Protocols BroadNet answer

What is an ESME?

Last reviewed July 22, 20261 min readReviewed by BroadNet engineering

Quick answer

ESME (External Short Messaging Entity) is the SMPP term for any application outside the SMSC that submits or receives SMS. In an A2P deployment your gateway is the ESME, binding to the operator's SMSC over SMPP. An ESME binds in one of three session modes — Transmitter (send-only), Receiver (receive-only), or Transceiver (both directions on one connection, added in SMPP 3.4). Modern deployments almost always use a single Transceiver bind.

Plain-language definitionVendor-neutralReviewed July 22, 2026

DiagramHow an A2P message reaches the phone

Your applicationSends over the REST API or SMPP
BroadNet platformValidates, routes and bills each message
Operator SMSCDirect operator connection
Subscriber handsetThe message is delivered

The delivery receipt (DLR) travels back along the same path to your webhook

The long answer

Everything worth knowing, nothing that isn't.

§01

The three bind types

Transmitter (TX) submits messages only; Receiver (RX) accepts delivery receipts and inbound MO only; Transceiver (TRX) does both over one socket and is the default today. Whatever the mode, the ESME keeps the session alive with periodic enquire_link heartbeats and reconnects with backoff on failure. See /answers/what-is-smpp and /answers/smpp-3-4-vs-5-0.

§02

ESME vs SMSC

The ESME is the client; the SMSC is the operator-side server that stores and forwards the message to the handset. The SMSC returns a message_id on submit and later streams the DLR back over the same bind. When a bind or submit fails, the SMSC returns an SMPP command_status you can decode with the /tools/smpp-error-codes lookup. See /answers/what-is-smsc and /answers/what-is-dlr.

BNWritten by the BroadNet engineering team·Operating carrier-grade messaging since 2003, headquartered in Dubai·Editorial standards

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