Implementation of a Peer-to-Peer Multiplayer Game with ... - DVS

Table 5.1: Client-server traffic depending on the total number of playersClientServer# Players Total (B/s) Up (B/s) Down (B/s) Total (B/s) Up (B/s) Down (B/s)2 7,511 4,514 2,997 14,933 5,955 8,9783 5,513 3,510 2,002 16,799 6,072 10,7274 6,518 4,649 1,869 26,030 7,440 18,5916 12,080 9,161 2,919 71,592 15,758 55,8348 16,805 13,328 3,477 131,114 24,210 106,90312 22,405 19,191 3,213 269,093 38,355 230,73816 26,834 23,594 3,240 427,596 53,215 374,38124 47,501 43,044 4,457 1,139,158 112,402 1,026,75632 63,338 58,788 4,551 2,012,340 142,783 1,869,557shooting. The incoming bandwidth grows linearly with the number of players because each client receivedthe updates of all others. The server’s traffic measurements show why the number of players islimited to less than 40. With 32 players, the average outgoing traffic already reaches about 20MB/s,and, more importantly, its growth is quadratic. The time-traffic plots 5.3 and 5.4 show the same picture.Despite any potential optimization, the server’s work always increases quadratically with the number ofplayers (of which everyone can see all others) that it has to serve. Message aggregation will help to significantlyreduce the outgoing traffic, but it will not change the complexity. A possible countermeasure isto reduce the level of detail of update messages depending on the load, e.g., by decreasing the frequencyof outgoing update messages.5.1.2 Peer-to-PeerThe peer-to-peer implementation using the slightly adapted pSense algorithm, which is run in the simulator,supports much larger numbers of players than the simple client-server version. For limiting simulationtime and memory requirements, the measurements are set to a maximum of 64 and 128 playersrespectively for the two measurements.The peer traffic (table 5.2, figures 5.5 and 5.6) shows a quadratic growth with the number of playersin the vision range, equally for both upstream and downstream. This behavior evidently results from thefact that in the simple scenario each player sends its updates to everyone else and also receives updatesfrom everyone. Because of the different message formats, the peer-to-peer traffic cannot be compareddirectly with the client-server version. The binary peer-to-peer position update messages have a fixed sizeof 64 bytes while client-server messages are variable in size, with an average position update messagesize of around 50 bytes. With 32 players, the resulting traffic in each direction is around 100KB/s whichcan be seen as an upper bound for upstream bandwidth of today’s internet connections. A client in theclient-server version requires far less bandwidth. But as for the client-server version, there is still a greatpotential of optimization for traffic reduction. The pSense algorithm describes a forwarding techniqueto disburden weak nodes which has not been implemented, and Donnybrook introduces different levelsof update accuracy.72 5.1 Networking Measurements