Android Telephony architecture works in 4 layers that are :

1. Communication Processor
2. Radio Interface Layer (RIL)
3. Framework Services
4. Applications

Let us try to understand them briefly one by one :

1. Communication Processor

It is an input/output processor to distribute and collect data from a number of remote terminals. It is a specialized processor designed to communicate with the data communication network.

2. Radio Interface Layer

It is a bridge between the hardware and Android phone framework services. Rather we say, it is a protocol stack for Telephone. It has two main components that are:

• RIL Daemon– It starts when the android system starts. It reads the system properties to find a library that is to be used for Vendor RIL.
• Vendor RIL– It is also known as RIL Driver. It can be understood as a library that is specific to each modem.

3. Framework Services

The telephony Framework starts and initializes along with the system. All the queries by Application API are directed to RIL using these services.

4. Application

These are the Application UI related to telephony such as Dialer, SMS, MMS, Call tracker, etc. These applications start with the android system boot up. These are tied with framework services of telephony.

Android Telephony Framework consists of two types of packages that are:

1. Internal Telephony Packages: This is generally the used for default telephony app.apk.

2. Open Technology Packages: This is for third-party apps.

These are 4 layers of Android Telephony

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