The BK9055 facilitates the connection of the Beckhoff I/O system to EtherNet/IP networks, and when used alone, is suitable for star wiring topologies. However, the BK9055 is software-compatible to the BK9105 EtherNet/IP bus coupler, which unlike the compact version has a second RJ 45 port (2-channel switch). As a result, the I/O stations can also be configured with a line topology, instead of the classic star topology. Beckhoff Automation LLChttp://www.beckhoff.com/