Sometimes an ISP prevents its users from using the full capacity of its network; this is called rate limiting. Some ISPs trigger rate limiting when your traffic rate crosses a threshold, other ISPs market a ‘burst’ technology, which means that they’re limiting your regular capacity, but give you more for short periods of time, e.g., during large downloads. In either case, your true available capacity is the one in rate-limited state.
AppNeta Performance Manager (APM) is capable of measuring rate-limited capacity, but only on dual-ended paths because a monitoring point is needed at both ends. APM instruments the path with controlled bursts of packets at the total capacity rate in order to trigger the rate limiting mechanism. The source sends packet bursts outbound and the target sends packet bursts inbound. The rate at which the monitoring points receive the packet bursts determines the rate-limited capacity. These bursts, though brief, have more impact on the network than standard monitoring, but they’re needed because the standard bursts aren’t enough to trigger the rate limiting mechanism.
To enable monitoring on rate-limited paths, open a support ticket. Once enabled, the rate limiting capacity chart appears on the path performance page. There are some chart controls in the analysis modules panel; if you disable rate-limited monitoring, only we can re-enable it.