Explain what's SMS, how does it work, and the SMS architecture. Explain the components of this architecture to a beginner

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SMS stands for Short Message Service. It's a text messaging service that allows you to send and receive short text messages between mobile phones. Unlike modern messaging apps that use the internet, SMS uses the cellular network's signaling channels. Each message is limited to 160 characters, and longer messages are split into multiple parts. Here's how SMS works step by step. First, you type and send a message on your phone. Your phone then sends the message to the nearest cell tower. The cell tower forwards the message through the mobile network to a special server called the SMS Centre or SMSC. The SMSC stores the message and finds out where the recipient's phone is located. Finally, the message is delivered to the recipient's phone. If the recipient's phone is turned off or out of coverage, the SMSC will hold the message and retry delivery later. The SMS architecture consists of four main components. First is the Mobile Station, which is simply your mobile phone. Second is the Base Station Subsystem, which includes the cell towers and related equipment that communicate directly with your phone. Third is the Network and Switching Subsystem, the core network that manages calls, data, and user information. It includes components like the Mobile Switching Centre, Home Location Register, and Visitor Location Register. Finally, there's the SMS Centre, which acts as the central hub for storing and forwarding SMS messages throughout the network. Let me explain each component in detail. The Mobile Station is simply your phone - the device you use to type and read messages. It connects wirelessly to the mobile network. The Base Station Subsystem consists of cell towers that you see everywhere. These towers provide the direct wireless connection between your phone and the rest of the network. The Network and Switching Subsystem is the brain and backbone of the mobile network. It includes the Mobile Switching Centre which acts like a big switchboard, the Home Location Register which stores permanent information about your phone number, and the Visitor Location Register which tracks where your phone is currently located. Finally, the SMS Centre acts like a post office for messages, storing and forwarding them to their destinations. To summarize, SMS is a reliable text messaging service that works on any mobile phone without requiring internet access. Each message is limited to 160 characters and travels through a well-defined architecture from your phone to cell towers, through the core network to the SMS Centre, and finally to the recipient's phone. The SMSC ensures reliable delivery by storing messages and retrying if the recipient's phone is unavailable. While modern messaging apps offer more features, SMS remains universally compatible and works even when internet connectivity is poor or unavailable. This makes SMS an essential communication tool that continues to be widely used today.