+#if defined(ARDUINO) || defined(__TIZENRT__)
+#define MAX_HEADER_OPTION_DATA_LENGTH (20)
+#else
+#define MAX_HEADER_OPTION_DATA_LENGTH (1024)
+#endif
+
+/**
+ * Sets the time to live (TTL) for response callback(s).
+ * The callback(s) will be up for deletion after such time but are not guaranteed
+ * to be deleted immediately and you may get responses even after timeout.
+ * This timeout will NOT apply to OBSERVE requests. OBSERVE needs an explicit cancel using OCCancel().
+ * @note: Changing the setting to a very long duration may lead to unsupported and untested
+ * operation. Setting this to as small a value as reasonable will reclaim memory faster.
+ */
+#define MAX_CB_TIMEOUT_SECONDS (2 * 60 * 60) // 2 hours = 7200 seconds.