The UK College of Policing recommends that conclusions based on GPRS / mobile data events use a phrase similar to: ‘the subject device used cell ID 12345 AT OR BEFORE the start time of the CDR’, or specifically for O2 data this would be ‘the subject device used cell ID 12345 AT OR BEFORE the end time of the CDR”. However, the National RF user group suggest that while you should follow the College of Policing guidance there are occasions when the user can be a little more specific, especially when you are able to identify the start of a new session within the relevant CDR.
Did you know that to start a new session the device used must contact the network to request a new session, therefore capturing a specific cell and consequently an accurate location?
There are methods to identify the start of a new session in CDR records:
- For Vodafone and O2 there will be a new charging ID (it’s worth noting that all CDRs that belong to the same session will have the same Charging ID)
- Change of technology, for example from 3G to 4G
Did you know that Chorus Analyse can help you to make your decisions on using “At or before” or specifically “at”?
- Users can now identify the Charging ID (added in 5.7.1). Prior to adding your CDRs into Analyse select the Rules Option “Charging ID – Retain in Content / Details” in the Manage Session section.
- Set yourself a layout for GPRS analysis displaying the following columns may be of benefit – Customise Label and “Save”. (See below) Filter to one file at a time and Type of data GPRS – then work through the data to identify any new charging IDs, standalone sessions, change of technology – these could all be inferred to be “at”.
In the next version of Chorus Analyse (5.8 due out in August 2021) we are adding the technology column to the map layout and locations pane. This data can already be found in the events pane which allows you to see when technology has changed.
Work through your data to identify a standalone session – those with no session records immediately before or after them can be trusted as having an accurate cell location at the time shown in the CDR’s Start Time column.
Once further guidance or information is published by the College of Policing Chorus will look to upgrade the software accordingly.
For support or any questions with anything relating to Chorus then please contact our support team.
020 3597 7350
[email protected]
Thanks
The Chorus Team
