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SCADA |
The SCADA (Supervisory Control and Data Acquisition) systems and the network environment they operate in are constantly changing. More computer power is engineered into the latest SCADA equipment thus more data must be moved to meet the information demands of such a system. Also these systems must operate over new types of networks, including Ethernet. A successful SCADA WAN network is usually a compromise between reliability, cost, scalability, and flexibility.
A typical SCADA system comprises of distributed Client SCADA nodes, which monitor the health of the flow to a centralized SCADA system. The flow could be a power system for a railway, or the flow of oil in a pipeline. The client SCADA nodes provide the monitoring information over an Ethernet interface to the transport network. The transport network then carries this Ethernet data on to the Centralized SCADA system. Let us look at what functionality a SCADA system expects from the transport network:
Ethernet Flows
The Ethernet flow emanating from a client SCADA node is continuous in nature. It is important that a Virtual Ethernet flow be created in the Transport network in order to ensure un-interrupted transmission of data from the client SCADA nodes to the centralized SCADA system.
The Ethernet data from client SCADA nodes could be multiplexed with other Ethernet data (e.g. SCADA data from other nodes, or data from LAN at each of the stations). The SCADA data could be differentiated from other Ethernet data based on either a specific VLAN assignment (e.g. all SCADA data could be assigned a VLAN of 40), from the source MAC address, or a combination of both (VLAN and MAC). Based on these parameters, the appropriate Quality of service can be provisioned across the network to ensure a continuous flow from the client nodes to the central SCADA system.
Alternately, the operator could also 'reserve' a few VC-12s in the SDH network exclusively for SCADA network. By keeping the SCADA data physically separate from other Ethernet data, the operator could also ensure a secure transmission. With either of the above arrangements, the data from all nodes could be multiplexed at the terminating node and handed over a 10/100 Base T or an optical Fast Ethernet link to the centralized SCADA system
Reliability
Protection can be built into the network in multiple ways. At the Ethernet layer, the protection mechanisms involve the implementation of variants of the Spanning Tree Protocol. At the SDH layer, multiple protection schemes can be implemented to ensure a reliable connection that is resilient to transmission problems arising from fiber cuts and other problems.
Security
A separate private network ensures considerable security, yet further security mechanisms can be built into the transmission network. For Ethernet data from client SCADA nodes, Access Control lists (ACLs) implemented in the transmission nodes ensure that only authorized sources of Ethernet data are allowed to transmit data. Ethernet data originating from unknown/unauthorized sources can be blocked out.
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