In a secure cell, all users and applications share a common security mechanism, in which they must verify their identities to each other before they are able to exchange information. Authentication across cells needs to be equally as secure. For example, assume there is a user named Mozart in cell-2 who wants access to a file in cell-1. A trust relationship allows cell-1 to believe that the user request really comes from Mozart in cell-2.
You also need namespace connectivity to make use of a trust relationship. See entry not found (dce / rpc) for more information about namespace connectivity.
The administrator of a cell sets up trust relationships. However, you can check to see if the trust relationship with another cell exists by looking for the name krbtgt/othercell in your local cell's Registry. If it does not exist, it means that a trust relationship was not established.