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Re: [rohc] Doubt regarding the Static chain termination for Profile 0x004

Simon Laurenz <simon.laurenz@acticom.de> Fri, 12 February 2010 06:31 UTC

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Date: Fri, 12 Feb 2010 07:33:04 +0100
From: Simon Laurenz <simon.laurenz@acticom.de>
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To: Ganesh <ganeshbabukamma@gmail.com>, rohc@ietf.org
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Subject: Re: [rohc] Doubt regarding the Static chain termination for Profile 0x004
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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
>
> ------------------------------------------------------------------------
>
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