A proposal to add a currency token to an anonymous email system. Each phone acts as its own email server running peer-to-peer between two phones. A central registry maintains identity and IP addresses so phones can communicate.

So. The biggest problem is that email is not a guaranteed delivery protocol. In 2014, this system was losing about 2% of its emails. No sane bank will sign up to lose 2% of its money. After a few days, I defined the overall design as a guaranteed delivery system between mobile devices and started researching.

A second problem is scalability. The client wanted to scale to 100 million devices. So guaranteed delivery and high scalability. Eventually, I looked at IoT solutions...

Other constraints - how well does the IoT toolkit match the existing environment? Cost, effort and applicability are concerns. I recommended the RTI toolkit as the best option with an annual licensing cost of $7500 per developer. At that point, this project died because company owner couldn't grasp why he couldn't just use email.

There's initial sequence diagrams and even coding of the Bank Manager, mock tokens, unit tests.