3com S7906E Installation Instruction

 

1-11 

 

The optical port of an SFP or XFP port does not support this function. 

 

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 on a device can 

operate in one of the following three Medium Dependent Port (MDI) modes: 

z 

Across mode 

z 

Normal mode 

z 

Auto mode 

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 through setting the MDI mode. For an Ethernet port in normal mode, the pin roles 

are not changed. For an Ethernet port in across mode, 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 should 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 useful 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.  

Follow these steps to configure the MDI mode for an Ethernet port: 

Enter system view 

— 

Enter Ethernet port view 

interface interface-type 
interface-number 

— 

Configure the MDI mode for the 
Ethernet port 

mdi { across | auto | normal }

Optional 

Defaults to auto. That is, the 
Ethernet port determines the 
physical pin roles (transmit or 
receive) through negotiation.