DRAFT minutes of IPDVB meeting in San Diego

[Joerg Ott <jo@tzi.uni-bremen.de>]

Folks,

please find below the draft minutes of the IPDVB meeting in
San Diego.  Please post any comments/corrections/additions
to the list.

Thanks,
Joerg


DRAFT MINUTES

IP over Digital Video Broadcast Networks WG (ipdvb)

Thursday, August 5 at 1300-1500
===============================
CHAIR: Gorry Fairhurst <gorry@erg.abdn.ac.uk>

Reported by Gorry Fairhurst and Joerg Ott.
Minutes recorded by Joerg Ott.


1. Agenda Bashing (5 minutes) - Chair

The agenda was accepted as is.


2. Working Group Status and Plans (15 minutes) - Chair

This was the first IPDVB WG meeting. The name of the group was "ipdvb"
rather than "ip-dvb", to match IETF naming policy. Note the change of
the mailing list to: ipdvb@erg.abdn.ac.uk (although for the moment the
old name continues to work).

The ipdvb milestones were reviewed.
- See slides, a few milestones are slipping, but nothing serious.


3. Requirements/Framework (20 minutes) Marie-Jose Montpetit
http://www.ietf.org/internet-drafts/draft-ipdvb-arch-00.txt
- See slides.

Marie-Jose described progress since last version. The document had
evolved and now contained more than just a ULE requirements
specification, rather a full framework is described. This major
revision is reflected in the name change.

The focus of the revised document was on "efficient and flexible"
delivery of IP via MPEG-2 transport streams providing compatibility
with services on DVB and ATSC (and different physical links). There
was new text describing the various scenarios.

Open issues included e2e management of IP flows. Various possibilities
were described:

- Should address resolution be used to map specific addresses to PIDs
  with special features?
- Should extension headers can carry e2e info about the cell content?

A question was raised about the meaning of e2e (end-to-end).  It was
clarified that the intended meaning is "edge-to-edge", essentially
speaking of the satellite link or, more general, an MPEG-2
Transmission Network.  Obviously, end-to-end should not be used as it
has a different meaning in the IETF.  A comment was made that even the
term edge-to-edge might be too close.  In any case, the document
should make clear how this term is used and end-to-end should be avoided.

Another question was raised whether the document can be advanced to
Wroking Group Last Call (WGLC).  It was found that further edits are
still necessary, including
  - removing redundant AR info and clarify AR reqs.
  - removing AR appendix
  - add "e2e" management reqs
  - fix last inconsistencies

Marie-Jose proposed it should be resubmitted to the list with the
intention of a fast WGLC of rev -01.

The chair asked that any further questions to be mailed to the list.


4. Ultra Lightweight Encapsulation (15 minutes) - Bernhard Collini-Nocker
http://www.ietf.org/internet-drafts/draft-ietf-ipdvb-ule-01.txt
- See slides.

B-CN outlined the changes since -01, including improvements of
clarity, refinement of the text on CRC generation to be
unambiguous. The text had been updated with revised CC processing at
the encapsulator and receiver. The MPEG-2 specification allowed
duplicate packets in a Transport Stream. MPEG is clear about this:
duplicate packets are to be discarded. There has been various updates
to improve clarity and correctnes, and a hex-code example had been
included to help implementors verify correct CRC operation.

Several open issues were identified:

- There had been a request for optional non-default CC processing.
  There had been little discussion of this and the doc now conforms to
  the MPEG-2 spec.  The question was raised whether anyone would have
  a strong motivation to change the ULE spec on this.  As no inputs
  were received, it was concluded to keep the spec as is.

- Another issue was whether Adaptation Field usage should be
  supported.  The proposal was that the document stays as is.
  One comment from the audience indicated that Performance Enhancing
  Proxies (PEPs) may benefit from such signaling feature.  It was
  noted, however, that those cannot be assumed to be right at the
  "edge" and that they should be using higher layer signaling
  (i.e. above IP) anyway.

- IP related: What was the correct code point value for Ethernet
  bridging?  The IEEE format for bridging has extra padding inserted,
  so the document stays as is.

Regarding the general ULE spec, a question was raised about packing:
Are there any timers associated with the packing process?  It was
confirmed that there are.  A variable can be set according to the
needs of an operator - there is no "one size fits all" solution. The
parameter was defined, and could be settable e.g. via SNMP.  A
sensible threshold may be 100ms, but this depends on the higher layer
protocols and such a packing threshold may also be influenced by
overall b/w constraints be a matter of policy, e.g. when trying use
left over pieces from TV.

