Rock Central

Rock Central is the name of the online services for the Rock Band series of games. They are ran by Harmonix themselves (using Amazon Web Services) and handle matchmaking, leaderboards, and additional features such as setlist sharing in Rock Band 3.

Projects that aim to recreate Rock Central are in the works, such as GoCentral. More information about Rock Central is available at the GoCentral project wiki.

Protocol

Connection to Rock Central is done via a custom UDP-based protocol licensed out by Quazal. Partial documentation on this protocol is available at the NintendoClients project wiki, as Quazal was either licensed or bought by Nintendo to be used in their online services.

Xbox 360

The Xbox 360 versions of these games used the Xbox Live Server Platform (XLSP) to connect to the Rock Central server, rather than a direct connection from the console. This means all traffic is encrypted and goes through Microsoft's servers. Additionally, matchmaking is not handled by Rock Central but rather by Xbox Live's XSession APIs, independent from Harmonix. Presumably this is because of the strict control Microsoft had over their consoles at the time.

Interestingly, the IP used to directly connect to Rock Central via the XLSP shows an ISP of "Viacom" (AS7256)

JSON protocol

The Quazal JSON handler is used for Rock Central, and this is used for leaderboards and other miscellaneous requests such as MOTD configuration. The GoCentral source code includes Go representations of the "services" provided by the JSON protocol.