In the traditional domain of teleprotection signalling, there is a recognised triangle of performance. This triangle depends upon the required speed of communication, the expected dependability of the command, and the security of receipt. These three aspects are interlinked, and the correct balance of each is required in order to offer the traditional functionality such as permissive signalling, blocking and intertripping schemes. This paper relates the traditional concepts to the application of automation schemes within digital substations. In this manner, it is anticipated that protection engineers can relate today's Ethernet technology by analogy with equivalent trusted practices. Firstly, the paper discusses aspects of speed, particularly in terms of the response required in message-based schemes, and the methods by which integrators can achieve accurate time-synchronising. Secondly, achieving adequate dependability by means of redundancy, and appropriate architectures is treated. Thirdly, security is covered, including aspects of cybersecurity and settings/configuration management.