Emergency Services Routing Key. A number used to route data through the 9‐1‐1 system. A 10‐digit routable, but not

necessarily dialable, number that is used not only for routing but also as a correlator or key for the mating of data that is

provided to a PSAP by different paths, such as the voice path and ALI data path. In daily use, the term ESRK is used to

distinguish operational environments where the “routing” digits are assigned on a per‐destination‐PSAP basis as

opposed to a per origination cell sector basis.