The IOS IP Service-Level Agreement (IP SLA) feature measures the ongoing behavior of the network. The measurement can be as simple as using the equivalent of a ping to determine if an IP address responds, or as sophisticated as measuring the jitter (delay variation) of VoIP packets that flow over a particular path. To use IP SLA, an engineer configures IP SLA operations on various routers, and the routers will then send packets, receive responses, and gather data about whether a response was received, and the specific characteristics of the results, such as delay and jitter measurements.About more about this,you can see this post talked about Cisco WS-C3750X-24T-S ip sla feature:
Ip sla in Cisco 3750X | The Latest News About Cisco 2960, Cisco 3560, Cisco 3750 Switch