[linux-dvb] Re: DVB MPE

[Alexander Nasonov <anasonov@GMD.DE>]

On Thursday 05 September 2002 10:29, gpastore@interfree.it wrote:
> Hello All,
> I have a question for you. Does someone knows which is the usage (if any
> exists that is specified)  of the Adaptation Field within the IP
> multiprotocol encapsulation over MPEG framework? Thank you
> Best Regards
> Gaetano Pastore

I already replied to Gaetano in private e-mail. Accidently, I clicked wrongly 
on 'Reply' button, not 'Reply to all' button and this is why my e-mail was 
private. You can find this e-mail below. But be careful. This sentence from 
my e-mail is completely wrong because I missed pointer_field when I 
calculated datagram_section header length:
> Without adaptation field datagram_section is aligned but data started
> after section_length is not. With the presence of ony-byte adaptation
> field the situation is reverted: datagram_section is not aligned while
> data started after section_length is.

Now I can give another reply. Recenly I received new IP inserter. This device 
has such option: Stuffing using adapation field.  I didn't check it yet but I 
can suggest that the adaptation field is used to eliminate the use of 
stuffing_byte when this option is set.

-- 
Best regards,
Alexander Nasonov
Fraunhofer Gesellschaft


Subject: Re: [linux-dvb] DVB MPE
Date: Fri, 6 Sep 2002 11:31:48 +0200
From: Alexander Nasonov <anasonov@gmd.de>
To: gpastore@interfree.it

On Thursday 05 September 2002 10:29, Gaetano Pastore wrote:
> I have a question for you. Does someone knows which is the usage (if any
> exists that is specified)  of the Adaptation Field within the IP
> multiprotocol encapsulation over MPEG framework? Thank you

May be for 4-byte alignment? Without adaptation field datagram_section is
aligned but data started after section_length is not. With the presence of
ony-byte adaptation field the situation is reverted: datagram_section is not
aligned while data started after section_length is.

I'm more interested in stuffing_byte. Standard EN 301 192 stated that
-- cut --
number of stuffing_bytes used should meet the data alignment requirements
defined in the data_broadcast_descriptor
-- cut --

This data_broadcast_descriptor should be inserted into SI. Does it mean that
if I'm going to implement CRC or checksum check (they are placed write after
stuffing bytes) for MP encapsulated data then I should read SI? Current
version of dvb_net module AFAIK read only DMC-CC sections with private data
and it's happy with them.



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