If the first AOR in the set (the AOR specified in the Request URI) is a local Account address, and the Request is an INVITE request, the Account device registration is retrieved, along with certain Account settings and preferences.
An Account can have Automated Signal Rules, which are retrieved with Account device registrations. These Rules are "mixed" with the Domain-wide Rules specified for the Account Domain and are applied to all requests sent to the Account.
The Signal component controls how many "calls" (initial INVITE requests with audio-video Session Descriptors) an Account receives over a specified period of time. If more calls are received, they are rejected without processing. This limit can be set individually, for each Account, or server/cluster-wide as well as Domain-wide default settings can be used. See the Accounts section for more details.