AT-8000/8POE Layer 2 Fast Ethernet Switch Installation Guide
Duplex mode refers to how an end node receives and transmits data. If an end node can receive or transmit data, but not both simultaneously, the end node is operating in what is referred to as half-duplex mode. If an end node can both receive and transmit data simultaneously, the end node is said to be operating in full-duplex mode. Naturally, an end node capable of operating in full-duplex can handle data much faster than an end node that can only operate in half-duplex mode.
The twisted pair ports on the AT-8000/8POE Fast Ethernet Switch can operate in either half-or full-duplex mode. They are IEEE 802.3u-compliant and use Auto-Negotiation to set the duplex mode setting for you automatically.
For Auto-Negotiation to operate properly on a switch, the end nodes connected to the switch should also use Auto-Negotiation. If an end node does not have this feature and has a fixed duplex mode of full-duplex, the result will be a duplex mode mismatch between the end node and a switch port. A port on the Gigabit Ethernet switch connected to an end node with
afixed duplex mode of full-duplex will operate at only half-duplex. This results in the end node using full-duplex and the switch port using half- duplex. This can produce network performance problems. If you encounter this situation, you must configure the port on the end node to use Auto- Negotiation or, if it lacks that feature, to half-duplex.
Note
Because the ports on the AT-8000/8POE Fast Ethernet Switch operate in Auto-Negotiate mode only, the end nodes connected to the switch must also be configured to operate in the Auto-Negotiate mode. If an end node is configured to a specific duplex setting in a manual mode, it will not respond to the Auto-Negotiate protocol from the AT-8000/8POE Fast Ethernet Switch. (The speed is determined from the link pulses, however, so the speed is always detected correctly.) As a result, the port setting on the switch will end up at half-duplex. If the end node is manually configured to full-duplex, there will be a duplex mismatch and data will be lost. If the end node is manually configured to half-duplex, both ports will have the speed and duplex match up correctly.
The AT-8000/8POE Fast Ethernet Switch uses store and forward as the method for receiving and transmitting frames. When a Ethernet frame is received on a switch port, the switch does not retransmit the frame out the destination port until it has received the entire frame and stored the frame in a port buffer. It then examines the frame to determine if it is a valid frame. Invalid frames, such as fragments or runts, are discarded by the switch. This insures that only valid frames are transmitted out the switch ports and that damaged frames are not propagated on your network.
