WCF Relays (formerly Service Bus Relays) uses the .NET Framework and WCF to establish a connection and sending a message. The on-premises application uses WCF Relay bindings which creates WCF channels that integrate with the Azure Service Bus.
For more information on How to use Azure Relay WCF Relays with .NET, you can refer to the following article: https://docs.microsoft.com/en-us/azure/service-bus-relay/relay-wcf-dotnet-get-started.
