How is working auto-sense MDI-X in T-GBIC?

[gubci]

Beacause:

1. 3550-T 10/100/1000 port to T-GBIC WS-G5482 in 3550-48.

These cables work(full duplex, speed 1Gb ):

a. 4 pair Cross-over(1,2<->3,6) (4,5<->7,8)

b. "Classic 10/100" 2 pair Cross-over(1,2<->3,6) (4,5,7,8 straight)

c. Straight (1,2,3,4,5,6,7,8 straight)

2. two 3550-T 10/100/1000 ports inbetween

These cables work(full duplex, speed 1Gb ):

a. 4 pair Cross-over(1,2<->3,6) (4,5<->7,8)

b. "Classic 10/100" 2 pair Cross-over(1,2<->3,6) (4,5,7,8 straight)

There is note about Auto-sense MDI-X in T-GBIC:

http://www.cisco.com/warp/public/cc/pd/si/casi/ca3550/prodlit/gbict_ds.htm

Can somebody clear this issue?

(Namely why classic crossover works with 3550 10/100/1000 ports... and if yes why not straight as it is with T-GBIC?)

[s-doyle]

Some Ethernet network devices (10/100BaseT hubs) have what is referred to as a MIDI port. This type of port allows the device to be connected to an Ethernet port on a switch using a straight-through patch cable by activating an internal cross-over function. This is typically done by turning the MIDI switch on. When the MIDI switch is in the out position the port is expecting to be connected to an end-user device.