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bandwidth-file-spec: add MaxAdvertisedBandwidth

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Add MaxAdvertisedBandwidth section in the bw KeyValue and explain
why measured bandwidths need to be limited to it and how current
implementations do it.
Co-authored-by: teor <teor2345@gmail.com>
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juga0 2018-06-25 07:26:45 +00:00
parent 4df184021b
commit 1aab99d170
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bandwidth-file-spec.txt
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@ -253,14 +253,17 @@ In version 1.1.0, the KeyValue can be in any arbitrary order.
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.
@ -270,6 +273,36 @@ In version 1.1.0, the KeyValue can be in any arbitrary order.
Appendix B for information about scaling, and one possible scaling
method.
MaxAdvertisedBandwidth:
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.
KeyValue
[Zero or more times.]