What is the difference between SMPP ESME and SMPP SMSC? SMPP ESME Trunk created: DIDWW SMPP will act as SMSC and wait for connection to be initiated. SMPP SMSC Trunk created: DIDWW SMPP will act as ESME and initiate, maintain the connection. If you are unable to find a satisfactory answer to your question in this FAQ, please explore our DIDWW knowledgebase, or contact customer service at firstname.lastname@example.org. For additional support options, see https://www.didww.com/Contacts/.