Fiddler should detect and capture weather the browser has created a new connection to the target host or reusing an existing one. It show the detected connection id on the same row as the request. If browser doesn't send the actual connection id along with the request, it should atleast assign own connection identifier and attach to the request. For e.g. a page has 50 additional resources like javascript, css, etc. First 8 are served using 8 different connection ids. Next 8 are served by using existing connection where previous resource has already completed the download. This will help identify which request was served using which connection and whether it was blocked on connection.