Feature: 'Propagation of Visual Entity Properties Under Bandwidth Constraints'

How does an MMO move its player characters naturally, despite the problem of lag and bandwidth constraints when interacting? In this latest exclusive Gamasutra feature, Olivier Cado, who worked on MMO Saga Of Ryzom, explains some of the techniques he used to make real-time interaction seem as smooth as silk. In this excerpt, Cado comments on why limited bandwidth, cheating, and lag were among the many challenges that had to overcome in bringing Saga Of Ryzom to life: “In an online game, especially a massively multiplayer one, the bandwidth constraints prevents from trivially sending every position change to all players. At the planned time of Ryzom launch, 56k modems still were widespread among players, ADSL was still in its infancy. Our MMORPG had to work nominally on a 56k or even 14k connection. Besides, in an online game, cheating utterly destroys the game experience of the victims (the players put at a disadvantage) and must be prevented. From the ever-popular adage “Don’t trust the client”, even more present as Nevrax’s founders’ intention was to release the Ryzom client under a free software license, it was quickly clear that the client would be a display and input device, while all game logic would have to be on the server. Handling dynamic game information on the server side would prevent the appearance of player-made radars, for instance. Then, after excluding a peer-to-peer network solution, the bandwidth constraints did not only originate from the low bandwidth available in consumers’ homes, but also in the server farms that we would have to rent. MMORPG playing experience was known to come with lag, an unpleasant noticeable delay between an action and its viewing, often visible as a stopped animation or animation jerk. This lag phenomenon had to be minimized by design. It usually originated either from an inadequate information propagation system under tight bandwidth constraints and latency-prone networks such as the Internet, or from delay in CPU-processing by the server. Our work then had to focus on studying the known techniques of visual property propagation, and possibly creating better ones. The CPU performance of the software was also critical, to avoid time-consuming peaks.” You can now read the entire feature, which includes much more from Cado offering an insider's view on techniques and other technical topics that played a role in Saga Of Ryzom's development (no registration required, please feel free to link to this column from external websites).