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torspec/bandwidth-file-spec.txt
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Tor Bandwidth File Format
juga
teor
Table of Contents
1. Scope and preliminaries
1.2. Acknowledgements
1.3. Outline
1.4. Format Versions
2. Format details
2.1. Definitions
2.2. Header List format
2.3. Relay Line format
2.4. Implementation details
2.4.1. Writing bandwidth files atomically
2.4.2. Additional KeyValue pair definitions
2.4.2.1. Simple Bandwidth Scanner
2.4.2.2. Torflow
A. Sample data
A.1. Generated by Torflow
A.2. Generated by sbws version 0.1.0
A.3. Generated by sbws version 1.0.3
A.4. Headers generated by sbws version 1.0.4
A.5 Generated by sbws version 1.1.0
B. Scaling bandwidths
B.1. Scaling requirements
B.2. A linear scaling method
B.3. Quota changes
B.4. Torflow aggregation
1. Scope and preliminaries
This document describes the format of Tor's Bandwidth File, version
1.0.0 and later.
It is a new specification for the existing bandwidth file format,
which we call version 1.0.0. It also specifies new format versions
1.1.0 and later, which are backwards compatible with 1.0.0 parsers.
Since Tor version 0.2.4.12-alpha, the directory authorities use
the Bandwidth File file called "V3BandwidthsFile" generated by
Torflow [1]. The details of this format are described in Torflow's
README.spec.txt. We also summarise the format in this specification.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119.
1.2. Acknowledgements
The original bandwidth generator (Torflow) and format was
created by mike. Teor suggested to write this specification while
contributing on pastly's new bandwidth generator implementation.
This specification was revised after feedback from:
Nick Mathewson (nickm)
Iain Learmonth (irl)
1.3. Outline
The Tor directory protocol (dir-spec.txt [3]) sections 3.4.1
and 3.4.2, use the term bandwidth measurements, to refer to what
here is called Bandwidth File.
A Bandwidth File contains information on relays' bandwidth
capacities and is produced by bandwidth generators, previously known
as bandwidth scanners.
1.4. Format Versions
1.0.0 - The legacy Bandwidth File format
1.1.0 - Adds a header containing information about the bandwidth
file. Document the sbws and Torflow relay line keys.
1.2.0 - If there are not enough eligible relays, the bandwidth file
SHOULD contain a header, but no relays. (To match Torflow's
existing behaviour.)
Adds scanner and destination countries to the header.
Adds new KeyValue Lines to the Header List section with
statistics about the number of relays included in the file.
Adds new KeyValues to Relay Bandwidth Lines, with different
bandwidth values (averages and descriptor bandwidths).
1.4.0 - Adds monitoring KeyValues to the header and relay lines.
RelayLines for excluded relays MAY be present in the bandwidth
file for diagnostic reasons. Similarly, if there are not enough
eligible relays, the bandwidth file MAY contain all known relays.
Diagnostic relay lines SHOULD be marked with vote=0, and
Tor SHOULD NOT use their bandwidths in its votes.
Also adds Tor version.
1.5.0 - Removes "recent_measurement_attempt_count" KeyValue.
All Tor versions can consume format version 1.0.0.
All Tor versions can consume format version 1.1.0 and later,
but Tor versions earlier than 0.3.5.1-alpha warn if the header
contains any KeyValue lines after the Timestamp.
Tor versions 0.4.0.3-alpha, 0.3.5.8, 0.3.4.11, and earlier do not
understand "vote=0". Instead, they will vote for the actual bandwidths
that sbws puts in diagnostic relay lines:
* 1 for relays with "unmeasured=1", and
* the relay's measured and scaled bandwidth when "under_min_report=1".
2. Format details
The Bandwidth File MUST contain the following sections:
- Header List (exactly once), which is a partially ordered list of
- Header Lines (one or more times), then
- Relay Lines (zero or more times), in an arbitrary order.
If it does not contain these sections, parsers SHOULD ignore the file.
2.1. Definitions
The following nonterminals are defined in Tor directory protocol
sections 1.2., 2.1.1., 2.1.3.:
bool
Int
SP (space)
NL (newline)
KeywordChar
ArgumentChar
nickname
hexdigest (a '$', followed by 40 hexadecimal characters
([A-Fa-f0-9]))
Nonterminal defined section 2 of version-spec.txt [4]:
version_number
We define the following nonterminals:
Line ::= ArgumentChar* NL
RelayLine ::= KeyValue (SP KeyValue)* NL
HeaderLine ::= KeyValue NL
KeyValue ::= Key "=" Value
Key ::= (KeywordChar | "_")+
Value ::= ArgumentCharValue+
ArgumentCharValue ::= any printing ASCII character except NL and SP.
