Before the internet became a thing and mobile apps like WhatsApp, Signal, etc emerged for text communication on mobile devices, there was SMS. SMS stands for Short Messaging Service and that's pretty self explanatory as messages are limited to 160 characters in length.

With that said, you have probably sent out an SMS message before and even if you have never sent one, you've definitely received one. Have you ever wondered how it's possible to send SMS messages across different networks to different devices? That's thanks to the GSM (Global System for Mobile Communications) standards which ensure compatibility and interoperability between mobile devices and networks.

A little about cellular networks

Cellular networks allow mobile devices such as smartphones, tablets, and other wireless-enabled devices to communicate with each other and access the internet. They are made up of several components that work hand in glove. These include the mobile switching center (MSC), central office (CO), cell, base station, antenna, etc. As time passes by, cellular networks have evolved with improvements communication capabilities, data speeds, and the range of services offered to users. This evolution happened in "generations" reason for the "G" you see in 2G, 3G, etc

2G, 3G, 4G & 5G

Before we dive into the these generations, it is worth talking about 1G - the first generation which laid the foundation for mobile communication. It made use of analog signals for voice communication and it had several limitations which includes limited capacity to support a high volume of users, no encryption, and low call quality. The other generations came in to improve the quality of service of previous generations.

• 2G ( Early 1990s to early 2000s): The second generation significantly advanced the shortcomings of is predecessor and played a crucial role in the advancement of mobile communication. It played a huge role in improving voice quality and this was where GSM became dominant as it was time-division multiple access (TDMA)-based. IN TDMA, all the signals are given timeslots to pass through a single channel. What made 2G really special was phone conversations became encrypted, more users per frequency band, the introduction of SMS messages and the SIM (Subscriber Identity Module) card. International roaming was also introduced where users could use their mobile devices in other countries with 2G network.

• 3G (Early 2000s to around 2010): The third generation came about with higher data transfer rates, introduction of mobile internet access, video calling, and multimedia services.It made use of Wideband Code Division Multiple Access (WCDMA), CDMA2000, and others

• 4G/4.5G(LTE Advanced and LTE Advanced Pro) (Around 2010 onwards): The generation brought about significant increase in data speeds, lower latency, and improved capacity. 4G enabled widespread mobile broadband access, supporting applications like video streaming and online gaming. The primary standard was Long-Term Evolution (LTE) which is a wireless broadband standard for mobile communication and data transfer.

• 5G (2019 onwards): The fifth generation came in with extremely high data speeds, low latency, and support for a massive number of connected devices. It was designed to meet the diverse requirements of applications like augmented reality, virtual reality, IoT, and autonomous vehicles. Its primary standard is 5G NR (New Radio) which is designed to provide faster and more responsive mobile experiences than previous 4G standards.

Handling of SMS in 2G, 3G, 4G & 5G

1. 2G
The user starts by composing a message on their mobile device which is then forwarded to the Short Message Service Center (SMSC) - a centralized server that is responsible for storing, forwarding, and delivering SMS messages. It receives the incoming message and checks the address of its recipient to know where the message will be delivered to. The SMSC then checks if the recipient's device is available. If it is reachable, the SMSC forwards the message to their home location register (HLR), which is a database that contains subscriber information. If the recipient isn't available, the SMSC stores the message until the recipient become available (e.g turning on device). After the message has been routed to the receiver, the SMSC requests for a an acknowledgement to prove the message has indeed been delivered. If you notice when you send out an SMS you will find a single tick by the message blob which signifies its been sent. When the SMSC receives the acknowledgement of successful delivery it then notifies the user's device reason you realize the single tick changes to double ticks.

2. 3G
With 3G, it follows the same steps as 2G. What makes 3G better is the rate of data transfer is faster and there is the ability for users to send pictures, videos, audios through Multimedia Messaging Service (MMS)

3. 4G
4G follows same steps as 2 & 3G. What makes it better than its predecessors is all the capabilities of the previous generations are further enhanced and more efficient.

4. 5G
With 5G, once the message is composed and sent, it goes to the 5G core (5GC) network. Within the 5GC, ther is the Session Management Function (SMF) which is responsible for handling the signaling and routing of messages. It also contains the Access and Mobility Management Function (AMF) which is for handling SMS when devices move across different areas within the 5G network. Furthermore, there is the User Plane Function (UPF) which ensures the efficient and reliable transport of SMS data between the sender and recipient. The 5G network processes and delivers the message similar to that of previous generations but with significantly higher data rates.
5G networks are designed to provide low-latency communication. This can enhance the real-time delivery of SMS messages, making the service more responsive.