"The present document contains design requirements applicable to IMS/PES/VoLTE exchange implementations based on Recommendation ITU-T Q.543 [1]. The definitions of IMS/PES/VoLTE design objectives are based on ""best practice"" performance of legacy PSTN/ISDN signalling. The values contained in the present document are ""best practice"" performance values measured on IMS and NGN implementations. The ISDN VGW values are based on carrier grade implementations. The handling of preconditions is out of the scope of the present document."