WHAT

In simple terms, SMPP (short messaging peer to peer) is the protocol which makes sms possible.

Just like HTTP, SMTP… SMPP is also an open, industry standard protocol.

It enables flexible exchange of data between devices also known as ESME(External short message entities).
This exchange of data or specifically short messages can happen without the internet being involved in the initial/final stage.

HOW

You may not know this, but your sms still needs the internet, for it to be routed successfully to your receiver.

When a user sends an SMS from their device, the internet is not required for the initial submission of the message from the sender's device to their mobile network operator (MNO). However, the internet becomes involved at various points in the message delivery process:

User's Device to MNO's Network:

Initially, when the user sends an SMS, the message is transmitted over the airwaves using the cellular network. No internet connection is required for this stage. The sender's device communicates directly with the nearest cell tower, which then forwards the message to the user's MNO.

Within the MNO's Network:

Inside the MNO's network, the message is routed to its destination. This typically involves communication between various network elements and switches within the MNO's infrastructure. The internet is not used for this purpose.

Interconnection Between MNOs:

If the recipient of the SMS is on a different mobile network operator, interconnection points are used to transfer messages between MNOs. These interconnections can be established through physical connections, dedicated links, or IP-based connections. In the case of IP-based connections, the internet may be involved in routing messages between MNOs.

Messaging Gateways and SMPP:

In many cases, SMS messages are exchanged between MNOs and messaging service providers or aggregators using protocols like SMPP (Short Message Peer-to-Peer). These connections may be made over the internet or private networks. If internet-based connections are used, the internet is involved in transmitting messages between MNOs and intermediaries.

Messaging Service Providers:

If a messaging service provider is involved (for example, for bulk SMS or application-based messaging), they may use internet-based APIs or SMPP connections to send messages to MNOs.

Recipient's MNO:

Finally, the message arrives at the recipient's MNO, which routes it to the recipient's device. This process typically occurs within the MNO's network and doesn't involve the internet.

WHY THE INTEREST IN SMPP

I’ve been working on an App that will allow sending crypto using sms.
It got me interested in how sms actually works, and if i could implement an sms gateway myself.
That will allow me to send sms directly to my intended receiver.
Turns out I still need mobile network operators to make it work(their infrastructure specifically).