# `XGW`
[🔗](https://github.com/Lazarus404/xgw/blob/main/lib/xgw.ex#L1)

XGW is a **media gateway**: it sits between a browser (or other WebRTC client)
and your application so you do not have to implement ICE, DTLS, and SRTP yourself.

## What problem this solves

Real-time audio/video on the public internet is not a plain TCP socket. Clients
must:

1. Find a working UDP (or TCP) path through NATs and firewalls (**ICE**).
2. Authenticate each other and encrypt the path (**DTLS**).
3. Protect media packets with short-lived keys (**SRTP** / **SRTCP**).

XGW terminates that stack per remote peer and delivers **plaintext** RTP/RTCP
(and optional data-channel bytes) to a handler you register. Your app owns
rooms, signaling (SIP/WebSocket/HTTP), and SDP answers -- the same split as
an SFU such as Janus or mediasoup, or a SIP path with
[xsip](https://github.com/Lazarus404/xsip) and
[xsdp](https://github.com/Lazarus404/xsdp).

## Main pieces

```text
UDP/TCP Listener  -- demux STUN / DTLS / media -->  Peer GenServer
                                                        |
                                                        v
                                                  ICE then DTLS
                                                        |
                                                        v
                                                  SRTP decrypt/encrypt
                                                        |
                                                        v
                                                  your handler (RTP callbacks)
```

- `XGW.Listener` -- shared socket(s) and packet demux.
- `XGW.Peer` -- one remote endpoint's ICE/DTLS/SRTP lifecycle.
- `XGW.ICE.*` -- connectivity checks and candidate gathering.
- `XGW.DTLS.*` -- handshake transport and SRTP key export.
- `XGW.SRTPSession` -- encrypt/decrypt media after DTLS.

See `ARCHITECTURE.md` in this package for ICE-lite vs full, demux, and the
module map.

## RFCs

Primary stack: RFC 8445 (ICE), RFC 8489 (STUN), RFC 8656 (TURN), RFC 9147 /
RFC 6347 (DTLS), RFC 5764 (DTLS-SRTP), RFC 3711 (SRTP), RFC 7983 (demux),
RFC 8866 (SDP). See child modules for narrower citations.

---

*Consult [api-reference.md](api-reference.md) for complete listing*