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update details on attenuation buckets 

fixes #135
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Thomas Klingbeil 2020-05-21 14:35:49 +02:00
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solution_architecture.md
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@ -107,6 +107,7 @@ The Corona-Warn-App Server needs to fulfill the following tasks:
- Verify association with a positive test through the Verification Server and the associated workflow (explained in the chapter “Retrieval of lab results and verification process”, shown in the center of the left side of *Figure 6*).
- Accept uploaded diagnosis keys and store them (optional) together with the corresponding transmission risk level parameter (integer value of 1-8) into the database. Note that the transport of metadata (e.g. IP) of the incoming connections for the upload of diagnosis keys is removed in a dedicated actor, labelled “Transport Metadata Removal” in *Figure 6*.
- Provide [configuration parameters](#data-format) to the mobile applications
- Threshold values for [attenuation buckets](#attenuation-buckets)
- Risk scores for defined values
- Threshold values for risk categories and alerts
- On a regular schedule (e.g. hourly)
@ -140,6 +141,7 @@ The server will make the following information available through a RESTful inter
- the newly added Diagnosis Keys (Temporary Exposure Keys) for the time frame
- configuration parameters
- 32 parameters for configuring the risk score of the Apple/Google Exposure Notification Framework
- [Attenuation bucket](#attenuation-buckets) thresholds
- Risk score threshold to issue a warning
- Risk score ranges for individual risk levels
@ -179,12 +181,21 @@ The encapsulation especially applies to the part where matches are calculated, a
[Information provided from the framework API to the app per exposure](https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ExposureNotification-FrameworkDocumentationv1.2.pdf):
- **Attenuation value** (Reported Transmit Power - Measured RSSI)
- **Attenuation “buckets”**, i.e. time spent with an attenuation <=50 and >50
- **Attenuation “buckets”**, i.e. times spent within certain attenuation ranges (see below)
- **Date** when the exposure occurred (with reduced precision, i.e. one day)
- **Duration** of the exposure (<5/5/10/15/20/25/30/>30 minutes)
- **Transmission risk level** associated with diagnosis key of other person (downloaded from server, together with diagnosis key)
- **Total Risk Score** calculated exposure risk level according to the defined parameters
- **Total Risk Score** calculated exposure risk level (with a range from 0-4096) according to the defined parameters
### Attenuation Buckets
Both, Apple and Google allow to define a low and a high threshold for the attenuation, forming three individual buckets:
- attenuation < low threshold
- low threshold <= attenuation < high threshold
- high threshold <= attenuation
While in the Google implementations of the Exposure Notification framework, those buckets are contained within the `ExposureSummary` (`attenuationDurations`), Apple has added them to the [`metadata`](https://developer.apple.com/documentation/exposurenotification/enexposureinfo/3586326-metadataenexposureinfo) attribute of the [`ENExposureInfo`](https://developer.apple.com/documentation/exposurenotification/enexposureinfo).
In the latter implementation, the [`attenuationDurations`](https://developer.apple.com/documentation/exposurenotification/enexposureinfo/3586325-attenuationdurations) of the `ENExposureInfo` contains two buckets around a fixed threshold of 50.
### Risk score calculation