Each AT-GS900/8PS switch port is configured for Auto-Negotiation mode which determines the speed and duplex mode. Each end-node connected to a twisted-pair port should also be configured for Auto-Negotiation mode. This insures that the speed and duplex mode is matched on each end.
Note
If an end-node connected to a AT-GS900/8PS twisted-pair port is set to a fixed speed and duplex, a speed and duplex mismatch may occur which can cause a reduction in the data flow.
When two end-nodes are set to different speeds, an Ethernet switch with the slower data rate capability may randomly be flooded with more data than it can process and may need to signal the opposite end-node to stop sending data until it is ready again. How a switch signals an end-node to stop transmitting data differs depending on the duplex mode of the Ethernet ports.
A port operating in full-duplex mode uses PAUSE frames, as specified in the IEEE 802.3x standard, to momentarily stop the transmission of data from an end-node. Whenever a switch port wants an end-node to stop transmitting data because it is being flooded by data, it issues a PAUSE frame. This frame instructs the end-node to temporarily cease transmission. The switch continues to issue PAUSE frames until it is ready to receive data again from the end-node. This is referred to as flow control.
Atwisted pair port operating at half-duplex mode stops its end-node from transmitting data by forcing a collision. A collision on an Ethernet network occurs when two end-nodes attempt to transmit data using the same data link at the same time. A collision causes the end-nodes to momentarily stop sending data. When a switch port has received more data than it can process, it needs to temporarily stop its end-node from transmitting data. The port does this by forcing a collision on the data link, which stops the opposite end-node from transmitting any more data. After the switch is ready to receive data again, the switch stops forcing collisions. This is referred to as back pressure.
