Ethernet Communication Streams
The ACR9000 supports up to four simultaneous communication "Streams" via Ethernet communication. This allows communication with up to four different Ethernet devices provided that each device is only using a single stream.
Ethernet/IP, sometimes referred to as CIP (Control and Information Protocol) will use two streams, one for Class 1 (UDP) broadcast information, another for Class 3 (TCP) polled information, leaving only two streams available for connection to other devices.
More information can be found in the "Ethernet Specification: ACR Series Products" and the "Ethernet/IP Specification: ACR Series Products" found in our Literature section.
UPDATE: (dm 10/16/15)
With ACR firmware 1.25 and above and the IPA, only 1 connection is used with EIP from a PLC