GOOSE messaging were defined by IEC 61850 as a communication method to be used between IEDs and, thus, eliminate the need for cables to carry out interlocks, locks, trips, as well as other information sent and exchanged between relays. This information is organized in datasets , or data sets, which contain the parameters whose IED will be used to send to other devices on the network.
This type of message is directly linked to the link and application layers of the OSI model and, therefore, does not have the capacity to implement features that are not supported by them.
However, for this to be possible, it is necessary that some measures are taken, in order to ensure that there are no performance problems, since electrical phenomena occur in the order of a few milliseconds, some of which may occur in microseconds.
In order to guarantee speed and reliability, GOOSE messages are, according to the IEC 61850-8.1 standard, of the multicast type and, thus, are sent to all equipment present in the same network or subnet, where the IED is located, according to IP Multicast Technology Overview, by Cisco Systems, Inc. Thus, it is up to the equipment present to analyze the message and decide whether or not to discard its content.
In addition, in order to guarantee the speed of the messages, no type of delivery guarantee is implemented, but as the system must have deterministic characteristics, a re-transmission system is used, in order to guarantee an appropriate level of reliability in the receiving the message by the recipient, as shown in Figure
Re-transmission of a goose messaging
When there is no change in the IED data, the re transmission time between messages is displayed in T0. This also serves as a mechanism for the device to report being active on the network. The period (T0) exists to exemplify that the “re transmission under stable conditions”, as defined in IEC 61850, can be reduced due to the occasion of the appearance of an event, as shown in Figure , since a message is immediately generated.
From this first message onwards, re transmission takes place at variable intervals not defined by the standard, but which are usually calculated according to an exponential back-off algorithm, until T0 is reached again, according to Hoyos, Dehus, & Brown, 2012 in Exploiting the GOOSE Protocol: A Practical Attack on Cyber-infrastructure.
When traveling over IEEE 802-3, the GOOSE protocol can use several Ethernet resources, such as physical addressing, which ensures that the message always has a source and a destination.
As there is no control over access to the medium by IEEE 802-3 and there is also no guarantee mechanism for delivering messages, it appears that the re transmission structure as expressed in Figure is extremely important to ensure message delivery.
In addition, due to the multi-casting characteristic of the GOOSE protocol and the fact that in an IEEE 802-3 network there may be other data that do not relate to the horizontal control of the substation traveling, and MMS messages are a good example of this, it can occur a large volume of data to circulate on the network, contributing to a reduction in transmission speed, which can negatively impact system performance.
Thus, the IEC 61850 standard suggests that message prioritization mechanisms be used, in order to ensure that GOOSE messages have a higher transmission priority on the network than other messages and are able to reach their recipient with satisfactory performance.
One of these message prioritization mechanisms uses the application of VLANs, as a way to segregate information from the IEC 61850 network from other data that can circulate on the same physical network.
With that, we come to the end of this post about GOOSE messages in the IEC 61850 series. I hope you enjoyed it and that this article has added something to your knowledge.