title: Call Detail Records (CDR) specifications
body: <p>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)</p>
  
  <p>I want to know...<br>
  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?)<br>
  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?<br>
  3. is there any standard specification (not official but used by most) about CDR? (like interfaces, protocols, file formats, etc)</p>
  
  <p>Thanks a lot</p>