RE: [Fecframe] IETF 67
"Mark Watson" <mark@digitalfountain.com> Mon, 09 October 2006 21:10 UTC
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Subject: RE: [Fecframe] IETF 67
Date: Mon, 09 Oct 2006 14:09:43 -0700
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Thread-Topic: [Fecframe] IETF 67
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From: Mark Watson <mark@digitalfountain.com>
To: Greg Shepherd <gjshep@gmail.com>
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Hi Greg, The main advantage that could be expected from fitting streaming into the RMT FEC BB would be that FEC Schemes already defined by RMT could be reused for streaming without modification. However, I'm not sure that would actually work, for the following reasons: Firstly, the FEC Schemes defined in RMT envisage objects with a finite size. So, to map streaming to this we would need to consider a stream as a sequence of FEC BB-style objects. We would then need to communicate the FEC Object Transmission Information for each object with that object. This could be done, but the problem is that for many FEC Schemes there would be advantages if certain pieces of FEC Object Transmission Information could be the same for every block (for example it makes sense in some cases for the Symbol Size and Block Size to be the same for every block). It's advantageous to be able to inform the receiver that these parameters won't change and also more efficient to signal them once, out-of-band, than with every block. Without streaming-specific additions to the FEC Scheme you could not specify how this "stream-level" FEC OTI was communicated to the receiver. So, you would not achieve the original aim of re-using the FEC Schemes without modification anyway. Secondly, FEC Schemes in RMT generally also include recommendations for parameter settings, which are based on single-object delivery. Although not essential it would be a good thing for people to provide recommendations for streaming cases too - which may be different for a variety of reasons. Given that we need streaming-specific modifications to FEC Schemes anyway, it seems better to me to do this cleanly. This does not mean that we lose the work done in RMT, but that we recognize that re-use of an RMT FEC Scheme for FECFRAME doesn't come for free - it requires a little work. A third reason is the question of how streaming source data is formatted into data blocks that an 'object-based' FEC Scheme could process. RMT FEC Schemes expect an object which is just a sequence of bytes. For streaming we need to build such an object out of a sequence of potentially variable-length source packets. We then have the problem that we don't just send the symbols generated by the FEC Scheme, but we may wish to send the original source packets themselves. The mapping between the source block that the RMT FEC Scheme understands and the Source Packets themselves may again be something where specification material which is both FEC-Scheme-specific and Streaming-specific is needed. This was a topic of discussion at the last meeting: The 3GPP FEC streaming framework makes this issue FEC-Scheme-independent (if that can be claimed of a spec which includes only one FEC Scheme!), whereas I had proposed last time we allow also for FEC-Scheme-specific approaches. We did not conclude on this, but I would propose that we allow FEC Schemes to specify their own approach (and of course, the Raptor FEC Scheme will use the 3GPP one to align with 3GPP's use of Raptor). Regards, Mark Watson -----Original Message----- From: Greg Shepherd [mailto:gjshep@gmail.com] Sent: Monday, October 09, 2006 4:25 PM To: Mark Watson Cc: weddy@grc.nasa.gov; fecframe@ietf.org Subject: Re: [Fecframe] IETF 67 Wow, no answers... no flames even. Maybe I need to be more offensive to get some discussions going. ;-) That said, where are we with agenda items for the IETF 67? As per our charter we have a milestone after this meeting for a WG approval of the reqs draft to move it up the tree. Can someone take the roll of eloquently stating the pros/cons of making streaming fit into an existing FEC BB (RMT) vs FECFrame BB defining streaming outside of RMT. Cheers, Greg On 9/25/06, Greg Shepherd <gjshep@gmail.com> wrote: > On 9/12/06, Mark Watson <mark@digitalfountain.com> wrote: > > Hi Wesley, > > > > Good point. This kind of consideration would be a good addition to the > > draft. > > > > The RMT FEC