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Networking

Description

The networking component handles the communication between a game client and one or more servers. Some servers are used to manage the player's account, some find a game for the player, and some run the game logic.

This component is compromised of 4 layers:

  1. Transportation
  2. Protocol
  3. Messages
  4. Game

1. Transportation

  • Handles connecting and disconnecting from a server (as a client)
  • Handles accepting new clients (as a server)
  • Handles detecting connection disconnect
  • Sends data as packets through a connection
  • Receives data as packets through a connection

2. Protocol

  • Validates packets
  • Takes messages off of the message layer queue and writes them to a buffer
  • Reads messages from a buffer and adds them to a processing queue
  • Handles large messages that are broken up
  • Implements as much of the messaging features as possible

3. Messages

  • Keeps a prioritized queue of messages to send through a connection
  • Handles messages which failed to send and may add them to the queue to retry
  • Handles dispatching processed (read) messages
    • Validates message by comparing message state to current connection state

4. Game

  • Uses messages to synchronize actors between client and server
    • Server handles how much actor state to communicate (all, just position, just sound, none)
    • Server determines which actors need synchronized each frame (frequency, relevancy)
  • Provides utilities for communicating between client and server via remote procedure calls

Dependencies

Game Layer

Sub-Components

Terms

  • x

Design

1. Transportation Layer

class Address

  • hostname: string
  • octets: byte[]
  • port: int

class Packet

  • data: byte[]
  • size: int

interface Transport

  • getMaximumTransmissionUnit(): int
  • getInactiveTime(): float
  • getDisconnectTime(): float
  • update( timestamp: long ): void
  • newConnection( address: Address ): Connection
  • newServer( address: Address ): Server
  • getConnections(): Connection[]
  • getServers(): Server[]
  • allocatePacket(): Packet
  • releasePacket( packet: Packet ): void

enum ConnectionState

  • Connecting
  • Connected
  • Inactive
  • Disconnected
  • Closed

interface Connection

  • getTransport(): Transport
  • getState(): ConnectionState
  • getAddress(): Address
  • getLastUpdate(): long
  • update( timestamp: long ): void
  • send( packet: Packet ): boolean
  • receive( out: Packet ): boolean
  • close(): void

enum ServerState

  • Initializing
  • Listening
  • Closed

interface Server

  • getTransport(): Transport
  • getState(): ServerState
  • getConnections(): Connection[]
  • getLastUpdate(): long
  • update( timestamp: long ): void
  • accept(): int
  • close(): void

2. Protocol Layer

Packet Format [ protocol ID ] [ size ] [ crc ] [ channel bits ] [ channel N ] [ header ] [ message count ] [ message N type ] [ message N data ]

class DataOptions

  • fixedMin: float
  • fixedMax: float
  • fixedBytes: int
  • compress: boolean // store ints with as few bytes as possible
  • useAngles: boolean // 2d normal = angle, 3d normal = yaw & pitch
  • forNormal( bytes: int, angles: boolean ): void
  • forPosition( bytes: int, min: float, max: float ): void

class DataBuffer

  • DataBuffer( bytes: number )
  • setOptions( options: DataOptions ): void
  • getOptions(): DataOptions
  • clear(): void
  • bits(): int
  • bytes(): int
  • align( bytes: int ): void
  • flush( out: byte[] ): int
  • position(): int
  • seek( position: int ): int
  • mark(): int
  • reset(): int
  • sizeBoolean( value: boolean ): int
  • writeBoolean( value: boolean ): int
  • readBoolean(): boolean
  • writeBits( value: int, bits: int ): int
  • readBits( bits: int ): int
  • sizeInt( value: int ): int
  • writeInt( value: int ): int
  • readInt(): int
  • sizeLong( value: long ): int
  • writeLong( value: long ): int
  • readLong(): long
  • sizeFloat( value: float ): int
  • writeFloat( value: float ): int
  • readFloat(): float
  • sizeDouble( value: double ): int
  • writeDouble( value: double ): int
  • readDouble(): double
  • size2f( x: float, y: float ): int
  • write2f( x: float, y: float ): int
  • read2f( components: float[] ): int
  • size2d( x: double, y: double ): int
  • write2d( x: double, y: double ): int
  • read2d( components: double[] ): int
  • size3f( x: float, y: float, z: float ): int
  • write3f( x: float, y: float, z: float ): int
  • read3f( components: float[] ): int
  • size3d( x: double, y: double, z: double ): int
  • write3d( x: double, y: double, z: double ): int
  • read3d( components: double[] ): int
  • size4f( x: float, y: float, z: float, theta: float ): int
  • write4f( x: float, y: float, z: float, theta: float ): int
  • read4f( components: float[] ): int
  • size4d( x: double, y: double, z: double, theta: double ): int
  • write4d( x: double, y: double, z: double, theta: double ): int
  • read4d( components: double[] ): int

