Comprehensive in-service measurement of QoS

Wide area networks have provided predominantly leased or switched, non-virtual circuit services. The traditional circuit services effectively provide the equivalent of a direct wire through the wide area network from one customer premise to another. If a service customer suspects that the service is faulty, the service provider may test using in-service methods which use management overhead information multiplexed in the circuit framing or out-of-service methods which use bit error rate techniques. Tests for traditional circuit services can conclusively establish that the contracted service is provided at a given time. The virtual circuit model of service has been widely provisioned only in the last few years, beginning with frame relay and evolving towards asynchronous transfer mode (ATM). Virtual circuits are multiplexed onto the traditional circuits at the point of customer access. Virtual circuits allow a customer to transmit information into and across the service provider's WAN at a rate less than the maximum provided at the point of access. Additional virtual circuits may be provided on the same access line. These additional virtual circuits may be terminated at other geographic locations. Thus a customer may reach many endpoints over a single access circuit. Each virtual circuit leads an independent existence, providing a unique service and experiencing its own set of problems.