Re: [PCN] Comments on draft-ietf-pcn-architecture-02.txt
<philip.eardley@bt.com> Thu, 07 February 2008 15:02 UTC
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Thread-Topic: Comments on draft-ietf-pcn-architecture-02.txt
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From: philip.eardley@bt.com
To: menth@informatik.uni-wuerzburg.de
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Subject: Re: [PCN] Comments on draft-ietf-pcn-architecture-02.txt
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Michael Thanks for the detailed review, I've now worked these into the revised arch draft phil > -----Original Message----- > From: Michael Menth [mailto:menth@informatik.uni-wuerzburg.de] > Sent: 23 November 2007 10:41 > To: Eardley,PL,Philip,CXR9 R > Cc: pcn@ietf.org > Subject: Comments on draft-ietf-pcn-architecture-02.txt > > > Introduction > > "PCN-egress-nodes make measurements of the packet markings and > send information as necessary to the nodes that make the decision > about which PCN-flows to accept/reject or terminate, based on this > information." > > [Michael] "PCN-egress nodes monitor the packet markings and ..." > (measurement is not necessarily required, both for admission and > termination.) joe made similar comments & have tried for mods in a few places. I actually left this one as is, as I found it too cumbersome to write "measure and/or monitor" [and I think "measure" is more inclusive of "monitor" than vice-versa] . Anyway, your point should be clear to anyone who gets beyond the intro! > > ===================== > > "The PCN-lower-rates can be chosen small enough that admitted > traffic can still be carried after a rerouting in most failure > cases." > > [Michael] The general concept of resilient admission control has > been proposed in [Menth04g] and applied to PCN in [PCN-Config] > including algorithms how to set PCN rate thresholds appropriately. > > [Menth04g] M. Menth, S. Kopf, and J. Charzinski: "Network > Admission Control for Fault-Tolerant QoS Provisioning" in IEEE > High-Speed Networks for Multimedia Communication (HSNMC), June > 2004 > > [PCN-Config] M. Menth, and M. Hartmann: "PCN-Based Resilient > Network Admission Control: The Impact of a Single Bit", > <http://www3.informatik.uni-wuerzburg.de/staff/menth/Publications/Menth0 7- > PCN-Config.pdf>", > 2007. > I added a ref to te 2nd. > ===================== > > Terminology want to avoid discussing /changing terminology, where it's just changing wording rather than changing meaning. > > ===================== > 4.1 > > "However, note that this description reflects the overall intent > of the algorithm rather than its instantaneous behaviour, since > the rate measured at a particular moment depends on the detailed > algorithm, its implementation (eg virtual queue, token bucket...) > and the traffic's variance as well as its rate (eg marking may > well continue after a recent overload even after the instantaneous > rate has dropped)." > > [Michael]: virtual queue and token bucket are absolutely > equivalent paradigms on which metering and marking may be based. > see also: > http://www.ietf.org/internet-drafts/draft-charny-pcn-comparison-00.txt > Just omit the example! Deleted. [by TB you mean upside down VQ; by TB I also imply no memory, cf VQ with marking threshold =0] > > ===================== > > (Hence, by analogy with ECN we call our mechanism Pre-Congestion > Notification.) > > [Michael] This should come earlier in the document. E.g. in the > terminology section. > ok > ===================== > > 5.5 > > o PCN-meter at PCN-egress-node - make "measurements of PCN-traffic" > from a particular PCN-ingress-node. > > [Michael] Could you add "(if required)" to that point? 3sm > http://www.ietf.org/internet-drafts/draft-babiarz-pcn-3sm-01.txt > does not need metering or measurement of marked packets for flow > termination. > > ===================== > > > o Make decision about flow termination - use the "measurements of > PCN-traffic" to decide which PCN-flow or PCN-flows to terminate. > The decision takes account of policy and application layer > requirements. > > [Michael] Similar issue: could you add "possibly" somewhere? > think I've covered these points when dealing with joe's comments. > ===================== > > 5.7 > > o NB the order of increasing severity is: unmarked; PCN-marking with > first encoding (ie associated with the PCN-lower-rate); PCN- > marking with second encoding (ie associated with the PCN-upper- > rate) > > [Michael] What does "NB" stand for? Changed to 'Note' [nb = nota bene] > > The downsides of probing for this viewpoint are: > > o Probing adds delay to the admission control process. > > o Sufficient probing traffic has to be generated to test the pre- > congestion level of the ECMP path. But there's the risk that the > probing traffic itself may cause pre-congestion, causing other > PCN-flows to be blocked or even terminated. > > [Michael] Could you please add "possibly" to these points? "risk ... may" is equivalent to "possibly" > > ===================== > > Viewpoint 3 or probably extra viewpoint: > > [Michael] Probing might be used because it is easier than > measuring and signalling aggregate packet markings. This is the > case when a signalling protocol already exists, e.g., to find out > the correct ingress-egress-aggregate of a flow. Then, this > signalling protocol might be reused for probing purposes saving > complex operations in the egress node and signalling. An example > is given in 2.4 of > http://www.ietf.org/internet-drafts/draft-babiarz-pcn-3sm-01.txt added > Also 4.3 of > http://tools.ietf.org/wg/pcn/draft-briscoe-pcn-boundary-behav-00.txt > suggests to use a protocol to find out the right egress node such > that probing would in fact lead to simplifications. > > ===================== > > 8.1.2 Parameters > > [Michael] A citation to our work on parameter settings would be > appropriate. > > [PCN-Config] M. Menth, and M. Hartmann: "PCN-Based Resilient > Network Admission Control: The Impact of a Single Bit", > <http://www3.informatik.uni-wuerzburg.de/staff/menth/Publications/Menth0 7- > PCN-Config.pdf>", > 2007. added _______________________________________________ PCN mailing list PCN@ietf.org http://www.ietf.org/mailman/listinfo/pcn
- [PCN] Comments on draft-ietf-pcn-architecture-02.… Michael Menth
- Re: [PCN] Comments on draft-ietf-pcn-architecture… philip.eardley