RE: [bmwg] WLAN switch controller I-Ds for BMWG to consider
"Tom Alexander" <tom@veriwave.com> Fri, 13 July 2007 01:16 UTC
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From: Tom Alexander <tom@veriwave.com>
To: 'David Newman' <dnewman@networktest.com>, bmwg@ietf.org
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Subject: RE: [bmwg] WLAN switch controller I-Ds for BMWG to consider
Date: Thu, 12 Jul 2007 18:15:49 -0700
Organization: VeriWave, Inc
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Cc: "'Muninder Sambi (msambi)'" <msambi@cisco.com>, 'Jerry Perser' <jperser@veriwave.com>
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David, Thanks for your support, and for your detailed review and feedback. Let me address each of your points in turn. Item 1. Generally agreed. I've found several vendors (no names, please! ;-) playing games with MAC protocol parameters to gain preferential access to the medium. I was trying to avoid the notion of running a functional test on the SUT, but you are quite correct that we need some way of either detecting or, at a minimum, reporting these games. (If anyone on this list can point us at an I-D or RFC to serve as an example, that would be great.) Item 2. Also generally agreed. This is an area that has to be cleaned up. There is a distinction between "open-air testing" (which should be heavily discouraged or outlawed for serious benchmarking efforts) versus "over-the-air testing" (which is done in calibrated anechoic chambers and is therefore both predictable and reproducible). The document fuzzes over the two. This needs to be fixed. Item 3. Thanks for pointing this out - the next revision will make this change. Item 4. I confess that my professorial instinct to say "... and this is left as an exercise for the reader" is showing through. :-) I will clean up all the casual "etc"s in the next revision. Again, I appreciate the review. Best regards, - Tom -----Original Message----- From: David Newman [mailto:dnewman@networktest.com] Sent: Tuesday, July 10, 2007 9:33 PM To: bmwg@ietf.org Cc: 'Muninder Sambi (msambi)'; 'Jerry Perser' Subject: Re: [bmwg] WLAN switch controller I-Ds for BMWG to consider -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 6/8/07 1:49 PM, Tom Alexander wrote: > BMWGers, > > Back at the 67th IETF last November, there was a presentation discussing a > proposal on CAPWAP (WLAN) switch controller benchmarking. The presentation > ended by threatening to solicit some help and submit some drafts. > > The help was solicited, and two drafts have been submitted to the IETF I-D > database: > > draft-alexander-bmwg-wlan-switch-term-00.txt -- terminology > draft-alexander-bmwg-wlan-switch-meth-00.txt -- methodology > > Review and comments on these drafts would be much appreciated. I support the bmwg undertaking these IDs as work items, and congratulate the authors for posting strong draft zeros. There are several areas where I believe more specifics would help: 1. In any environment where contention for the medium exists -- and 802.11 WLANs are a poster child for this -- the device that puts a frame on the medium first wins. This has led to a sort of arms race among vendors for control of the airwaves. The methodology makes no mention of three contention mechanisms that can heavily influence test results. In my experience these mechanisms have been the main factors in differentiating performance from different vendors' systems and thus should be included in any test methodology: The mechanisms are: a. Interframe space type. It is possible and standards-compliant to use SIFS instead of DIFS interframe space) under some circumstances. At a minimum, the type of IFS in use should be declared. Better still would be a test to measure the IFS in use. Early Ethernet switches cheated on IFS to gain an advantage in half-duplex environments. While I am not aware of IFS cheating in WLAN equipment, it is possible and desirable to measure the spaces between frames. b. Coordination function type. Some WLAN access points implement PCF (point coordination function) instead of the more common DCF (distributed coordination function). This can be highly desirable in situations where the flow of traffic is primarily downstream from WTP to end-station. It gives the WTP far more opportunities for access to the medium than end-stations. Again, the CF type in use should be declared at a minimum. More preferable would some externally observed measurement of the CF type. c. Client contention behavior. Most but not all WLAN stations use a exponential backoff algorithm to deal with contention for the medium. Obviously, a end-station or WTP that fudges this a bit will get its frame on the medium first, potentially "winning" every collision battle. (This is a crude example; more sophisticated variations of this might involve winning only some percentage of the time and/or altering the winning percentage in response to RF or other conditions.) It is possible and desirable to measure client contention behavior. I encourage development of tests in this area. 2. In section 3.3.3.1 of the test methodology ID, the description of the open-air test bed is seriously underspecified, which almost certainly will lead to a lack of reproducibility of test results in different labs. Rather than adding specificity, I would rather see open-air testing discouraged altogether in the context of this document. (Note: I have nothing against open-air testing in a *network* context, specific to one operators' network; in a *lab* context, however, there's just too much variability.) 3. Just a wording nit in both documents: s/best efforts/best effort/ 4. Also a wording nit, but again in both documents there are several instances of the term "etc." Specific enumeration would be better. dn -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (Darwin) iD8DBQFGlF2AyPxGVjntI4IRAnWOAKC3u/oHgUenovoMERdpvS88e0u8gwCdEOGY 2VKvbR7qDqCk+lLRovJyFIw= =uzNP -----END PGP SIGNATURE----- _______________________________________________ bmwg mailing list bmwg@ietf.org https://www1.ietf.org/mailman/listinfo/bmwg _______________________________________________ bmwg mailing list bmwg@ietf.org https://www1.ietf.org/mailman/listinfo/bmwg
- [bmwg] Inital COmments on draft-popoviciu-bmwg-ip… Jerry Perser
- [bmwg] WLAN switch controller I-Ds for BMWG to co… Tom Alexander
- Re: [bmwg] WLAN switch controller I-Ds for BMWG t… David Newman
- RE: [bmwg] WLAN switch controller I-Ds for BMWG t… Tom Alexander
- Re: [bmwg] WLAN switch controller I-Ds for BMWG t… David Newman
- [bmwg] WLAN switch controller I-Ds for BMWG to co… Tom Alexander
- Re: [bmwg] WLAN switch controller I-Ds for BMWG t… Curtis Villamizar
- Re: [bmwg] WLAN switch controller I-Ds for BMWG t… Al Morton
- RE: [bmwg] WLAN switch controller I-Ds for BMWG t… Tom Alexander
- RE: [bmwg] WLAN switch controller I-Ds for BMWG t… Romascanu, Dan (Dan)
- Re: [bmwg] WLAN switch controller I-Ds for BMWG t… Curtis Villamizar
- RE: [bmwg] WLAN switch controller I-Ds for BMWG t… Tom Alexander