Complete End to End Call Flow of Short Message Service(SMS)

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 We will use above picture as refference.

For example,  Subscriber A(MS A) want to send Short message to subscriber B(MS B)

1.  Then subscriber A will type the message on the phone and select subscriber B as the destination address.
2.  After subsriber A, hit send button, MS terminal will request channel assignment to the BTS and BSC and then forward the MS A Information to MSC A
3.  MSC A will check MS A(subscriber A) data from VLR, if the telecommunication operator has many SMSC, it will identified which SMSC this MS A belong to.
4.  After that MS A will transfer the short message to MSC A, at this point on MS A phone will display “sending…” notification
5.  MSC A routes the message to the interworking MSC(IW MSC), beside use IW MSC usually it can use STP
6.  IW MSC will route the short message to the SMSC.
7.  SMSC Send a notification report to IW MSC and then to MSC A, MSC B and come to subscriber. At this point MS A phone will display “Message Sent” but not yet delivered to MS B
8.  All Above step called MO(Message Originating), we will come on MT(Message Terminating) on the next step
9.  SMSC Transfer the short message to the Gateway MSC(GW MSC)
10.  The GW MSC ask information from the HLR for routing the short message
11.  GW MSC will forward the message to MSC B, and MSC B will check MS B data from VLR
12.  MSC B Transfer the short message to MS B through BSC and BTS
13.  MSC B Send delivery report to GW MSC, and GW MSC will forward to HLR and SMSC. At this point MS B receive the message and can read it.
14.  Delivery report will send by SMSC to MS A after MS B receive the message.

Quite log story  . but this simple thing need so many interworking between quite alot of telecommunication network element.