# SMPP protocol overview

> SMPP (Short Message Peer-to-Peer) is an open, binary, TCP-based protocol for exchanging SMS between an external application (ESME) and a Short Message Service Centre (SMSC). It is the standard interface for high-throughput A2P messaging because it is stateful, low-latency and supports delivery receipts natively.

- Canonical URL: https://www.broadnet.me/reference/smpp-protocol-overview
- Language: en
- Last updated: 2026-07-18
- Publisher: BroadNet (https://www.broadnet.me)

What SMPP is, how the ESME↔SMSC session works, the difference between v3.4 and v5.0, and why it remains the standard for high-throughput A2P SMS.

## What SMPP is and why it exists

SMPP is a level-7 application protocol that lets a message application exchange short messages with an SMSC or routing gateway. Where a REST API is convenient for low volumes, SMPP is a persistent binary session that avoids per-message HTTP overhead, sustains thousands of messages per second on a single connection, and carries submit, delivery, query, replace and cancel operations plus asynchronous delivery receipts. It is protocol-agnostic about the underlying network — the SMSC handles SS7/MAP, SIGTRAN or IP delivery to the handset. First published by Aldiscon/Logica in the late 1990s, it is now maintained by the SMPP Developers Forum; v3.4 (1999) remains the most widely deployed version.

## The ESME and the SMSC

The two peers are the ESME (External Short Message Entity — your application) and the SMSC (Short Message Service Centre — the operator or aggregator gateway). The ESME opens a TCP connection to the SMSC's listening port (IANA-registered 2775 for plaintext) and authenticates with a bind. Despite the 'peer-to-peer' name, the relationship is typically client (ESME) to server (SMSC); either side can originate PDUs once the session is bound, which is how the SMSC pushes mobile-originated messages and delivery receipts back to the ESME.

*Roles in an SMPP session*

| Term | Meaning |
|---|---|
| ESME | External Short Message Entity — the connecting application (your sender) |
| SMSC | Short Message Service Centre — the operator/aggregator gateway |
| MC | Message Centre — the v5.0 term that generalises SMSC |
| MT | Mobile-Terminated — a message delivered to a handset |
| MO | Mobile-Originated — a message sent from a handset to the ESME |

## Session model and transport

SMPP runs over a single long-lived TCP connection. After the TCP handshake the ESME sends a bind PDU; on a successful bind_resp the session enters a bound state and stays open indefinitely, kept alive with periodic enquire_link PDUs. Operations are request/response pairs correlated by sequence_number, and multiple requests can be outstanding at once (windowed / asynchronous mode) up to a negotiated window size. The session ends with an unbind exchange or a TCP close. SMPP has no built-in encryption; confidentiality is added by running the session over TLS.

## Versions: v3.3, v3.4 and v5.0

Three versions matter in practice. v3.3 is legacy and rarely used. v3.4 introduced the transceiver bind and optional TLV parameters and is the de-facto industry standard today. v5.0 is backward compatible with v3.4 and adds congestion-control signalling, broadcast operations and extra message states, but is less widely deployed. The negotiated version is carried in the bind's interface_version field: 0x34 for v3.4 and 0x50 for v5.0.

*interface_version values*

| Value | Version |
|---|---|
| 0x33 or lower | SMPP v3.3 or earlier |
| 0x34 | SMPP v3.4 |
| 0x50 | SMPP v5.0 |

## Frequently asked questions

### Is SMPP still used in 2026?

Yes. SMPP remains the dominant protocol for high-volume A2P SMS between applications, aggregators and operator SMSCs. REST APIs sit on top of SMPP for convenience, but the carrier-facing interconnect is almost always SMPP over TCP, usually secured with TLS.

### What port does SMPP use?

The IANA-registered default is TCP port 2775 for plaintext SMPP. There is no single standardised TLS port, so providers expose a separate TLS-enabled port (for example 3550 or a per-account port) for encrypted binds. Always use the port your provider provisions.

### What is the difference between SMPP and SMTP?

They are unrelated. SMTP moves email; SMPP moves SMS between applications and an SMSC. The similar acronyms cause confusion, but the protocols share no design, ports or message format.

### Do I need SMPP or is a REST SMS API enough?

A REST API is simpler and fine for low to moderate volumes and quick integration. SMPP earns its keep at high throughput, where a persistent binary session gives lower latency, higher sustained TPS and native, real-time delivery receipts on the same connection.

## Sources

- [SMPP v3.4 specification (Issue 1.2)](https://smpp.org/SMPP_v3_4_Issue1_2.pdf)
- [SMPP v5.0 specification](https://smpp.org/SMPP_v5.pdf)
- [3GPP TS 23.040 — SMS technical realization](https://www.3gpp.org/dynareport/23040.htm)

## Related

- [What is SMPP?](https://www.broadnet.me/answers/what-is-smpp)
- [SMPP PDU anatomy](https://www.broadnet.me/reference/smpp-pdu-anatomy)
- [SMSC gateway (operators)](https://www.broadnet.me/operators/smsc-gateway)
- [SMS API product](https://www.broadnet.me/products/sms-api)
- [Developer documentation](https://www.broadnet.me/developers)