Re: [tor-bugs] #8494 [Core Tor/Tor]: Document MaxAdvertisedBandwidth in the bandwidth list spec

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#8494: Document MaxAdvertisedBandwidth in the bandwidth list spec
-------------------------------------------------+-------------------------
 Reporter:  alphawolf                            |          Owner:  juga
     Type:  defect                               |         Status:
                                                 |  assigned
 Priority:  Low                                  |      Milestone:  Tor:
                                                 |  0.3.5.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tor-spec, consensus, bandwidth,      |  Actual Points:
  MaxAdvertisedBandwidth tor-relay tor-dirauth   |
  needs-insight tor-bwauth                       |
Parent ID:  #25925                               |         Points:
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------

Comment (by juga):

 Collecting all commented lines and including the examples, we would have:

     Bandwidth generators MUST limit the relays' measured bandwidth based
 on the MaxAdvertisedBadwidth.
     A relay's MaxAdvertisedBandwidth limits the bandwidth-avg in its
 descriptor. bandwidth-avg is the minimum of MaxAdvertisedBandwidth,
 BandwidthRate, RelayBandwidthRate, BandwidthBurst, and
 RelayBandwidthBurst.
     Therefore, generators MUST limit a relay's measured bandwidth to its
 descriptor's bandwidth-avg. This limit needs to be implemented in the
 generator, because generators may scale consensus weights before sending
 them to Tor.
     Generators SHOULD NOT limit measured bandwidths based on descriptors'
 bandwidth-observed, because that penalises new relays.

     sbws limits the relay's measured bandwidth to the bandwidth-avg
 advertised.

     Torflow partitions relays based on their bandwidth. For unmeasured
 relays, Torflow uses the minimum of all descriptor bandwidths, including
 bandwidth-avg (MaxAdvertisedBandwidth) and bandwidth-observed. Then
 Torflow measures the relays in each partition against each other, which
 implicitly limits a relay's measured bandwidth to the bandwidths of
 similar relays.

     Torflow also generates consensus weights based on the ratio between
 the measured bandwidth and the minimum of all descriptor bandwidths (at
 the time of the measurement). So when an operator reduces the
 MaxAdvertisedBandwidth for a relay, Torflow reduces that relay's measured
 bandwidth.

 > What do you think about these subsections?
 >
 > > >     No Zero Bandwidths
 > > >     Bandwidth Aggregation
 > > >     Bandwidth Scaling
 > > >     MaxAdvertisedBandwidth

 Sounds good, just not sure how you have in mind to include them.
 A possibility would be:

   "bw=" Bandwidth

     [Exactly once.]

     The measured bandwidth of this relay.

     No Zero Bandwidths:
     Tor accepts zero bandwidths, but they trigger bugs in older Tor
     implementations. Therefore, implementations SHOULD NOT produce zero
     bandwidths. Instead, they SHOULD use one as their minimum bandwidth.
     If there are zero bandwidths, the parser MAY ignore them.

     Bandwidth Aggregation:
     Multiple measurements can be aggregated using an averaging scheme,
     such as a mean, median, or decaying average.

     Bandwidth Scaling:
     Torflow scales bandwidths to kilobytes per second. Other
     implementations SHOULD use kilobytes per second for their initial
     bandwidth scaling.

     If different implementations or configurations are used in votes for
     the same network, their measurements MAY need further scaling. See
     Appendix B for information about scaling, and one possible scaling
     method.

     MaxAdvertisedBandwidth:
     Bandwidth generators MUST limit the relays' measured bandwidth based
     on the MaxAdvertisedBadwidth. See Appendix C for more information.

 [...]

     C. MaxAdvertisedBandwidth

     [The text above without 1st sentence]

 Does this sounds good?

 > Please open another ticket for changes to other specs.

 i've created #26478

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/8494#comment:19>
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