The Cisco IOS IP Service Level Agreement (IOS IP SLA, previously known as Cisco Service Assurance Agent) is part of the Cisco IOS router operating system, version 12.0 (5)T and later, and allows users to gather network performance metrics for troubleshooting purposes. As long as two Cisco routers are present in the path between the Target Devices, IOS IP SLA can measure one-way delay, packet loss, jitter, and other performance data between the routers. You may have to do some extra configuration to allow IOS IP SLA measurements. For more information, see Section 3.4, Tips for a Successful Diagnosis.
Network performance measurements are a vital part of any Diagnosis of a VoIP problem. Like Vivinet Diagnostics, IOS IP SLA sends out packets with sequencing information and timestamps to measure packet loss and one-way delay between routers. Vivinet Diagnostics normally uses Performance Endpoints to generate test VoIP traffic and measure call quality statistics. However, if no endpoints are installed near where a VoIP problem is occurring, Vivinet Diagnostics can gather performance measurements from IOS IP SLA by using SNMP.