Subject: RE: [rohc] a question about

From: "Ghyslain Pelletier (LU/EAB)" <[email-masked]>
Date: Tue, 30 Aug 2005 08:34:41 +0200

Hi Zhenghua,

Regarding your question (1), Recall that the concept of states in 3095 is not a normative concept, it is meant as a way to explain concepts. My understanding is that the rule to follow is that "The compressor MUST NOT use packet types 0 or 1 during transition" for any transition that changes between packet formats for packet types 0 and 1, in other word for U/O->R and R->U/O transitions. This is to avoid the risk of misinterpreting a packet of type e.g. R-0 for an UO-0. During this kind of transitions, a packet type common to all modes must be used (i.e. IR, IR-DYN or UOR-2).

Regarding your question (2), "/" means variable length in the sense that it means "more than one octet", and this field can be of a fixed sized if speficied to the right of the field, or its length is deduced from some other operation when it is explicitly mentionned "variable length" instead to the right. In the case of IP addresses that you provided as example, the size of the field is explicitly mentionned to the right of the field and it is thus always 16 octets when this particular format is used.

Hope this helps,

/Ghyslain

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On Behalf Of
> tangzhenghua
> Sent: den 30 augusti 2005 02:55
> To: [email-masked]
> Subject: [rohc] a question about
> 
> 
> Hi,experts,
> 
> I am implementing ROHC protocol and have some problem on the protocol
> 
> (1)In section 5.6.5,the limitation on the transition from 
> Reliable to Optimistic mode is the compressor must always run 
> in the FO state during transition.But this limitation is not 
> exist when transition from Optimistic to Reliable mode.So i 
> am confusing with it
> (2)Slashes "/" indicate variable length in section 5.2,but as follows
>     5.7.7.3.  Initialization of IPv6 Header [IPv6]
>     Static part:
> 
>       +---+---+---+---+---+---+---+---+
>       |  Version = 6  |Flow Label(msb)|   1 octet
>       +---+---+---+---+---+---+---+---+
>       /        Flow Label (lsb)       /   2 octets
>       +---+---+---+---+---+---+---+---+
>       |          Next Header          |   1 octet
>       +---+---+---+---+---+---+---+---+
>       /        Source Address         /   16 octets
>       +---+---+---+---+---+---+---+---+
>       /      Destination Address      /   16 octets
>       +---+---+---+---+---+---+---+---+
>      The Source Address and Destination Address are denoted 
> with Slashes "/" ,does it means these fields length are     
> variable?how can i know the exact length of these two fields?
> 
> Regards
> 
> Zhenghua
> 
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