Path
Reachability is only the first question. Where traffic travels can matter as much as whether it arrives.
NETWORK / OBSERVATION
The path is part
of the system.
A network is not simply a connection between two addresses. It is a changing path with latency, loss, routing decisions and failure modes of its own.
Latency
Useful latency measurements separate connection setup, processing time and transport behaviour.
Loss
Small changes in packet loss can produce large changes in application behaviour.
Change
Routes change. Providers change. A dependable system should make those changes observable.