Clarify IDs for VCU communication

Author: oliverrahner

modules/ROOT/pages/ids-and-definitions.adoc

@@ -22,16 +22,17 @@ The agrirouter API uses several IDs, which can be a little confusing. But don’
 |A UUID representing a Certification for one app. An app has to be certified every time, a new version with changed capabilities against agrirouter are implemented.
 
 |deviceAlternateId 
-|The Id of the endpoint of an application instance. It’s used to address the outbox and inbox.
-
+|The Id of the endpoint of an application instance. +
+For communication _on behalf_ of a VCU, this is the *owning telemetry platform's* endpoint Id.
 |endpointId 
 |The endpointId is the unique address of an Application Instance on the agrirouter.  It's used to directly address an endpoint from a different endpoint and to mark the source of a message. 
 
 |gatewayId 
 |This is a simple enumeration to determine the protocol type of the communication. It’s either 2=MQTT or 3=REST
 
 |sensorAlternateId 
-|The endpointId equals the sensorAlternateId
+|The endpointId equals the sensorAlternateId. +
+For communication _on behalf_ of a VCU, this is the *VCU's endpoint Id*.
 
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