In First Person Shooter (FPS) games the Round Trip Time (RTT), i.e., the sum of the network delay from client to server and the network delay from server to client, impacts the gamer's performance considerably. Game client software usually has a built-in process to measure this RTT (also referred to as ping time), and therefore gamers do not want to connect to servers with a long ping time. This paper develops a methodology to evaluate the ping time in a scenario where gamers access a common gaming server over an access network, consisting of a link per user that connects this user to a shared aggregation node that in turn is connected to the gaming server via a bottleneck link. First, a model for the traffic the users and the server generate, is proposed based on experimental results of previous papers. It turns out that the characteristics of the (downstream) traffic from server to clients differ substantially from the characteristics of the client-to-server (upstream) traffic. Then, two queuing models are developed (one for the upstream and one for the downstream direction) and combined such that a quantile of the RTT can be calculated given all traffic and network parameters (packet sizes, packet inter-arrival times, link rate, network load, ...). This methodology is subsequently used to assess the (quantile of the) RTT in a typical Digital Subscriber Line (DSL) access scenario. In particular, given the capacity dedicated to gaming traffic on the bottleneck link (between the aggregation node and gaming server), the number of gamers (or equivalently the gaming load the bottleneck link can support) is determined under the restriction that the quantile of the RTT should not exceed a predefined bound. It turns out that this tolerable load is surprisingly low in most circumstances. Finally, it is remarked that this conclusion depends to some extent on the details of the downstream traffic characteristics and that measurements reported in literature do not give conclusive evidence on the exact value of all parameters, such that, although the qualitative conclusion still remains valid, additional experiments could refine the detailed quantitative results.
['Natalie Degrande', 'Danny De Vleeschauwer', 'Robert E. Kooij', 'Michel Mandjes']
Modeling ping times in first person shooter games