Re: Subject: I-D ACTION:draft-clausen-ipdvb-enc-00.txt

[Ghassane Aniba <Ghassane.Aniba@sophia.inria.fr>]

Patrick Cipiere wrote:
> 
> I am pretty much OK with what is said about the packing, but today,
> the mpeg2 transport packets I am dealing with, do not use the
> adaptation field, but just use the first byte of the transport packet
> payload as an offset if PUSI bit is 1.
> Of course doing this, breaks the 32 bits alignment.
> If we think we need to respect this alignment, having this offset == 3
> might do the job.
> I am not sure we have to use the 32 bits AFC in all cases.
> If saving bits is the goal, let's keep a single byte offset.
> 
> I have a lot of concerns about the lack of layer 2 adresses in the new
> design.
> I think there are a lot of situations where we need layer 2 MAC
> addresses in the datagram:
> Without layer 2 destination address, the filtering has to be done at
> layer 3.
> Without layer 2 destination address, what will be the behaviour of a
> router receiving a layer 3 packet.
> Without layer 2 source address, how do we recognize our own datagrams,
> when we get them back on the link several ms after sending them.
> ...
> 
> If we are really convinced that in some cases either the destination
> and/or source MAC address are uneeded, and if the goal is to save some
> bits not having them, we could use 2 bits out of the length field
> The length field would then be 14 bits ([0,16383])
> MAC_FLAG
> 
> 00 : no dst MAC, no src MAC
> 01 : dst MAC, no src MAC
> 10 : src MAC, no dst MAC
> 11 : dst MAC, src MAC
> 
> MAC is IEEE 48 bits
> no dst MAC is equivalent to a broadcast: ff:ff:ff:ff:ff:ff
> 
> +--+--------------+----------------+----------
> |00|    length    |      type      |Payload
> +--+--------------+----------------+----------
> 
> +--+--------------+----------------+-----------  --+----------
> |01|    length    |      type      |48 bits dst ~  | Paylaod
> +--+--------------+----------------+-----------  --+----------
> 
> +--+--------------+----------------+-----------  --+----------
> |10|    length    |      type      |48 bits src  ~ | Paylaod
> +--+--------------+----------------+-----------  --+----------
> 
> +--+--------------+----------------+-----------  --+-----------  --+---------
> |11|    length    |      type      |48 bits dst ~  |48 bits src ~  |Payload
> +--+--------------+----------------+-----------  --+-----------  --+---------
> 
> Patrick.
But for the satellite network, how we can switch MPEG2-TS packet
onboard?

-- 
Ghassane ANIBA
INRIA (Projet PLANETE)             | Email :
ghassane.aniba@sophia.inria.fr  
2004, Route des Lucioles BP 93     | Phone : +33 4 92 38 75 63
06902 Sophia Antipolis CEDEX France| Fax   : +33 4 92 38 79 78