Terminator ::= "=====" or "===="
Generators SHOULD use a 5-character terminator.
Timestamp ::= Int
Bandwidth ::= Int
MasterKey ::= a base64-encoded Ed25519 public key, with
padding characters omitted.
DateTime ::= "YYYY-MM-DDTHH:MM:SS", as in ISO 8601
CountryCode ::= Two capital ASCII letters ([A-Z]{2}), as defined in
ISO 3166-1 alpha-2 plus "ZZ" to denote unknown country
(eg the destination is in a Content Delivery Network).
CountryCodeList ::= One or more CountryCode(s) separated by a comma
([A-Z]{2}(,[A-Z]{2})*).
Note that key_value and value are defined in Tor directory protocol
with different formats to KeyValue and Value here.
Tor versions earlier than 0.3.5.1-alpha require all lines in the file
to be 510 characters or less. The previous limit was 254 characters in
Tor 0.2.6.2-alpha and earlier. Parsers MAY ignore longer Lines.
Note that directory authorities are only supported on the two most
recent stable Tor versions, so we expect that line limits will be
removed after Tor 0.4.0 is released in 2019.
2.2. Header List format
It consists of a Timestamp line and zero or more HeaderLines.
All the header lines MUST conform to the HeaderLine format, except
the first Timestamp line.
The Timestamp line is not a HeaderLine to keep compatibility with
the legacy Bandwidth File format.
Some header Lines MUST appear in specific positions, as documented
below. All other Lines can appear in any order.
If a parser does not recognize any extra material in a header Line,
the Line MUST be ignored.
If a header Line does not conform to this format, the Line SHOULD be
ignored by parsers.
It consists of:
Timestamp NL
[At start, exactly once.]
The Unix Epoch time in seconds of the most recent generator bandwidth
result.
If the generator implementation has multiple threads or
subprocesses which can fail independently, it SHOULD take the most
recent timestamp from each thread and use the oldest value. This
ensures all the threads continue running.
If there are threads that do not run continuously, they SHOULD be
excluded from the timestamp calculation.
If there are no recent results, the generator MUST NOT generate a new
file.
It does not follow the KeyValue format for backwards compatibility
with version 1.0.0.
"version=" version_number NL
[In second position, zero or one time.]
The specification document format version.
It uses semantic versioning [5].
This Line was added in version 1.1.0 of this specification.
Version 1.0.0 documents do not contain this Line, and the
version_number is considered to be "1.0.0".
"software=" Value NL
[Zero or one time.]
The name of the software that created the document.
This Line was added in version 1.1.0 of this specification.
Version 1.0.0 documents do not contain this Line, and the software
is considered to be "torflow".
"software_version=" Value NL
[Zero or one time.]
The version of the software that created the document.
The version may be a version_number, a git commit, or some other
version scheme.
This Line was added in version 1.1.0 of this specification.
"file_created=" DateTime NL
[Zero or one time.]
The date and time timestamp in ISO 8601 format and UTC time zone
when the file was created.
This Line was added in version 1.1.0 of this specification.
"generator_started=" DateTime NL
[Zero or one time.]
The date and time timestamp in ISO 8601 format and UTC time zone
when the generator started.
This Line was added in version 1.1.0 of this specification.
"earliest_bandwidth=" DateTime NL
[Zero or one time.]
The date and time timestamp in ISO 8601 format and UTC time zone
when the first relay bandwidth was obtained.
This Line was added in version 1.1.0 of this specification.
"latest_bandwidth=" DateTime NL
[Zero or one time.]
The date and time timestamp in ISO 8601 format and UTC time zone
of the most recent generator bandwidth result.
This time MUST be identical to the initial Timestamp line.
This duplicate value is included to make the format easier for people
to read.
This Line was added in version 1.1.0 of this specification.
"number_eligible_relays=" Int NL
[Zero or one time.]
The number of relays that have enough measurements to be
included in the bandwidth file.
This Line was added in version 1.2.0 of this specification.
"minimum_percent_eligible_relays=" Int NL
[Zero or one time.]
The percentage of relays in the consensus that SHOULD be
included in every generated bandwidth file.
If this threshold is not reached, format versions 1.3.0 and earlier
SHOULD NOT contain any relays. (Bandwidth files always include a
header.)
Format versions 1.4.0 and later SHOULD include all the relays for
diagnostic purposes, even if this threshold is not reached. But these
relays SHOULD be marked so that Tor does not vote on them.
See section 1.4 for details.
