External users access Lync Web App through the Lync Web Services. Lync Web Services are published for several critical Lync client services including Meeting Join, Dial-in Conferencing information page, Address Book Service, Collaboration Services, and Lync Web App. Lync Web Services, and as a result, Lync Web App, must be securely published through a reverse-proxy solution to provide access to external users. For information on deploying Lync Web Services through a reverse proxy, see Chapter 12, “Firewall and Security Requirements.”