SMPP (Short Message Peer-to-Peer)

SMPP (Short Message Peer-to-Peer) is a binary TCP/IP protocol that establishes a persistent connection between a messaging application (the External Short Messaging Entity, or ESME) and a carrier’s SMS Centre (SMSC). Once the connection is established with bind authentication, the ESME can submit messages (submit_sm command), receive delivery receipts (deliver_sm), and handle inbound SMS over the same persistent connection. Unlike HTTP REST APIs — which open a new connection per request — SMPP’s persistent connection enables very high message throughput with minimal overhead.

SMPP uses a persistent binary TCP connection, requires specialised client libraries, supports very high throughput (thousands of messages per second), and is lower latency once connected. REST SMS APIs use standard HTTP/HTTPS requests, are simpler to implement with any programming language, support lower to moderate throughput, and require no persistent connection management. REST APIs are the right choice for most business applications — they’re easier to implement, debug, and scale horizontally. SMPP is preferred for enterprise-grade or wholesale applications where throughput, latency, and bidirectional messaging efficiency are critical requirements.

Use SMPP when: your application sends more than a few hundred messages per second and needs to sustain that throughput consistently; you require the lowest possible latency between message submission and delivery; you are building a messaging aggregator or wholesale SMS platform that needs direct carrier-grade integration; or you need fine-grained control over SMPP-specific features such as message priority, scheduled delivery windows, or advanced PDU parameters. For most business applications — OTP delivery, notifications, marketing campaigns under 100 messages per second — a REST API is simpler, sufficient, and easier to operate.

SMPP throughput is limited by the transmit rate negotiated with the carrier during bind, typically expressed in messages per second (MPS). A single SMPP connection typically supports 50–300 MPS depending on the provider and account tier. For higher throughput, multiple parallel SMPP connections (multi-binding) are used, with each connection handling a portion of the traffic. Enterprise senders and messaging aggregators commonly run 10–50 parallel SMPP connections for aggregate throughput of thousands of messages per second. IDT Express SMPP accounts support multi-binding for high-volume requirements.