# Signal Composer

## Architecture

Here is a quick picture about the signaling architecture :

![GlobalArchitecture]

Key here are on both layer, **low** and **high**.

- **Low level** are in charge of handle a data exchange protocol to decode/encode and retransmit
 with an AGL compatible format, most convenient way using **Application Framework** event. These are divised in two parts, which are :
  - Transport Layer plug-in that read/write 1 protocol.
  - Decoding/Encoding part that expose signals and a way to access them.
- **High level signal composer** gathers multiple **low level** signaling sources and creates new
 virtuals signals from the **raw** signals defined (eg. signal made from gps latitude and
 longitude that calcul the heading of vehicle). It is modular and each signal source should be
 handled by specific plugins which take care of get the underlying event from **low level** or
 define signaling composition with simple or complex operation to output value from **raw** signals

There are three main parts with **Signal Composer**:

- Configuration files which could be splitted in differents files. That will define:
  - metadata with name of **signal composer** api name
  - additionnals configurations files
  - plugins used if so, **low level** signals sources
  - signals definitions
- Dedicated plugins
- Signal composer API

## Terminology

Here is a little terminology guide to set the vocabulary:

- **sources**
- **signals**
- **api**
- **event**
- **callbacks**
- **action**
- **virtual signals**
- **raw signals**

[GlobalArchitecture]: pictures/Global_Signaling_Architecture.png "Global architecture"