I recently ran into this issue with a few customers.
Clients running Lync Online were not able to add users from other companies that run Lync on Premise.
I have a user whose status in MS Lync does not change to busy when a meeting/appointment that was scheduled in Outlook occurs.
The normal behavior is when one has a meeting that they create or were invited to in Outlook their Lync station changes to "Busy" once that meeting starts.
Front End servers were required not only to handle the core workloads of Lync, such as IM/presence, application sharing, conferencing, and Enterprise Voice, but also were responsible for publishing users' current presence status for other users (known as publishing and subscribing of presence), subscriptions of contacts, and dynamic updates for conferences.
Each Lync Server Front End server was tightly coupled to the back end and in constant communication with the SQL Server database for presence updates and subscriptions, as well as all business logic.
When they would add the users to their Lync, they would see the user as ‘Presence Unknown’ and all communications to they would bounce back.
The problem is that because Lync Online (Office 365) is a true multitenant environment, they have to be added as a PIC provider like AOL, MSN and Yahoo! One would assume that since this is Microsoft it would just work, but it doesn’t. Please comment or email me with what you would like to see.
So split DNS is recommended (at least for Autodiscover)Autodiscover will never use the internal URL and external URL.
For example, if you don’t want to be disturbed by most people, you can set your status as Do Not Disturb and then grant certain people permission to interrupt you by adding them to your Workgroup.
Top of Page You can specify the number of minutes (of idle activity that elapses) before your presence status changes to Inactive and Away, if you don’t want to use the default settings.
The tight coupling between the Front End server and the back end server as well as potential bottlenecks in areas such as high processor or I/O load led to many customers not leveraging virtualization and relying more on physical hardware for the Lync and SQL Server deployment.
In addition, this architecture also contributed to the hard limit of Lync 2010 Front End servers in a pool to a maximum of 10 servers -- SQL Server is the bottleneck that prevents larger pools from being deployed that could otherwise contain over 100,000 users.
Figure 1 shows a sample Lync Server 2010 Front End server architecture.