Packet based telephony

This paper describes methods used to place telephone calls over packet-based networks with emphasis on Internet point-to-point communication. Two approaches will be described-H.323 and SIP (session initiation protocol). The first is an ITU standard and is already widely deployed by commercial vendors. The second, SIP, was developed by IETF activists and represents an "Internet approach" to telephony. First, a brief overview of reasons for the growing importance of IP telephony is given. It is followed by a short introduction to voice transmission over packet networks and an overview of the existing standards. In the second part of the paper, short examples of H.323 and SIP call setup are given.