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Avatar Mobility in
黃瑋璨新加坡國立大學
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Wei Tsang Ooi Mehul MotaniHuiguang Liang Ian Tay Ming Feng Neo
National University of Singapore
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“My life is so great that I literally wanted a second one!”- Dwight Schrute, The Office
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256x256 m regions.
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avatar mobility:who is where, when
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why do we care?
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research in systems support for NVE
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How to partition a world into regions and assign regions to servers considering
- communication cost- hand-over rate- balancing server load :
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How to predict avatar movement (end therefore what a user will see next)?
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AoI-based scheme
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How many connections?
How stable are the connections?
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supernode-based scheme
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How to pick supernodes?
How stable are the supernodes?
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how to simulate avatar mobility?
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random walkrandom waypoint
clustered movement:
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or, small-scale
implementation
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no large-scale NVE available until recently
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482,594residents logged in between 2-9 June 2008
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secondlife.com/whatis/economy-graphs.php
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• collect mobility traces of avatars in Second Life
• what it means w.r.t. systems design for NVEs?
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collecting traces
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how do avatars move inside a distributed
virtual environment?
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how are avatars distributed within a
region?
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how long do they stay at a location?
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do they move in groups?
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etc.
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FPS MMORPG NVE
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Linden, can we get access to the server traces?
No.
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• Wrote our own client
• Parses packets using libsecondlife
• Insert bots into regions
• Log positions of avatars every 10s
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difficulties
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running out of memory
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anti-bots policy
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over crowded region
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inter-region tracking
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• Wrote our own client
• Parses packets using libsecondlife
• Insert bots into regions
• Log positions of avatars every 10s
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who is where, when
(doing what)
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Freebies
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The Pharm
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Isis
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Ross
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Mobility Patterns
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Freebies: number of visits to a cell
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Freebies: average pause time in a cell
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Freebies: average speed in a cell
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Isis: number of visits to a cell
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caching/prefetching based on popularity of
locations?
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Isis: average pause time in a cell
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pick supernodes from sticky location?
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Isis: average speed in a cell
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mobility model:random walk +
pathway ?
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churn rate
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Reasonably high churn (up to 6/min)
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1 min 10 min
1 hr 2 hr
Highly skewed. Some stay for hours.
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cannot pick supernodes uniformly
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clustering of avatars
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meeting: encounter between two avatars
(within each other AoI)
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Meet many different avatars.
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1 min
10 min
1 hr
2 hr
Most meetings are short.
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Meeting size is large.
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high overhead in maintaining AoI
neighbors
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meeting stability:
avg meeting sizeover
num of avatars met
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Wide range of stability
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other tidbits
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little temporal variations
can use historical information to predict future
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rotate 18% of the time
Second Life’s prefetching is wasteful
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25-35% revisits the same region in a day
region-based caching?
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proxy-based texture caching
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why textures?
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62 - 81%of traffic are textures
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316 MBof textures in Isis
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64m
80o
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64m
80o
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403 TBof textures retrieved
in Isis in a day
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SL servers texture proxy
clients
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what caching algorithm to used?
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2Q
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FIFO
LRU
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FIFO
LRU
cache miss
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FIFO
LRU
cache hit
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FIFO
LRU
cache hit
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FIFO
LRU
scan resistant
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3Q
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FIFO
LRU
Victim Buffer
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FIFO
LRU
cache hit
Victim Buffer
(sorted by popularity)
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how to define popularity of texture?
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Freebies: number of visits to a cell
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little temporal variations
can use historical information to predict future
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popularity of texture = popularity of cell
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2Q 3Q OPT
Ross 50 MB 0.58 0.62 0.70
Ross 25 MB 0.28 0.36 0.47
Freebies 50 MB 0.48 0.50 0.68
Freebies 25 MB 0.21 0.33 0.50
Per-byte Hit Rate
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conclusion
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understanding real avatar mobility is crucial to design good NVEs
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謝謝歡迎發問及指教
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