3Com 3CRBSG2893 User Guide - Page 86

Item MDI Flow Control Power Save Max MAC Count Description Set the Medium Dependent Interface (MDI) mode of the port. Two types of Ethernet cables can be used to connect Ethernet devices: crossover cable and straight-through cable. To accommodate these two types of cables, an Ethernet port can operate in one of the following three MDI modes: across, normal, and auto. An Ethernet port is composed of eight pins. By default, each pin has its particular role. For example, pin 1 and pin 2 are used for transmitting signals; pin 3 and pin 6 are used for receiving signals. You can change the pin roles by setting the MDI mode. z For an Ethernet port in across mode, pin 1 and pin 2 are used for transmitting signals; pin 3 and pin 6 are used for receiving signals. The pin roles are not changed. z For an Ethernet port in auto mode, the pin roles are decided through auto negotiation. z For an Ethernet port in normal mode, the pin roles are changed. Pin 1 and pin 2 are used for receiving signals; pin 3 and pin 6 are used for transmitting signals. To enable normal communication, you must connect the local transmit pins to the remote receive pins. Therefore, you should configure the MDI mode depending on the cable types. z Normally, the auto mode is recommended. The other two modes are used only when the device cannot determine the cable type. z When straight-through cables are used, the local MDI mode must be different from the remote MDI mode. z When crossover cables are used, the local MDI mode must be the same as the remote MDI mode, or the MDI mode of at least one end must be set to auto. SFP optical ports do not support this feature. Enable or disable flow control on the port. With flow control enabled at both sides, when traffic congestion occurs on the ingress port, the ingress port will send a Pause frame notifying the egress port to temporarily suspend the sending of packets. The egress port is expected to stop sending any new packet when it receives the Pause frame. In this way, flow control helps to avoid dropping of packets. Flow control works only after it is enabled on both the ingress and egress ports. Enable or disable auto power down on the port. With auto power down enabled, when an Ethernet port does not receive any packet for a certain period of time, it automatically enters the power save mode and resumes its normal state upon the arrival of a packet. By default, auto power down is disabled. Set the MAC learning limit on the port. Available options include: z User Defined: Select this option to set the limit manually. z No Limited: Select this option to set no limit. 1-3