# Modeling Intelligent Control Switch IEC 61850 Based Substation Automation Communication
## 2 GOOSE Protocol  
Timing in the operation of the electrical SAS is significantly important, as well as the need for high reliability and accessibility of the substation Communication Network (SCN) [12]. These constraints can be met by utilizing the IEC 61850 standard, due to it is ability to deliver fast response information via the Generic substation Events (GSE) for peer-to-peer communication mode by using the GOOSE protocol. GOOSE protocol is an abbreviation of Generic Object Oriented substation Event. It works to maintain the exchange of a broad range of common information that is structured by a DATA-SET, for example, the synchronization of the circuit breakers, distance protection and overcurrent breakers [13]. In addition, the GOOSE is planned to support the means of the high priority as well as support the high-speed peer-to-peer communication of the IEDs (Intelligent Electronic Devices) of the Ethernet LAN to protect the network. In other words, GOOSE protocol is designed to replace the conventional way of the hard-wired technique [13].  
One of the unique functional requirements identified for the IEC 61850 standard is the high-speed communication from one device to several devices of simple binary state data. Forwarding many messages to several devices simultaneously can cause undesirable delay; this kind of function is called multicast, as shown in Figure 2. The multicast utilization is applied by the MMS information (Manufacturing Message Specification) report service. The data report uses a binary object model (device combination of the binary states) known as GOOSE [14]. The Multicast function address is usually forwarded to all devices on a Local Area Network (LAN). Normally, the messages forward to a few specific devices in the network and do not need to be forwarded to all devices. Therefore, to reduce this problem (Ethernet traffic), the conception of a \"Virtual\" LAN or VLAN is employed [8].  
Figure 2: Generic Object Oriented Substation Event.(GOOSE) multicast concept [14].  
IEC 61850 GOOSE message transmits a set of information that is \"Published\", based on any changes in IED information. Any device connected to the LAN and involved in the published information has the ability to \"Subscribe\" to the Publisher's GOOSE message and utilize the information that is provided by logical node or logical device in the message when it is required, as illustrated in Figure 3. Accordingly, the GOOSE protocol is known as a Publish-Subscribe message. The GOOSE message is launched in three scenarios. The first scenario is when an IED is switched on and becomes ready to operate, then a GOOSE message is sent to inform all devices of the IED statement. The second scenario occurs when there is a change in the status of any IED device in the network, then the GOOSE message is sent to inform other devices [14; 15]. The third scenario occurs when the user-selectable periodic basis occurs [16]. This latter scenario is when there is no update of the publisher statement devices, the subscriber devices cannot identify if they are still alive (or, connected) in the network. Therefore, if the subscriber devices fail to receive the regular GOOSE message from the publisher, then the publisher would be assumed \"dead\" and set default statements on the binary variables that are expected from a dead device. Consequently, the third scenario is useful for the communication situations that have a huge information flow and need high real-time speed.  
Indeed, GOOSE has been planned to be utilized in a high speed and reliable way over the SAS. Meanwhile, the IEC 61850 devices have been tested by many vendors, such as KEMA. The results of that test indicated the reliability of the GOOSE messages in the tripping of breakers. The GOOSE message takes 4 ms, from occurring fault position to the trip operation, to take the necessary action to correct the fault and protect the substation from shutdown; this characteristic has made GOOSE protocol the superior protocol for the IEC 61850 Standards [18; 19].