Network Syncing
How Basis keeps players in sync — the authoritative server model, what gets replicated, how movement stays smooth, and client/server version compatibility.
Overview
Basis is client–server: every client connects to a server, and the server is the authority that relays state between players. There's no direct mesh of clients by default — your client sends its state to the server, and the server forwards it to the others (with an optional peer-to-peer path for specific cases, see below).
The transport is LiteNetLib over UDP, with several delivery guarantees chosen per message type:
- Unreliable for high-rate state like avatar pose and voice — the occasional dropped packet is cheaper to skip than to resend, because a newer update is always close behind.
- Reliable / ordered for things that must arrive and must arrive in order, such as ownership changes.
What gets synced
- Avatar pose — your body and bone transforms, streamed continuously so others see you move.
- Voice — spatialised by default, so a player's voice comes from their position in the world. There's also a non-spatialised broadcast path.
- Object ownership — networked props track which player currently owns them, so only one client drives a given object at a time. Ownership transfers are sent reliably and in order.
Keeping movement smooth
A few things work together so other players look smooth even over an imperfect connection:
- Interpolation — remote avatars are interpolated between received updates rather than snapped to each one, and bone rotations are blended frame to frame.
- Jitter absorption — a smoothing filter absorbs small variations in packet timing without distorting the actual motion path.
- Distance-based update rate — the server sends pose updates for nearby players more often than distant ones. As a player gets further away, their update interval grows, which keeps bandwidth and CPU under control in busy instances while keeping close interactions crisp.
Because update rate scales with distance, someone across a large world updates less often than someone next to you. This is deliberate — it's what lets instances hold a lot of players without flooding everyone's connection.
Peer-to-peer connections
Alongside the server relay, two players can establish a direct peer-to-peer connection to each other — used for the per-player direct-connect feature in the players menu. The server still mediates everyone else; P2P is an addition for a specific pair, not a replacement for the server.
Client and server versions must match
The network protocol is versioned. When a client connects, the server checks the client's protocol version against its own. If the client is older than the server expects, the server rejects the connection with an "Outdated client version" reason rather than letting a mismatched client join.
If you self-host, keep your server and clients on compatible builds. A client that's behind the server's protocol version is refused at connect time; protocol changes ship by bumping this version, so an out-of-date client or server is the usual cause of a connection that's rejected immediately.
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