RexaThe short answer
A DID is the phone number a voice agent answers on or calls from. It is the unit of provisioning in telephony: numbers are purchased, assigned to a route, registered against a business identity, and can acquire a reputation. Which DID an outbound call presents affects whether it is answered at all.
In detail
DIDs are provisioned from a carrier or number provider and mapped to a destination — a SIP endpoint, an application, a queue. Inbound routing is a lookup on the dialled number. Outbound, the DID is the number presented as caller ID, and providers validate that the presenting party is entitled to that number.
Numbers carry attributes that matter beyond routing. Geographic numbers signal a location and typically see higher answer rates locally. Toll-free numbers are free to the caller and are treated differently by some analytics platforms. Numbers registered under a verified business identity can display a caller name, and numbers used for outbound campaigns accumulate reputation that spam-analytics vendors act on.
Reputation degradation is the recurring operational problem in outbound voice. A number that generates many short, unanswered or reported calls gets flagged by carrier analytics and begins showing as suspected spam, at which point answer rates collapse. Monitoring per-number health and rotating away from degraded numbers — rather than dialling harder from them — is the standard mitigation.
How Rexa handles it
Inbound DID routing is a first-class part of the Rexa API: numbers are managed as inbound-number resources and mapped to the agent that answers them, and an outbound call’s from_number must be a DID on your connected provider rather than an arbitrary string. Rexa also tracks per-number health and surfaces a degradation warning that recommends rotating to a fresh number and reviewing CNAM and brand registration.
Calls APIRelated terms
E.164
E.164 is the ITU standard that defines the international public telephone numbering plan, giving every number a unique globally routable form.
CNAM
CNAM is the caller-name information displayed alongside a calling number on the recipient’s handset.
Carrier
A carrier is a company that operates telephone network infrastructure and terminates or originates calls on it.
A2P 10DLC
A2P 10DLC is the US registration framework under which businesses declare their identity and messaging use case before sending application-to-person traffic from ordinary ten-digit numbers.