Re: Remarks concerning IP-over-DVB

[Gorry Fairhurst <gorry@erg.abdn.ac.uk>]

Patrick Cipiere wrote:
> 
> Torsten.Jaekel@FTK.rohde-schwarz.com wrote:
> 
> > Imagine we transmit each IP connection in a dedicated DVB sub-channel,
> > given by the PID
> 
> We only have 8191 PIDs, and in some cases like Eutelsat Skyplex, or
> TDMA access, this number might be reduced to less than a hundred.
> So the number of available PIDs might be an issue.
> 
> This might also raise some issues from the manufacturers. Currently
> most of the cards do hardware filtering on only from 8 to 32 PIDs
> simultaneously.

Yes, this current PID limit is true of other potential next generation 
schemes too.

I wonder how much this is due to the complexity of current MPE / DSM-CC
solutions? If we were to re-think this, I do wonder whether one
could come up with a scheme which significantly simplified the
re-assembly of IP datagrams and the information needed by the driver
or on-card processing that is needed to know which PIDs needed
to be forwarded by this particular receive interface. Is this
an interesting area?

> I am also using cards that do not hardware filter the PIDs, but leave
> this task to the driver. With these  cards it is easier to deal with the
> whole 8191 PIDs, but cost more cpu cycles.
> 

Yes - I also presume this offers a way to modify the IP protocol
processing with some existing cards. How much experience do you
have of this?

> I guess that some questions we will have to discuss on this
> mailing-list are about layering:
> - what is our layer 1?
>   for me: it is MPEG2 TP (included) and under.
>   it even can be MPE (included) and under.
> 
> Of course considering MPE as the layer 1 you need to encapsulate the
> layer 2 (ethernet for example) using LLC_SNAP and RFC1483 with either
> - Ethertype 0x6558 `transparent ethernet bridging'
> - Bridged Ethernet/802.3
> This is will add some extra bytes and therefore waste some bandwith,
> but we get something that we might consider as a valuable information
> with the IEEE 48 bits source MAC address (which is not in the MPE
> datagram section).
> 

Yes, that is, if you want to do a MAC level bridge, rather than 
full IP routing?

> Patrick.
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