Glossary

CPaaS terms, defined

Plain-English definitions for the CPaaS terms you'll run into building communications: A2P 10DLC, STIR/SHAKEN, DLR, sender ID, RCS, OTP, SIP trunking, and number pooling.

Messaging compliance
A2P 10DLC — Application-to-Person 10-Digit Long Code
A2P 10DLC is the US and Canada carrier program for application-to-person SMS sent from standard 10-digit long-code numbers. Carriers require every business sender to register a brand and a campaign (“use case”) before long-code traffic is allowed through at full throughput — unregistered traffic is heavily filtered or blocked. Registration sets your per-message throughput and trust score, and applies once per brand and per campaign, not per message.
Voice trust & compliance
STIR/SHAKEN — Secure Telephone Identity Revisited / Signature-based Handling of Asserted information using toKENs
STIR/SHAKEN is the US telecom framework that cryptographically signs a call's Caller ID so the terminating carrier can verify where the call actually originated before it rings. Every call carries an attestation level — A (full attestation), B (partial), or C (gateway) — and carriers weigh that signal, alongside reputation, when deciding whether to label a call “Spam Likely” or block it outright. Higher attestation generally means a higher answer rate.
Messaging delivery
DLR — Delivery Receipt
A DLR (delivery receipt) is the status callback a carrier or messaging gateway sends back after an SMS, MMS, or WhatsApp message is submitted, confirming whether it was delivered, failed, or is still pending — and why, via a carrier status code. DLRs let a sending platform close the loop on every message instead of guessing from silence, and are the signal integrations use to retry a failed send or report an accurate delivery rate.
Messaging compliance
Sender ID
A sender ID is the identifier a recipient sees as the source of a message or call — a phone number, a short code, or, outside the US, an alphanumeric name such as “ORBIT”. Which sender ID types a country allows, and whether they must be pre-registered, is set by each country's carriers and regulators; sending from an unregistered or mismatched sender ID is one of the most common reasons a message gets filtered or blocked entirely.
Messaging channels
RCS — Rich Communication Services
RCS (Rich Communication Services) is the GSMA carrier standard that upgrades SMS with read receipts, typing indicators, high-resolution media, suggested replies, and a verified sender name and logo — while still landing in the phone's native messaging app rather than a separate app like WhatsApp. RCS Business Messaging lets a verified brand send these richer messages to Android, and a growing set of iOS, users through their default texting app.
Identity & verification
OTP — One-Time Passcode
An OTP (one-time passcode) is a short numeric or alphanumeric code sent once — over SMS, voice, WhatsApp, email, or generated by an authenticator app — to prove a user controls a phone number, device, or account before letting them log in, reset a password, or complete a sensitive action. Because it expires and cannot be reused, an OTP is one of the most common second factors in two-factor authentication and phone-number verification flows.
Voice infrastructure
SIP trunking — Session Initiation Protocol trunking
SIP trunking connects a business phone system — an on-premise PBX or a cloud UCaaS platform — to the public telephone network over a SIP (Session Initiation Protocol) connection instead of physical phone lines, so calls travel as data over an internet connection. It lets a company keep its existing PBX and phone numbers while modernizing how calls reach the network, scale call capacity up or down by adding trunks, and consolidate multiple office lines under a single connection.
Voice & messaging infrastructure
Number pooling
Number pooling is the practice of provisioning and rotating outbound calls or messages across a shared set of phone numbers, rather than sending everything from a single number, to spread volume, avoid overloading one number's reputation or throughput limit, and route by geography or use case. Messaging platforms pool numbers to keep per-number send rates within carrier limits; voice platforms pool numbers to spread outbound Caller ID across multiple registered lines instead of concentrating volume on one.