diff --git a/worker.md b/worker.md
index f874ff2..67acec5 100644
--- a/worker.md
+++ b/worker.md
@@ -288,6 +288,24 @@ Or to clear the session:
 > **Note:**
 > - The worker should store the session ID for the given subscription and use it in subsequent detection or patch messages as appropriate. If `sessionId` is `null`, the worker should treat the subscription as having no active session.
 
+## Subscription Identifier Format
+
+The `subscriptionIdentifier` used in all messages is constructed as:
+
+```
+displayIdentifier;cameraIdentifier
+```
+
+This uniquely identifies a camera subscription for a specific display.
+
+### Session ID Association
+
+When the backend sends a `setSessionId` command, it will only provide the `displayIdentifier` (not the full `subscriptionIdentifier`).
+
+**Worker Responsibility:**
+- The worker must match the `displayIdentifier` to all active subscriptions for that display (i.e., all `subscriptionIdentifier` values that start with `displayIdentifier;`).
+- The worker should set or clear the session ID for all matching subscriptions.
+
 ## 6. Example Communication Log
 
 This section shows a typical sequence of messages between the backend and the worker. Patch messages are not included, as they are only used when the worker cannot keep up.