An External Connector (EC) license is a licensing option available to address a specific customer scenario. When you need to allow your business partners or customers to access your network, you have two choices. You can purchase Windows CALs for each one of your external users; or, you can purchase External Connector licenses for each copy of the Windows Server 2003 software that those external users will access.
Note: An example of an external user is a person who is not an employee, or similar personnel of the company or its affiliates. Access via the Internet, in an unauthenticated fashion, does not require a Windows CAL or an EC license-(for example, browsing a public Web site).