# Data Subscription
After you opened a [session](/cortex-api/session.md) with a headset, you can [subscribe](/cortex-api/data-subscription/subscribe.md) to one or more data streams.
Each data stream gives you **real time** access to data from the headset (EEG, motion...) or data calculated by Cortex (band powers, mental command...)
After you successfully subscribe to a data stream, Cortex will keep sending you [data sample objects](/cortex-api/data-subscription/data-sample-object.md).
A subscription is linked to a [session](/cortex-api/session.md). All the subscriptions of a session are automatically cancelled when the session is closed. You can call [unsubscribe](/cortex-api/data-subscription/unsubscribe.md) to cancel a subscription.
The available data streams depend on the [license](/cortex-api/authentication/getlicenseinfo.md) of the user, and the model and [settings](/cortex-api/headset/updateheadset.md) of the headset. For an EPOC Flex, it also depends on the EEG sensor mapping.
## Data streams
Each data stream is identified by its name: "eeg", "mot", "dev", "eq", "pow", "met", "com", "fac", "sys".
| Stream | Description |
| ------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| eeg | The raw EEG data from the headset. |
| mot | The motion data from the headset. |
| dev | The device data from the headset. It includes the battery level, the wireless signal strength, and the contact quality of each EEG sensor. |
| eq | The EEG quality of each EEG sensor.
Please read this page to understand the difference between the contact quality and the EEG quality.
|
| pow | The band power of each EEG sensor. It includes the alpha, low beta, high beta, gamma, and theta bands. |
| met | The results of the performance metrics detection. |
| com | The results of the mental commands detection. You must [load a profile](/cortex-api/bci/setupprofile.md) to get meaningful results. |
| fac | The results of the facial expressions detection. |
| sys | The system events. These events are related to the training of the mental commands and facial expressions. See [BCI](/cortex-api/bci.md) for details. |
## Data streams availability
Depending on the license and the model of the headset, some streams may be available or not, and may send [data samples objects](/cortex-api/data-subscription/data-sample-object.md) at a different rate.
| Stream | Supported headsets | Sample rate in hertz |
| ------ | -------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| eeg | All, but requires a license | 128 or 256, depends on the headset and its settings.
The license must contain the scope "eeg".
You must activate the session before you subscribe.
Please check the documentation of your headset.
|
| mot | All | Disabled, 32, 64, 128, depends on the headset and its settings.
6.4 hertz for MN8.
Please check the documentation of your headset.
|
| dev | All | 2 |
| eq | All | 2 |
| pow | All | 8 |
| met | All (EPOC Flex requires a [special EEG sensor mapping](/cortex-api/headset/controldevice.md#special-eeg-sensor-mapping-for-epoc-flex)). | 2 if the license contains the scope "pm" and you activate the session before you subscribe.
0.1 otherwise (1 sample every 10 seconds)
|
| com | All (EPOC Flex requires a [special EEG sensor mapping](/cortex-api/headset/controldevice.md#special-eeg-sensor-mapping-for-epoc-flex)). | 8 |
| fac | All (EPOC Flex requires a [special EEG sensor mapping](/cortex-api/headset/controldevice.md#special-eeg-sensor-mapping-for-epoc-flex)) except MN8. | 32 |
| sys | All | No fixed rate, see [BCI](/cortex-api/bci.md) for details. |
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