This happens a lot in retail, the DMV, post office, etc. The best way to model it is with a meta-process where servers randomly disappear and reappear. This als

This happens a lot in retail, the DMV, post office, etc. The best way to model it is with a meta-process where servers randomly disappear and reappear. This also captures the infuriating phenomenon of tellers going on break or (worse) looking like they're available when they're not because they have to stop and count the till or something.