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, as well as view the presence of remote, federated, and public IM users. They can also add remote users, federated users, and public IM users to their Contact Lists.
  
  
• Web conferencing. Meeting organizers can invite remote users, federated users, and anonymous users to Web 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 Communications Server deployment.
  
  

Essentially, remote users have the same capabilities as internal users:

• 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 contact list, and they can view those users’ presence status, even while they are signed in remotely.
  
  
• Web conferencing. Users can participate in Web 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.
  
  

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 Communications Server users in your organization and access presence information, but they cannot participate in Communications Server-based multi-party 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 Communications Server users in your organization and access presence information, as well as participate in Web conferences and A/V conferences (if they are supported by your Communications Server deployment). Federated users have access to the full feature set, except for the Communications Server 2010 Address Book.
  
  

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 Communications Server users in your organization and access presence information, but they cannot participate in Communications Server-based IM multi-party conferences, it is strictly peer-to-peer conferencing.
  
  
• IM and presence, Web conferencing, and A/V conferencing. In addition to peer-to-peer IM conferencing and viewing presence, Public IM users can participate in A/V conferencing with Windows Live Messenger users.
  
  

Some conferencing 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 conferencing is 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.