Zhiguo Cao Caixia Chi Ruibing Hao Yang Xiao User Behavior Modeling and Traffic Analysis of IMS Presence Servers. 2469-2473 2008 GLOBECOM http://dx.doi.org/10.1109/GLOCOM.2008.ECP.474 conf/globecom/2008 db/conf/globecom/globecom2008.html#CaoCHX08