How does MSC forward a SMS to the mobile

Question

What is the role of BSC and BTS in forwarding the message to the mobile..

Answer 1

The BSC and BTS are concerned with lower layer protocols, eg setting up a connection with an MS over the air interface. The short message service protocol is defined in 3GPP TS 23.040 (Technical realization of the Short Message Service (SMS)), and it is part of the Communication Management (CM) layer, which is higher.

What this means in reality, is that SMS PDUs look like data load to the BSC. It doesn't unpack them or do anything with them, but just passes them straight on. This is illustrated in a standard GSM protocol stack diagram, like the one half way down the page [here http://personal.ee.surrey.ac.uk/Personal/L.Wood/constellations/tables/gsm.html] . You can see that the CM layer is only implemented on the MS and MSC, not in the BSC or BTS.