@Override
  public void fromData(DataInput in,
      DeserializationContext context) throws IOException, ClassNotFoundException {
    requestId = in.readInt();
  }
RequestId identifies the HeartbeatRequestMessage for which this is a response. If it is < 0
this is a periodic heartbeat message.
geode-membership/src/main/java/org/apache/geode/distributed/internal/membership/gms/messages/HeartbeatMessage.java