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Demystifying RDP pt.2: Understanding Microsoft’s RDS & VDI licensing

In this blog post, we’ll try to put some structure in RDS and VDI licensing and explain some of the main concepts and options. Just to be sure: by no means will this be a complete reference. Yes, even in this 2000+ words post, we will (need to) cut some corners.

When we talk with partners and customers, we are frequently confronted with questions about Microsoft RDS & VDI licensing. ”How much does it cost?” is one that we hear often, and that is… pretty complex matter, to say the least. Firstly, because the technology and architecture basis below RDS and VDI is complex, and secondly because the rules of the game have evolved over time. The matrix of possibilities is vast! In short, when buying RDP related licenses, make sure that you have a good advisor or that you work your way through Microsoft Product terms.

Before continuing this blog post, we would recommend the reader to read our blog post on the options and components of RDP.


What is a CAL?

“If the workstations in your organization are networked, you likely depend on network server software to perform certain functions, such as file and print sharing. To access this server software legally, a Client Access License (CAL) may be required. A CAL is not a software product; rather, it is a license that gives a user the right to access the services of the server.” Read more!

When do you need a Microsoft RDS (Remote Desktop Services) CAL?

Simply put, in every situation where you use ‘Remote Desktop Services’ (RDS). Microsoft writes: “Each user and device that connects to a Remote Desktop Session host needs a client access licenses (CAL).” Read more!

What about an RDP connection to a VDI (without the use of RDS)?

In that case, you won’t need an RDS CAL. However, you will need a Windows VDA (Virtual Desktop Access) license. This is covered in Windows E3 and E5 licenses and can also be purchased on top of Windows in case you don’t have the E3 or E5 flavour. Windows E3 or E5 is the evolution of the former Windows SA (Software Assurance). The former is typically user-based, while the latter was device-based licensing.
“Windows Virtual Desktop Access (VDA) is an authorization strategy that requires each device seeking access to a Windows virtual desktop in a virtual desktop infrastructure (VDI) to be licensed.” Read more!
VDA is included as a feature of Windows E3 and E5 subscriptions, meaning that primary users of devices with such a license can access their virtual desktops at no extra charge.
As a “special case”: in case you would access a Windows client (and thus a VDI scenario) by using an RDS platform, you would require both the Windows VDA license (as part of Windows E3 or E5, or standalone) as well as an RDS CAL.

At the highest level, the picture below gives some guidance:

Understanding RDS licensing
RDS and VDI licensing options at a glance


With the basics out the door, let’s go one level deeper into RDS CAL licensing.

The RD License server

This is a mandatory role for Microsoft to be set up in your RDS environment. For small deployments, it can be deployed on the RD Session Host. For larger deployments, a separate VM is advised. When purchasing CALs, they must be uploaded in the license server. As such, if an appropriate RDS CAL is available from a license server, the RDS CAL is issued to the client, and the client can connect to the RD Session Host server and from there to the desktop or apps they’re trying to use. There are typically grace periods during which the license server will accept connection.

What types of RDS CAL existing?

Basically, you must choose between a “user CAL” and a “device CAL”. An overview:


CALs are physically assigned to each device

CALs are tracked by the license server

CALs can be tracked regardless of AD membership

You can revoke up to 20% of CALs

CALs cannot be overallocated


CALs are assigned to a user in AD

CALs are tracked by the license server

CALs cannot be tracked within a workgroup

You cannot revoke any CALs

CALs can be overallocated (breach w/ agreement)

Comparison for RDS CALs (for Windows Server 2016)

Not upwards compatible

As we explained in our RDP introduction blog, RDS is tied to a Windows Server version; ie. the RDS version of Windows Server 2008R2 and 2016 are hardwired into each platform and are pretty different from each other in terms of functionalities and performance.

Now comes the tricky part: the CALs you bought for a Windows Server 2012 deployment will not be accepted on a Windows Server 2016 platform if you didn’t buy for the Software Assurance. However, the 2016 RDS CAL is downwards compatible with RDS 2012. Microsoft writes: “Any RDS license server can host licenses from all previous versions of Remote Desktop Services and the current version of Remote Desktop Services. For example, a Windows Server 2016 RDS license server can host licenses from all previous versions of RDS, while a Windows Server 2012 R2 RDS license server can only host licenses up to Windows Server 2012 R2.”

However, upwards compatibility is possible if Software Assurance is purchased for the RDS CAL licenses. In that case, you can just upgrade to the latest available version. If Software Assurance is not purchased, new RDS CALs need to be purchased.

The following table puts the theory in the practice (in case of no Software Assurance):

Microsoft RDS CAL version compatibility
The Windows Server CAL

When writing about the RDS CAL, we didn’t talk about the Windows Server licensing yet. Given that in most cases ‘desktops’ or applications are deployed on Windows Server, licensing applies here too. Typically, you’ll need to take a Windows Server CAL (available ‘per user’ or ‘per device), next to (or on top of) the RDS CAL into account.

Licensing model

And then, obviously, Microsoft has different models for the consumption of RDS CALs. From a high-level perspective, there are 3 main categories:

Volume Licensing: this is a term used by Microsoft to describe a program for organizations that need multiple Microsoft product licenses, but do not need multiple copies of the software media and the documentation that comes with the software. Microsoft Volume Licensing typically offers organizations lower pricing, two or three-year license agreements and often product use rights not included with FPP (Full Packaged Product) licenses, such as rights to copy the software onto multiple devices.

