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What is the role of a Short Message Service Center (SMSC) in GSM?

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The Short Message Service Center (SMSC) is a crucial component in GSM (Global System for Mobile Communications) networks, responsible for the storage, forwarding, and delivery of Short Message Service (SMS) messages. Here's a detailed technical explanation of the role of an SMSC in GSM networks:

  1. SMS Origination:
    • When a mobile subscriber initiates the sending of an SMS, the SMS message is first sent to the Short Message Service Center (SMSC). This process is known as SMS origination.
  2. Message Submission:
    • The SMS message is submitted to the SMSC by the Mobile Station (MS), typically through the Mobile Switching Center (MSC). The MSC serves as the interface between the MS and the SMSC.
  3. Message Storage:
    • The SMSC stores the SMS message temporarily until it can be successfully delivered to the intended recipient. The storage includes information about the sender, recipient, and the content of the message.
  4. Recipient Address Resolution:
    • The SMSC determines the routing information for the recipient's location. It queries the Home Location Register (HLR) to obtain the current location of the recipient's Mobile Station (MS).
  5. Delivery Attempt:
    • The SMSC attempts to deliver the SMS message to the recipient's MS. If the recipient is within the same network, the SMSC routes the message to the appropriate MSC for further delivery. If the recipient is in a different network, the SMSC interacts with other network elements, including Gateway MSCs (GMSCs) and external SMSCs.
  6. SMSC Interconnection:
    • In the case of an SMS message destined for a subscriber in another network or when interconnecting with external networks, the SMSC may communicate with other SMSCs or External Short Message Entities (ESMEs) through signaling protocols such as the Short Message Peer-to-Peer (SMPP) protocol or other relevant protocols.
  7. Message Delivery:
    • The SMSC forwards the SMS message to the recipient's MSC for final delivery to the recipient's MS. The MSC routes the message to the appropriate Base Station System (BSS) and cell for radio transmission to the recipient's mobile device.
  8. Delivery Confirmation:
    • Upon successful delivery of the SMS message to the recipient's MS, the recipient's MS sends an acknowledgment (delivery report) back to the SMSC, confirming that the message has been received.
  9. Message Routing Decisions:
    • The SMSC makes routing decisions based on factors such as the availability and location of the recipient, network conditions, and the delivery status of the SMS message. It ensures that the message is efficiently routed through the network to reach the recipient.
  10. Message Storage for Retry:
    • If the initial delivery attempt fails (e.g., due to the recipient being unavailable or out of coverage), the SMSC may store the message temporarily and retry the delivery later based on predefined retry intervals.
  11. Message Expire and Deletion:
    • The SMSC manages the expiration of SMS messages. If a message is not successfully delivered within a specified time frame, the SMSC may delete the message from its storage.
  12. Message Billing and Charging:
    • The SMSC is involved in the billing and charging processes related to SMS messages. It tracks the number of messages sent and received, contributing to the accurate billing of subscribers.

In summary, the Short Message Service Center (SMSC) in GSM networks plays a central role in the storage, forwarding, and delivery of SMS messages. It interacts with various network elements, including the MSC, HLR, BSS, and other SMSCs, to ensure the efficient and reliable delivery of SMS messages between mobile subscribers within the same network or across different networks.