I know they came later, so I'm still confused why RTSP and SIP weren't implemented atop HTTP. I realize that RTSP and SIP can push server to client, but there's ways around that, though perhaps long polling and Websockets weren't conceivable when RTSP and SIP were invented. I mean, in a pinch, I have an HTTP server serving a folder where SDP files are generated, and I've written clients that just look for a well-known SDP file and use that to consume an RDP stream. It's a ghetto form of "signaling" that I love using when doing experiments (not suitable for production for various reasons obvious to you I imagine.)

I'm not saying WebRTC had poor design decisions or anything. I think it was very smart for WebRTC to reuse SDP, RDP, etc so the same libraries and pipelines could keep working with minimal changes. It also means very little new learning for folks familiar with the rest of the stack.

> For realtime media, if we are able combine “locator:identifier” issue, we will be able to make media and signaling work inband.

+1000. I think RTSP+TCP is a decent way to do in-band signaling and media, and RTMP defines strict ways to send both anyway.