If you want to monitor extremely low-level network traffic (e.g. TCP/IP packet flags, HTTPS alert records, etc), then Fiddler typically cannot help you; you will need to use a packet capture tool like Wireshark or Microsoft’s Network Monitor (old) or Message Analyzer (new).
Yesterday, Microsoft released the newest version of Microsoft Message Analyzer (v1.1), which offers packet capture as well as more exotic capture types (ETW, etc). You can read the announcement and download from here: http://blogs.technet.com/b/messageanalyzer/archive/2014/09/15/announcing-the-message-analyzer-1-1-release.aspx.
Note: If someone else happens to send you a Message Analyzer capture in .cap format, you can extract any HTTP traffic from it into Fiddler by choosing File > Import > Packet Capture.
MVP, Internet Explorer