The minimum percentage is 60% in Torflow, so sbws uses
60% as the default.
This Line was added in version 1.2.0 of this specification.
"number_consensus_relays=" Int NL
[Zero or one time.]
The number of relays in the consensus.
This Line was added in version 1.2.0 of this specification.
"percent_eligible_relays=" Int NL
[Zero or one time.]
The number of eligible relays, as a percentage of the number
of relays in the consensus.
This line SHOULD be equal to:
(number_eligible_relays * 100.0) / number_consensus_relays
to the number of relays in the consensus to include in this file.
This Line was added in version 1.2.0 of this specification.
"minimum_number_eligible_relays=" Int NL
[Zero or one time.]
The minimum number of relays that SHOULD be included in the bandwidth
file. See minimum_percent_eligible_relays for details.
This line SHOULD be equal to:
number_consensus_relays * (minimum_percent_eligible_relays / 100.0)
This Line was added in version 1.2.0 of this specification.
"scanner_country=" CountryCode NL
[Zero or one time.]
The country, as in political geolocation, where the generator is run.
This Line was added in version 1.2.0 of this specification.
"destinations_countries=" CountryCodeList NL
[Zero or one time.]
The country, as in political geolocation, or countries where the
destination Web server(s) are located.
The destination Web Servers serve the data that the generator retrieves
to measure the bandwidth.
This Line was added in version 1.2.0 of this specification.
"recent_consensus_count=" Int NL
[Zero or one time.].
The number of the different consensuses seen in the last data_period
days. (data_period is 5 by default.)
Assuming that Tor clients fetch a consensus every 1-2 hours,
and that the data_period is 5 days, the Value of this Key SHOULD be
between:
data_period * 24 / 2 = 60
data_period * 24 = 120
This Line was added in version 1.4.0 of this specification.
"recent_priority_list_count=" Int NL
[Zero or one time.]
The number of times that a list with a subset of relays prioritized
to be measured has been created in the last data_period days.
(data_period is 5 by default.)
In 2019, with 7000 relays in the network, the Value of this Key SHOULD be
approximately:
data_period * 24 / 1.5 = 80
Being 1.5 the approximate number of hours it takes to measure a
priority list of 7000 * 0.05 (350) relays, when the fraction of relays
in a priority list is the 5% (0.05).
This Line was added in version 1.4.0 of this specification.
"recent_priority_relay_count=" Int NL
[Zero or one time.]
The number of relays that has been in in the list of relays prioritized
to be measured in the last data_period days. (data_period is 5 by
default.)
In 2019, with 7000 relays in the network, the Value of this Key SHOULD be
approximately:
80 * (7000 * 0.05) = 28000
Being 0.05 (5%) the fraction of relays in a priority list and 80
the approximate number of priority lists (see
"recent_priority_list_count").
This Line was added in version 1.4.0 of this specification.
"recent_measurement_attempt_count=" Int NL
[Zero or one time.]
The number of times that any relay has been queued to be measured
in the last data_period days. (data_period is 5 by default.)
In 2019, with 7000 relays in the network, the Value of this Key SHOULD be
approximately the same as "recent_priority_relay_count",
assuming that there is one attempt to measure a relay for each relay that
has been prioritized unless there are system, network or implementation
issues.
This Line was added in version 1.4.0 of this specification and removed
in version 1.5.0.
"recent_measurement_failure_count=" Int NL
[Zero or one time.]
The number of times that the scanner attempted to measure a relay in
the last data_period days (5 by default), but the relay has not been
measured because of system, network or implementation issues.
This Line was added in version 1.4.0 of this specification.
"recent_measurements_excluded_error_count=" Int NL
[Zero or one time.]
The number of relays that have no successful measurements in the last
data_period days (5 by default).
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This Line was added in version 1.4.0 of this specification.
"recent_measurements_excluded_near_count=" Int NL
[Zero or one time.]
The number of relays that have some successful measurements in the last
data_period days (5 by default), but all those measurements were
performed in a period of time that was too short (by default 1 day).
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This Line was added in version 1.4.0 of this specification.
"recent_measurements_excluded_old_count=" Int NL
[Zero or one time.]
The number of relays that have some successful measurements, but all
those measurements are too old (more than 5 days, by default).
Excludes relays that are already counted in
recent_measurements_excluded_near_count.
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This Line was added in version 1.4.0 of this specification.
"recent_measurements_excluded_few_count=" Int NL
[Zero or one time.]
The number of relays that don't have enough recent successful
measurements. (Fewer than 2 measurements in the last 5 days, by
default).
