优化设备状态保持，自动记录心跳间隔，三次心跳失败则设备离线，不在使用设备有效期字段作为唯一判断标准，提高容错能力和稳定性。

src/main/java/com/genersoft/iot/vmp/gb28181/bean/Device.java

@@ -94,6 +94,13 @@ public class Device {
 	@Schema(description = "心跳时间")
 	private String keepaliveTime;
 
+
+	/**
+	 * 心跳间隔
+	 */
+	@Schema(description = "心跳间隔")
+	private int keepaliveIntervalTime;
+
 	/**
 	 * 通道个数
 	 */
@@ -413,4 +420,12 @@ public class Device {
 	public void setLocalIp(String localIp) {
 		this.localIp = localIp;
 	}
+
+	public int getKeepaliveIntervalTime() {
+		return keepaliveIntervalTime;
+	}
+
+	public void setKeepaliveIntervalTime(int keepaliveIntervalTime) {
+		this.keepaliveIntervalTime = keepaliveIntervalTime;
+	}
 }