Fiddler Time Taken for a Request v.s IIS Log Time Taken

[oyao 16]

Hi,

Need some help on the time taken in Fiddler compare to time taken that logged in IIS Logging. Below shown the statistics captured in Fiddler (it took 2.566 for the request):

And below is the IIS log time-taken:

As shown the time taken in fiddler has difference with the one in IIS log; as my understanding IIS log time-taken already include network time (starting with version 6 and above). May I know why there is the differences between fiddler and iis log time taken. 

Thank you so much

[EricLaw]

IIS cannot possibly know how how long the request took on the network before it received it. 

IIS could conceivably know when it received the last ACK for the last byte of its response, but even that is going to be slightly misleading (because the ACK still has to travel from the client to the server).

[oyao 16]

is that means the time differences between fiddler and iis could due to the network time?