The first phones came in pairs, like wired walkie-talkies or fancy tin can telephones. If you took one and gave the other to Charlotte, you’d have a hard time if you wanted to talk with James. Eventually the idea of central exchange came about, stolen from the telegram industry (not the app).

With this fancy new tech you no longer had to manage the wires yourself. You would connect directly to the exchange and phone them whenever you wanted to call someone. An operator would answer, ask for the phone number and dial you through.

They would also note down a record of the call – who’s calling, the time, the duration, etc. – so they could charge you at a later date (none of this was/is free!). And so the idea of a Call Detail Record was born, or CDR.

## Call records today

Nowadays everything is automated, but the concept remains. As more capabilities were added like SMS and data, the ‘Call’ in CDR became a catch-all term for anything that passes through the network.

The specifics depend on the operator, but for Zevvle it goes something like this:

1. ~1 minute after you’ve sent an SMS, hung up the phone or used some data, we get an ‘unrated’ CDR, meaning we don’t yet know what it will cost us . These all go through our billing system and we figure out what to charge you, if anything, for the usage.
2. Every 30 minutes we get a batch of ‘rated’ records with our wholesale prices included. The unrated/rated distinction only affects us, not our customers.

## What’s in them?

You’ll find the usual suspects like the calling number, dialled number, time, duration, charge, etc. In the case of data usage you don’t exactly dial a number, so it’s instead the name of the gateway used to connect to the internet — the Access Point Name, or APN — which for us on EE’s network is called everywhere.

You’ll also find a call type, answering the question “What kind of call record is this?” Is it an SMS, an incoming call, a call while roaming, normal data usage, data via the Blackberry Internet Service (not available with us…), etc.? We have over 80 possibilities, but have only used 27 to date.

In order of popularity, our top call types are for 1) data in the UK, 2) data in Europe, 3) outgoing SMS while in the UK and 4) incoming calls.

2 more things you’ll often find are the Mobile Country Code and Mobile Network Code, or MCC and MNC. These in combination are used to identify any mobile network in the world, and some operators wind up with multiple MNCs. For example, the UK’s MCC is 234 and EE have the range 30-34, but mostly use 30 and 33 which used to be T-Mobile UK and Orange UK respectively. You can find a list of them all here.

## How do I get them?

If you’re a mobile network, call your billing supplier or network operator and see what they can do. Otherwise, without submitting a Subject Access Request, your only option as far as we know is to use a Zevvle SIM. We made our API available last year, giving you access to all your call record data.

Traditionally CDRs are batched in Excel spreadsheet-like files, but with ever-cheaper computing power, making them individually available via an API seemed like an obvious choice.

Have a great weekend! 😊

Co-Founder