ESME_RALYBND in SMPP

What is ESME_RALYBND?

ESME_RALYBND (Error Code: 0x0000000B) is an SMPP error that indicates that the ESME (External Short Messaging Entity) is already bound. This happens when an SMPP client attempts to bind while an active session with the same system ID is already established.

Possible Causes

The client is already bound but attempts another bind_transmitter, bind_receiver, or bind_transceiver request without unbinding first.
The previous session was not properly closed, leading the SMSC to believe that the client is still connected.
Multiple instances of the same client with the same system ID are trying to bind at the same time.
The SMSC enforces a restriction on concurrent binds for the same system ID.

When Does It Happen?

This error occurs when an SMPP client sends a bind request while it is already bound or if a previous connection was not properly closed.

Example SMPP PDU Transaction

The following is an example of an incorrect scenario where a second bind_transmitter request is sent while already bound:

0000001C (Length)
00000002 (Command ID for bind_transmitter)
00000000 (Command Status)
00000001 (Sequence Number)
74657374 000000 (System ID: "test")
000000 (Password)

Issue: The client is already bound, and the SMSC rejects the second bind attempt with an ESME_RALYBND response.

Correct approach:

First, unbind before attempting a new bind:

    00000010 (Length)
    00000006 (Command ID for unbind)
    00000000 (Command Status)
    00000002 (Sequence Number)

Wait for an unbind_resp before sending a new bind request.

How to Solve It?

Ensure that only one active session exists per system ID.
Before rebinding, send an unbind request and wait for an unbind_resp from the SMSC.
Configure the client to detect and handle session timeouts or disconnections properly.
Check for duplicate instances of the same client running concurrently.
If the issue persists, contact the SMSC provider to confirm their session handling rules.

If the problem continues, enable debugging logs to trace bind requests and session states.