I have a web application written by asp.net (c#) sql server 2005. we host it on 2 dedicated server ( IIS and SQL server )
From some month ago , in some days of week we have many reports about speed issue.
we have some other application on this server using same database.
when we have speed problem all aplication on these server have this problem, but applications on other server in same data center work correctly.
ram and cpu usage are ok. how can I check that the problem related to internet connection or my application design? which parameters must be checked.
Some other information 
In applications users can upload several files to server , each file up to 3 MB.
we use a sql web admin application, on same server that has same problem, this is a standard application which work perfectly on other servers.
-Ftp connection also is very slow
- in local area network also application is slow too
Thanks