If you're administering a XenApp infrastructure for a while, someone has probably already asked you to give access to published applications for users who are not connected to your local LAN. The external access could be for teleworkers, branch offices, or outsourcers that even work in a different continent.
Differences between LAN and WAN links
Specific optimizations available in XenApp for WAN links
How to test your farm's behavior over WAN links before going to production
How to monitor network connections
Solutions that Citrix offers to optimize and accelerate WAN connections