RE: UDP encaps for SCTP and SCCP

[Bob Briscoe <[e-mail]>]

Tom,

At 15:08 18/05/2010, Phelan, Tom wrote:
>Hi Lars,
>
>Well, I like option 1.
>
>I feel that option 2 is a chimera.  The 'G' in the GUT proposal stands
>for "generic", but it is not entirely generic.  The decapsulation stage
>is specific to the encapsulated protocol.  The GUT draft gives one decap
>rule that is more-or-less suitable for TCP and DCCP.  It doesn't work
>for SCTP.
>
>You have to look in detail at the encapsulated protocols to see if a
>proposed decap works.  With my non-detail understanding of TCP, it looks
>like it works, but we'll need someone to look at that in detail.

The G in GUT is certainly not true for host implementations, but 
importantly the wire protocol is generic for all e2e protocols it 
encapsulates, which is what is important for middleboxes.


>For DCCP, the proposed decap makes partial checksums ineffective.  I
>think it's OK to do that, but you need to state that explicitly in the
>draft, and probably offer guidance on how to deal with partial checksum
>feature negotiation.  You also need to deal with how to signal the use
>of UDP encap, and the other things included in my draft.  Once you've
>done that, you have my draft.
>
>GUT has similar issues for SCTP.  SCTP uses a CRC checksum that doesn't
>include the IP addresses, so the proposed GUT decap doesn't work for it.
>What's needed is actually easier to do.  I don't know enough about SCTP
>to know what else needs to be done.

Earlier on the tsvwg list I was proposing how to get GUT to do a 
partial checksum that only covers its own headers, stopping at the 
encapsulated headers.


>As I've stated before, if you really think through a generic approach,
>it becomes an overall scheme that can be used by all protocols, plus a
>set of protocol-specific adaptations.  That's where we're at with the
>DCCP- and SCTP-specific drafts.
>
>Tom P.
>
> > -----Original Message-----
> > From: [e-mail] [mailto:[e-mail]] On
> > Behalf Of Lars Eggert
> > Sent: Tuesday, May 18, 2010 3:38 AM
> > To: [e-mail]
> > Cc: DCCP working group; TSV Area
> > Subject: Re: UDP encaps for SCTP and SCCP
> >
> > Hi,
> >
> > the discussion has touched on lots of things related to UDP encaps,
>but I
> > haven't seen anything I'd call consensus on the question below. I'd
> > therefore like to ask folks to specifically state which option they
> > support:
> >
> > (1) do one SCTP-specific and one DCCP-specific UDP encaps
> > (2) do one generic UDP encaps that can be used with both
> > (3) do neither (don't do any sort of UDP encaps for SCTP and DCCP)
> >
> > Thanks,
> > Lars
> >
> > On 2010-4-22, at 12:57, Eggert Lars (Nokia-NRC/Espoo) wrote:
> > > Hi,
> > >
> > > as most of you probably know, there are two different proposals for
>how
> > to encapsulate SCTP and DCCP inside UDP.
> > >
> > > One approach proposes two protocol-specific encapsulation schemes
> > (described in draft-tuexen-sctp-udp-encaps and
>draft-ietf-dccp-udpencap).
> > >
> > > The second approach proposes a generic encapsulation scheme that can
>be
> > applied to both SCTP and DCCP (draft-manner-tsvwg-gut).
> > >
> > > As a community, we do need to come to consensus on which of these
>two
> > approaches we want to follow when it comes to UDP encapsulation of
>SCTP
> > and DCCP. I believe it would be very confusing if we were to
>standardize
> > both approaches.
> > >
> > > I'd hence like to ask folks to read the three documents and post
>their
> > views to the [e-mail] list. I'm personally especially interested
>in
> > hearing from folks who aren't on the author lists of the documents,
>but
> > obviously, the authors expert opinions do matter.
> > >
> > > Thanks,
> > > Lars
> > >
> > > PS: I'm pushing on this topic, because UDP encapsulation is the last
> > remaining work item in the DCCP working group before it can close...

________________________________________________________________
Bob Briscoe,                                BT Innovate & Design