Re: [rohc] Generic CSRC List Issue

["Gurushant" <gurushant at tataelxsi.co.in>]

Hi Klaus,
Thanks for the quick reply.
But we are adding one extra byte ( 0x00) unnecessarily when the CC indicates
that there is no CSRC value.
I think everybody who reads RoHC RFC, they understand that "/" means it is
variable, how feasible it to mandate to at least one byte for the "/"
meaning. Specially in this example ,  isn't the understanding differs.

I am wondering, is there any special purpose to add one octet in case
generic CSRC list. I understand in case of Generic Extension Header list one
octet makes sense as there is no previous bytes or information  to indicates
its presence.

Thanks & Best Regards
Gurushant.Kotagi


-----Original Message-----
From: Klaus Warnke [mailto:klaus.warnke at acticom.de]
Sent: Wednesday, August 19, 2009 3:54 PM
To: gurushant at tataelxsi.co.in
Cc: rohc at ietf.org
Subject: Re: [rohc] Generic CSRC List Issue


Gurushant,

> If I am correct the last line "as opposed to the CSRC list in the
> uncompressed RTP header, which is not present when the RTP CC field
> is set to 0" , does it mean that for IR packet , one octet( first
> byte) of generic scheme need not present.

No. If the CC field (CSRC count) in the original RTP header is set to
zero, there is no CSRC item at the end of the original RTP header
present. Then the CC field at the beginning of the RTP IR dynamic part
is also set to zero, but you can not omit the first octet of the
generic CSRC list. Set it simply to 0x00 (ET=0, GP=0, PS=0,
CC=0). That is, what the RFC4815-5.1. says.

I think, that the definition of the "/" means at least of octet
(3095. p 43 (in the diagram, slashes "/" indicate variable length))
where the ":" is defined (p. 42 (in the diagram, colons ":" indicate
that the part is optional)) means it can be omitted. But the generic
CSRC list field is surround by "/".

br
Klaus

At Wed, 19 Aug 2009 14:59:24 +0530,
Gurushant wrote:
>
> Dear All,
>
> We have one small issue while understanding the following information from
> the RTP implementation guidelines. Kind request you clarify on the last
> sentence mentioned in below paragraph.
>    Section RFC3095-5.7.7.6 defines the static and dynamic parts of the
>    RTP header. This section indicates a 'Generic CSRC list' field in the
>    dynamic chain, which has a variable length (see section RFC3095-
>    5.8.6). This field is always at least one octet in size, even if the
>    list is empty (as opposed to the CSRC list in the uncompressed RTP
>    header, which is not present when the RTP CC field is set to 0).
>
> If I am correct the last line "as opposed to the CSRC list in the
> uncompressed RTP header, which is not present when the RTP CC field is set
> to 0" , does it mean that for IR packet , one octet( first byte) of
generic
> scheme need not present.
>
> Thanks
> Gurushant