Transcript Introduction to Multiplayer Network Technology

Introduction to
Multiplayer Network Technology
Thomas Lidy
Introduction
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Networking - used in ...
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Thomas Lidy
e-commerce
training & education
distributed engineering & design
entertainment
multi player games
 „networked virtual environments“
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Multiplayer Network Technology
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Networked Virtual Environment
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software system
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multiple users interact in real-time
shared sense of space and time
realistic 3D graphics and sound
a way to communicate
interaction with the virtual environment
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Multiplayer Network Technology
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Networked Virtual Environment
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components
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graphics engines and displays
communication and control devices
processing systems
data network
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Multiplayer Network Technology
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Origins of virtual environments
origins in military
(and industry)
 academic research in
networked virtual environments
 virtual worlds on PC class systems
- 3D games
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Thomas Lidy
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Multiplayer Network Technology
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Origins in military
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SIMNET
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started 1983
developed for DARPA
DIS (protocol)
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defined after 1989
standardized packets (PDUs)
distributed & heterogeneous
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Multiplayer Network Technology
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Origins in industry
SGI - Flight (1984)
 SGI - Dogfight (1985)
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Academic origins
Flight
NPSNET (1986)
 PARADISE (1993)
 BrickNet (1991)
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Thomas Lidy
Introduction to
Multiplayer Network Technology
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Origins on PC class machines
Doom (1993)
 Macintosh:
 Marathon (1994)
 Bolo (tank game)
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Doom
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... and many others
Bolo
Thomas Lidy
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Multiplayer Network Technology
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Network Technology
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Issues for networking
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Latency
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Bandwidth
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data rate: how many bits per second
Reliability
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time required from one host to another
how much data is lost
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Multiplayer Network Technology
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Sockets and Ports
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allow multiple applications to use the network
Applications
ftp
port #s
protocols
IP layer
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www
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netVEs
65535
TCP
games
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UDP
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Other Prot.
IP (Internet Protocol)
Introduction to
Multiplayer Network Technology
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Internet Protocol (IP)
low-level protocol
 basic services
 splits & reassembles packets
 TTL field („time to live“)
 other protocols lie on top of IP
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Thomas Lidy
Introduction to
Multiplayer Network Technology
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Transmission Control Protocol (TCP)
layered on top of IP ( TCP/IP)
 simple point-to-point connection
 automatic acknowledgments
 error checking
 correct packet order
 reliability
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Thomas Lidy
Introduction to
Multiplayer Network Technology
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User Datagram Protocol (UDP)
also layered on top of IP
 connectionless
 packet-by-packet basis
 best-efforts delivery (not reliable)
 less processing time  faster
 deal with packet loss and ordering!
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Thomas Lidy
Introduction to
Multiplayer Network Technology
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IP Broadcasting
instead of sending multiple copies
of a packet to all destinations
 single transmission to all hosts in the
network
 broadcasting to address 255.255.255.255
 disadvantages:
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expensive for hosts that are not interested
delivery only on LAN - not Internet-wide!
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Multiplayer Network Technology
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IP Multicasting
receiver-controlled distribution
 interested hosts subscribe to a list
 packets are sent down distribution paths
 no burdens for hosts not interested
 less overhead than broadcasting
 appropriate for Internet use
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Thomas Lidy
Introduction to
Multiplayer Network Technology
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Multicast routing
New York
Moscow
Washington
Denver
London
Munich
Tokyo
Prague
Vienna
Graz
Thomas Lidy
Introduction to
Multiplayer Network Technology
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IP Multicasting
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addressing
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pseudo IP (class D address):
range 224.0.0.0 - 239.255.255.255
can be used temporarily or reserved by IANA
problems
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routers must be multicast-capable
not yet available troughout the Internet
multicast routers communicate directly with
each other through the MBONE
Introduction to
Multiplayer Network Technology
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Overview (1)
delivery:
flow:
ordering:
error handling:
advantages:
disadvant.:
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TCP
UDP
guaranteed
best-effort
stream-based
packet-based
ordered
packets
checksums
immediate
delivery
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reliable
low overhead
delays,
overhead
no ordering,
no acknowl.
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Multiplayer Network Technology
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Overview (2)
Broadcasting
delivery to: all hosts on
local network
strengths: fast delivery,
as with UDP
limitations: same as UDP,
limited to LAN
Multicasting
subscribed hosts
efficient Internetwide delivery
same as UDP,
routers must be
multicast-capable
suitable for: small-scale p2p large-scale p2p
netVEs with
and client/server
high data
netVEs in the
requirements
Internet
Thomas Lidy
Introduction to
Multiplayer Network Technology
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Networking today - Conclusion
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networking:
essential part of multi player environments
designers must carefully select
protocols and network archtitecture
multicasting: most efficient technique
for large-scale netVEs
games today use client/server, peer-to-peer
multicasting probably becomes more globally
available with IPv6
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Introduction to
Multiplayer Network Technology
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The End
Thomas Lidy