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Networking.md

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Quake 2 Networking Communication Protocol

NetworkPacket

Every frame both client and servers are sending a jake2.qcommon.network.messages.NetworkPacket to each other. Each such packet contains a header and several (Client|Server)Messages

"Connectionless" (Out of band) packet

Such packets/messages are sent ad-hoc and don't require a running map instance, therefore could be sent by not connected clients. They are sent separately, not as a part of jake2.qcommon.network.messages.NetworkPacket. Mostly such packets contain a single string (though there are some cases when 2 strings are sent - info & print)

see jake2.qcommon.network.messages.ConnectionlessCommand

Reliability

Since quake2 utilizes only UDP protocol, reliability should be handled by the quake2 engine itself. Each frame server tries to send a reliable message first, then if there is room append an unreliable buffer and send.

Check the jake2.qcommon.network.Netchan.Transmit

TBD

Delta compression

The bulk of the network traffic between server & client constitute entity updates and move messages. In order to minimize the amount of information sent over the network quake2 protocol uses delta compression - an attempt to send only the difference from the previously sent command. The following messages use delta compression:

  1. PlayerInfoMessage (from server)
  2. PacketEntitiesMessage (from server)
  3. MoveMessage (from client)

The approach is the same for all of them - first identify what fields have changed (deltaFlags, like a bitmask), then sent only those fields.

Server Messages

see package jake2.qcommon.network.messages.server

Client Messages

see package jake2.qcommon.network.messages.client

Client States

see jake2.server.ClientStates

Connection initialization

The following diagram illustrates client/server communication when client connectos to server. Starting from typing connect 'someaddress' and until client becomes connected and receives the updates from the server. Connection initialization

Further improvements - TODO

Api improvements

Network package should expose only message classes and couple of source/sink classes/interfaces for them. Nothing else is relevant and should be hidden with package private visibility.

Example of the network api:

// holding the network connection state, manages reliability, checksums, etc
class <T> NetworkConnection {
    // called multiple times per frame by client/server modules
    void sendConnectionLessPacket(...) 

    // called multiple times per frame by client/server/game modules, adds the message to the pending queue
    void write(T) 

    // called once every frame, packs all pending messages into packet and transmits over the network
    void flush() 

    // called every frame, unpacks the packet of incoming messages and validates
    Collection<T> receive()
}