LLC support in DVB , ATSC, MPEG-2?

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

So, I'd like to ask the group as a whole, what they see as the usage of LLC 
within DVB, ATSC, or any MPEG-2 based transmission network?

Carsten Bormann wrote:

<snip - see response in separate email>
> One question though: Why is it that ethertype frames can be sent without 
> MAC but length (LLC) frames can't?

So the WG did discuss this, but it seems worthwhile checking again that we 
have got this correct.

The history as I recall is:

(i) Do we need LLC?
Yes (discussed at both ipdvb BoF as well as at other times), we should 
supportLLC, because of it use/potential use for OSPF;
Bridging; L2 Management/devcice discovery

(ii) Non-issues for ULE.
LLC is also used:
 - To raise the ETnerenet frame size above that of traditional Ethernet
 - To provide a Type field (not present in basic MPE header).
Both of these are supported natively within ULE without the need for LLC/SNAP


> Is the assumption that all LLC protocols need full MAC addresses?

So, yes that was it.

- My understanding was that because this was an IEEE protocol, and much of the 
use of LLC reflected use in a bridged network, then it was best to include 
both a source and destination MAC address.

> I don't know all existing LLC protocols,

Nor me --- can anyone else on this list help?

> but I know at least one
> proposal for one that probably doesn't.

Aha - Do tell more...



> It would be easy to introduce a mandatory extension header 2, which is 
> like 1 (i.e., does not allow chaining) but leaves out the 14 bytes of 
> (DA, SA, Type -- the latter is redundant with the LLC length), leading to:
>
>        0                   1                   2                   3
>        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>       |1|        Length  (15b)        |         Type = 0x0002         |
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>       |                                                               |
>       =                           LLC payload                         =
>       |                                                               |
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>       |                             (CRC-32)                          |
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> (and the obvious equivalent for D=0).

I'm keen to understand first the intended usage....

<snip - see response in separate email>


> Gruesse, Carsten


Best wishes,

Gorry Fairhurst