Call Detail Records (CDR) specifications

Question

My question is about CDR (Call detail Records). I want to know more about that. I searched a lot (in Google and other sites) but unfortunately there is few reference and i couldn't find answere of my questions in none of them (Please share any reference you know and think will be useful)

I want to know...
1. Where is CDR element in network structures? i mean for example in LTE, it is connected to which elements? (S-GW, MME, HSS, PCRF.etc) (As i read about that, CDR is "mediation" but where is it in practical networks?..where should be?)
2. as i searched, i couldn't find any big company (Vendor) specific hardware which made for CDR..is there any specific hardware which most mobile network operators use?
3. is there any standard specification (not official but used by most) about CDR? (like interfaces, protocols, file formats, etc)

Thanks a lot

Answer 1

A CDR, Call or Charging Data Record, is actually just a record of the call's details - i.e. the name is literally correct.

You can think of it as a data structure or a group of data including the called number, calling number, duration, time of call, network nodes used etc.

It is used to feed billing systems, analytics, and simply to record details on calls, which can help with diagnosing problems for example.

It is not a node or a physical element itself, and once the CDRs are collected, for example on a Switch, they can be transferred and stored elsewhere.

All the big switching vendors, Nokia, Ericsson, Huawei etc will 'make' or generate the CDR's on their switches, as it is a basic requirement that operators demand.

The 3GPP origination defines the specification for CDR's - this covers areas like the structure of the CDR, the info the CDR contains and how CDRs are transferred between network elements. You can find the spec here:

• https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1912

Answer 2

CDR is an "old" word that comes from old fixed networks where the only service was voice and Call Data Records were generated by the switch. By extension, today, CDR means any information generated by a network equipment. It can still be voice, or mobile data, or wifi, or SMS, etc Some times they are called also UDR, "U" for Usage Data Record.

The MSC generated CDR about : incoming calls, outgoing calls, transit calls, SMS traffic. Basically it says that number A has called the number B during S seconds, that the location of A is a given Cell ID and LAC, that the call has used some trunc, and so on. The is no information about the price, for example. The same for the "CDR" from SGSN or GGSN or MME where the usually provided information is location, type of (data) protocol used (TCP, UDP, ARP, HTTP, SMTP, ...), volume, etc. SMSC, USSD, and others also produce this kind of CDR. I use to call those CDRs "Traffic CDRs" as they describe the traffic information.

There are complementary to the "Charging CDRs" where the price information is produce. For example, for a voice call, the IN platform (sometimes called the OCS; Online Charging System) will generate CDRs with A number, B number, Call duration (which usually is different from the duration seen on the MSC), the accounts that had been used to pay the call, etc. Same hold for data, sms and all services charging. Those CDRs may also be used for offline billing.

I'm not aware of any standard. They are maybe specifications about what CDR produced by a given (standard) platform needs to produce but my (quite long) experience in the field says you should not rely on this but on the spec defined by the equipment vendor and your own test procedure.

This is where the mediation comes into the game. It's an IT system that is able to

1. get (or receive) unprocessed CDR files from all the network equipment
2. identify and filter out some unnecessary fields
3. sometimes aggregate some traffic CDRs in to one CDR
4. sometimes deduplicate some CDRs, or make sure that there is only one CDR per network event
5. eventually produce output files that will be used by other systems like billing or data warehouse