1. A method comprising: determining call initiation rate statistics; determining a denial-of-service attack mitigation rule based on the call initiation rate statistics; sending the denial-of-service attack mitigation rule to an attack mitigator via a session initiation protocol NOTIFY message; and determining whether to reject a communication session request message based on the denial-of-service attack mitigation rule by: comparing a first parameter of the communication session request message to a second parameter of the denial-of-service attack mitigation rule; sending a session initiation protocol 5XX message to a calling device associated with the communication session request message when the first and second parameters match; and forwarding the communication session request message to an Internet protocol multimedia subsystem core when the first and second parameters do not match.