Here's an interesting one:

Reader Question: Hi Ken, Can you explain the difference between CDRs and CMRs? Thanks!

I'm going to start with some very basic basics, and share a resource at the same time. The resource, if you've never used it, is Wikipedia. And awful lot of people put a lot of effort into this user maintained online encyclopedia, and there's a wealth of information in there. So lets start with what they have to say about CDR.

A Call Detail Record (CDR) (also Call Detail Recording) or Station Message Detail Recording (SMDR) in the telecom sector is a file containing information about recent system usage such as the identities of sources (points of origin), the identities of destinations (endpoints), the duration of each call, the amount billed for each call, the total usage time in the billing period, the total free time remaining in the billing period, and the running total charged during the billing period. The format of the CDR varies among telecom providers or programs. Some programs allow CDRs to be configured by the user.

A CDR for a particular account can be downloaded at the request of the subscriber who holds that account. If the telecom provider supplies users with itemized bills, a CDR will show up in each bill, in a format similar to that of an itemized long-distance telephone bill supplied by a conventional telephone company.

In the traditional telecommunications world, Call accounting software or communication management software (CMS) has generally been used to retrieve and process CDR data.

That's a pretty comprehensive definition of a CDR and hopefully explains what it is.

A Call Management Record (CMR) is a database record used to record diagnostic information about the network. This information includes things like a count of the bytes sent, number of packets sent, jitter, latency, dropped packets,  and such. CMRs are also referred to as call diagnostic records, confusing the acronym CDR further. The CMR view is very popular and heavily supported in the Cisco Call Manager VoIP environment, but other VoIP vendors support the same sorts of measures in different degrees.

What this means in the VoIP world is that there is a correlation between CDR and CMR.

A CDR provides information about that call that's generally used for billing purposes. Things about the nature of the call - caller, called party, duration of conversation. CDRs are all about usage and driven by the legacy telecommunications industry practice of billing for minutes of use.

A CMR provides technical information about the technical aspects of the call. These are used in troubleshooting and diagnosing call quality problems. They help quantify the performance characteristics of the network transporting the VoIP service.

If full diagnostics are enabled, there will be a corresponding CMR for every CDR. Looking at the CDRs and corresponding CMR records one can derive voice quality statistics.

In the Cisco VoIP environment, CMR records are normally generated for each call when a call involves an IP phone as an endpoint. If both endpoints are IP Phones then there will be two CMR records generated, one for each phone.  That approach carries through to the other mention I could find of CMR.

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