In this context, some further discussion arose around the scope of the
encapsulation: does this just cover IP-over-DVB or other protocols
(e.g. Ethernet bridging) as well.  The latter is perceived to be
within the charter, was also explicitly mentioned at the BoF in
Vienna.  Similarly, other L3 protocols are allowed; even some
experiments using MPLS over ULE were reported.  Because of timing
issues of other protocols, many scenarios become much more interesting
over DVB-T/C/H rather than -S.

The issue of carrying ULE over an arbitrary Internetwork was also
brought up.  But this is outside the scope of ULE.  ULE is just for
transmission over MPEG TS.  The AVT WG is a place where one could talk
about MPEG-TS over RTP.

The document was now consided stable and there were several existing
implementations. The authors would like to produce one more rev and
move to WGLC.


5. ULE Extension Headers (10 minutes) - Bernhard Collini-Nocker
     http://www.ietf.org/internet-drafts/draft-collini-xule-00.txt
- See slides.

The draft described optional headers for encyrption, FEC, etc. This
followed much discussion on the list about _HOW_ to do extensions, how
to know there are extensions, how to encode them, how much overhead,
how many may be used, etc.

This draft came out of this debate and includes ideas and points
raised by various people. It was intended to move the core of the
document to the ULE Spec and to leave the encryption to a separate
document (FEC could also go to a separate document).

Discussion on including encryption was controversial.  People seem to
have different assumptions about which level of security to provide at
which layer.  Following a statement that encryption should be
supported, there was much discussion of what was required, could be
implemented, should be implemented, etc.  It was observed that
security is non-trivial and that IPDBV is a group doing a mapping (and
may not understand well enough the actual security requirements).  If
encryption is supported at the link-layer (which is the case, e.g. for
pay TV), an ecnryption specification may as well be done by the link
layer folks.  It was noted, however, that the appropriateness of this
depends on the scenario in which you are operating.

The discussion was inconclusive and is to be taken to the list.

Within this slot, some discussion of XULE (next agenda item) surfaced.
The current wording of XULE ID proposes just one IANA registry, using
12 bits. This was observed to be fairly complicated.

It was also noted that, while extensibility of ULE is a desirable
goal, its flexibility should not the simplicity requirement -- since
people may want/need to implement this in hardware in the end.  It may
be conceivable to consider a simpler design but, for the time being,
people do not feel uncomfortable.


6. Outstanding ULE Issues to progress to a WGLC (10 minutes) - Chair

Many issues of XULE were already covered in the context of the
previous slot and were not repeated.

There was tentative agreement to merge the basic spec with that of
ULE.


7. Address Resolution (15 minutes) - Marie-Jose Montpetit
     http://www.ietf.org/internet-drafts/draft-fair-ipdvb-ar-01.txt
- See slides.

Marie-Jose reviewed progress since -00. She noted that this was still
an the individual draft, and that much of the work was to introduce
new material, and closer coordination with the ARCH draft. The focus
of this document was on "what exists" and  "what is needed". New
approaches are necessary to make the assignment more easily integrated
in ISPs configuration and provisioning.

Marie-Jose asked for inputs (via the mailing list) on topics relevant
to this draft - how should systems determine IP to PID mapping? - are
there issues concerning QoS or use of MPEG-2 transmission networks as
one part of a larger network? - At this stage offers of text, ideas,
and discussion would be very welcome to understand who can contribute.

The next version will also look for inputs from the working group on the 
following:
  - how-to guides for DHCP over ULE
  - how-to guides for ND or ARP over ULE

For the time being, this is not a WG document?  After the next
revision, the authors will ask the list whether not to adapt.


8. Address Resolution with UDLR (10 minutes) - Hidetaka Izumiyama
- See slides.

The presentation described IP address mapping dynamically. It followed
the current address resolution standard, and described how these
mapped on UDLR mechanisms to turn a unidirectional-link into a
bidirectional one. The group welcomed the inputs and the author
promised to send some text to assist in preparing the next rev of the
WG documents.


9. Other Issues / Future Work

There was a brief discussion of the text that had been posted to the
ipdvb mailing list 14/7/04 Art Allison describing ATSC and the way in
which IP multicast was supported.

Slides were presented by Gorry Fairhurst describing progress of
various implementations. Gorry Fairhurst promised to build a web page
to summarise the status of ULE implementations.