Microsoft Lync Server 2010, Group Chat relies on AD DS for the pool of internal Lync 2010 Group Chat users. After you install Group Chat, you add domains of users and user groups to the root category scope. You can then add these users and groups to the scope and membership of your categories and chat rooms.

You can also enable federated users to access chat rooms. Because federated users are not defined in AD DS, you must explicitly provision federated users by using Microsoft Lync Server 2010, Group Chat Admin Tool. For details about federated users, see Setting the Scope for the Root Category.

The scope of a category specifies all the users and groups that can be members in a membership list of a chat room in that category. For example, if you set the scope to contoso.com, you can add any group or user at Contoso as a member. If you set the scope to Sales, only groups and users in this distribution list can be added as members.

Defining a membership list for a category has the following benefits:

• All chat rooms (and subcategories) of this category inherit the membership list from the parent category, unless the chat room manager chooses to override it. This way, if you create many chat rooms in a category, you don’t have to define membership for each one.
  
  
• A user who is a member of a category can create new chat rooms in that category. This feature can also be disabled at the category level if you, as the chat room administrator, want to restrict creating new chat rooms in that category.
  
  

The scope of the root category must include all users who will use any chat room in your organization. Federated users who are to have access to any chat rooms must also be included in the root category scope.

If you will be allowing any access to federated users, we recommend that you first create two subcategories under the root category. One category will be for chat rooms that will be available to all users, including federated users, and the other for all chat rooms that will be restricted to your organization’s employees. Then in the top-level subcategory for the chat rooms restricted to your employees, narrow the scope so that federated users are not listed.

In the top-level subcategory for chat rooms that will be open to federated users, you may want to restrict file transfers.

In each of these two main branches, create additional levels of categories according to your organization’s structure and needs. As you do this, we recommend that you leave the scope as broad as possible in each category level, only restricting scope when it is necessary for security. This way, if you need to provide additional access to a chat room, you can add members to the channel instead of adjusting the scope, which can affect other chat rooms.

When you add a domain to the root category scope, the user groups whose group objects are contained in that domain are made available to you to specify as members of categories and chat rooms on the server.

However, these groups are not automatically made available to you for defining the scope. The reason for this restriction is that Group Chat enforces a rule that scope can be narrowed only by using subcategories. If a subcategory were permitted to define its scope with a user group that is not explicitly named on the parent category's scope, this rule would be violated. The violation occurs because the membership list of a user group is not constrained to the scope list of the parent category. The only way to ensure that all members of a user group are in the scope on the parent category is to explicitly add the user group to the scope of the parent category. For this reason, we recommend, as a general rule, that you use Active Directory containers, such as domains and organizational units, for defining the scope. If it is necessary to use a user group for defining the scope, you must add the user group to the scope of the root category and also to all subcategories that are in the path.

Only members of domains to which you specifically grant access can join chat rooms. Domains that you add to the scope of a category can contain user groups that include members from other domains. If you add one of these groups to the membership list of a category or channel and not all the domains that contain the group’s members are in the scope of the category, only the members whose domain is in the scope have access to the chat room.

An ethical wall is a construct that separates two groups in one organization from communicating with each other, for example by using Group Chat as the communication tool. The purpose of the ethical wall is to maintain ethical standards and avoid conflicts of interest. Ethical walls are used in several types of industries, including financial services industries. For example, in a large investment company, employees in the investment advisory group should be separated from those in the mergers group so that there is no appearance of insider trading using knowledge of upcoming mergers before they are announced.