With the popularity of smart devices such as smartphones, tablets, contents that traditionally be viewed on a personal computer, can also be viewed on these smart devices. The demand for contents thus is increasing year by year, which makes the content providers (CPs) get high revenue from either users' subscription or advertisement. On the other hand, Internet service providers (ISPs), who keep investing in the network technology or capacity to support the huge traffic generated by contents, do not benefit directly from the content traffic. One choice for ISPs is to charge CPs to share the revenue from the huge content traffic. Then ISPs will have enough incentives to invest in network infrastructure to improve quality of services (QoS), which eventually benefit CPs and users. This paper presents a novel economic model called Stackelberg-Bertrand game to capture the interaction and competitions among ISPs, CPs and users when ISPs charge CPs. A generic user demand function is assumed to capture the sensitivity of demand to prices of ISPs and CPs. The numerical results show that the price elasticity of ISP and CP plays an important part on the payoff of the ISP and CP.