A Client Access License ("CAL") is a kind of software license, distributed by Microsoft, to allow clients to connect to its server software programs.
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Licensing
Most Microsoft software is licensed to end users or businesses and this allows the owner of the license to use the product specified in the license agreement, subject to the terms and conditions set forth in the license agreement. Microsoft usually has notices on the packaging of their products which state that using the software constitutes agreement of the license terms. Microsoft offers many types of licensing for a range of their products which are designed to be cost effective, flexible, or both (see Microsoft Licensing). Server software, such as Windows Server 2003 and SQL Server 2005 require licenses that are more expensive than those which are purchased for desktop software like Windows Vista. In recent versions of many of their products, Microsoft require that all clients that connect to these server applications have a license to connect to and use the services of that software. These licenses come in the form of a Client Access License.
Client Access Licenses
A Client Access License (CAL) is a kind of license that allows client machines to connect to Microsoft server software. They usually come in the form of a Certificate of Authenticity (CoA) and a license key, which may or may not be on the certificate itself. The various editions of Windows Server 2003 usually include a small number of CALs, and this allows either a few users or a few computers to connect to it at once (depending on the CAL licensing mode). If more simultaneous connections are needed, then additional CALs must be purchased. Most CALs are paper only and are distributed for compliance to the software license agreement only. Technically, any individual or business can use the software with an unlimited number of users and buy no CALs at all - but they will be in breach of the license agreement and very large penalties will apply if they are caught. Some CALs, however, are electronically enforced: they are files that are imported into the software which will not service clients unless there are valid CALs installed. The software will authenticate and serve the number of clients licensed under the CALs. Once that number is met, the server can accept a small number of additional connections and then warn administrators before refusing to serve further connections, however usually it will simply refuse to authenticate additional clients until one or more of them disconnects. In this way, the server electronically enforces the Client Access licensing. At present, the only Microsoft software that uses this form of electronic license enforcement is Windows Small Business Server. This may be due to the fact that most small businesses that run the Small Business Server do not have dedicated IT staff to ensure compliance, whereas larger organisations usually have dedicated IT staff that monitor CAL usage and organise the acquisition of additional CALs when necessary.
Per-User vs. Per-Device
CALs apply to either a "device" (as defined in the license agreement) or a "user". A business is free to choose either mode. In Per-User mode, a CAL is purchased to allow one user to connect to the server software. Any user can connect, but only one user may use a given CAL at any given time. Any number of CALs can be purchased to allow five, five hundred, or any number of users to simultaneously connect to the server. Any number of devices may connect to the server software, but only a set number of users can connect to it at once. Per-Device mode operates in much the same way, but limits connections made by devices, rather than users. One CAL enables one device to connect to and use the server software, regardless of how many users are connecting.
Software Editions
CALs usually enable connectivity to server software regardless of the edition of the software[1]. For example, CALs purchased to enable client connectivity with Windows Server 2003 Enterprise Edition can be used with Windows Server 2003 Datacenter Edition, and vice-versa.
Terminal Services
Terminal Services is a function of Microsoft Windows that allows several types of connection to the server components of the system. Terminal Services is a product that requires CALs in order to use, however Microsoft Windows XP and Vista allow one connection via Terminal Services without having to purchase any additional CALs [2]. Similarly, Windows 2000 Server and Windows Server 2003 allow two simultaneous connectons, for remote administration purposes, without the purchase of additional CALs. Windows Server versions prior to 2003 do not necessarily require the use of specialized Terminal Services CALs; rather, clients which are of at least the same or lower version of the operating system are allowed access automatically. For example, Windows NT 4.0 clients may connect to Windows NT 4.0 terminal servers but not Windows 2000 or later; Windows 2000 or Windows XP clients may connect to Windows NT 4.0 or Windows 2000 terminal servers. Windows Server 2003 requires separate CALs for all clients in Terminal Server mode, regardless of the client operating system. A new type of CAL was introduced in Windows Server 2003: the "Per User" CAL. However, in Windows Server 2003 SP1, there is no technical enforcement of these. This means, any number of users can technically connect, and the Windows Server 2003 will not decrease the number of available CALs. Reportedly, this is because Microsoft did not have time to finalize technical enforcement before the release of the operating system.
References
- ^ http://www.microsoft.com/licensing/resources/volbrief.mspx Microsoft Volume Licensing Briefs
- ^ http://www.microsoft.com/resources/sam/lic_cal.mspx Microsoft CAL guide