Within Volume licensing there are multiple options – have a look at this page for more info.

· Enterprise Agreement (EA)
· Open Value
· MPSA – Microsoft Product and Service Agreement

SPLA (Server Provider License Agreement): “With the SPLA, service providers and ISVs can license eligible Microsoft products on a monthly basis, during a three-year agreement term, to host software services and applications for their customers. The SPLA supports a variety of hosting scenarios to help you provide highly customized and robust solutions to a wide set of customers.” Read more!

CSP (Cloud Service Provider): On Nov 20th 2018, Microsoft announced that it would be possible to also purchase RDS CALs via a CSP model. “Previously, your customers needed to bring their own RDS CAL with SA to support your RDS deployment in the customers’ environment. Now a CSP can directly sell RDS subscriptions through our CSP program, eliminating the extra step of customers and partners acquiring different licenses through various programs. With this model, one can enjoy a faster licensing cycle due to CSP integration with other Microsoft licenses including Windows Server, SQL Server, and Office to make it easy for partners to simplify the buying process.” Read more!

Next to the above license models, special pricing exists for organizations that are non-profit, educational, etc. but those discounts don’t apply to all models.


When do you need VDA?

In the VDI scenario, you remotely connect to a Windows Client (i.e. the operating system that might run on your laptop/desktop). When using VDI, and thus not connecting to an RD Session Host or a Windows Server, you don’t need RDS and Windows Server CALs. However, you do need to make sure that your Windows (client) licensing is properly set up: in comes “Windows Virtual Desktop Access, or VDA”.

You will require such a VDA license every time you connect to a Windows client that is centrally hosted (i.e. running in a datacentre or on a virtual machine on a hypervisor). You will also require VDA licensing if you remotely connect to a Windows desktop that is not your primary device (let’s say, not your main desktop that is connected at work).

You will not require any additional VDA licensing if you remotely connect from a Windows device to your primary desktop/laptop that is connected to the company network. A typical scenario is that the desktop is left powered on in the office at night. Homeworkers can then access that workspace from a personal home device over RDP. Clearly, this is not the most scalable, secure, or cost-efficient scenario (from a power perspective), but it is an option, nonetheless.

Now, let’s assume a different user accesses your VDI. In that case, it’s not the primary user accessing his principal device, and thus additional VDA licensing will apply to add this additional user. A typical ‘extra user’ is a contractor or a colleague.

Let’s take it one additional step further: if you connect to your primary desktop/laptop that is connected to the company network, and you try to connect from a non-Windows device (let’s say an Apple MacBook) then you’ll also need a VDA license (or a Windows 10 Enterprise E3/E5 as you’ll read below).

Are you still with us?

Windows 10 Enterprise E3, E5 and SA licensing

Windows “Virtual Desktop Access” (VDA) is included in Windows 10 Enterprise E3 and E5 licenses. With Windows 10 Enterprise E3 and E5 user licensing, you have the rights for remote access for up to 5 different devices (linked to the same user). Those include devices with non-Windows operating systems (e.g. an iPad). The ‘host’ Windows client system can also be hosted in a datacentre.

Windows 10 Enterprise E3 or E5 is available in ‘per device’ and ‘per user’ licensing. Windows SA used to be exclusively available for licensing on a per-device basis. Starting December 1st 2014, Windows SA and Windows VDA are also licensed on a “per-user” basis. Windows SA also came with VDA built-in. These days, however, Microsoft is mainly selling Windows 10 E3 and E5 user licenses.

Windows Virtual Desktop

Microsoft has introduced Windows Virtual Desktop on Azure, which is in public beta since March 2019. The licensing requirements for WVD on Azure are different compared to the default rules. Read more in our blog post about the topic!

Can I connect to VDI over RDS?

Yes, that’s a possibility. In such a case, you access the Windows client by using the Remote Desktop Services setup. You will need to purchase both a VDA license (which might be covered by Windows 10 Enterprise E3 or E5) as well as an RDS CAL. You will not need the Windows Server CAL, however.


Given Windows E3 and E5 basically include the Software Assurance, you have the right to upgrade (or downgrade in theory) at any time.

License models

Similar to RDS, Windows E3, E5 and VDA are available in multiple licensing models. It’s “slightly” more complex however. This table gives a good overview:

Summary table

The following tree tries to summarize the options for some scenarios:


Last but not least, another option we have not touched upon yet, is the option to use the Remote Desktop Protocol (RDP) to access a machine without Windows. Let’s safely assume that’s Linux in today’s world. From a Microsoft license perspective, no costs apply. Which only makes sense, give you don’t use Windows client (no VDA needed), no Windows Server (no Windows Server CAL needed) and no RDS (no RDS CAL needed). However, license costs might apply for other (non-Microsoft) RDP suites.


Here, we can be short. Awingu doesn’t enable you to cut in RDS or VDI related licenses as such. Awingu is a layer on top, and all the rules of the game will apply. On the bright side, however, Awingu’s licensing is a lot less complex as it is user-based on a concurrent level. No matter what features you use, how often you use them, from what device you use, or how many applications/desktops you use. Simple and transparent.

Find out more about Awingu!

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