[Tsvwg] Re: [rdma] a proposal for a different No-Data-Touch framer for TCP
Stephen Bailey <steph@cs.uchicago.edu> Mon, 11 February 2002 23:25 UTC
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To: John Hufferd <hufferd@us.ibm.com>
Cc: tsvwg@ietf.org, rdma@yahoogroups.com
In-Reply-To: Message from "John Hufferd" <hufferd@us.ibm.com> of "Sat, 09 Feb 2002 17:05:37 PST." <OF31443FAC.EDF1393F-ON88256B5B.006A9AA4@boulder.ibm.com>
References: <OF31443FAC.EDF1393F-ON88256B5B.006A9AA4@boulder.ibm.com>
Date: Mon, 11 Feb 2002 17:41:26 -0500
From: Stephen Bailey <steph@cs.uchicago.edu>
Message-Id: <20020211224132.63F364E8F@sandmail.sandburst.com>
Subject: [Tsvwg] Re: [rdma] a proposal for a different No-Data-Touch framer for TCP
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John, Thanks for the exhausting analysis. As Paul points out, you do not want to scan the received segment to recover synchronization with either of these techniques, since it's too risky. The TUF draft specifically makes this point. Basically, you get one event per segment. However, if you want to be really pessemistic you could say the stream IS segmented into tiny frames that almost result in scanning. The TUF draft also says that the use of a TUF-derived PDU containment property should be discontinued after repeated failure of PDU containment. Given Julian's repeated statements that TUF should be analyzed against an infinite stream, I can conclude that the draft does not make this point strongly or clearly enough. The TUF assumption is that there are two distinct, quasi-stable scenarios: segmentation is preserved or it is not. Obviously if segmentation is not preserved, there's no point in trying to use the PDU containment property because it will never hold. If a receiver detect that the PDU containment property does not hold for longer than would represent a transient condition like PMTU change, it gives up and stops using it. Julian's argument that TUF needs to be analyzed against an infinite stream is a straw man. You can pick the threshold at which a TUF receiver gives up to be any number that makes you comfortable (10e6 packets, 10e4, whatever). I'm not clear on how your analysis incorporates worst case data pattern distribution assumptions. There is a ULP running inside the framing protocol, and if we assume the ULP is efficient, MOST of the data IT carries is actually controlled by the user of the ULP. This user data can just as well be a `search and destroy' sequence that tries every `eye catcher' in a well-formed context. This technique boils down to a blind search for a 32-bit integer, and there's the additional probability of hitting any particular element of the blind search pattern (basically like your ex and ey). Julian's extra 64 bits (salt & digest) are not doing anything for you in this case. It's as simple as the probability of the resegmented stream hitting the correct 32-bit number. Thanks again for your work on this. Steph > Steph, Julian, > The following is an attempt to determine the probability of a false > positive, both with the TUF approach as defined in > draft-ietf-tsvwg-tcp-ulp-frame-01.txt, and the semi draft that Julian > proposed. > _______________________________________________ tsvwg mailing list tsvwg@ietf.org https://www1.ietf.org/mailman/listinfo/tsvwg
- [Tsvwg] a proposal for a different No-Data-Touch … Julian Satran
- RE: [Tsvwg] a proposal for a different No-Data-To… Douglas Otis
- [Tsvwg] RE: [rdma] a proposal for a different No-… Julian Satran
- [Tsvwg] RE: [rdma] a proposal for a different No-… Culley, Paul
- [Tsvwg] RE: [rdma] a proposal for a different No-… Julian Satran
- Re: [Tsvwg] RE: [rdma] a proposal for a different… Lloyd Wood
- [Tsvwg] RE: [rdma] a proposal for a different No-… Julian Satran
- [Tsvwg] Re: [rdma] a proposal for a different No-… Stephen Bailey
- Re: [Tsvwg] RE: [rdma] a proposal for a different… Julian Satran
- [Tsvwg] Re: [rdma] a proposal for a different No-… Julian Satran
- [Tsvwg] Re: [rdma] a proposal for a different No-… Stephen Bailey
- [Tsvwg] Re: [rdma] a proposal for a different No-… John Hufferd
- [Tsvwg] Re: [rdma] a proposal for a different No-… Julian Satran
- [Tsvwg] Re: [rdma] a proposal for a different No-… John Hufferd
- [Tsvwg] Re: [rdma] a proposal for a different No-… John Hufferd
- [Tsvwg] Re: [rdma] a proposal for a different No-… Julian Satran
- [Tsvwg] Re: [rdma] a proposal for a different No-… Stephen Bailey
- RE: [Tsvwg] a proposal for a different No-Data-To… Douglas Otis
- [Tsvwg] Re: [rdma] a proposal for a different No-… John Hufferd
- [Tsvwg] Re: [rdma] a proposal for a different No-… Julian Satran
- RE: [Tsvwg] a proposal for a different No-Data-To… Douglas Otis
- [Tsvwg] Re: [rdma] a proposal for a different No-… Stephen Bailey
- [Tsvwg] Re: [rdma] a proposal for a different No-… Stephen Bailey