Re: ULE extensions

[Alain RITOUX <alain.ritoux@6wind.com>]

Gorry Fairhurst wrote:
> William StanisLaus wrote:
>
> > Hi Alain and all,
> >
> > I have a small concern here on
> >  
> >
> > > > < ----------------------------- SNDU ----------------------------- >
> > > > +-+-------------------------------------------------------+--------+
> > > > |D| Length | ENC |ETYPE |                PDU              | CRC-32 |
> > > > +-+-------------------------------------------------------+--------+
> > > >     
> >
> > here, always ENC which is 2 bytes wasted even if we don't support ULE 
> > encryption.
>
> No that's not what I meant, here is the suggestion:
>
> The basic ULE frame type in this hypothetical example would be 
> "ENCRYPTED-CONTENT"
> some well known code-point. This adds a null (zero byte) header, 
> followed by a new type field.

> The new type field that follows carries the TYPE of the ULE payload 
> being transported over the link.
> - Of course, you could define another TYPE value at this point too,
> such as bridging, but that also adds more overhead.

OK I got it.
I fact, if there is a code point for that with well known/defined data,
the the "encrypt" thing can de fully done.

What William and I were proposing was a more generic mechanism,
available for extension-to-come. So what we proposed was to introduce
an Extension Header format :

- The presence of extension headers is specified by  a bit
  in ULE header
- Each extension header has a bit telling whether what follows is the
  payload or another extension header.
- Each extension header includes its own length, so Ext Header chain
  can be parsed blindly
- Each Extension Header includes its own type, and this type has
  a field indicating what to do if this type is unknown.
    + drop SNDU
    + ignore, and parse blindly to the next (if present) Ext Header
      or to the playload.

In fact the generic Ext Header processing would then be MANDATORY
It will allow implem to parse blindly unknwon Ext Headers

The "encryption" stuff can easily fit into this generic scheme
with the same overhead. The plus is that it would be able to live
its own life independanlty from (ExtHdr aware)ULE base specs.

What is the feeling of the WG on this header chaining ?

Cheers.
Alain.
--
Alain RITOUX
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