5G signaling is the nervous system of a 5G Standalone Core - it consists of the encrypted connections between network functions they use to communicate with one another. The main 5G network function in support of signaling is the Service Communication Proxy, or SCP. But the SCP is not strictly required in a 5G core since communication links can be manually provisioned. This is similar to directly connecting every computer in a campus to every other computer. But it is far more efficient to use Ethernet switches instead; similarly the SCP is like a switch for communication between network functions. Nevertheless, many CSPs have deployed 5G SA networks without an SCP as an initial deployment. This eBook explains signaling, and why the SCP is important. It presents the four different signaling models, and the benefits to including the SCP. It should be used by Sales and Pre-sales to convince customers to include the SCP from the very start of deployment, or to add one if they have not yet done so.