Inside the Cloud - Network Communications Basics for the Relay Engineer

This paper addresses basic communications network technology and explains the differences between Ethernet, TCP/IP, T1 and SONET with respect to relaying applications. It also makes an attempt to clarify how the access method and application protocols influence (or not) the transport method. LAN, VLAN, VPN and WAN/Internet are also explained. Cyber security issues are discussed for the different networks. Ethernet networks are addressed in some detail as they are becoming more commonly accessible in substations and are a tempting alternative for protective relaying due to their simplicity and lower cost. Wireless Ethernet seems to be an especially attractive, low-cost solution. The paper presents test results that compare the performance of TDMolP with Ethernet GOOSE communications according to the IEC 61850 standard. The IEC 61850 standard is based on an Ethernet LAN but was originally intended for within substations communications only. The cloud is a term used to depict a telecommunication network.