diff --git a/interfaces/SimpleScene/SimpleScene.proto b/interfaces/SimpleScene/SimpleScene.proto
index 5d3f8ccfa9452578a34fe635b6266c61468c5cb5..45040dbafb127c9ee9cb8329e670c38a6fdf718b 100644
--- a/interfaces/SimpleScene/SimpleScene.proto
+++ b/interfaces/SimpleScene/SimpleScene.proto
@@ -53,7 +53,7 @@ message RefSystem {
 
 message IposMonitoringRequest {
   string frameId = 1; // deprecated
-  // repeated string frameIds = 1;
+  // repeated string frameIds = 1; // a monitoring request can be concerned with multiple overlapping frames
   float delta = 2; // min. change in position to trigger a position update, setting delta and updateFrequency to -1 cancels the (existing) monitoring task
   float updateFrequency = 3; // defines how many times per second a PositionUpdateEvent is sent
   repeated string type = 4; // object-types to be observed; CeTI will send BOX,BIN,ZONE,ROBOT,HUMAN,OTHER
@@ -63,6 +63,7 @@ message IposMonitoringRequest {
   repeated string properties = 8; // properties that shall be monitored: position or id or type
   string monitoringTaskId = 9; // unique for each monitoringRequest. IPosFW uses this info for configuring the communication protocol, e.g., for selecting a specific topic for MQTT-communication; a monitoringRequest with the same monitoringTaskId like a previous request updates this request
   string requestorProtocol = 10; // communication protocol, e.g., "mqtt"; Assumption: requestor = receiver
+  string serializationType = 11; // accepted values: "protobuf" or "json"
 }
 
 message IposMonitoringResponse {