I. Introduction
This paper deals with the network neutrality debate. The possibility of introducing non-neutrality comes from the increasing traffic asymmetry between Internet Service Providers (ISPs), mainly due to some prominent and resource consuming content providers (CPs) which are usually connected to a single ISP. The typical example is YouTube (owned by Google), accessed by all users while hosted by a single Tier 1 ISP, and whose traffic now constitutes a non-negligible part of the whole Internet traffic. For this reason, there has been a surge of protest among ISPs, complaining that the current Internet business model where ISPs charge both end-users and content providers directly connected to them, and have public peering or transit agreements with other ISPs, is not relevant anymore, because they should charge content providers that are associated with other ISPs. This was first advocated at the end of 2005, by Ed Whitacre (CEO of AT&T) [1]. The underlying concern is that investment is made by ISPs but content providers get an important part of the dividends. The revenue arising from online advertising (meaning showing graphical ads on regular web pages) is estimated at approximately a $24 billion in 2009 [2] while textual ads on search pages has led to a combined revenue of $8.5 billion in 2007 [3], those figures increasing every year. Meanwhile, transit prices - which constitutes the main source of revenues for transit ISPs - are decreasing. ISPs argue that there is no sufficient incentive for them to continue to invest on the network infrastructures if most benefits go to content providers. The threat is to lower the quality of service of CPs that do not pay any fee to them, or even to block their traffic. This possibility has led to protests from CPs and user associations, complaining that this might impact the network development and is an impingement of freedom of speech [1]. This has launched a debate, essentially at the law and policy makers level, to decide whether the Internet should be neutral, i.e. all packets should receive equal treatments in terms of price and service. In the US, the Federal Trade Commission (FTC) released in 2007 a report not supporting neutrality constraints, increasing the debate at the political level. This debate is also active in Europe and in France, as illustrated by the open consultation on network neutrality launched in 2010. For instance, the French regulation authority, ARCEP, has published in its response a proposal intending to define how net neutrality could be implemented [4], [5].