计算机远程通信和远程控制_外文翻译

一、以数据库为中心的监控方案

传统的监控方法基本上都是以数据库为中心的解决方案，其中的控制网络可以是各种现场总线，也可以是其它工业控制网络，各个控制节点通过它进行通讯，监控机通过发射电台对电源运行状况进行监测，收集现场信息，经处理后传送给实时数据库服务器；Web服务器根据客户端浏览器发来的HTTP请求，通过服务器扩展模块，从实时数据库中获取数据，然后传回给客户端浏览器进行显示。可以看出，整个过程都是围绕着实时数据库服务器展开的。这种方法在实际应用中存在许多不足。例如，相对于监测功能，控制功能的实现比较困难，编程上难度较大，特别是安全性方面如认证、加密。为解决实时性问题，一般采用轮询方式，由客户浏览器定时刷新网页，而这会导致效率低下，有些系统也采用事件触发方式，利用数据库服务器的触发器功能主动推(push)数据，但它一般要求Web服务器与数据库服务器位于同一台机器上，不便于系统扩展; 数据库服务器是整个系统的核心，需处理Web服务器与监控机的请求，工作负载很重，有可能成为系统性能瓶颈。这些不足之处随着应用模型的扩大显得越来越明显，需要新的解决方案。

1.1服务器方面

1.打开一通信通道并告知本地主机，它愿意在某一公认地址上接收客户请求；

2. 等待客户请求到达该端口；

3. 接收到重复服务请求，处理该请求并发送应答信号。接收到并发服务请求，要激活一新进程来处理这个客户请求。新进程处理此客户请求，并不需要对其它请求作出应答。服务完成后，关闭此新进程与客户的通信链路，并终止。

4. 返回第二步，等待另一客户请求；

5.关闭服务器。

1.2客户方面

1.打开一通信通道，并连接到服务器所在主机的特定端口；

2.向服务器发送服务请求报文，等待并接收应答;继续提出请求；

3.请求结束后关闭通信通道并终止。

从上面所描述过程可知：

1.客户与服务器进程的作用是非对称的，因此编码不同。

2.服务进程一般是先于客户请求而启动的。只要系统运行，该服务进程一直存在，直到正常或强迫终止。面向连接的基于Socket的客户机/服务器结构应用程序的基本流程如图

 一下是英文部分译文

Database-centred programme to control

Traditional control methods are basically a database-centred solutions, which can be controlled network of ground radar, and can also be other industrial control network, the control node through its communication, surveillance plane fired by radio to power performance monitoring, collection site information processed immediately after transmission to the database server; Web server devices based on customer-made to the web browser request through server extension modules from real-time databases, and then sent back to the client side browser for show. We can see that the whole process is around real-time database server started. Practical application of this method in the presence of many inadequacies. For example, in relation to the monitoring functions, control functions to achieve more difficult, it is quite difficult programming, and in particular the safety aspects such as authentication, encryption. To address immediate issues, the general polling methods used by the client browser regularly updated website, which would lead to inefficiency, and some also use the system to trigger events, the use of the database server to push functional capability (computer) data, but it generally requires Web server devices and database servers located in the same machine. not easy system expansion; database server is the core of the system as a whole, to deal with Web server devices and surveillance aircraft request, heavy work load, the system may become performance bottlenecks. With these deficiencies in the application of models to become increasingly evident that the need for new solutions.

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