                 "$ref": "#/definitions/timestamp"
                }
            }
        }
      </pre>

      <h3>Subscribe</h3>
      <pre>
        {
            "$schema": "http://json-schema.org/draft-04/schema#",
            "title": "Subscribe Request",
            "description": "Allows the client to subscribe to time-varying signal notifications on the server.",
            "type": "object",
            "required": ["action", "path", "filters", "requestId"],
            "properties":