How is the architecture in Exchange 2013 different to 2010? Let’s find out.
As always, a picture is worth a thousand words. The below slide from the TechEd presentation by Scott Schnoll gives a clear picture of how the architecture in 2013 is different from 2010.
In 2013, CAS is a stateless server and is used for authentication, proxying and redirection. The developer APIs, business logic & protocols in CAS 2010 has been moved to the 2013 Mailbox Role. Because of the stateless architecture of CAS 2013, only a layer 4 load balancer is required for CAS load balancing. Easier and cheaper deployment!
All the functionality in 2010 is still there in 2013, but it is split differently across the two roles. Hope this helps