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How Does SMS Work?

Sometimes we take crucial things for granted–like the 560 billion SMS that are sent every month. Here’s what happens behind the scenes when an SMS is sent.

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According to our screentime survey, Americans spend close to 3 hours a day on their phone.

What do most people do when using them? Check, send, and answer text messages.

97% of American adults text weekly. Despite this, many don’t know how it works.

That’s understandable: as one of the oldest and most commonly used mobile communication methods, there’s quite a lot that happens in the background when you hit send.

This article lifts the veil and explains exactly how SMS works–all in a layperson-friendly way.

What Is SMS?

Cellphones constantly send and receive data from cell towers for general updates and information. 

SMS came from the realization that text characters could be piggybacked onto these “signals” and text messaging as we know it was born

That’s why most SMS definitions reference communications protocols–a “protocol” is just a set of rules for how two entities communicate. 

With that in mind, we can say that Short Messaging Service (SMS) is a communications protocol created to send and receive text messages over cell towers.

On December 3, 1993, the English software engineer Neil Papworth used his computer to send the world’s first short SMS to Vodafone director Richard Jarvis wishing him a Merry Christmas.

How Does SMS Work?

Let’s say you want to text a friend that you’re running late for dinner. You type up the message, “Hello! Sorry, I’m running late. Be there in 10.”

First, your phone converts your message into the GSM 7-bit alphabet

Without going into too much detail, this alphabet takes the words in the above message and turns them into the tiniest bits of data that can then be transmitted to a cell tower. 

This includes your message and some basic info about it such as its timestamp and the recipient’s phone number.

Once the cell tower receives your message, it sends it to a system called the Short Message Service Center (SMSC). 

The SMSC checks who your friend–the recipient–is and then checks if they are in range. If they are, the message is then sent to the tower nearest to them and then, finally, their mobile phone. 

Your friend’s phone then turns the messages back from the GSM 7-bit alphabet into characters by using the same code, but in reverse.

What’s particularly neat is that if the SMSC can’t find the phone, the message will just bounce around in its system until the moment the phone reconnects, at which point it sends it immediately.

With modern mobile devices you’ll notice that messages longer than 160 characters–the standard character limit for SMS–are being sent to your phone and delivered as one message. These messages are known as MMS (multimedia messaging service.)

The difference between MMS and SMS is that MMS uses a different communications protocol that allows people to send multimedia content like images, audio, and video. MMS message supports a maximum of 1,600 characters. 

If you want an even more granular view of how SMS works, from the voltage fluctuations of tapping a glass on a phone to more technical details on the SMS cellular network, this detailed article on the route of a text message is for you.

What Is A2P SMS Messaging?

Person-to-Person SMS (P2P) is text messaging that follows the above journey. There is also application-to-person messaging.

A2P SMS messaging is defined as the process of sending text messages from an application, such as SimpleTexting, directly to a mobile user. It’s also known as “business” or “enterprise” SMS.

One of the main differences is that SMS aggregators sit between an A2P platform and all of the wireless carriers to ensure carrier compliance and that the message goes to the right carrier SMSC.

You can use A2P SMS messaging to send a large number of text messages (mass texting) or for two-way communication (business texting).

What Is an SMS Delivery Report?

An SMS delivery report is a message from an SMCS that notifies you that your SMS message sent from your device was delivered to the intended recipient.

You can calculate the delivery rate in an A2P messaging service by looking at the percentage of delivered versus intended messages. In SimpleTexting, you can see the success rate underneath each sent campaign.

The Difference Between SMS and OTT Applications

Over-the-top messaging apps also referred to as “OTT messaging apps” are instant messaging services provided by third parties. 

They are often seen as an alternative to SMS and include apps like WeChat, Facebook Messenger, and WhatsApp. They bypass the telecommunications companies and mobile networks by using the internet to transfer data.

However, there are a few benefits to SMS versus these messaging apps, including:

  • Texting doesn’t require an internet connection
  • Not everyone uses the same messaging apps–but everyone can send and receive texts
  • You don’t need a smartphone to use SMS
  • SMS doesn’t require sharing personal information or granting access to a phone’s software or hardware

The Wrap on How SMS Works

The next time you’re running late for a dinner, and you quickly tap out an apology, you’ll be a little more aware of the magic that happens behind the scenes.

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