Table:
|  |  | December 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
| Beginning balances | $36,836 | $42,432 | $49,904 |
| Deferral of revenue | 45,040 | 40,003 | 46,193 |
| Recognition of deferred revenue | (41,034) | (45,599) | (53,665) |
| Ending balances | $40,842 | $36,836 | $42,432 |
Paragraphs:
5. Balance Sheet Components
Deferred Revenue
Deferred revenue relates to performance obligations for which payments have been received by the customer prior to revenue recognition. Deferred revenue primarily consists of deferred software, or amounts allocated to mobile dashboard and on-line apps and unspecified upgrade rights. Deferred revenue also includes deferred subscription-based services. The deferred software and deferred subscription-based service performance obligations are anticipated to be recognized over the useful life or service periods of one to eighteen months.
Changes in the total short-term and long-term deferred revenue balance were as follows (in thousands):
Question:
What is the anticipated duration of useful life for the deferred software and deferred subscription-based service performance obligations to be recognised?