how does SMPP fit in the SMS architecture

[sms_guy]

Hello,

I am a noob and am trying to understand the SMS archatecture.
I am not sure hwo does SMPP fit in the SMS world.
Is SMPP just a layer 4 (transport protocol) which sets up a session between an ESME and a SMSC and the regular SMS PDU (as defined by 23.040) is transmitted between the, the format of the SMS being the same which is received by the SMS client.

or is the format of the SMS between the ESME and SMSC & the SMSC and the MS different. with the format of the PDU between SMSC and MS being defined by 23.040 and a different format between SMSC and the ESME?

i was trying to figure out where SMPP fit and came across this article
http://expertanswercenter.techtarget.com/eac/knowledgebaseAnswer/0,295199,sid63_gci984255,00.html

which states "The SMS Forum has recently released an XML variant of SMPP called Mobile Messaging Access Protocol (MMAP). It essentially provides a mechanism to package the SMPP commands as SOAP messages and send them over SMS."

now i am confused how can SMPP be sent over SMS? i thought SMS is sent using SMPP between the ESME and the SMSC

[SMS Forum Support]

read the introduction of SMPP V5.0 and look at the diagram that depicts SMPP in the context of the mobile network

[sms_guy]

thanks for the link,

i have gone through the introduction and i have come to the conclusion that SMPP is only used
between the ESME and the SMSC (from picture 1)
it sits on top of TCP/IP

Is MMAP used over the air, hence it uses SMS as a carrier?