Definition of $request_time

Hi,

Can you someone please clarify the time that is being measured as part of $request_time?

Documentation states the following:
request processing time in seconds with a milliseconds resolution; time elapsed between the first bytes were read from the client and the log write after the last bytes were sent to the client

Does this imply that it is the full round trip time which also includes network time?
Depending on speed of client/server network or network issues, could this affect the request_time?

Thanks