
**
 **MSB     **LSB |
+---+---+---+---+---+---+---+---+
|     0xC         |     0x5         |
+---+---+---+---+---+---+---+---+
*
|     1100       |  0101           |
+---+---+---+---+---+---+---+---+
*
*
2. For IPv6:

*
+---+---+---+---+---+---+---+---+
 Version        |  Flowlabel
+---+---+---+---+---+---+---+---+
**
 **MSB     **LSB |
+---+---+---+---+---+---+---+---+
|     0x6        |     0xXX        |
+---+---+---+---+---+---+---+---+
*
|     0110       |    xxxx         |
+---+---+---+---+---+---+---+---+
*
*
*
becomes
*
*
+---+---+---+---+---+---+---+---+
 Version        |  Flowlabel
+---+---+---+---+---+---+---+---+
**
 **MSB     **LSB |
+---+---+---+---+---+---+---+---+
|     0xE         |     0xXX       |
+---+---+---+---+---+---+---+---+
*
|     1110       |     xxxx       |
+---+---+---+---+---+---+---+---+
*
*
Best regards

Simon Laurenz




Ganesh wrote:
> Hi All,
> I have one doubt regarding the Static chain termination part for
> Profile No 0x004,
> as per the RFC 3843
>
> *3.1. Static Chain Termination RFC 3843*
> *
> compressor can choose to end the static chain at any IP header, and
> indicate this by setting the MSB of the IP version field to 1 (0xC for
> IPv4 or 0xE for IPv6).
>
> as per my Understanding
> 1. For IPV4,
> +---+---+---+---+---+---+---+---+
>  LSB             | MSB
> +---+---+---+---+---+---+---+---+
> | Version = 4 | 0          |
> +---+---+---+---+---+---+---+---+
>
> the MSB 0 has to be replaced By 1, so it will be as below (0xC for IPv4)
> +---+---+---+---+---+---+---+---+
>  LSB             | MSB
> +---+---+---+---+---+---+---+---+
> | Version = 4 | 1          |
> +---+---+---+---+---+---+---+---+
>
> 2. For IPV6.  ( 0xE for IPv6)
> +---+---+---+---+---+---+---+---+
>  LSB             | MSB
> +---+---+---+---+---+---+---+---+
> | Version = 6 | Flow Label(msb)  |
> +---+---+---+---+---+---+---+---+
>
> RFC 3843 Mentions that MSB has to be replaced by 1, how can the 4 bits
> of the flow Label MSB can be changed to 1??
> is my understanding correct??
> can anyone clarify my doubt??
>
>
>
>
>
> *Thanks & Regards,
> Ganesh Babu Kamma
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Rohc mailing list
> Rohc@ietf.org
> https://www.ietf.org/mailman/listinfo/rohc
>

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