-#define CHAR_FOR_CALL 'K'
-#define CHAR_FOR_REPLY 'k'
-#define CHAR_FOR_EVT_BROADCAST 'B'
-#define CHAR_FOR_EVT_ADD 'E'
-#define CHAR_FOR_EVT_DEL 'e'
-#define CHAR_FOR_EVT_PUSH 'P'
-#define CHAR_FOR_EVT_SUBSCRIBE 'X'
-#define CHAR_FOR_EVT_UNSUBSCRIBE 'x'
-#define CHAR_FOR_DESCRIBE 'D'
-#define CHAR_FOR_DESCRIPTION 'd'
-#define CHAR_FOR_TOKEN_ADD 'T'
-#define CHAR_FOR_TOKEN_DROP 't'
-#define CHAR_FOR_SESSION_ADD 'S'
-#define CHAR_FOR_SESSION_DROP 's'
-#define CHAR_FOR_VERSION_OFFER 'V'
-#define CHAR_FOR_VERSION_SET 'v'
+#define CHAR_FOR_CALL 'K' /* client -> server */
+#define CHAR_FOR_REPLY 'k' /* server -> client */
+#define CHAR_FOR_EVT_BROADCAST 'B' /* server -> client */
+#define CHAR_FOR_EVT_ADD 'E' /* server -> client */
+#define CHAR_FOR_EVT_DEL 'e' /* server -> client */
+#define CHAR_FOR_EVT_PUSH 'P' /* server -> client */
+#define CHAR_FOR_EVT_SUBSCRIBE 'X' /* server -> client */
+#define CHAR_FOR_EVT_UNSUBSCRIBE 'x' /* server -> client */
+#define CHAR_FOR_EVT_UNEXPECTED 'U' /* client -> server */
+#define CHAR_FOR_DESCRIBE 'D' /* client -> server */
+#define CHAR_FOR_DESCRIPTION 'd' /* server -> client */
+#define CHAR_FOR_TOKEN_ADD 'T' /* client -> server */
+#define CHAR_FOR_TOKEN_DROP 't' /* client -> server */
+#define CHAR_FOR_SESSION_ADD 'S' /* client -> server */
+#define CHAR_FOR_SESSION_DROP 's' /* client -> server */
+#define CHAR_FOR_VERSION_OFFER 'V' /* client -> server */
+#define CHAR_FOR_VERSION_SET 'v' /* server -> client */