Open Source VoIP Traffic Monitoring

Luca Deri ntop.org Email: deri@ntop.org http://luca.ntop.org/ Abstract These days voice over IP (VoIP) is quite popular as it is a cost effective ay to reduce telephony costs using the Internet. Although many projects are focusing on developing tools and solutions for building the voice infrastructure, there is very little available in terms of tools and metrics for measuring the impact of VoIP on a network. This paper describes the design and implementation of open source tools for detecting and measuring VoIP traffic based on both standard and proprietary protocols. Keywords Voice Over IP, passive packet capture, network traffic measurement, NetFlow.

1. Introduction

VoIP is a solid technology available since some years that allows people to communicate via voice using the IP protocol instead of telephone lines. Unfortunately this technology has been relegated in a niche market due to several factors such as proprietary standards, high price tag, limited integration with existing telephony environments. However in the last couple of years the situation changed dramatically since some open source tools such as asterisk [asterisk] as well as low-cost VoIP telephone adapters and services become available. In fact, today it is quite common for internet providers to provide their customers VoIP calls at very low cost, if any, in addition to standard xDSL connectivity. Standard VoIP protocol such as SIP [sip] and H.323 [h323] are very popular in the carrier environment and in many other fields not limited to VoIP, such as messenger and chat. In addition to these standards-based applications, there are other applications such as Skype [skype] or voipstunt [voipstunt] that instead are based on proprietary communication protocols and codecs, and other hybrid applications partially based on open standards such as google talk [googletalk] and gizmo [gizmo]. The result is that VoIP is becoming in some ways similar to P2P (peer to peer), as: • new applications appear, grow and disappear very often. • some VoIP applications (e.g. Skype) are using P2P as communication transport for building the communication infrastructure and crossing firewalls, a typical scenario where many standard-based VoIP application fail to operate. In a nutshell, VoIP solutions are often used at corporate level as a cost effective solution to telephone communications, whereas proprietary VoIP applications are used for letting people talk either computer-to-computer or computer-to-telephone using a PC equipped with a special application and a headset.