Design Private Cloud of Oil and Gas SCADA System

SCADA (Supervisory Control and Data Acquisition) system is computer control system based on supervisory. SCADA system is very important to oil and gas pipeline engineering. Cloud computing is fundamentally altering the expectations for how and when computing, storage and networking resources should be allocated, managed and consumed. In order to increase resource utilization, reliability and availability of oil and gas pipeline SCADA system, the SCADA system based on cloud computing is proposed in the paper. This paper introduces the system framework of SCADA system based on cloud computing and the realization details about the private cloud platform of SCADA system.


Introduction
SCADA (Supervisory Control and Data Acquisition) system is computer control system based on supervisory.The SCADA system of oil and gas pipeline can manage sequential control transmission of petroleum pipeline, equipment monitoring, data synchronization transmission record and monitoring operation conditions of every station control system.In addition, the SCADA system has more features, such as leaking detection, system simulation, water hammer protection in advance, and so on.SCADA system can continuously monitor equipments which are scattered over the wide regions and it can operate remote devices from the control center so that the operating efficiency is improved, the energy is saved and the cost is reduced.And, the SCADA system can guarantee the integrity of pipeline by continuous monitoring the key parameters of system, such as pressure, flow, oil tank liquid level and so on [1].So, SCADA system is very important to oil and gas pipeline engineering.
Cloud computing, as a current commercial offering, started to become apparent in late 2007 [2].It was intended to enable computing across widespread and diverse resources, rather than on local machines or at remote server farms.Although there is no standard definition of Cloud Computing, most authors seem to agree that it consists of clusters of distributed computers (Clouds) providing on-demand resources or services over a network with the scale and reliability of a data centre [3]; notions familiar from resource virtualization and Grid computing.Where these clusters supply instances of ondemand Cloud computing; provision may be comprised of software (e.g.Software as a Service, SaaS) or of the physical resources (e.g.Platform as a Service, PaaS).The Amazon Elastic Compute Cloud (Amazon EC2) [4] is an example of such an approach, where a computing platform is provided.In common with many commercial approaches provision is the primary objective; management and governance handled via redundancy or replication, scaling capacity up or down as required.In contrast the authors proposed a Cloud Coordination framework in 2005 with the notion of a Cloud being a system of loose boundaries, which interacts and merges with other systems [5].This definition of a Cloud is refined to a federation of interacting services and resources, which share and pool resources for greater efficiency.Thus governance, in general, and scalability are handled as part of the separated coordination framework.In order to increase resource utilization, reliability and availability of oil and gas SCADA system, the SCADA system based on cloud computing is proposed in the paper.The remainder of this paper is organized as follows.In Sect.2, traditional structure of SCADA system is described.The framework of cloud computing and the key features and characteristics of cloud computing are detailed in Sect.3. Section 4 the system architecture of SCADA system based on cloud computing is proposed.In Sect.5, the realization details about the private cloud platform of SCADA system is described.Finally, the paper concludes in Sect.6.

Traditional structure of SCADA system
The SCADA system adopts distributed supervisory control and centralized management.The traditional structure of SCADA system is described in figure1.The system is organized by the supervision center, a lot of site control systems and communication medium.The supervision center (master station) is the core of system and in charge of controlling and managing system running.It is organized by a lot of data processing servers and database servers.The outside site is the intelligent measure and control module by microprocessor or DSP.It can collect and process the data of remote sites, control local sites and communicate with remote supervision center.
The SCADA system includes: information acquisition subsystem, information transmission subsystem and information processing subsystem.The information acquisition subsystem includes all kinds of sensors and controllers.It takes charge of data collection and devices controlling of local site.The information transmission subsystem can transport collected data and system controlling signal of local site by efficient communication technologies.It is the bridge of information acquisition subsystem and information processing subsystem.It includes RTU (Remote Terminal Unit), modem and central communication controller.The information processing subsystem is located at supervision center and it can gather, process and analysis the data of remote sites.It includes master computer and all kinds of expert software.

Figure1. The structure of SCADA system
However, the current SCADA system has problems as follow: (1) Reliability problem Servers of supervision center are the command center of system.They can gather the pipeline running data, state and warning information and provide the real-time database for all operating sites.Now, the SCADA system of oil and gas pipeline adopts Hot Standby as the way of redundant configuration to ensure the reliability of system.When master server is working online, the slave server monitors work state of master server and get the data from master server for keeping the data consistency between the master server and slave server.Once the master server breaks down, the slave server takes over the work from the master server immediately, and the slave server becomes the master server, the repaired master server becomes the slave server.As the controlling core of SCADA system, the central servers are responsible for data collecting and controlling of all line.It is important to ensure the data transmission between the servers and site control system for all SCADA system network normal operation.The single backup server cannot ensure the reliability of system completely.
(2) Source wasting problem Hot Standby is used for ensuring the reliability of system.With system scaling out constantly, the number of server increases.Redundant configuration can cause wasting server source and the workload of operation administration and maintenance increasing.So, it is necessary to find more advanced resource configuration mode to increase resource utilization rate.
(3) Load balancing problem With SCADA system of oil and gas pipeline scaling out constantly, the number of server increases.There is lots of operation and data are processed on different servers.However, CPU load is different with different site data.So, different servers have different load, some servers overload but some servers just are idle.It is necessary to study new load balancing strategy for improving the performance of system.

