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.. _generator:
How aggregation and scaling works
=================================
.. seealso:: :ref:`scanner` (scanner part).
Every hour, the generator:
#. Aggregate all the measurements (not older than 6 six days) for every relay.
#. Filter the measurements
#. Scale the measurements
#. Write the bandwidth file
Source code: :func:`sbws.lib.v3bwfile.V3BWFile.from_results`
.. _filtering-measurements:
Filtering the bandwidth measurements
-------------------------------------
Each relay bandwidth measurements are selected in the following way:
#. At least two bandwidth measurements (``Result`` s) MUST have been obtained
within an arbitrary number of seconds (currently one day).
If they are not, the relay MUST NOT be included in the Bandwidth File.
#. The measurements than are are older than an arbitrary number of seconds
in the past MUST be discarded.
Currently this number is the same as ``data_period`` (5 days) when not
scaling as Torflow and 28 days when scaling as Torflow.
If the number of relays to include in the Bandwidth File are less than
a percententage (currently 60%) than the number of relays in the consensus,
additional Header Lines MUST be added (see XXX) to the Bandwidth File and the
relays SHOULD NOT be included.
.. image:: ./images/activity_aggr_file.svg
.. image:: ./images/activity_aggr_lines.svg
.. _scaling-the-bandwidth-measurements:
Scaling the bandwidth measurements
------------------------------------
Consensus bandwidth obtained by new implementations MUST be comparable to the
consensus bandwidth, therefore they MUST implement torflow_scaling_.
The bandwidth_file_spec_ appendix B describes torflow scaling and a linear
scaling method.
.. image:: ./images/activity_scaling_as_torflow.svg
.. seealso:: :ref:`torflow_aggr` and :ref:`differences`.
Writing the bandwidth file
---------------------------
The bandwidth file format is defined in the bandwidth_file_spec_.
.. _torflow_scaling: https://gitlab.torproject.org/tpo/network-health/torflow/-/blob/main/NetworkScanners/BwAuthority/README.spec.txt?ref_type=heads#L298
.. _bandwidth_file_spec: https://spec.torproject.org/bandwidth-file-spec/
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