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# DDS4CCM basics

The DDS4CCM connector itself is a CCM component placed between your component and DDS itself.
In DDS there're basically two entities which exchange data: DataWriters and DataReaders. To gain access to these entities, the DDS4CCM connector offers two basic types of ports (connectors) : DDS_Event and DDS_State. These basic ports have extended ports which allow the user to access the actual datareaders and datawriters. It'll depend on the functionality of your component which type of basic port you're going to use.
A DDS_Event DDS4CCM connector consists of the following extented ports:

- A DDS_Write port
- A DDS_Get port
- A DDS_Listen port

A DDS_State DDS4CCM connector consists of the following extended ports:

- A DDS_Update port
- A DDS_Read port
- A DDS_Get port
- A DDS_Listen port
- A DDS_StateListen port

See ccm_dds.idl for a complete overview of connector types, extend ports and their methods.

## Example

The Sender component of this Shapes tutorial writes a ShapeType struct (sample) to DDS every time the Controller invokes setSize or setLocation. The Sender therefor is connected to a DDS_Event connector and uses the DDS_Write extended port. To write a sample, the Sender uses the write_one method of the DDS_Write extended port (see ccm_dds.idl and the Shapes Sender executor file).

The Receiver listens to DDS for data. DDS invokes a listener callback method ( on_data_available) on the DDS4CCM connector which in turn invokes the on_data_available method on the Receiver component. To establish all this the Receiver is connected to a DDS_Event connector and uses the DDS_Listen extended port (see ccm_dds.idl and the Shapes Receiver executor file).

All this will be discussed in more detail later in this tutorial.

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