[CORD-3109] Adding docs
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+# vOLT Service
+
+The `vOLTService` is responsible to configure the access network in RCORD and it
+does that leveraging `VOLTHA`.
+
+## vOLT Modeling
+
+Here is an image describing the models that compose this service,
+followed by a brief description of any of them.
+For a full reference on these models, please take a look at their
+[xProto](https://github.com/opencord/olt-service/blob/master/xos/synchronizer/models/volt.xproto)
+representation.
+
+
+
+**vOLTService**
+
+Contains the information that the synchronizer needs to access `VOLTHA` and
+`ONOS-VOLTHA`
+
+**vOLTServiceInstance**
+
+Represent a subscriber in the service chain
+
+**OLTDevice**
+
+Contains the information needed to pre-provision and activate an OLT device in
+VOLTHA
+
+**PONPort, NNIPort, ONUDevice**
+These models contain informations about the respective components of the PON
+network. In an RCORD deployment these models are pulled from VOLTHA to keep an
+inventory of the system.
+
+## Synchronizations steps
+
+### Push steps
+
+There are two top-down steps in this service:
+
+- `SyncOLTDevice` to pre-provision and enable OLT devices
+- `SyncVOLTServiceInstance` to add the subscriber in `ONOS-VOLTHA`
+
+### Pull steps
+
+The vOLT synchronizer is currently pulling `OLTDevice`, `PONPort`, `NNIPort` and
+`ONUDevices` from `VOLTHA`.
+
+### Event steps
+
+The vOLT synchronizer is listening over the kafka bus for events in the `onu.events`
+topic.
+
+#### ONU Activate event
+
+Event format:
+
+```json
+{
+ "status": "activated",
+ "serial_number": "BRCM1234",
+ "uni_port_id": 16,
+ "of_dpid": "of:109299321"
+}
+```
+
+When an event is received:
+
+- the `vOLTService` checks if in between is provider services there is one with `kind = oss`
+- It calls the `validate_onu` method exposed by that service
+- the OSS Service will be responsible to create a subscriber in XOS
+
+If no OSS Service is found in between the providers of `vOLTService`
+no action is taken as a consequence of an event.
+
+For more informations about the OSS Service, please look
+[here](../hippie-oss/README.md) and in the [R-CORD Configuration guide](../profiles/rcord/configuration.md)
+
+## Test configuration
+
+If you are testing the R-CORD Service chain (meaning that you don't have a
+running VOLTHA), you will need to manually create a `PONPort` and an `ONUDevice`.
+
+To do that, please check the example TOSCA in the repository
+[samples](https://github.com/opencord/olt-service/tree/master/samples) folder.
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