Mirror is a high level Networking Library that can use several different low level transports. To use a transport, simply add it as component to the NetworkManager and drag it into the NetworkManager's Transport field.
TCP - Telepathy Simple, message based, MMO Scale TCP networking in C#. And no magic.
TCP - Apathy Apathy is a fast, lightweight, allocation-free low level TCP library for Unity developed by vis2k. Apathy was developed in native C for maximum MMO Scale networking performance.
WebGL - WebSockets WebSockets transport layer for Mirror that target WebGL clients, without relying on Unity's stodgy old LLAPI.
Multiplexer Multiplexer is a bridging transport to allow a server to handle clients on different transports concurrently, for example desktop clients using Telepathy together with WebGL clients using Websockets.
Fallback Fallback is a compatibility transport for transports that don't run on all platforms and need fallback options to cover all other platforms.
UDP - Ignorance Ignorance implements a reliable and unreliable sequenced UDP transport based on ENet.
UDP - LiteNetLib4Mirror LiteNetLib4Mirror implements a UDP transport based on LiteNetLib with Network Discovery and uPnP included.
Steam - Fizzy A complete rebuild utilising Async (Previously SteamNetNetworkTransport) of a Steam P2P network transport layer.