By Alan Swahn
We live in a mobile world and are fast approaching the point of getting our desktop and applications served on demand to a variety of devices—laptops, tablets, and smart phones. Enabling technologies include Cloud-based desktop virtualization that serve clients running on endpoints, such as Citrix Receiver and VMware View Client.
Organizations are faced with the challenge of providing access to their applications and data for consultants, contractors, and employees working from home, while maintaining license compliance. Virtual desktops provide a managed environment on a standard image for 3rd party devices. Besides being a convenient and scalable solution, it brings the user to the data with less possibility of data leaks. But, is software licensing going to get in the way of accessing virtual nirvana?
For users in this category, a Microsoft Virtual Desktop Access (VDA) license is required to access a Microsoft-based virtual desktop, for devices that are not covered by Software Assurance.1 The subscription period is one year and costs $100.2 VDA licenses have a reassignment limitation, where once the license is assigned; it can’t be reassigned for 90 days.2 Example: If a contractor needs access for a month, it’s locked up for an additional two months and can’t be used by another contractor. If a contractor needs access for two months, it’s locked up for an additional month. By comparison, if there was no minimum time period before reassignment, then you could reallocate licenses to achieve maximum utility.
What is the effective overcharge of this reassignment blocking rule? The answer depends on how frequently your company uses short-term contractors and how many devices they have that need VDA licenses. Considering the potential randomness of how long a contractor needs a VDA license, the number of contractors at any one time, and the number of licenses required per contractor, I took a simulation approach to the problem.
To get my head around the problem, I simulated 40,000,000 scenarios in Excel as follows.
- The “Term” (months) of the Contractor and associated licenses.
- Randomly selected in these ranges: 1-3 months; 1-6 m; 1-9 m; 1-12 m.
- Number of new licenses required at the start of each month over a 1 year period
- Randomly selected between 0 and 100.
- Licenses are allocated at the start of each month.
Example- licenses not blocked due to reassignment rule:
Contractor A (50 devices) and Contractor B (25 devices) start January 1st with a 4 month contract. 75 licenses are required from January through April and 75 licenses are ready for reassignment on May 1st.
Example- licenses blocked due to reassignment rule:
Contractor C (80 devices) and Contractor D (20 devices) start January 1st with a 2 month contract. 100 licenses are required from January through February. The licenses are can’t be reassigned or used by another contractor in March and won’t be ready for reassignment until April 1st.
- Number of new licenses that would need to be purchased each month with no 3 month reassignment rule (NRR) imposed.
- Number of new licenses that would need to be purchased each month with the 3 month reassignment rule imposed (WRR).
- Total NRR licenses for the year (TNRR); Total WRR licenses for the year (TWRR)
- The amount overcharged over the course of a year (because of reassignment rule) expressed as a percent: AO = 100 * (TWRR-TNRR) /TNRR
- How often the overcharge occurred in the range of amount overcharged (0%; 0+ to -10%; 10--20%; 20--30%; 30--40%; 40--50%; 50--60%....90-100+%)
- Set Term range 1-3 months
- Run simulation--number of new licenses and license Term are randomly selected at the beginning of each month over a 1 year period
- Calculate TNRR, TWRR, and AO (% extra licenses required--overcharge)
- Add 1 to How Often bucket in the range of amount overcharged
- Rerun simulation 10,000,000 times
- Plot How Often Overcharge occurred versus Amount Overcharged
- Reset Term range and repeat process (Term reset to 1-6 m; then 1-9 m; then 1-12 m)
The reassignment rule comes into play, if the term of the licenses needed by contractors is less than 3 months. Table 1 shows that if the term randomly varies between 1-3 months, you could expect to over pay ~77% of the time and ~63% of the time (grayed) the overcharge would be 10% or more. For terms that randomly vary between 1-12 months, you could expect to overpay ~33% of the time and ~15% of the time (grayed) the overcharge would be 10% or more. Graph 1 illustrates how longer terms dampen the reassignment rule effect.
Notes: Graph 1, x-axis points are really ranges as per Table 1.
Example: For a Term of 1-3 months, the amount overcharged of 50 % to less than 60% is represented as a single point x=60% (how much) and y=5.965% (how often)
- Microsoft VDA Brochure:
- Licensing Windows for Virtual Desktops: