Short Message Peer-to-Peer
Short Message Peer-to-Peer (SMPP) in the telecommunications industry is an open, industry standard protocol designed to provide a flexible data communication interface for the transfer of short message data between External Short Messaging Entities (ESMEs), Routing Entities (REs) and Message Centres.[1]
SMPP is often used to allow third parties (e.g. value-added service providers like news organizations) to submit messages, often in bulk, but it may be used for SMS peering as well. SMPP is able to carry short messages including EMS, voicemail notifications, Cell Broadcasts, WAP messages including WAP Push messages (used to deliver MMS notifications), USSD messages and others. Because of its versatility and support for non-GSM SMS protocols, like UMTS, IS-95 (CDMA), CDMA2000, ANSI-136 (TDMA) and iDEN, SMPP is the most commonly used protocol for short message exchange outside SS7 networks.
SMPP information credits: Wiki