On 1 Jun 2010, at 11:12, Erik Möller wrote: > The use case I'd like to address in this post is Real-time client/server > games. > > The majority of the on-line games of today use a client/server model over UDP > and we should try to give game developers the tools they require to create > browser based games. For many simpler games a TCP based protocol is exactly > what's needed but for most real-time games a UDP based protocol is a > requirement. Games typically send small updates to its server at 20-30Hz over > UDP and can with the help of entity interpolation and if required entity > extrapolation cope well with intermittent packet loss. When a packet loss > occur in a TCP based protocol the entire stream of data is held up until the > packet is resent meaning a game would have to revert to entity extrapolation > possibly over several seconds, leading to an unacceptable gameplay experience. > > It seems to me the WebSocket interface can be easily modified to cope with > UDP sockets (a wsd: scheme perhaps?) and it sounds like a good idea to > leverage the work already done for WebSockets in terms of interface and > framing. > > The most important distinction between ws: and wsd: is that messages sent by > send() in wsd: need not be acknowledged by the peer nor be resent. To keep > the interface the same to the largest possible extent I'd suggest > implementing a simple reliable 3-way handshake over UDP, keep-alive messages > (and timeouts) and reliable close frames. If these are implemented right the > interface in it's entirety could be kept. Only one new readonly attribute > long maxMessageSize could be introduced to describe the min path MTU (perhaps > only valid once in connected mode, or perhaps set to 0 or 576 initially and > updated once in connected mode). This attribute could also be useful to > expose in ws: and wss: but in that case be set to the internal limit of the > browser / server.
SCTP would be ideal for this. It's connection-oriented, but supports multistreaming (can deliver messages out of order, without head of line blocking). http://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocol -- regards, Kornel
