Requested revision
Standard: | IEEE 802.1Q-2018 | Clause: | 8.6.5.1.3 |
Clause title: | Flow meter instance table |
Rationale for revision
Color-aware operation of MEF 10.3 flow meters in clause 8.6.5.1.3 is effectively unsupported, the Color mode parameter is unused. The Color mode (CM) parameter originates from MEF 10.3. In MEF 10.3, the operation of a flow meter (Bandwidth Profile) differs dependent the CM value, and more important, on the color assigned to a frame _before_ it is processed by the flow meter. The following expression is evaluated in a branch decision of the underlying algorithm [MEF 10.3, Fig. 28]: 1: [ 2: (CM == color-blind) OR 3: (Service Frame Color == Green) OR 4: (no Service Frame Color) 5: ] 6: AND <...unrelated sub-expr. ...> "Service Frame Color" is the color of the frame _before_ it is processed by a flow meter. In IEEE Std 802.1Q-2018, there is no color assigned to frames _before_ they are processed by flow meters. Thus, the sub-expression in line 4 is constant TRUE, and so the entire expression in lines 1 through 5 is constant TRUE, regardless whether parameter CM (line 2 above) is set color-blind or color-aware. In other words, parameter CM in IEEE Std 802.1Q-2018 is "dead".
Proposed text
Two options for discussion: Opt. 1) -- Remove the color-aware mode and parameter CM -- * Delete all occurrences of the CM parameter in clauses 8 and 12. * Change the text "The parameters for each flow meter instance are as specified in Bandwidth Profile Parameters and Algorithm in MEF 10.3," in clause 8.6.5.1.3 to "The parameters for each flow meter instance are as specified in Bandwidth Profile Parameters and Algorithm in MEF 10.3 in color-blind mode," * Add a table note to Table 17-30 at parameter ieee8021PSFPFlowMeterCM: "Parameter ieee8021PSFPFlowMeterCM is retained for compatibility with IEEE Std 802.1Q-2018 of the MIB. Flow meters, as specified in 8.6.5.1.3, always operate in color-blind mode." * Delete contents of the Reference column of table 17-30 in the row of parameter ieee8021PSFPFlowMeterCM. * Change The REFERENCE string of MIB parameter ieee8021PSFPFlowMeterCM in clause 17.7.24 to "17.2.24" Opt. 2) -- Repair the color-aware mode -- * Add the following text after item j) of clause 8.6.5.1.3: "The color of a frame for subsequent processing by a flow meter is determined by the frame's drop_eligible parameter (6.9.1): k) If the drop_eligibile parameter is FALSE, the color is green. l) If the drop_eligibile parameter is TRUE, the color is yellow."
Impact on existing networks
The impact on the conformance of existing implementations with support
for flow meters according to clause 8.6.5.1.3 depends on the chosen
option:
Opt. 1) Likely none, although it cannot be ruled out that some existing
implementations realized an initial color assignment beyond what is
specified in IEEE Std 802.1Q-2018 (see also the note below).
Such implementations remain conformant to a future revision of
IEEE Std 802.1Q, if they internally (SW) override parameter CM to
color-blind.
Opt. 2) Existing implementations with support for PSFP may not support
color-aware mode, if these implementations where optimized (HW)
according to the description provided in the RATIONALE section above.
Repairing support for the color-aware mode renders such implementations
non-conformant to a future revision of IEEE Std 802.1Q.
Note that I've searched through IEEE Std 802.1Q-2018 for "MEF 10.3",
"yellow", "color-aware", "color-blind". These terms only appear in the
context of flow meters. Thus:
a) Regardless which algorithm is used for color assignment before flow
meters in existing implementations, it is beyond spec.
b) The proposed changes for both options are limited to the scope of flow
meters accordingly.
Originator
Name: | Johannes Specht | Email: | johannes.specht.standards@gmail.com |
Affiliation: | University of Duisburg-Essen, General Motors | ||
Submitted: | 2019-10-31 |