database mirroring error - Error: 1479, Severity: 16, State: 2.

we are getting database mirroring timeout issue when ever our transaction file groows larger.for eg. sunday we will do reindexing and the file size will be !10 - 12 GB.
and it's tkaing more time to synchronize the files between the mirroring and principal server.
and also our lan is about 1 GB speed,and it's using max 1 percent only.
If i look into the mirroing history log, is the send rate is higher , the time to send the log is very low.
or else it's higher.i am confused about the bottle neck here.I am thinking the network is the bottle neck.is there a way i can isolate the problem.
any help will be appreciated.
thanks

Check if this could help
DB Mirroring 1479