IP networks are designed to support non-real time applications, such as file transfer or e-mail. These applications are characterized by their burst traffic and high bandwidth demands at burst times, but they are not very sensitive to delay or delay variation (jitter). On the other hand VoIP requires timely packet delivery with low delay, jitter and packet loss values. We need some sort of Quos mechanisms included into IP networks to bring Voice into it. Because low latency and jitter is the key requirement for supporting high quality interactive conversations, VoIP applications use UDP/RTP to transfer data, thereby subjecting them selves to performance degradations caused by packet loss and network failures.