Excludes relays that are already counted in
recent_measurements_excluded_near_count and
recent_measurements_excluded_old_count.
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This Line was added in version 1.4.0 of this specification.
"time_to_report_half_network=" Int NL
[Zero or one time.]
The time in seconds that it would take to report measurements about the
half of the network, given the number of eligible relays and the time
it took in the last days (5 days, by default).
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This Line was added in version 1.4.0 of this specification.
"tor_version=" version_number NL
[Zero or one time.]
The Tor version of the Tor process controlled by the generator.
This Line was added in version 1.4.0 of this specification.
KeyValue NL
[Zero or more times.]
There MUST NOT be multiple KeyValue header Lines with the same key.
If there are, the parser SHOULD choose an arbitrary Line.
If a parser does not recognize a Keyword in a KeyValue Line, it
MUST be ignored.
Future format versions may include additional KeyValue header Lines.
Additional header Lines will be accompanied by a minor version
increment.
Implementations MAY add additional header Lines as needed. This
specification SHOULD be updated to avoid conflicting meanings for
the same header keys.
Parsers MUST NOT rely on the order of these additional Lines.
Additional header Lines MUST NOT use any keywords specified in the
relay measurements format.
If there are, the parser MAY ignore conflicting keywords.
Terminator NL
[Zero or one time.]
The Header List section ends with a Terminator.
In version 1.0.0, Header List ends when the first relay bandwidth
is found conforming to the next section.
Implementations of version 1.1.0 and later SHOULD use a 5-character
terminator.
Tor 0.4.0.1-alpha and later look for a 5-character terminator,
or the first relay bandwidth line. sbws versions 0.1.0 to 1.0.2
used a 4-character terminator, this bug was fixed in 1.0.3.
2.3. Relay Line format
It consists of zero or more RelayLines containing relay ids and
bandwidths. The relays and their KeyValues are in arbitrary order.
There MUST NOT be multiple KeyValue pairs with the same key in the same
RelayLine. If there are, the parser SHOULD choose an arbitrary Value.
There MUST NOT be multiple RelayLines per relay identity (node_id or
master_key_ed25519). If there are, parsers SHOULD issue a warning.
Parers MAY reject the file, choose an arbitrary RelayLine, or ignore
both RelayLines.
If a parser does not recognize any extra material in a RelayLine,
the extra material MUST be ignored.
Each RelayLine includes the following KeyValue pairs:
"node_id=" hexdigest
[Exactly once.]
The fingerprint for the relay's RSA identity key.
Note: In bandwidth files read by Tor versions earlier than
0.3.4.1-alpha, node_id MUST NOT be at the end of the Line.
These authority versions are no longer supported.
Current Tor versions ignore master_key_ed25519, so node_id MUST be
present in each relay Line.
Implementations of version 1.1.0 and later SHOULD include both node_id
and master_key_ed25519. Parsers SHOULD accept Lines that contain at
least one of them.
"master_key_ed25519=" MasterKey
[Zero or one time.]
The relays's master Ed25519 key, base64 encoded,
without trailing "="s, to avoid ambiguity with KeyValue "="
character.
This KeyValue pair SHOULD be present, see the note under node_id.
This KeyValue was added in version 1.1.0 of this specification.
"bw=" Bandwidth
[Exactly once.]
The bandwidth of this relay in kilobytes per second.
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.
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.]
Future format versions may include additional KeyValue pairs on a
RelayLine.
Additional KeyValue pairs will be accompanied by a minor version
increment.
Implementations MAY add additional relay KeyValue pairs as needed.
This specification SHOULD be updated to avoid conflicting meanings
for the same Keywords.
Parsers MUST NOT rely on the order of these additional KeyValue
pairs.
Additional KeyValue pairs MUST NOT use any keywords specified in the
header format.
If there are, the parser MAY ignore conflicting keywords.
2.4. Implementation details
2.4.1. Writing bandwidth files atomically
To avoid inconsistent reads, implementations SHOULD write bandwidth files
atomically. If the file is transferred from another host, it SHOULD be
written to a temporary path, then renamed to the V3BandwidthsFile path.
sbws versions 0.7.0 and later write the bandwidth file to an archival
location, create a temporary symlink to that location, then atomically rename
the symlink
to the configured V3BandwidthsFile path.
Torflow does not write bandwidth files atomically.
2.4.2. Additional KeyValue pair definitions
KeyValue pairs in RelayLines that current implementations generate.
2.4.2.1. Simple Bandwidth Scanner
sbws RelayLines contain these keys:
"node_id=" hexdigest
As above.
"bw=" Bandwidth
As above.
"nick=" nickname
[Exactly once.]
