Cannot call between non-domain users in public network (internet)

Question

We set up a test lync servers. It is only a single server behind a firewall. On the firewall, we did port forwarding to send all the packets destined for a specific public IP to Lyncs private address.
The problem is that we can make calls between lync clients as long as one of them is located in the same subnet as the lync server. If both clients are on internet, the call cannot be setup.
If the clients are connecting remotely to lync; and they are both in the same private network, then that works.
If the clients are connecting remotely to lync; and they are at different locations between different firewalls, that does not work.
If one of the clients are on a mobile phone connecting to the Lync server using the DATA connection; and the other one is connecting from home (no vpn); that does not work.
If one of the clients VPN into the lync server's network and starts the lync client to talk to another client connecting to lync remotely via internet; that works.
Any ideas what might be the problem?
It is a demo Lync environment where we have everything loaded on one single server.
Please advise.

Answer 1

You need to deploy edge components for Microsoft Lync Server 2013 makes it possible for external users who are not logged into your organization’s internal network, including authenticated and anonymous
remote users, federated partners (including XMPP partners), mobile clients and users of public instant messaging (IM) services, to communicate with other users in your organization using Lync Server.
Please check
http://technet.microsoft.com/en-us/library/gg398918.aspx
Lisa Zheng
TechNet Community Support