Editing External Short Messaging Entity (section)

==Relation between SMSC and ESME==
ESME always connects to SMSC using a [[TCP/IP]], [[X.25]], etc. and then binds for the service it needs from SMSC.

For [[Short Message Peer-to-Peer|SMPP]] it can bind for Receiving only service, Transmitting only service or both (Transceiver service). Before [[Short Message Peer-to-Peer|SMPP]] 3.4 it was required to have two different connections, one for Transmitting and the other one for Receiving. Starting with [[Short Message Peer-to-Peer|SMPP]] 3.4 a Transceiver connection is enough for both.

The relation between ESME and SMSC is somehow a master-slave relation because SMSC is providing services to ESME, and usually ESME just uses these services from SMSC. One of the functions of the SMSC is to store and forward the messages while the ESME does not have this function. When a message is sent by an ESME to SMSC towards its destination, this message may stay in a SMSC queue until its destination will become available. During this time the ESME has the options to cancel the message in queue, to replace it or to check its status. ESME can also send a message to multiple destinations which will be handled by SMSC.

ESME are usually termination points of an SMS network while SMSC are the core of it. SMSC can connect between them while ESME only connects to an SMSC. [[Short Message Peer-to-Peer|SMPP]] protocol is designed exactly in this manner for connecting a small end of the SMS network (which is an ESME) to the entire SMS network (which is done through the SMSC)

ESME is submitting MTs to SMSC, while SMSC is delivering MOs to ESME.