The relay nickname.
Torflow also has a "nick=" KeyValue.
"rtt=" Int
[Zero or one time.]
The Round Trip Time in milliseconds to obtain 1 byte of data.
This KeyValue was added in version 1.1.0 of this specification.
It became optional in version 1.3.0 or 1.4.0 of this specification.
"time=" DateTime
[Exactly once.]
The date and time timestamp in ISO 8601 format and UTC time zone
when the last bandwidth was obtained.
This KeyValue was added in version 1.1.0 of this specification.
The Torflow equivalent is "measured_at=".
"success=" Int
[Zero or one time.]
The number of times that the bandwidth measurements for this relay were
successful.
This KeyValue was added in version 1.1.0 of this specification.
"error_circ=" Int
[Zero or one time.]
The number of times that the bandwidth measurements for this relay
failed because of circuit failures.
This KeyValue was added in version 1.1.0 of this specification.
The Torflow equivalent is "circ_fail=".
"error_stream=" Int
[Zero or one time.]
The number of times that the bandwidth measurements for this relay
failed because of stream failures.
This KeyValue was added in version 1.1.0 of this specification.
"error_destination=" Int
[Zero or one time.]
The number of times that the bandwidth measurements for this relay
failed because the destination Web server was not available.
This KeyValue was added in version 1.4.0 of this specification.
"error_second_relay=" Int
[Zero or one time.]
The number of times that the bandwidth measurements for this relay
failed because sbws could not find a second relay for the test circuit.
This KeyValue was added in version 1.4.0 of this specification.
"error_misc=" Int
[Zero or one time.]
The number of times that the bandwidth measurements for this relay
failed because of other reasons.
This KeyValue was added in version 1.1.0 of this specification.
"bw_mean=" Int
[Zero or one time.]
The measured bandwidth mean for this relay in bytes per second.
This KeyValue was added in version 1.2.0 of this specification.
"bw_median=" Int
[Zero or one time.]
The measured bandwidth median for this relay in bytes per second.
This KeyValue was added in version 1.2.0 of this specification.
"desc_bw_avg=" Int
[Zero or one time.]
The descriptor average bandwidth for this relay in bytes per second.
This KeyValue was added in version 1.2.0 of this specification.
"desc_bw_obs_last=" Int
[Zero or one time.]
The last descriptor observed bandwidth for this relay in bytes per
second.
This KeyValue was added in version 1.2.0 of this specification.
"desc_bw_obs_mean=" Int
[Zero or one time.]
The descriptor observed bandwidth mean for this relay in bytes per
second.
This KeyValue was added in version 1.2.0 of this specification.
"desc_bw_bur=" Int
[Zero or one time.]
The descriptor burst bandwidth for this relay in bytes per
second.
This KeyValue was added in version 1.2.0 of this specification.
"consensus_bandwidth" Int
[Zero or one time.]
The consensus bandwidth for this relay in bytes per second.
This KeyValue was added in version 1.2.0 of this specification.
"consensus_bandwidth_is_unmeasured" Bool
[Zero or one time.]
If the consensus bandwidth for this relay was not obtained from
three or more bandwidth authorities, this KeyValue is True or
False otherwise.
This KeyValue was added in version 1.2.0 of this specification.
"relay_in_recent_consensus_count" Int
[Zero or one time.]
The number of times this relay was found in a consensus in the
last data_period days. (Unless otherwise stated, data_period is
5 by default.)
This KeyValue was added in version 1.4.0 of this specification.
"relay_recent_priority_list_count" Int
[Zero or one time.]
The number of times this relay has been prioritized to be measured
in the last data_period days.
This KeyValue was added in version 1.4.0 of this specification.
"relay_recent_measurement_attempt_count" Int
[Zero or one time.]
The number of times this relay was tried to be measured in the
last data_period days.
This KeyValue was added in version 1.4.0 of this specification.
"relay_recent_measurement_failure_count" Int
[Zero or one time.]
The number of times this relay was tried to be measured in the
last data_period days, but it was not possible to obtain a
measurement.
This KeyValue was added in version 1.4.0 of this specification.
"relay_recent_measurements_excluded_error_count=" Int
[Zero or one time.]
The number of recent relay measurement attempts that failed.
Measurements are recent if they are in the last data_period days
(5 by default).
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This KeyValue was added in version 1.4.0 of this specification.
"relay_recent_measurements_excluded_near_count=" Int
[Zero or one time.]
When all of a relay's recent successful measurements were performed in
a period of time that was too short (by default 1 day), the relay is
excluded. This KeyValue contains the number of recent successful
measurements for the relay that were ignored for this reason.
