To clarify basic Bayeux concepts like server, client and local sessions, messages or channels you can have a look at the CometD 2 Java Concepts book. It's not that well polished and detailed as the Reference Documentation but explanation is concise.
Oort (not Seti which basically provides user presence and user node associations within Oort) uses local sessions between CometD servers to support basic clustering features.
Depending on your feature usage, your topology (any relation to persistence or business tiers behind CometD)... you could have a try to the Oort replicated objects, for example the OortMap object, to support user contacts replication.