With your authorization, users who are logged on to your intranet can communicate with external users in the following ways:

• IM and presence   Users can participate in one-on-one IM conversations with public IM users and IM Conferences with remote and federated users. Users can view the presence of remote, federated, and public IM users. They can also add remote users, federated users, and public IM users to their Contacts list.
  
  
• Web conferencing   Meeting organizers can invite remote users, federated users, and anonymous users to conferences as either presenter or attendee. Presenters can share applications or their desktop with federated users, and they can give federated users control.
  
  
• A/V conferencing   Meeting organizers can specify that meeting audio and video for conferences be hosted on your internal Lync Server deployment.
  
  

Remote users have the following capabilities:

• IM and presence   Users can send instant messages and view presence status without using a virtual private network (VPN) to log on to the internal network. They can add users from federated partners and users of supported public IM service providers to their Contacts list, and they can view those users’ presence status, even while they are signed in remotely.
  
  
• Web conferencing   Users can participate in conferences as if they were logged on to the internal network.
  
  
• A/V conferencing   Users can participate in A/V conferences as if they were logged on to the internal network.
  
  

Essentially, remote users have the same capabilities as internal users and in most situations will not notice any difference in performance.

The functionality available to federated users depends on the option you choose during deployment. You can choose either of these options:

• IM and presence only   Users can participate in IM conversations with individual Lync Server users in your organization and access presence information, but they cannot participate in Lync Server-based multiparty conferences, it is strictly peer-to-peer conferencing. You can choose this option whether or not you deploy conferencing support internally.
  
  
• IM and presence, web conferencing, and A/V conferencing   Users can participate in IM conversations with individual Lync Server users in your organization and access presence information. Users can participate in web conferences and A/V conferences (if they are supported by your Lync Server deployment). Federated users have access to the full feature set, except for the Lync Server 2010 Address Book of the federated company.
  
  

The functionality available to federated and public IM users depends on the option you choose during deployment. You can choose either of these options:

• IM and presence only   Users can participate in IM conversations with individual Lync Server users in your organization and access presence information, but they cannot participate in Lync Server-based IM multiparty conferences, it is strictly peer-to-peer communication.
  
  
• IM and presence, web conferencing, and A/V conferencing   In addition to peer-to-peer IM communication and viewing presence, public IM users can participate in A/V sessions with Windows Live Messenger users.
  
  

Some features, including file transfer and application sharing, are not available for public IM users. The availability of features to public IM users depends on their public IM service provider. For example, A/V sessions are available to public IM users only if they are Windows Live users. You can specify whether you want the edge topology to support IM and presence only or IM and presence, web conferencing, and A/V conferencing as part of the deployment process, but you can change this option after deployment.

Anonymous users can participate in IM, web conferences, and audio conferences that are hosted on your internal deployment. Anonymous users require an invitation to access these features.