SMPP(Short Message Peer to Peer) is a standardized protocol that handles the communication between SMSC and other SMS entities. It is an interface between the SMSC and NON-PLMN SMEs ( Short Message Entity). Typically it specifies the interface used between the SMSC and ESME ( External Short Message Entity) systems. This SMPP protocol may be implemented over a variety of underlying communications protocols  X.25 or TCP/IP over internet or leased line by pluging in the IP cables into the SMPP server and opening the correct SMPP port.

The diagram below shows how ESME is connected to the SMSC via the SMPP server (SMPP gateway).

Fig: ESME to SMSC Interconnection (click to enlarge)

The SMPP Agent (process) is responsible for maintaining the communication link with the ESME, accomplishing the conversion of the SMPP standard message and the internal message of the SMSC ( Short Message Service Centre ) system, and providing the external short message entity (ESME) with the open interface to access the SMSC system. The current version of SMPP protocol is 3.4  (SMPP3.4).

As explained in the communication between ESME and SMSC servers post, there are two transmission modes between ESME and SMSC servers, namely-

1. Transmitter Mode
2. Receiver Mode

The following diagram explains the role of SMPP server during the connection establishment and release between the ESME server and SMS server

Transmission Mode:

Fig: Role of SMPP server during transmission mode(click to enlarge)

In the figure,

Fig: Role of SMPP server in Receiver Mode(Click to Enlarge)

In the figure:

•Steps (1) to (4): ESME is bound with SMSC in Receiver mode and is ready to receive short messages from SMSC;

•Steps (5) to (8): SMSC distributes a short message to ESME.

•Steps (9) to  (12): Disconnect the link between ESME and SMSC.