The state of multiplayer games over the network. Presented at TGF 2013.

1. “Let’s
Play
Together”
Networked
Mul-player
Games
Amir
H.
Fassihi
Fanafzar

2. Background
Garshasp:
The
Monster
Slayer,
PC
2011
Garshasp:
Temple
of
the
Dragon,
PC
2012
Shadow
Blade,
iOS,
Android
Fall,
2013

3. Current
Game
• Coopera-ve
Mul-player
Game

4. Mul-player
Games
• Co-­‐op/PvP
• Local/LAN/Internet
• Real-­‐-me/Asynchronous

5. This
Talk
• LAN/Internet
• Co-­‐op/PvP
• Real-me

6. Game
Networking
Gameplay
Code
High
Level
Network
Code
Low
Level
Network
Code

7. Low
Level
Networking
• Sockets
• Transfer
Protocols
• NAT
(Network
Address
Transla9on)

8. Sockets
• Socket
– IP
– Port
• OS
Support
– BSD
Sockets
– WinSock
– …

9. Transfer
Protocols
• UDP
– Unreliable
– Un-­‐ordered
– Connec-on-­‐less
using
Datagrams
(1400
bytes)
• TCP
– Reliable
– Ordered
– Stream
Based

10. Game
Networking
UDP
+
reliability
+
order

11. NAT
• Network
Address
Transla-on
• Connec-on
Problem
with
NAT
Box
– Server
Listening
on
Port
– Client
changing
port
• NAT
Punch-­‐through
with
Facilitator
Server

12. High
Level
Networking
• Architecture
• Data
to
Transfer
• Lag
Compensa-on

13. Network
Architecture
• Peer
to
Peer
• Client
Server
• Mixed

14. Peer
to
Peer
Client
1
Client
2
Client
3
Client
4

15. Client-­‐Server
Client
1
Client
2
Client
3
Server

16. Data
Transfer
How
To
Share
The
Same
Experience?

17. What
to
Send?
1. Share
Inputs
2. Share
Input
and
State
(Authorita-ve
Server)
3. Share
Input
and
State
(Mixed
Authority)

18. Game
Loop
(Simplified)
1. Read
User
Input
2. Do
Simula-on
1. Logic
2. AI
3. Physics
…
3. Output
1. Render
Graphics
2. Play
Sound/Music
3. Update
UI
…

19. Sharing
Input
Client
1
Client
2
User
1
Input
User
2
Input

20. Shared
Input
P2P
Main
Requirement:
Determinis=c
Simula=on

21. Shared
Input
P2P
Constraint
(for
Lockstep):
Lag
Effect
On
Clients
No
mid-­‐game
join!

22. Shared
Input
P2P
Risk:
Chea=ng

23. Shared
Input
P2P
Advantage:
Low
Bandwidth
Requirements

24. Shared
Input
P2P
Used
for:
Strategy
Games
(Starcra',
Age
of
Empires,
…)

25. 1500
Archers
• 1500
Archers
on
a
28.8:
Network
Programming
in
Age
of
Empires
and
Beyond,
Gamasutra

26. Shared
State
Server
Client
1
Client
2
Input
1
Input
2
Game
State
Game
State

27. Shared
State
Main
Requirement:
Simula=on
Only
On
Server

28. Shared
State
Constraint:
High
Bandwidth
(Especially
the
Server!)

29. Shared
State
• Cheat
Proof
• Non-­‐determinis-c
simula-on
is
ok
• Different
client
lag
will
not
stall
• Mid-­‐game
joining
possible

30. Shared
State
Good
For:
Ac=on
Games
Compe==ve
Games
(eSports)

31. Main
Challenge
Biggest
Challenge
in
Game
Networking
is:

32.
Lag!!!

33. Lag
in
Client-­‐Server
Client
Server
Press
Buaon
Press
Buaon
Fire
Fire

34. Lag
in
Client-­‐Server
Client
Server
Press
Buaon
Press
Buaon
Fire
Fire
Lag

35. Solu-on
#1
Client
Side
Predic=on

36. Client-­‐side
Predic-on
Client
Server
Press
Buaon
Press
Buaon
Fire
Fire
Check
Validity

37. Client-­‐side
Predic-on
• Fix
Client
State
if
different
• State
History
on
Client
• Useful
for
player
state
• Can
be
used
for
other
objects
(extrapola-on)

38. Client-­‐side
Predic-on
Popularized
by:

39. Solu-on
#2
Input
Latency

40. Input
Latency
• Input
marked
for
future
• 50-­‐100ms
• Client
will
interpolate

41. Input
Latency
Client
Server
Move
Forward
T
=
+100ms
Move
Forward
Find
posi-on
for:
+100
Pos:
+100ms
Current
t:
+70ms
Interpolate
between
previous
pos
and
pos
at
+100ms
for
+70ms

42. Client
Interpola-on
-me
=
1200
-me
=
1300
pos
=
1,
1,
1
pos
=
2,
2,
1
9me
=
1250
pos
=
1.5,
1.5,
1
Interpolated
State

