- Queueing theory originated in 1909 with a paper written by a mathematician named Agner Krarup Erlang.
- He accurately estimated the probability that a call would be blocked at different capacity utilization levels.
- It can provide essential insights to product developers because there're similar problems of unpredictable work arrival time and unpredictable task durations.
- Queueing systems:
- **Queue**: the waiting work.
- **Server**: the resource performing the work, whose time to complete the work may be unpredictable.
- **Arrival Process**: the pattern with which work arrives, which is usually unpredictable.
- [**Service Process**](/zettel/queue-service-process): the process in which the server accomplishes the work.
- **Queueing discipline**: how queue handles the waiting work.
- Kendall notation: $M/M/1/\infty$ queue.
- The first $M$ refers to the **arrival process**, in this case, is the [Markov process](/zettel/markov-process).
- The second $M$ refers to the **service process**, which is also a [Markov process](/zettel/markov-process).
- The number $1$ refers to the number of parallel **servers** in the system.
- The final term $\infty$ describes the upper limit on queue size.
- [The Principles of Product Development Flow](/books/the-principles-of-product-development-flow)
- [M/G/1 Queue](/zettel/m-g-1-queue)
- [Queue Capacity Utilization](/zettel/queue-capacity-utilization)