Understanding CALs

CALs, or Client Access Licenses, are often a confusing matter.  I've been working with them ever since I got started in IT, however, not until recently have I had a full understanding of when and where you'd use a CAL.  Not to mention, there are different types of CALs which add to the confusion.

Let me break down a few things for you:
-What's a CAL
-What CAL do I use?
-When not to use a CAL.

CAL,  a client access license. 
When you buy or manage a Windows server, it'll be licensed to end users or to businesses.  The CAL gives you rights to connect to a server, or server application. Most editions of server or a specific service, come with some CALs already.  This allows the software to be used by either a few users or a few computers.  The more users/computer, the more CALs required.  Think of it this way, one CAL per concurrent connection.

There are two types of CALs; a device and a user. 
User CALs allow one user to connect to a server or service.  Any user can connect, however, only one user may utilize the CAL at any given time.  Let's say you have SQL Enterprise 2k8 w/ a 5 CAL, then 5 users can utilize that service at the same time.

Device CALs allows one device to connect to the server or service.  Connections are limited by device, rather than user.  So if you have a lot of users and a small amount of devices, utilizing CALs for each of those devices is more cost-effective.

Core CALs, are special CALs offered by Microsoft via corporate licensing.  Core CALs include CALs for Microsoft Windows Server, Exchange, Systems Management Server, and Sharepoint.  Think of it as a suite of CAL offerings to license basic server components across your computers.  Less overhead equals less management of your CALs.  So if you're going to utilize many Microsoft services, look into Core CAL licensing.

Lastly, when don't you need a CAL?  When your users access the server anonymously or when they require privacy via authentication.  You do not need to add CALs for users who are authenticating.  If you are gearing your server or services for customers and not internal-employees, you'll want to utilize an External Connector.  An EC allows an unlimited number of outside users to access a server or service.  However, EC's should only be considered when you have a large customer-base because they are rather expensive.  If you have a smaller external user-base, CALs are a much more cost-effective solution.