Here are a number of relevant tools:
Network packet studies, including TCP window scaling and much more
- Microsoft Netmon
- WireShark
- TCPDump
- Microsoft Message Analyzer
Round-trip performance and path tracing
- PSPING on Windows, paping on Linux
- TraceTCP on Windows, tcptraceroute on Linux
- tracert on Windows, traceroute on Linux
Application-level data study
- HTTPWatch
- Fiddler
- Outlook Connection Status