CDR
CNG (Confort Noise Generation)
Codec
Congestion

Call Detail Record (CDR)
Call Detail Record Computer record containing data unique to a specific call. (This information is processed as a unit and contains such details as originating switch, terminating switch, call length and time of day.)

Confort Noise Generation (CNG)
If the VAD ( Voice Activity Detection ) algorithm is actived and there is no voice signal in the communication no packet is sent, so the other user can consider that like a false disconnection or problem. Confort Noise Generation (CNG) is an algorithm to send a low noise packet and let the other user know that the communication is still active.

Codec
Compression-decompression. A technique used to compress/decompress speech or audio signals. The most popular ones in VoIP are G.711, G.721 and G.729.

Congestion
The situation in which the traffic present on the network exceeds available network bandwidth/capacity.