Re: MPE Question

[Siva Veerepalli <sivaveer@yahoo.com>]

Thanks for the response Bernhard, but I am a bit
confused about the answer. Please see my question
below:

--- Bernhard Collini-Nocker <bnocker@cosy.sbg.ac.at>
wrote:
> Siva Veerepalli wrote:
> > A couple of questions about MPE-FEC framing.
> > 
> > 1. The interim IP datacast standard A079 (meant to
> > facilitate DVB-H trials) specifies that only one
> > datagram should be used per MPE section i.e., no
> > fragmentation of IP datagram over multiple MPE
> > sections. However, the DVB Databroadcast
> specification
> > allows fragmentation of the IP datagram over
> multiple
> > sections. Does anyone know what the usual practice
> is?
> 
> In order to reduce encapsulation overhead, section
> packing is used, i.e. 
> if the (remainder of an) IP packet does not fit
> exactly in a TS packet a 
> subsequent IP packet may start in that TS packet as
> well.
> In order to reduce jitter and latency, section
> packing is not used.

I understand that two MPE sections could probably
start in the same TS packet (I guess that is what you
mean by section packing).

My original questions was, what is the usual practice
with regards to fragmenting an IP datagram over
multiple MPE sections (irrespective of how these
sections are transported in TS packets)? The DVB-H
(data broadcast standard) allows for this, however,
the IPDC interim specification requires that one
datagram be encapsulated entirely in one mpe section
i.e., no datagram fragmentation over multiple MPE
sections.

thanks,
Siva

> 
> You can find both on existing services.
> 
> > Do the final DVB/IP datacast standards specify
> this
> > for DVB-H?
> 
> The difficulty with section peckaing on the transmit
> side is that the 
> encapsulator needs to wait for subsequent IP packets
> to fill an 
> partially filled TS packet and therefor has
> typically a time-out 
> associated to that waiting, ie before flushing the
> buffer and 
> transmitting the final TS packet.
> 
> > 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.
> 
> > thanks,
> > Siva
> > 
> > 
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> 
> 


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