We describe a method for monitoring Voice over IP (VolP) applications based upon a reduction of the ITU-T's E-Model to transport level, measurable quantities. In the process, 1) we identify the relevant transport level quantities, 2) we discuss the tradeoffs between placing the monitors within the VolP gateways versus placement of the monitors within the transport path, and 3) we identify several areas where further work and consensus within the industry are required. We discover that the relevant transport level quantities are the delay, network packet loss and the decoder's de-jitter buffer packet loss. We find that an in-path monitor requires the definition of a reference de-jitter buffer implementation to estimate voice quality based upon observed transport measurements. Finally, we suggest that more studies are required, which evaluate the quality of various VolP codecs in the presence of representative packet loss patterns. There is great interest in supporting voice applications over both the public Internet and private intra-nets, i.e., Voice over IP (VoIP). Several popular Internet implementations are the Video Audio Tool (VAT) [1] and the Robust Audio Tool (RAT) [2] , as well as a host of ITU-T H.323 implementations. An important aspect of VoIP is developing a performance monitoring capability to track the quality of the voice transport. In this paper, we discuss one approach to monitoring the performance of conversational voice applications over Internet transport. Specifically, we investigate the use of the 1TU-T's E-Model[3] as a tool to relate several transport level metrics to an estimate of conversational voice quality. To accomplish this, we analyze the reduction of the existing E-Model in terms of transport-level metrics for the purpose of monitoring conversational voice quality. In the process, we discuss the advantages and shortcomings of our approach and identify a set of issues which we believe need to be addressed within the open literature. The ITU-T's E-Model is a network planning tool used in the design of hybrid circuit-switched and packet-switched networks for carrying high quality voice applications. The tool estimates the relative impairments to voice quality when comparing different network equipment and network designs. The tool provides a means to estimate the subjective Mean Opinion Score (MOS) rating of voice quality over these planned network environments. We describe the E-Model in more detail in Section 3 below. The specific method we advocate is to: Measure the low-level transport metrics (characterizing the channel), which impact voice performance, i.e., delay, delay variation and packet IOSS~ Combine the packet loss and delay variation measurements, de-jitter buffer operations, packet size and coder frame size into an error mask (the exact sequence of good and bad coder frames) that can be characterized in a simple manner (e.g., average frame loss rate along with some measure of burstiness), Combine the characterized error mask with the coder and its frameqoss concealment algorithm via a look-up table (or curve fit) based on ACM SIGCOMM 9 Computer Communication Review
It can be translated to Mean Opinion Score (MOS), which ranges from 0 (bad) to 5 (good) using a simple expression REF .
Voice over IP performance monitoring
CCRV
Computer Science