Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-protocol-02.txt
Arno Bakker <arno@cs.vu.nl> Wed, 11 July 2012 07:20 UTC
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Date: Wed, 11 Jul 2012 09:21:11 +0200
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Subject: Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-protocol-02.txt
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Hi Yunfei (et al) Thanks for the feedback. Responses inline. On 20/06/2012 09:09, zhangyunfei wrote: > Hi Arno and Riccardo (Speaking individually), > > 2) bin numbers in 1^st paragraph: Since there are at least two schemes > introduced in section 4, the range scheme should be stated here as well. Sorry, forgot to update the introduction section in a vain effort to keep changes to a minimum. Scheduled for -03. > 3)Merkle hash tree in section 2.2:Occur for the first time without > explaining before.It's better to add the term in section 1.3. Done for -03. > 4)INTEGRITY in section 2.2: It should be stated that this message is not > used all the time. Clarified in -03. > 5)Section3.3: The sentence "it MUST send a ACK message containing a > chunk specification for C". MUST or SHOULD. Riccardo is looking into sending batched acknowledgements in relationship to the latest LEDBAT draft, so we may update this section. At present, it is a "MUST" when run over unreliable transports. > 6)Section 3.9, since TCP is abandoned by PPSPP, do we need to explain > the related case? Good that you mention transports, AFAIK that still needs to be discussed. Candidates are: * UDP with congestion control (e.g. LEDBAT) * RTP * Both UDP+cc and RTP I see no direct use case of TCP, but IMHO we should not exclude it either. Support for RTP may make the standard more appealing to the RTCWEB crowd. Perhaps we should ask them for an opinion on this issue. Yunfei/Stefano, do you know somebody we could ask? > 7)Section 4.3 PEX_ADD, no explanation before. PEX_ADD was renamed to PEX_RES except in this location :-( > 8)Section 6: I suggest to exclude this section because it involves a > over-strong limitation:fixed chunk size.Furthermore I am not clear of > the necessity of this scheme.Just as the background of section 7? IMHO, fixed-size chunks will be rather common with static content, and the ability to detect content size is a nice property to achieve minimal metadata (cf. info centric networking) In any case, the concept of peak hashes enhances security and eases implementation, therefore I think it should be explained in the draft. The peak hashes provide a secure method of determining (a) the height of the MHT and (b) more importantly, how many chunks there are at the base of the tree. This helps to protect against malicious peers sending confusing information, e.g. a HAVE for a chunk outside the actual chunk range. The ability to judge incoming information as being good or bad greatly eases implementation (otherwise you may need e.g. majority votes on how many chunks there are, etc.) Peak hashes also ease implementation in another respect. With the knowledge about the tree they provide, datastructures can be preallocated, such as the storage of the MHT and chunk availability bitmaps. Pre-allocated datastructures are easier to implement than data structures that have to dynamically adapt. > 9) Section 7:for the similar reason, remove the section 7.1.1 I don't quite follow this comment. Live streaming is not dependent on fixed-sized chunks and mini Merkle Hash Trees are already a common way of efficiently authenticating live data (Wong and Lam scheme). IMHO, it makes sense to extend to extend this mechanism to a big tree. This would enable people that tune in late to a show and want to watch it from the start to use the same swarm as the live watchers. > 10)Section 9.3.2, why placed here? I suggest to remove this section. I'd like to start the discussion on which transport to use (see above) and then update this part of the spec, if that's alright. Regards, Arno
- [ppsp] I-D Action: draft-ietf-ppsp-peer-protocol-… internet-drafts
- Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-proto… zhangyunfei
- Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-proto… Arno Bakker
- Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-proto… Wesley Eddy
- Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-proto… Wesley Eddy
- Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-proto… zhangyunfei
- Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-proto… Arno Bakker
- Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-proto… Riccardo Petrocco
- Re: [ppsp] I-D Action: draft-ietf-ppsp-peer-proto… Arno Bakker