Re: MPE Question

[Bernhard Collini-Nocker <bnocker@cosy.sbg.ac.at>]

Hello again,

the famous words stuffing and padding are

Siva Veerepalli wrote:
> --- Bernhard Collini-Nocker <bnocker@cosy.sbg.ac.at>
> wrote:
>
> > Siva Veerepalli wrote:
> >
> > > A couple of questions about MPE-FEC framing.
>
> <snip>
>
> > > 2. The MPE section has optional stuffing bytes at
> >
> > the
> >
> > > end of the section. Are these used? If yes, for
> >
> > what?
> >
> > Whenver an IP packets leaves "enough" space in the
> > last TS packet 
> > another IP packet could be inserted. If not wanted
> > or needed, stuffing 
> > takes care that the empty space is filled up with
> > pattern 0xFF.
>
>
> I was actually referring to the stuffing bytes in the
> MPE section, not the TS packet. I understand the use
> of stuffing bytes in TS packets, but am not clear why
> stuffing bytes are used in MPE sections.

According to EN301192 "stuffing_byte: this is an optional 8-bit field 
whose value is not specified. If the payload of the section is scrambled
(see payload_scrambling_mode), these bytes are scrambled. They are to 
assist with block encryption and data processing in wide bus 
environments. The number of stuffing_bytes used should meet the data 
alignment requirements defined in the data_broadcast_descriptor."

So, for block encryption one typically has some arbitariy number of bits 
to encrypt and needs to ensure that the MPE payload is on auch a 
multiple bit boundary for what MPE internal stuffing might be needed...

> thanks,
> Siva
>
> > > thanks,
> > > Siva
> > >
> > >
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