43. Solu-on
#3
Server-­‐side
Lag
Compensa=on

44. Server-­‐side
Lag
Compensa-on
• Rewind
simula-on
on
server
based
on
client
lag.
• Re-­‐simulate
game.

45. Source
Engine
Lag
Compensa-on

46. Gameplay
Inconsistencies
• Wrong
posi-on
(no
compensa9on)
• Late
Hits
(with
compensa9on)

47. Problem
with
Lag
Compensa-on
A
B
High
Lag
Low
Lag

48. Problem
with
Lag
Compensa-on
A
B
High
Lag
Low
Lag
B

49. Design
Lag
Compensa=on
Strategy
can
be
a
“Game
Design”
decision.

50. Doom
III
Solu-on
Player
Extrapola=on

51. Player
Extrapola-on
• A
kind
of
Predic-on
• Assume
controls
don’t
change
• Simulate
fully
(with
Physics)
like
the
server
• AKA
Dead
Reckoning

52. Mixed
Authority
• Clients
with
Authority
over
some
objects.
• Example:
Sync
Host
in
FUSE
(Overstrike),
Game
Developer
Magazine,
Feb
2012

53. Network
Op-miza-on
• High
Level
– Architecture
Selec-on
– Update
Frequency
– Data
Relevancy
– Priori-za-on

54. Network
Op-miza-on
• Low
Level
– Bitpacking
(bitstreams)
– Compression
– Delta
Values

55. Delta
Compression
in
Quake
(1996)

56. Quake
Delta
Compression

57. Delta
+
Reliable
UDP

58. Quake
Network
Stack

59. Doom
(1993)
• Doom
used
P2P
Lockstep
Model.
Good
for
LAN
only.

60. Quake
Engine
Evolu-on

61. Quake
Engine
Evolu-on

62. Quake
Engine
Evolu-on

63. Quake
Engine
Evolu-on

64. Cloud
Gaming
Main
Challenge:
Lag!

65. Figh-ng
Game
Networking
• Peer
to
Peer
– Input
Latency
– Rollback
Technique
Example:
GGPO
Networking
Library

66. Networking
Libraries
• Enet
• RakNet
• Ice
• PocoProject
• Torque
Network
Library
• ZeroMQ
• Boost
ASIO

67. Conclusion
• Networking
is
a
tradeoff
between:
– Consistency
– Responsiveness
– Bandwidth
– Latency

68. References
1
• Robust
Efficient
Networking,
Ben
Garney,
GDC
2008
• Torque
Networking
Library
(opentnl.org)
• Video
Game
Op-miza-on,
Ben
Garney
• “I
Shot
You
First”,
Halo
Reach
Networking,
David
Aldridge,
GDC
2011

69. References
2
• QuakeWorld
hap://en.wikipedia.org/wiki/QuakeWorld
• Network
Systems
in
Insomniac
Games’
Overstrike
(FUSE),
Game
Developer
Magazine,
Feb
2012
• 1500
Archers
on
a
28.8,
hap://www.gamasutra.com/view/feature/
131503/1500_archers_on_a_288_network_.php?page=1

70. References
3
• “The
TRIBES
Engine
Networking
Model”,
Frohnmayer
and
Gis,
GDC
1999
• Understanding
Figh-ng
Game
Networking,
hap://mauve.mizuumi.net/2012/07/05/understanding-­‐figh-ng-­‐game-­‐
networking/
• GGOP
Networking
Library,
hap://ggpo.net/
• The
Doom
III
Network
Architecture
hap://mrelusive.com/publica-ons/papers/The-­‐DOOM-­‐III-­‐Network-­‐
Architecture.pdf

71. References
4
• The
Quake
3
Networking
Model,
Brian
Hook,
hap://trac.bookouook.com/bookouook/trac.cgi/wiki/
Quake3Networking
• What
Every
Programmer
Needs
To
Know
About
Game
Networking,
Glenn
Fiedler,
hap://gafferongames.com/networking-­‐for-­‐game-­‐programmers/what-­‐
every-­‐programmer-­‐needs-­‐to-­‐know-­‐about-­‐game-­‐networking/
• Unreal
Networking
Architectures
hap://udn.epicgames.com/Three/NetworkingOverview.html

72. References
5
• “Latency
Compensa-ng
Methods
in
Client/Server
in-­‐game
Protocol
Design”,
Yahn
Bernier,
Valve
haps://developer.valvesosware.com/wiki/
Latency_Compensa-ng_Methods_in_Client/Server_In-­‐
game_Protocol_Design_and_Op-miza-on#Lag_Compensa-on
• Believable
Dead
Reckoning
for
Networked
Games,
Cur-ss
Murphy,
Game
Engine
Gems
2
• Choosing
a
Game
Network
Library,
Patrick
Wyaa,
hap://www.codeouonor.com/blog/choosing-­‐a-­‐game-­‐network-­‐lib

73. References
6
• Dead
Reckoning:
Latency
Hiding
for
Networked
games
hap://www.gamasutra.com/view/feature/3230/
dead_reckoning_latency_hiding_for_.php

74. Special
Thanks
• Yaser
Zhian
• Hojjat
Jafary
• Ashkan
Saeidi

75. Ques-ons?
fassihi@fanafzar.com