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  • 1. IEEE 802.11 WLAN Capacity and Optimization for Multiplayer Network Games Hanghang Qi David Malone Dmitri Botvich Hamilton Institute, National University of Hamilton Institute, National University of TSSG, Waterford Institute of Technology, Ireland, Maynooth, Ireland. Ireland, Maynooth, Ireland. Ireland. hanghang.qi@nuim.ie david.malone@nuim.ie dbotvich@tssg.org 1 Problem define:network game within an WLAN 1 stations 0.014 stations game server 0.012 AP AP 0.8 game server Throughput efficiency 0.01 0.6 Delay (s) 0.008 AP nλs 0.006 0.4 n(λc + λs ) S 0.004 0.2 0.002 0 0 λc λc λc 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 Number of stations Number of stations C C ... C (a) Throughput efficiency (b) Delay n 0.04 4.5 stations DCF 0.035 AP 4 Figure 1: How many players can play a good game within a 802.11 WLAN? 0.03 game server 3.5 0.025 Jitter (s) MOS 0.02 3 0.015 2.5 2 Network games traffic 0.005 0.01 2 We did many experiments in our 4 PCs wireless game network testbed and got 0 1.5 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 the game traffic in packet transmission level. The key characteristics are shown Number of stations Number of stations in Fig. 2 (c) Jitter (d) Mean Opinion Score AtoS StoA Figure 4: Performance of a basic 802.11 DCF network 14000 500 450 12000 400 10000 8000 350 300 4 AP and Server with larger TXOP n 6000 250 200 Larger TXOP, one of the 802.11e parameters, are given to AP and Server as n 4000 150 100 increases (n is the number of clients; normal client’s TXOP is 1) to give AP 2000 0 50 0 and Server larger transmission opportunity, the network performance can be 0 0.02 0.04 0.06 0.08 interarrival time (s) 0.1 0.12 0 0.02 0.04 0.06 0.08 interarrival time (s) 0.1 0.12 improved for the games. (a) Client to Server (b) Server to Client 1 0.02 AtoS StoA game server game server 5000 700 0.9 stations stations 4500 AP AP 600 0.8 0.015 Throughput efficiency 4000 3500 500 0.7 Delay (s) 3000 400 2500 0.6 0.01 300 2000 0.5 1500 200 1000 0.4 0.005 100 500 0.3 0 0 0 50 100 150 200 0 50 100 150 200 packet size (bytes) packet size (bytes) 0.2 0 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 Number of stations Number of stations (c) Client to Server (d) Server to Client (a) Throughput efficiency (b) Delay Figure 2: Quake 4 game traffic characteristics 0.05 4.5 game server TXOP stations 4 0.04 AP 3 802.11 network model and performance 0.03 3.5 Jitter (s) MOS IEEE 802.11 MAC DCF uses a CSMA/CA with exponential backoff scheme 3 0.02 which can be modelled with a 2-D Markov Chain. 2.5 0.01 2 0 1.5 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 Number of stations Number of stations 0,0e 1−q 0,1e 0,2e ... 0,w0−1e 1−q 1−q q q q (c) Jitter (d) MOS q 0,0 0,1 0,2 ... 0,w0−1 Figure 5: AP and Server priority with TXOP 1−p 1 1 1 ... ... ... ... 1−p i−1,0 ... 5 Conclusions Our analytical model suggests that a basic DCF 802.11b WLAN can support 1−p i,0 1 i,1 1 i,2 ... 1 i,wi−1 maximum 10 players of Quake 4. By using 11e parameter TXOP to give AP ... ... ... ... and Game Server higher priority to access the channel, the network perfor- mance can be improved to 15 players. 1−p m,0 1 m,1 1 m,2 ... 1 m,wm−1 References [Bianchi, 2000] Bianchi, G. (2000). Performance analysis of the ieee 802.11 Figure 3: Markov chain model of 802.11 MAC distributed coordination function. Selected Areas in Communications, IEEE Journal on, 18(3):535–547. [Cricenti and Branch, 2007] Cricenti, A. and Branch, P. (2007). Arma(1,1) The Bianchi’s 2-D Markov chain model together with the traffic arrival modeling of quake4 server to client game traffic. In NetGames ’07, NY, model are used to calculate the throughput, delay and jitter. Then Frank’s em- USA. ACM. pirical mapping model is used to get Mean Opinion Score (MOS) from delay and jitter. [Wattimena et al., 2006] Wattimena, A. F., Kooij, R. E., van Vugt, J. M., and Ahmed, O. K. (2006). Predicting the perceived quality of a first person

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