Editing Short Message Peer-to-Peer (section)

==Operation==

SMPP uses the [[client–server model]] of operation, despite "peer-to-peer" in the name. The [[short message service center|Short Message Service Center (SMSC)]] usually acts as a server, awaiting connections from ESMEs. When SMPP is used for SMS peering, the sending MC usually acts as a client.

The protocol is based on pairs of request/response PDUs ([[protocol data unit]]s, or packets) exchanged over [[Open Systems Interconnection|OSI]] layer 4 ([[Transmission Control Protocol|TCP]] session or [[X.25]] SVC3) connections.<ref>{{cite book
 |author=Neil Croft
 |title=2012 Information Security for South Africa
 |chapter=On forensics: A silent SMS attack
 |chapter-url=https://ieeexplore.ieee.org/document/6320454
 |publisher=[[IEEE]]
 |year=2012
 |pages=1–4
 |issn=2330-9881
 |doi=10.1109/ISSA.2012.6320454|isbn=978-1-4673-2159-4
 |s2cid=13448347
 }}</ref> The [[well-known port]] assigned by the [[Internet Assigned Numbers Authority|IANA]] for SMPP when operating over [[Transmission Control Protocol|TCP]] is 2775, but multiple arbitrary port numbers are often used in messaging environments.

Before exchanging any messages, a bind command must be sent and acknowledged. The bind command determines in which direction will be possible to send messages; bind_transmitter only allows client to submit messages to the server, bind_receiver means that the client will only receive the messages, and bind_transceiver (introduced in SMPP 3.4) allows message transfer in both directions.<ref>{{cite book|url=https://books.google.com/books?id=P0xs_9NSIy8C|pages=137–138|title=SMS and MMS Interworking in Mobile Networks|author1=A. Henry-Labordère|author2=Vincent Jonack|publisher=[[Artech House]]|year=2004|isbn=1-58053-890-8}}</ref> In the bind command the ESME identifies itself using system_id, system_type and password; the address_range field designed to contain ESME address is usually left empty. The bind command contains interface_version parameter to specify which version of SMPP protocol will be used.

Message exchange may be synchronous, where each peer waits for a response for each PDU being sent, or asynchronous, where multiple requests can be issued without waiting and acknowledged in a skew order by the other peer; the number of unacknowledged requests is called a ''window''; for the best performance both communicating sides must be configured with the same window size.

===Versions===

The SMPP standard has evolved during the time. The most commonly used versions of SMPP are:

* SMPP 3.3 the oldest used version (despite its limitations, it is still widely used); supports [[GSM]] only. Generates an immediate response for each message sent.
* SMPP 3.4 adds optional [[tag–length–value]] (TLV) parameters, support of non-GSM SMS technologies and the [[transceiver]] support (single connections that can send and receive messages). The exchange of SMPP request and response PDUs between an ESME Transmitter and SMSC may occur synchronously or asynchronously.
* SMPP 5.0 is the latest version of SMPP; adds support for cell broadcasting, smart flow control. {{Asof|2025|post=,}} it is not widely used.

The applicable version is passed in the interface_version parameter of a bind command.