Modeling the Effects of Burst Packet Loss and Recency on Subjective Voice Quality

A. INTRODUCTION Voice over IP networks differ from conventional telephone networks in that voice quality is affected by a wider variety of network impairments and can vary from call to call and even during a call. It is therefore desirable to monitor call quality in order that service providers can properly provision networks and that network resources are properly allocated. Passive monitoring systems examine operating characteristics of a system in order to assess or measure performance level. This may involve examining elements of the system, for example buffer levels, or examining the data stream being transmitted through the system. This contrasts with Active measurement systems in which test data is inserted into the system and used to obtain performance measurements. This paper describes a passive monitoring system (VQmon) for Voice over IP networks that is able to monitor per-call quality, providing feedback to a service management or CDR (Call Detail Record) system. The VQmon monitoring system also considers the effects of time varying impai rments such as bursty packet loss and recency. B. EMBEDDED PASSIVE MONITORING Passive monitoring systems examine operating characteristics of a system in order to assess or measure performance level. This may involve examining elements of the system, for example buffer levels, or examining the data stream being transmitted through the system. This contrasts with Active measurement systems in which test data is inserted into the system and used to obtain performance measurements. Embedded passive monitoring systems employ some form of monitoring function embedded into the equipment that comprises the system under test. This has the advantage of a closer relationship with system elements, allowing access to real time data and control information however has the disadvantage that implementation cost and complexity must be low. This contrasts with external passive monitoring systems which may, for example, be connected to T1 trunks or Ethernet LANs. Within the context of a VoIP network embedded passive monitoring can be integrated into VoIP Gateways, IP Phones or other end-systems, providing access on a per-call basis to CODEC selection, packet loss and delay information. This permits per-call estimates of transmission quality to be made with minimal impact on the service being monitored. Active monitoring systems typically make test calls through the VoIP network, transmit speech files and compare transmitted and received files using PSQM, PESQ or some similar method. This approach allows the CODEC performance to be directly measured however provides only …