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This KeyValue was added in version 1.4.0 of this specification.
"relay_recent_measurements_excluded_old_count=" Int
[Zero or one time.]
The number of successful measurements for this relay that are too old
(more than data_period days, 5 by default).
Excludes measurements that are already counted in
relay_recent_measurements_excluded_near_count.
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This KeyValue was added in version 1.4.0 of this specification.
"relay_recent_measurements_excluded_few_count=" Int
[Zero or one time.]
The number of successful measurements for this relay that were ignored
because the relay did not have enough successful measurements (fewer
than 2, by default).
Excludes measurements that are already counted in
relay_recent_measurements_excluded_near_count or
relay_recent_measurements_excluded_old_count.
(See the note in section 1.4, version 1.4.0, about excluded relays.)
This KeyValue was added in version 1.4.0 of this specification.
"under_min_report=" bool
[Zero or one time.]
If the value is 1, there are not enough eligible relays in the
bandwidth file, and Tor bandwidth authorities MAY NOT vote on this
relay. (Current Tor versions do not change their behaviour based on
the "under_min_report" key.)
If the value is 0 or the KeyValue is not present, there are enough
relays in the bandwidth file.
Because Tor versions released before April 2019 (see section 1.4. for
the full list of versions) ignore "vote=0", generator implementations
MUST NOT change the bandwidths for under_min_report relays. Using the
same bw value makes authorities that do not understand "vote=0"
or "under_min_report=1" produce votes that don't change relay weights
too much. It also avoids flapping when the reporting threshold is
reached.
This KeyValue was added in version 1.4.0 of this specification.
"unmeasured=" bool
[Zero or one time.]
If the value is 1, this relay was not successfully measured and
Tor bandwidth authorities MAY NOT vote on this relay.
(Current Tor versions do not change their behaviour based on
the "unmeasured" key.)
If the value is 0 or the KeyValue is not present, this relay
was successfully measured.
Because Tor versions released before April 2019 (see section 1.4. for
the full list of versions) ignore "vote=0", generator implementations
MUST set "bw=1" for unmeasured relays. Using the minimum bw value
makes authorities that do not understand "vote=0" or "unmeasured=1"
produce votes that don't change relay weights too much.
This KeyValue was added in version 1.4.0 of this specification.
"vote=" bool
[Zero or one time.]
If the value is 0, Tor directory authorities SHOULD ignore the relay's
entry in the bandwidth file. They SHOULD vote for the relay the same
way they would vote for a relay that is not present in the file.
This MAY be the case when this relay was not successfully measured but
it is included in the Bandwidth File, to diagnose why they were not
measured.
If the value is 1 or the KeyValue is not present, Tor directory
authorities MUST use the relay's bw value in any votes for that relay.
Implementations MUST also set "bw=1" for unmeasured relays.
But they MUST NOT change the bw for under_min_report relays.
(See the explanations under "unmeasured" and "under_min_report"
for more details.)
This KeyValue was added in version 1.4.0 of this specification.
2.4.2.2. Torflow
Torflow RelayLines include node_id and bw, and other KeyValue pairs [2].
References:
1. https://gitweb.torproject.org/torflow.git
2. https://gitweb.torproject.org/torflow.git/tree/NetworkScanners/BwAuthority/README.spec.txt#n332
The Torflow specification is outdated, and does not match the current
implementation. See section A.1. for the format produced by Torflow.
3. https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt
4. https://gitweb.torproject.org/torspec.git/tree/version-spec.txt
5. https://semver.org/
A. Sample data
The following has not been obtained from any real measurement.
