NEC Europe Ltd. NEC Europe Ltd. Goettingen University The deployment of Voice-over-IP (VoIP) telephony is increasing fast. VoIP's paradigm and the features it offers differ significantly from that of regular telephony, and, as a result, its monitoring requirements do so as well. This draft employs use cases to derive these requirements and introduces SIPFIX, an extension to IPFIX (IP Flow Information eXchange), that meets them.