What is SMS?
–Short Message Service
SMS Send from A Party to B Party
How Does SMS Work?
SMS has 2 parts
–MO SMS (Mobile Originating)
- SMS sent from A Party and will received by service center SMSC (Short message service center)
–MT SMS (Mobile Terminating)
- SMSC forward the SMS to B Party
- Every mobile subscriber attached with a MSC. MO SMS initiated by handset and transfer to MSC where destination address will be service center. Service center is known as SMSC. This MO SMS is called MO-FWSM (MO-Forward SM)
- SMSC forward SMS in 2 step communication
–First it will search for location(VLR). This is called SRI-SM ( Send Routing Information for SM)
–2nd it will forward the SMS to the identified location (MSC/VLR). This is called MT-FWSM (MT Forward SM)
- SMSC send this request to HLR to get the subscriber VLR(Visitor Location Register) which is co-located with MSC and IMSI (International Mobile Subscriber Identity).
- On return HLR will provide the MSC/VLR Address and subscriber IMSI.
- SMSC Initiate the MT-FWSM(MT Forward SM) as soon as it gets the SRISM feedback. MSC/VLR will forward the SMS to the B Party. In case any error like subscriber unavailable or memory full MSC will return the error code.
- Alert Service Center
–HLR will initiate ASC in case of subscriber return. HLR flag is set by SRISM in case of subscriber is absent.