A.1. Generated by Torflow
This an example version 1.0.0 document:
1523911758
node_id=$68A483E05A2ABDCA6DA5A3EF8DB5177638A27F80 bw=760 nick=Test measured_at=1523911725 updated_at=1523911725 pid_error=4.11374090719 pid_error_sum=4.11374090719 pid_bw=57136645 pid_delta=2.12168374577 circ_fail=0.2 scanner=/filepath
node_id=$96C15995F30895689291F455587BD94CA427B6FC bw=189 nick=Test2 measured_at=1523911623 updated_at=1523911623 pid_error=3.96703337994 pid_error_sum=3.96703337994 pid_bw=47422125 pid_delta=2.65469736988 circ_fail=0.0 scanner=/filepath
A.2. Generated by sbws version 0.1.0
1523911758
version=1.1.0
software=sbws
software_version=0.1.0
latest_bandwidth=2018-04-16T20:49:18
file_created=2018-04-16T21:49:18
generator_started=2018-04-16T15:13:25
earliest_bandwidth=2018-04-16T15:13:26
====
bw=380 error_circ=0 error_misc=0 error_stream=1 master_key_ed25519=YaqV4vbvPYKucElk297eVdNArDz9HtIwUoIeo0+cVIpQ nick=Test node_id=$68A483E05A2ABDCA6DA5A3EF8DB5177638A27F80 rtt=380 success=1 time=2018-05-08T16:13:26
bw=189 error_circ=0 error_misc=0 error_stream=0 master_key_ed25519=a6a+dZadrQBtfSbmQkP7j2ardCmLnm5NJ4ZzkvDxbo0I nick=Test2 node_id=$96C15995F30895689291F455587BD94CA427B6FC rtt=378 success=1 time=2018-05-08T16:13:36
A.3. Generated by sbws version 1.0.3
1523911758
version=1.2.0
latest_bandwidth=2018-04-16T20:49:18
file_created=2018-04-16T21:49:18
generator_started=2018-04-16T15:13:25
earliest_bandwidth=2018-04-16T15:13:26
minimum_number_eligible_relays=3862
minimum_percent_eligible_relays=60
number_consensus_relays=6436
number_eligible_relays=6000
percent_eligible_relays=93
software=sbws
software_version=1.0.3
=====
bw=38000 bw_mean=1127824 bw_median=1180062 desc_bw_avg=1073741824 desc_bw_obs_last=17230879 desc_bw_obs_mean=14732306 error_circ=0 error_misc=0 error_stream=1 master_key_ed25519=YaqV4vbvPYKucElk297eVdNArDz9HtIwUoIeo0+cVIpQ nick=Test node_id=$68A483E05A2ABDCA6DA5A3EF8DB5177638A27F80 rtt=380 success=1 time=2018-05-08T16:13:26
bw=1 bw_mean=199162 bw_median=185675 desc_bw_avg=409600 desc_bw_obs_last=836165 desc_bw_obs_mean=858030 error_circ=0 error_misc=0 error_stream=0 master_key_ed25519=a6a+dZadrQBtfSbmQkP7j2ardCmLnm5NJ4ZzkvDxbo0I nick=Test2 node_id=$96C15995F30895689291F455587BD94CA427B6FC rtt=378 success=1 time=2018-05-08T16:13:36
A.3.1. When there are not enough eligible measured relays:
1540496079
version=1.2.0
earliest_bandwidth=2018-10-20T19:35:52
file_created=2018-10-25T19:35:03
generator_started=2018-10-25T11:42:56
latest_bandwidth=2018-10-25T19:34:39
minimum_number_eligible_relays=3862
minimum_percent_eligible_relays=60
number_consensus_relays=6436
number_eligible_relays=2960
percent_eligible_relays=46
software=sbws
software_version=1.0.3
=====
A.4. Headers generated by sbws version 1.0.4
1523911758
version=1.2.0
latest_bandwidth=2018-04-16T20:49:18
destinations_countries=TH,ZZ
file_created=2018-04-16T21:49:18
generator_started=2018-04-16T15:13:25
earliest_bandwidth=2018-04-16T15:13:26
minimum_number_eligible_relays=3862
minimum_percent_eligible_relays=60
number_consensus_relays=6436
number_eligible_relays=6000
percent_eligible_relays=93
scanner_country=SN
software=sbws
software_version=1.0.4
=====
A.5 Generated by sbws version 1.1.0
1523911758
version=1.4.0
latest_bandwidth=2018-04-16T20:49:18
destinations_countries=TH,ZZ
file_created=2018-04-16T21:49:18
generator_started=2018-04-16T15:13:25
earliest_bandwidth=2018-04-16T15:13:26
minimum_number_eligible_relays=3862
minimum_percent_eligible_relays=60
number_consensus_relays=6436
number_eligible_relays=6000
percent_eligible_relays=93
recent_measurement_attempt_count=6243
recent_measurement_failure_count=732
recent_measurements_excluded_error_count=969
recent_measurements_excluded_few_count=3946
recent_measurements_excluded_near_count=90
recent_measurements_excluded_old_count=0
recent_priority_list_count=20
recent_priority_relay_count=6243
scanner_country=SN
software=sbws
software_version=1.1.0
time_to_report_half_network=57273
=====
bw=1 error_circ=1 error_destination=0 error_misc=0 error_second_relay=0 error_stream=0 master_key_ed25519=J3HQ24kOQWac3L1xlFLp7gY91qkb5NuKxjj1BhDi+m8 nick=snap269 node_id=$DC4D609F95A52614D1E69C752168AF1FCAE0B05F relay_recent_measurement_attempt_count=3 relay_recent_measurements_excluded_error_count=1 relay_recent_measurements_excluded_near_count=3 relay_recent_consensus_count=3 relay_recent_priority_list_count=3 success=3 time=2019-03-16T18:20:57 unmeasured=1 vote=0
bw=1 error_circ=0 error_destination=0 error_misc=0 error_second_relay=0 error_stream=2 master_key_ed25519=h6ZB1E1yBFWIMloUm9IWwjgaPXEpL5cUbuoQDgdSDKg nick=relay node_id=$C4544F9E209A9A9B99591D548B3E2822236C0503 relay_recent_measurement_attempt_count=3 relay_recent_measurements_excluded_error_count=2 relay_recent_measurements_excluded_few_count=1 relay_recent_consensus_count=3 relay_recent_priority_list_count=3 success=1 time=2019-03-17T06:50:58 unmeasured=1 vote=0
B. Scaling bandwidths
B.1. Scaling requirements
Tor accepts zero bandwidths, but they trigger bugs in older Tor
implementations. Therefore, scaling methods SHOULD perform the
following checks:
* If the total bandwidth is zero, all relays should be given equal
bandwidths.
