1.) OpenSTA is at my company site
2.) Application is at Live Environment at client site.
Note : That is client and Server are at different Domain
I highly recommend you contact the OpenSTA portal and post your specific question. Submit your question here OpenSTA portal,
Also check their FAQ portion of the site FAQ for OpenSTA users
However, to answer your question generally and not speaking for OpenSTA as Ihave no idea if it'll do this or not, I'd say any performance testing tool should be able to function across the Internet. However, when you carry out performance testing this way, you'll hardly have useable results. Network latency is variable, not to mention the fact that you'll have NAT happening internally to your network and possibly at the client. Even if the client's site isn't NAT'ed, it will have a firewall which, in fact, might categorize traffic from your source as a DOS attempt and might shut you down. All of that address translation, packet inspection, and network latency means you'll never get the same results twice, and your test will be skewed. The only truly effective approach is to take your site into a lab and test it there—independent of other influences.
This was first published in July 2009