To fully appreciate SIP you need to understand its routing capabilities and how they enable SIP to traverse a network. These capabilities also help SIP deal with common network issues such as NAT and firewalls. SIP's flexible routing also enables features like application composition, a very valuable asset when designing, implementing, and building a loosely coupled system. This presentation is for those that are looking to get a deeper understanding of SIP. Perhaps you have been tasked to spin up a completely new SIP infrastructure at work? Then you really need to understand how SIP finds its way through a network. By understanding the routing decisions SIP makes, you will be successful in your next SIP endeavor. Questions that will be answered: - How does a SIP request traverse the network? - How do we know which transport to use? - How do responses find their way back? - Any difference for in-dialog requests?