Unet intro

High Level API(HLAPI)

HLAPI is a server authoritative system, triggered from UnityEngine.Networking

authority

host has the authority over all non-player GameObjects; Player GameObjects are a special case and treated as having “local authority”.

local/client authority for npc

method1: spawn the npc using NetworkServer.SpawnWithClientAuthority
method2: NetworkIdentity.AssignClientAuthority

network context properties

isServer()
isClient()
sLOcalPlayer()
hasAuthority()

networked GameObjects

multiplayer games typically built using Scenes that contain a mix of networked GOs and regular GOs.  networked GOs needs t obe synchronized across all users; non-networked GOs are either static obstacles or GOs don't need to synchronized across players 

 networked GO is one which has a NetworkIdentiy component. beyond that, you need define what to syncronize. e.g. transform ,variables ..

player GO

NetworkBehavior class has a property: isLocalPlayer, each client player GO.isLocalPlayer == true, and invoke OnStartLOcalPlayer()

Player GOs represent the player on the server, and has the ability to run comands from the player’s client.

spawning GOs

the Network Manager can only spawn and synchronize GOs from registered prefabs, and these prefabs must have a NetworkIdentity component

spawning GOs with client authority

NetworkServer.SpawnWithClientAuthority(go, NetworkConnection),
for these objects, hasAuthority is true on this client and OnStartAuthority() is called on this client. Spawned with client authority must have LocalPlayerAuthority set to NetworkIdentity,

state synchronization

[SyncVars] synchronzed from server to client; if opposite, use [Commands]

the state of SyncVars is applied to GO on clients before OnStartClient() called.

engine and editor integration

NetworkIdentity component for networked objects
NetworkBehaviour for networked scripts
configurable automatic synchronization of object transforms
automatic snyc var

build-in Internet services

network visibility

relates to whether data should or not sent about the GOs to a particulr clinet.

method1: add Network Proximity Checker component to networked GO
method2:

Scene GOs

saved as part of a Scene, no runtime spawn

actions and communication

method1: remote actions, call a method across network
method2: networking manager/behavior callbacks
method3: LL network messages

host migration

host: a player whose game is acting as a server and a “local client”
remote client: all other players
so when the host left, host need migrate to one remote client to keep the game alive

how it works:
enable host migration. so Unity will distribute the address of all peers to other peers. so when host left, one peer was selected to be the new host (heart-keeping)

network discovery

allow players to find each other on a local area network(LAN)

need component ,

in server mode, the Network Discovery sends broadcast message over the network o nthe specified port in Inspector;

in client mode, the component listens for broadcast message on the specified port

using transport Layer API (LL API)

socket-based networking

in the end

network is basic cornerstone in server-client applications, Unet is deprecated at this moment, but still many good network resource can take in charge. e.g. websockets, nodejs, and what behind these network protocol or languages, e.g. async/coroutines are charming as well.