The Short Message Peer to Peer (SMPP) protocol is an open, industry standard protocol designed to provide a flexible data communications interface for transfer of short message data between a Message Center, such as a Short Message Service Centre (SMSC), GSM Unstructured Supplementary Services Data (USSD) Server or other type of Message Centerand a SMS application system, such as a WAP Proxy Server, EMail Gateway or other Messaging Gateway. Using the SMPP protocol, an SMS application system called the ‘External Short Message Entity’ (ESME) may initiate an application layer connection with an SMSC over a TCP/IP network connection and may then send short messages and receive short messages to and from the SMSC respectively. The ESME may also query, cancel or replace short messages using SMPP. SMPP supports a full featured set of two-way messaging functions such as: