Communication within the LAT is provided by the LCB, a cPCI module residing in every cPCI crate within the LAT. A LCB can communicate directly with other LCBs (in other crates) on the event fabric or with other LATp nodes on the LAT's command/response fabric [huffer2].
The LCB manages traffic on the Command/Response fabric and the Event Data fabric. With the Command/Response fabric a node can issue a command to another LATp node and receive the solicited response. For example, this is used to read a register on a remote electronics module. The key point is the response is solicited, so it is expected to arrive.
Event data, however, arrives unsolicited, i.e. whenever it is ready. A special case of "event data" is the unsolicited LCB-to-LCB communication, which is also unsolicited. In either case a handler is is notified and proceeds to processes the unsolicited data in a timely manner.