Building Block does indeed provide a lot of what we need. > > The main differences are in places where the FEC BB makes assumptions > > related to the delivered data being a single 'object' rather than a > > collection of streams/packet flows. > > > > Streams/packet flows have some additional properties - such as somewhat > > different needs for timely delivery, the fact that packet sizes for > > source packets are a property of the stream, not something that the FEC > > mechanism can determine as with object delivery and the requirement to > > protect multiple streams together. > > > > Now, one approach would be to define a way to map a collection of > > streams/packet flows into an 'object' of the kind addressed in the FEC > > BB and then concatenate this mapping with what we already have in the > > FEC BB. > > > > This might be a little contrived though, so I think what we are aiming > > at is essentially a 'stream/packet flow' version of the FEC BB - reusing > > as much as possible of course. > > > > As with the FEC BB, there is an open question about exactly what > > functionality to specify in the BB and what to delegate to FEC Schemes. > > Delegation has the advantage of generality, whereas specification at the > > FEC BB has the advantage of introducing greater commonality between > > different instantiations of the whole system. > > So which direction do we take? Should this be an agenda item for the > upcoming meeting? To stay on track we should have the framework draft > ready for submission after IETF 67 so getting the discussion going now > is best. > > I agree that stuffing streaming functions into an object to make it > fit FEC BB is a bit contrived, but can it be done? What functionality > would be compromised? Would this prevent extensibiliy in streaming > functions over having an independent (though inheriting) FECFrame > spec? > > Greg > > > Regards, > > > > Mark > > > > -----Original Message----- > > From: Wesley Eddy [mailto:weddy@grc.nasa.gov] > > Sent: Tuesday, September 12, 2006 10:12 AM > > To: Greg Shepherd > > Cc: fecframe@ietf.org > > Subject: Re: [Fecframe] IETF 67 > > > > On Tue, Sep 12, 2006 at 04:37:12AM -0700, Greg Shepherd wrote: > > > Hello, > > > > > > We're coming up on IETF 67 and our next milestone of approving our > > > requirements as presented in: > > > > > > draft-ietf-fecframe-req-00 > > > > > > Since IETF 66 there has been little or no discussion on the list > > > regarding the reqs, or anything else for that matter. Heck, many other > > > IETF WG lists find plenty of non-issues to flame about but we can't > > > even find the time or interest to discuss real topics. ;-) > > > > > > So, please, read the above req draft and send your feedback here to > > > the list. Sure, we could move the draft forward with the assumption > > > that no feedback is positive feedback but that seems a bit > > > disingenuous and actually pretty boring to be honest. > > > > > > > I've read the draft. Since the RMT FEC building block is described as > > the basis for FECFRAME, I think there should be a short section on why > > the FEC building block alone isn't sufficient for FECFRAME's goals. > > Looking at the requirements, the FEC building block meets many of these > > already, so it would be valuable to discuss exactly which requirements > > require additional mechanisms. Without this kind of "gap-analysis" of > > the existing solution, the real goal of the work is unclear. > > > > Also, a minor comment, I'd prefer if the requirements were numbered in > > units of 1's rather than in 10's, but this really doesn't matter. There > > are also two requirements numbered 30 in the 00 version of the draft. > > > > -- > > Wesley M. Eddy > > Verizon Federal Network Systems > > > > _______________________________________________ > > Fecframe mailing list > > Fecframe@ietf.org > > https://www1.ietf.org/mailman/listinfo/fecframe > > > _______________________________________________ Fecframe mailing list Fecframe@ietf.org https://www1.ietf.org/mailman/listinfo/fecframe
- [Fecframe] IETF 67 Greg Shepherd
- Re: [Fecframe] IETF 67 Wesley Eddy
- RE: [Fecframe] IETF 67 Mark Watson
- Re: [Fecframe] IETF 67 Greg Shepherd
- Re: [Fecframe] IETF 67 Greg Shepherd
- RE: [Fecframe] IETF 67 Mark Watson
- Re: [Fecframe] IETF 67 Marshall Eubanks
- Re: [Fecframe] IETF 67 Greg Shepherd
- RE: [Fecframe] IETF 67 Mark Watson
- Re: [Fecframe] IETF 67 Marshall Eubanks