+static const long USEC_PER_SEC = 1000000;
+static const long NSEC_PER_SEC = 1000000000;
+static const int DEFAULT_USER_TIMEOUT = 60; // sec
+static const long START_RTO = 1 * USEC_PER_SEC; // usec
+static const long MAX_RTO = 3 * USEC_PER_SEC; // usec