A SIP Proxy is a very common application and the examples herein are showing how you can build everything from a very simple proxy with very minimal support from sipstack.io, to a full featured proxy with flow support, transaction support and more. Each example is designed to highlight certain aspects of the support provided by sipstack.io but for most people, the last example is probably where you would start unless you really want to know the inner details of sipstack.io as well as SIP as a protocol.