interface DataTransformer< T >

  • size( data: T ): number
  • write( data: T, buffer: DataBuffer ): number
  • read( out: T, buffer: DataBuffer ): T

interface Protocol

  • getId(): number
  • getTransport(): Transport
  • newClient( address: Address ): GameClient
  • newServer( address: Address ): GameServer
  • getChannels(): Channel
  • setChannel( id: number, reliable: boolean, ordered: boolean ): Channel
  • getChannel( id: number ): Channel

interface GameClient

  • getClient(): Client
  • getState(): Flags
  • init(): void
  • isInitialized(): boolean
  • read(): void
  • update(): void
  • isReadyToSend(): boolean
  • queue( message: Message )
  • addFactory( factory: MessageFactory ): void
  • send(): void
  • sendAllNow(): void
  • close(): void
  • isClosed(): boolean
  • getServer(): Server
  • getProtocol(): Protocol
  • getAddress(): Address
  • getOutbound(): PriorityQueue< Message >
  • getInbound(): Queue< Message >
  • getUpdateRate(): long
  • setUpdateRate( millis: number ): void
  • getLastUpdateTime(): long
  • getMessagesSent(): int
  • getPacketsRead(): int
  • getPacketIndex(): int
  • getLastPacketSize(): int
  • getReadNanos(): long
  • getUpdateNanos(): long
  • getWriteNanos(): long
  • getSendNanos(): long
  • getSendIndex(): int

interface GameServer

  • getServer(): Server
  • getState(): Flags

class Channel

  • getId(): number
  • getReliable(): boolean
  • getOrdered(): boolean
  • getLastPacket(): number

Headers

  • Unordered & unreliable: no header
  • Ordered & unreliable: sequence number
  • Reliable: sequence number & acks

class MessageType

  • getId(): number
  • getPriority(): number
  • getChannel(): Channel
  • getRetryCount(): number
  • getReadStates(): FlagsMatch
  • getWriteStates(): FlagsMatch

Message

  • getType(): MessageType
  • getTries(): number
  • getPriority(): number
  • write( out: buffer ): boolean
  • read( in: buffer ): boolean
  • size(): number

MessageFactory : Factory< Message >

  • getCreateStates(): FlagsMatch
  • create(): Message

Services

  • newService< T >( remoteInterface: T ): Service< T >
  • addInterface< T >( remoteInterface: T ): void
  • addListener< T >( listener: T ): void

Service< T >

4. Game Layer

What does the developer need to do to run a networked game?

  • Configure network properties
    • MTU, send rate (determined by flow control), number of channels
  • Configure simulation properties
  • Create a component producer for each type of object that may be communicated between server and client. This allows the networking system to get and set values to a subject.
  • Define the actor types and their attributes.
    • Attributes have a calculator, level of detail information, interpolation information, and serialization information
  • Create an applier which takes the state of a network actor and applies any additional logic to a subject
  • Define how relevant an actor is to a player
  • Handle actor creation and destruction events
  • Define which inputs are sent for a player to the server (mouse movement, directional keys, shooting)
  • Define how inputs affect the actors for a player (used in client-side prediction and server simulation)
  • Visible actor state can be compressed based on how far away/out of focus the actor is

ComponentProducer< S >

  • getComponent< T >( subject: S, component: number ): T
  • setComponent< T >( subject: S, component: number, value: T ): void

NetworkStateMessage : Message

  • time: number
  • actors: NetworkActorState[]

Format [ remote time ] [ actor count ] [ actor N id ] [ actor N action type ] [ actor N component bits ] - only for partial updates [ actor N creation flags ] - only for creation events (type, player, alwaysRelevant) [ actor N component data ] - only for creation, full updates, and partial updates

Notes

  • Action types:
    • 0 = creation
    • 1 = full update
    • 2 = partial update
    • 3 = destruction
    • 4 = deactivate (hide the actor)
    • 5 = activate (show the actor)
  • When actor id does not exist locally and all component bits sent - its a creation event
  • When actor id exists locally and component bits is empty - its a destruction event

NetworkActorState

  • actor: NetworkActor
  • messageType: number
  • type: number
  • player: number
  • alwaysRelevant: boolean
  • componentBits: number
  • componentData: number[]

NetworkSimulation

  • player: NetworkPlayer
  • otherPlayers: NetworkPlayer[]
  • latencyCompensation: number // set remote actors X ms (ex: 100) behind the latest state in the event we miss state updates
  • processors: NetworkProcessorInstance[]
  • input: NetworkInputs

NetworkPlayer

  • id: number
  • currentActor: NetworkActor
  • actors: NetworkActor[]
  • relevantActors: NetworkActorRelevance[]
  • relevancies: NetworkActorRelevancy[]

