MSMQ routing servers support dynamic routing and intermediate store-and-forward message queuing. They allow computers using different protocols to communicate and can be used to provide session concentration. Unlike BSCs, MSMQ routing servers do not hold a read-only replica of the PSC or PEC database. You must install a PEC before you can install any MSMQ routing servers.
Because every PEC, PSC, and BSC functions as an MSMQ routing server, the number of additional MSMQ routing servers you install depends on your MSMQ connectivity requirements (number of dependent clients, independent clients, sites, CNs, session concentration needs, and message volume). As a minimum, you should strategically install enough MSMQ routing servers to allow messages to reach target queues through different servers.