Infinite queue length. M/M/1/k would be a system where once k items are enqueued, some work shedding policy takes over (either rejecting new work or often preferably dropping at the head of the queue.)
Infinite queue length. M/M/1/k would be a system where once k items are enqueued, some work shedding policy takes over (either rejecting new work or often preferably dropping at the head of the queue.)