[Did You Know] Why can you call from Docomo to au? The 'universal rules' behind smartphone communication

I'm ShibuYoshi, a network engineer.
Do you ever think about which mobile carrier the other person is using when you make a call or send a LINE message?

You probably don't think about it at all.
Whether you are on Docomo, or the other person is on au, SoftBank, Rakuten Mobile, or even a friend abroad, as long as you know their phone number, it connects as if it were the most natural thing in the world.

But if you think about it carefully, isn't it a bit mysterious?
“Even though we are using different companies' networks, why does it connect without getting lost?”you might wonder.

Actually, this is because there is a“universal rule (blueprint) that must be strictly followed”in the world of smartphone communication.

Today, I would like to explain the organization that supports the background of smartphone communication called “3GPP (3rd Generation Partnership Project)” and the “architecture (network mechanism)” they create, using analogies and avoiding technical jargon as much as possible!

📱 The reason it connects to other companies' smartphones is that they speak the “same language”

In conclusion, the reason smartphones from different mobile carriers can connect to each other is thatmobile carriers around the world build their networks based on the “exact same blueprint.”

What would happen if each company built its communication system using different standards?
Languages like Docomo-ese, au-ese, and SoftBank-ese wouldn't be understood, and a special translation system would be needed every time you called another company, making it impossible to connect instantly as we do now.

To prevent that, there is an international team that has decided, “Let's all build our networks using the same rules (blueprints)!”
That is the **“3GPP (Third Generation Partnership Project).”**

🌍 The mobile industry's rule-making team “3GPP”

3GPP is a project where the brightest minds from telecommunications companies and manufacturers around the world (such as Apple, Samsung, and Ericsson) gather to decide the rules for mobile phone communication.

The terms “4G” and “5G” that we often hear—those are also the names of the rules created by 3GPP after discussing, “Let's make the next mechanism like this!”

The rules they create are technically called **“architecture (structure/blueprint).”**

This is the overall picture of 5G's SBA (Service-Based Architecture), but it has too much technical jargon and is difficult, isn't it? Don't worry, I will explain it in a super simplified way.

🚗 Let's compare the “3GPP architecture” to roads and cars

“Architecture” might sound difficult, but it is essentially like **“traffic rules for roads and the mechanism of a traffic control center.”**

Let's compare smartphone communication to “traveling by car” and see what kind of blueprint 3GPP is drawing. There are only “three” main characters!

1. Smartphone (device) = “A moving car”

This is the smartphone you are holding in your hand. In the world of communication, it is the starting point that makes the request to “connect to the network!”

2. Base station (antenna) = “Highway toll gate/interchange”

These are the antennas found all over town. They act as an entry point, catching radio waves sent from your smartphone (the car) and guiding them to a dedicated network (the highway).

3. Core Network = "The Super-Efficient Traffic Control Center (The Brain)"

This is the most important part! Located even further behind the base stations, this is a massive group of servers that acts as the "brain" of communication.
The control center handles tasks like the following in an instant.

• "Who does this car (smartphone) belong to? Have they paid their service plan?" (Identity/Contract Verification)

• "Where is this car currently located in Tokyo?" (Location Management)

• "Where does the caller want to reach? Here is the shortest route!" (Route Determination)

• "Let's record the charges for the usage." (Billing)

🤝 Why can you connect to other companies? (The Answer)

Once you've come this far, the answer to the biggest question becomes clear.

When you call from Company A's smartphone to Company B's smartphone, Company A's "control center (core network)" and Company B's "control center" exchange data directly.

"I want to connect a call from one of our customers to you; where is the recipient?"
"Okay, the recipient is currently under this base station, so I'll connect you!"

The reason they can coordinate smoothly across companies like this is because both Company A and Company B have built their control centers according to the "same architecture (blueprint) created by 3GPP".

Since the internal systems are built to the same standards, they can coordinate perfectly even if the companies are different or if the call crosses national borders.

Bonus

Question 1: If the blueprints are the same, how do mobile companies create their own "differences"?

This brings up a question.
"If everything is built using the same global rules (3GPP), where do they differentiate themselves from other companies?"

Actually, even though the "rules are the same," each carrier is free to decide "what materials to use and how to maintain the roads." Each company focuses on intense innovation (differentiation) in the following areas.

• Differences in allocated "radio waves"
  The radio waves (frequencies) allocated to each company by the government are different. Which roads (radio waves) you own—such as "platinum bands that easily wrap around obstacles" or "speed-focused radio waves"—becomes the foundation of your strength.
  

• "Where and how many" base stations to build
  Differences in "ease of connection" arise depending on where they concentrate their capital investment, such as "We will strengthen subway and building coverage!" or "We will cover mountainous areas and campsites!"
  

• Craftsman-level "tuning"
  This might be the biggest difference of all. Comfort can change dramatically just by changing the angle of a base station antenna by a few degrees or fine-tuning the timing of radio wave handovers. Even when using the same equipment, it is a world where the "tuning skills of radio wave craftsmen (engineers)" behind the scenes make all the difference.

Question 2: Why does such a complex system never stop?

And one more thing. Smartphone communication is now a 'social infrastructure that must never stop.' To ensure communication remains active even during disasters or technical issues, 'extraordinary safety measures based on the premise of failure' are taken behind the scenes.

1. Always having a 'shadow' ready (redundancy)
   The servers and communication cables that act as the brain are always provided in 'two or more' sets. Even if the main one breaks, the sub takes over instantly, so we don't even notice the failure.
   

2. Distributing the brain nationwide (disaster recovery)
   To ensure that even if the Tokyo control center goes down completely due to a major earthquake, it will be okay, centers with the same functions are built in distant places like Osaka and Kyushu. A cooperative system is in place where if Tokyo fails, Osaka takes over.
   

3. Predicting congestion and changing routes (load balancing)
   When people gather all at once, such as during New Year's, large-scale concerts, or disasters, 'communication congestion' occurs. To prevent this, the system is monitored 24/7, 365 days a year, and recently AI is also used to predict that 'this area is likely to be congested in a few minutes.' It automatically diverts cars (data) to other empty routes to prevent a breakdown.
   

4. 'In-house generators' that withstand power outages
   The reason smartphones can be used even when the city loses power due to a typhoon is that important base stations and centers have 'large batteries' or 'private power generators.' Ingenuity to maintain communication on its own is spread throughout the system.

💡 Summary: The amazing mechanism that supports the ordinary

The reason we can naturally call friends on other carriers or send messages every day is thanks to an organization called 3GPP that creates a precise 'universal communication blueprint (architecture)' for us.

Smartphones, antennas, and the brain that works behind the scenes (core network).
It is because these perform a perfect relay according to the rules that our lives are so convenient.

Next time you call someone, try to imagine the back side of the communication for a moment, thinking, 'Oh, my smartphone just went through a base station, and the control center found the other party for me!'

Thank you for reading until the end.

I write various other articles, so please feel free to check them out if you like.