Introduction toMultiplayer Network Technology

Thomas Lidy

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Introduction

Networking - used in ...– e-commerce– training & education– distributed engineering & design– entertainment– multi player games „networked virtual environments“

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Networked Virtual Environment

software system– 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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Networked Virtual Environment

components– graphics engines and displays– communication and control devices– processing systems– data network

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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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Origins in military

SIMNET– started 1983– developed for DARPA

DIS (protocol)– defined after 1989– standardized packets (PDUs)– distributed & heterogeneous

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Origins in industry

SGI - Flight (1984) SGI - Dogfight (1985)

Academic origins NPSNET (1986) PARADISE (1993) BrickNet (1991)

Flight

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Origins on PC class machines

Doom (1993) Macintosh: Marathon (1994) Bolo (tank game)

Doom

... and many othersBolo

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Network Technology

Issues for networking– Latency

time required from one host to another– Bandwidth

data rate: how many bits per second– Reliability

how much data is lost

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Sockets and Ports

allow multiple applications to use the network

TCP

0 65535

UDP

0 65535

Other Prot.

0 65535

Applications ftp www netVEs games

IP (Internet Protocol)

port #s

protocols

IP layer

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Internet Protocol (IP)

low-level protocol basic services splits & reassembles packets TTL field („time to live“) other protocols lie on topon top of IP

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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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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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IP Broadcasting

instead of sending multiple copiesof a packet to all destinations

single transmission to allall hosts in the network

broadcasting to address 255.255.255.255 disadvantages:

– expensive for hosts that are not interested– delivery only on LAN - not Internet-wide!

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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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Multicast routing

LondonWashington

Vienna

Moscow

TokyoDenver

New York

MunichPrague

Graz

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IP Multicasting

addressing– pseudo IP (class D address):

range 224.0.0.0 - 239.255.255.255– can be used temporarily or reserved by IANA

problems– routers must be multicast-capable– not yet available troughout the Internet multicast routers communicate directly with each

other through the MBONE

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Overview (1)

TCP UDPdelivery: guaranteed best-effortflow: stream-based packet-basedordering: ordered

packetsimmediate

deliveryerror handling: checksums -advantages: reliable low overheaddisadvant.: delays,

overheadno ordering,no acknowl.

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Overview (2)Broadcasting Multicasting

delivery to: all hosts onlocal network

subscribed hosts

strengths: fast delivery,as with UDP

efficient Internet-wide delivery

limitations: same as UDP,limited to LAN

same as UDP,routers must bemulticast-capable

suitable for: small-scale p2pnetVEs withhigh datarequirements

large-scale p2pand client/servernetVEs in theInternet

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Networking today - Conclusion

networking:essential part of multi player environments

designers must carefully selectprotocols 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

Thomas Lidy

The EndThe End