Abstract
   IP telephony presents some big advantages over traditional circuit-switched telephony especially in the sense of increased utilization of expensive backbones and significantly reduced cost. However, in order to win the competition, IP telephony must provide the same quality of voice service as the traditional telephony, which has been proven as a major challenge. In today’s VoIP market, multiple vendors have developed different IP telephony products based on some well-known IP telephony Standards such as ITU-T H.323 and IETF Session Initiation Protocol (SIP). In Part I of this paper, we present some metrics to help evaluate IP Telephony Performance, discuss a new architecture proposed by Pawan and etc.[1], Distributed Open Signaling Architecture (DOSA), as an enhancement to H.323 and SIP. Then in Part II, we conduct a simulation experiment to demonstrate the backbone-scheduling
requirements for this robust IP telephony architecture.

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IP Telephony Performance Evaluation and Simulation