SMPP Mechanics

SMPP and RESTful APIs both serve as interfaces for sending and receiving SMS messages, but they operate in fundamentally different ways. While RESTful APIs follow a stateless, request-response model over HTTP, SMPP is a session-based, binary protocol that maintains a continuous connection between the client (ESME) and the SMSC.

RESTful API Model

In a RESTful API, each interaction is a separate HTTP request to a specific endpoint. For example, sending an SMS:

POST /messages/send
{
  "to": "+1234567890",
  "text": "Hello!"
}

Checking message status:

GET /messages/status?message_id=12345

Each of these requests is independent, and the server does not maintain session state between calls.

SMPP Model

SMPP, on the other hand, maintains a persistent TCP/IP socket connection, where communication is handled through PDUs - structured binary messages containing both commands and data.
Instead of calling REST endpoints, an SMPP client follows a structured sequence of interactions:

Session Establishment → bind_transmitter, bind_receiver, or bind_transceiver

Message Submission → submit_sm (equivalent to /messages/send)

Delivery Reports → deliver_sm (equivalent to webhook notifications)

Session Maintenance → enquire_link (heartbeat mechanism to keep the connection alive)

Session Termination → unbind

Unlike REST, where each request completes a transaction, SMPP relies on an open session, meaning the server retains state for the duration of the connection.
By defining a structured set of PDUs, SMPP enables applications to interact with SMSCs using a low-latency, binary protocol that is more efficient for handling large-scale messaging, but it requires proper connection management.

By drawing parallels between SMPP PDUs and RESTful APIs, we aim to help developers familiar with HTTP-based interfaces quickly understand SMPP’s binary, session-oriented model. With a structured overview of PDU formats, request-response handling, and error codes, we want to make building reliable and scalable SMS applications easier.