NetworkActorRelevancy

  • update( player: NetworkPlayer, relevance: NetworkActorRelevance, time: number, elapsed: GameTime ): void

Implementations

  • Distance { componentPosition, maxDistance, maxDistancePriority, maxDistanceLOD, minDistance, minDistancePriority, minDistanceLOD, lookbehind, lookahead }
  • Field Of View { componentLookAt, fovAngle, priority, lod, lookbehind, lookahead }
  • Coherency { seconds }
  • Running Average { samples }

NetworkActorRelevance

  • actor: NetworkActor
  • priority: number
  • levelOfDetail: number
  • reset(): void
  • addLevelOfDetail( lod: number ): void // ensures the level of detail is the minimum necessary
  • setPriority( priority: number ): void // ensures the priority is the maximum necessary
  • addPriority( priority: number ): void // adds priority to the relevance

NetworkProcessor< S >

  • update( subject: S, inputs: NetworkInputs, time: GameTime ): void

NetworkProcessorInstance< S >

  • subject: S
  • processor: NetworkProcessor< S >

NetworkActorType< S >

  • id: number // an id that uniquely identifies this type
  • priority: number // the default send priority for actors
  • deactivateTime: number // if the actor hasn't received data in X seconds, automatically deactivate it
  • attributes: NetworkAttributeType[] // the descriptions of each of the attributes
  • components: ComponentProducer< S > // takes an attribute from a subject instance
  • factory: Factory< S > // creates a subject instance
  • applier: NetworkActorApplier< S > // applies the network actor state at a given time to a subject. some properties of an actor require events on change (like animation state)

NetworkActor< S >

  • id: number // and id that uniquely identifies this actor
  • priority: number // the send priority for the actor
  • owner: NetworkPlayer // which player created this actor
  • author: boolean // if i'm the author, I need to send the state
  • simulating: boolean // whether the attribute history is being applied to the subject
  • remote: boolean // whether this actor is processed remotely or locally
  • active: boolean // if the actor is visible / should be be updated
  • alwaysRelevant: boolean // if this actor's state should always be sent
  • type: NetworkActorType< S > // the actor type
  • attributes: NetworkAttribute[] // the attributes
  • subject: S // the subject being synchronized

NetworkActorApplier< S >

  • apply( subject: S, actor: NetworkActor< S >, time: number ): void

NetworkAttributeType< T >

  • index: number // the index of the attribute in the actor
  • component: number // the component index on the subject
  • maximumLevelOfDetail: number // the level of detail this attribute is on (0 = all details, 1 = fewer, 2 = fewest, etc)
  • allowableDistance: number // the maximum allowed distance a value can be from the authoritative source before it needs to be harshly corrected
  • calculator: Calculator< T > // the calculator which is passed to path calculations
  • pathGenerator: PathGenerator< T > // generate a path of values based on the current values
  • maxExtrapolationTime: number // the maximum amount of time we go past the latest value in an attempt to guess the unknown future position due to latency
  • extrapolationDamping: number // a value which discourages extrapolation over time (a slowing down of extrapolation over time)
  • dataOptions: DataOptions // the options for reading & writing this type
  • dataTransformer: DataTransformer< T > // writes & reads the attribute to a data buffer

NetworkAttribute< T >

  • path: Path // the path generated based on the values available
  • history: AttributeHistory< T > // the history of values for this attribute

NetworkInput< T >

  • index: number // the input
  • value: T // the input value
  • dataOptions: DataOptions // the options for reading & writing this input
  • dataTransformer: DataTransformer< T > // writes & reads the network input to a data buffer
  • history: AttributeHistory< T > // the history of inputs

NetworkInputs

  • inputs: NetworkInput[]

Format [ input bits ] [ input N data ]

AttributeHistory< T >

  • calculator: Calculator< T >
  • times: number[]
  • values: T[]
  • size: number
  • current: number
  • setValue( time: number, value: T ): void
  • getValue( time: number ): T
  • hasValue( time: number ): boolean
  • getValueAtIndex( index: number ): T
  • getIndexBeforeTime( time: number ): number
  • getTimeMinimum(): number
  • getTimeMaximum(): number
  • getValueCount(): number

References

  1. https://docs.unrealengine.com/udk/Three/NetworkingOverview.html#Relevancy
  2. https://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking
  3. https://0fps.net/2014/02/10/replication-in-networked-games-overview-part-1/
  4. https://0fps.net/2014/02/17/replication-in-networked-games-latency-part-2/
  5. https://0fps.net/2014/02/26/replication-in-networked-games-spacetime-consistency-part-3/
  6. https://0fps.net/2014/03/09/replication-in-network-games-bandwidth-part-4/
  7. http://www.gabrielgambetta.com/fast_paced_multiplayer.html
  8. http://gafferongames.com/networking-for-game-programmers/