We have site to site tunnels across all of our offices and everything is configured properly and is working fine. The problem I am facing is that when users try to access Microsoft Office files such as WORD , EXCEL… there is a latency of about 10-15 seconds before the document will even open and once it opens there is some more latency before I can make any changes to the document. Once the changes are made, and the document is saved, it will be again 15-20 seconds before I can use the document again. The MTU settings on all the firewalls are at 1500. The sysopt connection tcpmss is set to default of 1388.There is no slowness otherwise; email, remote desktop and other functionalities are working just fine.
I wonder if you could shed some light on this issue as I have looked everywhere else, but have not found a reasonable explanation
I'm not in the least surprised at this. One thing that is important to remember, no matter what the deployment scenario is: CIFS sucks. (CIFS = NetBios over TCP = Windows file sharing protocol). It's great on the same LAN, or over really fast WAN links with little or no latency. The moment you add a bit of complexity in there - like 70 - 80 ms of latency, or multiple hops, etc etc - CIFS chokes.
This is just one of the many reasons why Cisco acquired Actona and the WAFS File Caching devices. Like web caches, the WAFS (wide area file system) caches CIFS-based file share data, and they optimize CIFS traffic over WAN links. Check out Cisco's web site for more info on this, and why it does what it does - it will help you understand why you are seeing what you are.