HTTP/2

5G's core did something unusual for a telecom architecture: it dropped the bespoke signalling protocols between core functions and adopted a web protocol. The service-based interfaces between network functions are HTTP/2 REST-style APIs with JSON payloads. The reason HTTP/2 specifically, and not HTTP/1.1, is performance under signalling load — HTTP/2 is binary-framed and multiplexes many concurrent requests over a single TCP connection, so one function can have many outstanding calls to another without opening a connection per request or suffering head-of-line blocking at the message level.

For engineers crossing over from the Diameter/GTP world, this is a real shift in mindset: NF interactions look like microservice API calls, discoverable via the NRF, with normal HTTP status codes and methods. It also brings the web's tooling and the cloud-native operational model into the core. The flip side is that protecting these interfaces — especially across operator boundaries — needs deliberate work, which is exactly the job of TLS within a network and the SEPP at the N32 edge between networks.