It is NDS that enables the network to appear as a single cohesive entity to the user. With NDS, a user performs a single login to the network and is authenticated as necessary with respect to resources on the network. NDS is structured and represented using the tree model. Under the organization name are a number of organizational units. This is usually reflective of structure of the organization.
Org units can themselves contains org units.
Designing the NDS tree is a subjective process. You can use the organizational model as shown above, or a geographic model if your organization is dispersed. The underlying objective in designing the tree is making the resources in it easy to manage. There are over 30,000 user objects alone in our tree, which makes Clemson one of the largest users of NDS in the world. In Figure 2 above, see that there are 3 org units that are used at the organizational level to basically hold user objects.