Paging Procedure in 2G
When the UE is in STANDBY state in 2G, the SGSN can't send packets to the UE.
When the SGSN receives down-link packets, that it should deliver to the UE, the SGSN initiates 'Paging' procedure towards the UE.
This is done, in order to move the UE to READY state. Then the SGSN, will be able to deliver the packets to the UE.
Please remember that, in STANDBY state, the network knows the UE exists in which RA, but it doesn't know the UE exists under which cell in this RA.
Therefore, the SGSN will send the paging to all cells under the RA the UE exists in.
'Paging' signaling in 2G
- The SGSN receives down link data, that it should send to the UE that exists in STANDBY state.
- The SGSN sends 'paging request' to the BSC. This message includes the RA the UE exists in.
- The BSC will forward the paging request to all the cells exist under this RA.
- When the UE receives the paging, it will reply with any frame, which will be interpreted by the BSC as a paging response.
- The BSC, will forward the frame sent from the UE to the SGSN, including the cell identity the UE is currently under. Now the UE moved to READY state, and the SGSN will be able to send the data to it.
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