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What is SMS and How does it work

SS7

What is SMS?

–Short Message Service

–Unicode message

–ASCII

SMS Send from A Party to B Party

SMS-a-b

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

SMS-work

 




MO SMS

  • 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)

SMS-mo

MT SMS

  • 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)

 

SRI-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.

SMS-srism

MT FWSM

  • 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.

SMS-fwsm

ASC

  • Alert Service Center

–HLR will initiate ASC in case of subscriber return. HLR flag is set by SRISM in case of subscriber is absent.

SMS-asc

 

 

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