Let us assume you are in conversation with someone on your phone while traveling on a train. Currently, your phone is connected to a nearby cellular tower that provides a wireless connection to your phone and transfers voice signals to the other end of the phone call. When you move far away from your current connected cellular tower, do you think the phone will still be connected to the current cellular tower? You might be thinking, the phone will connect to a different cellular tower and get the operator signal. Yes, you are right!. But wait! you were in a conversation on the phone, which means your voice packets are in transit, but even after the phone switched the wireless connection from one cellular tower to another cellular tower, you did not experience call drop or voice quality deterioration. How is this even possible?
Before answering this question, let us watch the following video.
Now probably you can imagine how a mobile device can use cellular technology to remain connected in a different geographic location without losing connection. But this does not explain the scenario we explained before the video. How the audio call is being continued even after the phone loses its connection with the previous cellular tower. Its time to watch the second video.
Ok!
Now you got an overall idea of the handover procedure. If you are from an engineering background, you may realize the following problems:
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What about the internet connection? How does your youtube streaming video keep playing without loss of quality?
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With what protocol your cell phone is talking to nearby towers? (I assume you are familiar with the concept of “Protocol” from Networking)
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Which is the enabler entity for the quality of service of a video call you did using a 4G capable phone?
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In a roaming scenario, how can your phone gets a connection from the roaming operator network?
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What is the role of the operator network in the services they provide, for example, audio, video call, internet service?
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When you power on your phone, how your phone remembers the previously connected location (cell area)? Even if the phone remembers the previous cell area, how it can get access from the operator network? What about authentication, identity, and security issues?
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Assuming your phone talks to the operator network through a cell tower, how the operator network locates your phone and signal you for incoming calls?
To know the answers to the above questions, we need to understand the Mobility Management Protocol and Session Management Protocol. These protocols are defined by the 3GPP organization. In short, Mobility Management Protocol handles, location tracking, roaming, handovers like scenarios, and Session Management Protocol handles data service (Volte/Vilte call, Internet, etc.). I will end this article here. In the upcoming article, I will discuss more on the Cellular Processor (or the modem) and Mobility Management Protocols. You can check further on Cellular Processor on this link (https://android.stackexchange.com/questions/120680/what-is-cp-and-ap-and-what-are-these-options-used-for)
Video Reference
- [Mobile Communication 3 - What is a Handoff Procedure ?] by EzEd Channel
- [How does your mobile phone work? | ICT #1] by Learn Engineering