* If the scaled bandwidth is zero, it should be rounded up to one.
Initial experiments indicate that scaling may not be needed for
torflow and sbws, because their measured bandwidths are similar
enough already.
B.2. A linear scaling method
If scaling is required, here is a simple linear bandwidth scaling
method, which ensures that all bandwidth votes contain approximately
the same total bandwidth:
1. Calculate the relay quota by dividing the total measured bandwidth
in all votes, by the number of relays with measured bandwidth
votes. In the public tor network, this is approximately 7500 as of
April 2018. The quota should be a consensus parameter, so it can be
adjusted for all generators on the network.
2. Calculate a vote quota by multiplying the relay quota by the number
of relays this bandwidth authority has measured
bandwidths for.
3. Calculate a scaling factor by dividing the vote quota by the
total unscaled measured bandwidth in this bandwidth
authority's upcoming vote.
4. Multiply each unscaled measured bandwidth by the scaling
factor.
Now, the total scaled bandwidth in the upcoming vote is
approximately equal to the quota.
B.3. Quota changes
If all generators are using scaling, the quota can be gradually
reduced or increased as needed. Smaller quotas decrease the size
of uncompressed consensuses, and may decrease the size of
consensus diffs and compressed consensuses. But if the relay
quota is too small, some relays may be over- or under-weighted.
B.4. Torflow aggregation
Torflow implements two methods to compute the bandwidth values from the
(stream) bandwidth measurements: with and without PID control feedback.
The method described here is without PID control (see Torflow
specification, section 2.2).
In the following sections, the relays' measured bandwidth refer to the
ones that this bandwidth authority has measured for the relays that
would be included in the next bandwidth authority's upcoming vote.
1. Calculate the filtered bandwidth for each relay:
- choose the relay's measurements (`bw_j`) that are equal or greater
than the mean of the measurements for this relay
- calculate the mean of those measurements
In pseudocode:
bw_filt_i = mean(max(mean(bw_j), bw_j))
2. Calculate network averages:
- calculate the filtered average by dividing the sum of all the
relays' filtered bandwidth by the number of relays that have been
measured (`n`), ie, calculate the mean average of the relays'
filtered bandwidth.
- calculate the stream average by dividing the sum of all the
relays' measured bandwidth by the number of relays that have been
measured (`n`), ie, calculate the mean average or the relays'
measured bandwidth.
In pseudocode:
bw_avg_filt_ = bw_filt_i / n
bw_avg_strm = bw_i / n
3. Calculate ratios for each relay:
- calculate the filtered ratio by dividing each relay filtered
bandwidth by the filtered average
- calculate the stream ratio by dividing each relay measured
bandwidth by the stream average
In pseudocode:
r_filt_i = bw_filt_i / bw_avg_filt
r_strm_i = bw_i / bw_avg_strm
4. Calculate the final ratio for each relay:
The final ratio is the larger between the filtered bandwidth's and the
stream bandwidth's ratio.
In pseudocode:
r_i = max(r_filt_i, r_strm_i)
5. Calculate the scaled bandwidth for each relay:
The most recent descriptor observed bandwidth (`bw_obs_i`) is
multiplied by the ratio
In pseudocode:
bw_new_i = r_i * bw_obs_i
<<In this way, the resulting network status consensus bandwidth
values are effectively re-weighted proportional to how much faster
the node was as compared to the rest of the network.>>
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