TCP Retransmit Ratio Is Better Than Counting Retransmits Alone
A few retransmissions during heavy traffic may be normal, while the same count during low traffic can represent a serious quality problem.
TCP
Ping Works but the Browser Does Not: Separating IP, DNS and Applications
Connectivity tests become useful only when each test is tied to a layer: local addressing, routing, DNS resolution, TCP reachability and the application itself.