Non-repudiation is a fundamental attribute of network defense that ensures that neither party can deny the authenticity of their communications. In the context of Simran's actions as a network administrator, by mandating authentication before any connection establishment or message transfer, she is ensuring that the identity of the communicating parties can be confirmed and that the parties cannot later deny having sent or received the messages. This is crucial for maintaining accountability and trust within the network, as it provides irrefutable proof of the origin and integrity of the communications.