The framework and the key features of cloud computing
Generally, the architecture of a cloud computing environment can be divided into 4 layers, as shown in Fig.The hardware layer: This layer is responsible for managing the physical resources of the cloud, including physical servers, routers, switches, power and cooling systems.In practice, the hardware layer is typically implemented in data centers.A data center usually contains thousands of servers that are organized in racks and interconnected through switches, routers or other fabrics.Typical issues at hardware layer include hardware configuration, fault tolerance, traffic management, power and cooling resource management.
The infrastructure layer: Also known as the virtualization layer, the infrastructure layer creates a pool of storage and computing resources by partitioning the physical resources using virtualization technologies such as Xen [7], KVM [8] and VMware [9].The infrastructure layer is an essential component of cloud computing, since many key features, such as dynamic resource assignment, are only made available through virtualization technologies.
The platform layer: Built on top of the infrastructure layer, the platform layer consists of operating systems and application frameworks.The purpose of the platform layer is to minimize the burden of deploying applications directly into VM containers.For example, Google App Engine operates at the platform layer to provide API support for implementing storage, database and business logic of typical web applications.
The application layer: At the highest level of the hierarchy, the application layer consists of the actual cloud applications.Different from traditional applications, cloud applications can leverage the automatic-scaling feature to achieve better performance, availability and lower operating cost.Compared to traditional service hosting environments such as dedicated server farms, the architecture of cloud computing is more modular.Each layer is loosely coupled with the layers above and below, allowing each layer to evolve separately.This is similar to the design of the OSI model for network protocols.The architectural modularity allows cloud computing to support a wide range of application requirements while reducing management and maintenance overhead.

The system framework of SCADA system based on cloud computing
Compare to traditional structure of SCADA system, the SCADA system based on cloud computing used cloud computing technologies to integrate server resource of supervision center, manage and assign this resource uniform, but not allocate a certain server to be in charge of a certain pipe line.In addition, the local site control systems are redeployed at the cloud server of remote private cloud platform.The structure of SCADA system based on cloud computing is shown in Fig. 3.The virtualization technology enables the abstraction or decoupling of the application payload from the underlying physical resource.The physical resource can then be carved up into logical or virtual resources as needed.This is known as provisioning.With server virtualization, we can create complete logical (virtual) servers that are independent of the underlying physical infrastructure or their physical location.We can specify the computing, network and storage resources for each logical server (virtual machine) and even move workloads from one virtual machine to another in real-time (live migration).Every practitioner of server virtualization is aware of how virtualization can result in "Virtual Machine (VM) Sprawl" and the associated management burden it creates.VM Sprawl is a result of the ease with which new VMs can be created and proliferated on virtualized servers.This is however not the only factor affecting management complexity.Since VMs are cheaper to setup and run than a physical server, load balancers, routers and other applications that required physical servers are all now being run as in VMs within a physical server.Consequently, we now have to manage and route network traffic resulting from all these VMs within a server as well as the network traffic being routed across server.Adding to this confusion are the various OS vendor, each  offering the other vendor's OS as a "guest" without providing the same level integration services.This makes the real life implementations, very management intensive, cumber some and error-prone to really operate in a heterogeneous environment.It is our contention that the cost of this additional management may yet offset any cost benefits that virtualization has enabled through consolidation.A traditional management system with human-dependency is just an untenable solution for cloud computing.
The SCADA system model of oil and gas pipeline is created as follow: The real-time data processing tasks of SCADA system are expressed by .Each task of SCADA system is independent and the task is nonpreemptive.
Each real-time task can be defined as ( , , , )

T d T T T  (1)
i d is the deadline of real-time task; 1 2 3  , , T T T is the one primary copy and two backup copies, respectively; the code of three tasks is same completely.( , , ) ( , , ) ( , , ) There, , , T T T on processor j P .
If SCADA system can tolerate 2 processors disable, the sum of primary copy execution time and backup copy execution time should be less than or equal to deadline.
For each processor i P of SCADA system

Realization details about the private cloud platform of SCADA system
The physical architecture of Private cloud includes: controller node, compute nodes, NFS server and network devices.It is shown in Fig. 4.

Figure4. The physical architecture of private cloud
The function of Controller node includes showing, monitoring, management and scheduling.The controller node provide a database and web server to support the management interface of system.The users issue control commands and operate the system by the management interface of the controller node.Information of other nodes must register to the controller node and the controller node schedule the resource constantly.
Compute nodes is the operating foundation of virtual machine.They are in charge of the specific operating work of private cloud system.Compute nodes compose the resource pool together and provide the resource with form of virtulization.The virtual machines which privat cloud system provide for outside users to use run in compute nodes.Compute nodes are dominated and managed by the controller node.
NFS server provides NFS service which supports dynamic extension function of private cloud system.
Network devices include routers and switches.They connect every devices of private cloud system and access to network.In addtion, they take charge in network address assignment.
The logical architecture of Private cloud is shown in Fig. 5.

3 Figure2.
Figure2.The architechture of cloud computing Figure3.The structure of SCADA system based on cloud computing

2 i  and 3 i
are processors assigned to three task copies.There are different execution time for different processors so defining a computing time vector for each task i T as follow, [ ( ,1),..., ( , )]