carriers-sip
Call blocking
Call blocking is when a carrier, app, or device stops your outbound calls from reaching the person you dialed, often because your number looks like spam.
Call blocking happens when something between your dialer and the called party decides not to let the call through. It might be the phone company itself, a carrier-level analytics service, or a spam-filtering app on the person's handset. From your side, the call may ring forever, drop instantly, or show as completed with no audio. The frustrating part is that the call left your system fine — it was stopped downstream.
Most blocking is triggered by reputation. If your caller ID, also called the Automatic Number Identification or ani, makes a lot of short calls in a row, gets few answers, or attracts complaints, it can earn a spam likely label. Once that label sticks, carriers may downgrade or block the number outright. Attestation frameworks like stir shaken and the call attestation grade attached to your calls also feed into these decisions.
How to reduce blocking
- Rotate a healthy pool of did numbers instead of hammering one caller ID all day.
- Register your numbers and verify they are not tied to past robocall complaints.
- Avoid spoofing — using a number you do not own can trip carrier filters and is covered under rules the fcc enforces.
Blocking is not the same as a busy network. If you see widespread failures with no answers across all numbers, check whether it is genuine blocking, congestion on the carrier, or simply your numbers having aged into a bad reputation. Keeping answer rates up and call volume sane per number is the most reliable defense, far more than chasing any single technical fix.
Related terms
ANI
ANI, short for Automatic Number Identification, is the phone number your call carries as its source, which the person you dialed usually sees as caller ID.
Call attestation
The confidence rating a carrier attaches to a call under STIR/SHAKEN, saying how sure it is that you actually own the number you are calling from.
DID (direct inward dialing)
A DID (direct inward dialing) is a phone number you own that routes incoming calls straight into VICIdial, usually to a chosen inbound group.
Robocall
An automated phone call that plays a recorded message or dials by machine, often without a live agent on the line when the call connects.
Spam Likely label
A warning that phone carriers display on incoming calls they think might be unwanted, which sharply lowers how often people pick up your calls.
STIR/SHAKEN
A system carriers use to digitally sign caller ID, proving a call really comes from the number it claims, which helps cut down on spoofed and fraudulent calls.