We recently installed an Avaya IP PBX here, which has a number of G450 media gateways. When we did the install, we had no problems using straight-through cables between the G450 gateways and our Cisco Catalyst 4507R switches.
After the install, the vendor claimed that this should not work, as the G450 gateways are ethernet switches, and therefore we should be using crossover cables. He also claimed that we must be using auto-negotiation on the Catalyst switch ports, otherwise this would be broken.
I confirmed that we had the switch ports forced as 100/full, and consulted the Cisco documentation with regard to the Auto-MDIX behavior of the line cards. The documentation suggested that the switch was not doing Auto-MDIX when forced to 100/full:
Auto-MDIX is enabled by default. When you enable auto-MDIX, you must also set the speed on the port to auto so that for the feature to operate correctly. auto-MDIX is supported on copper media ports. It is not supported on fiber media ports.
So, I setup a test… a known 10/100 PC (that does not do Auto-MDIX) into a similarly configured switchport worked when using a straight-through cable and did not work when using a crossover cable. This confirms the behavior is in line with the Cisco docs.
I then did the same test with the PC connecting to the Avaya G450. We got a good link using both the straight-through and the crossover cable.
Verdict: The Avaya G450 ethernet controller is doing Auto-MDIX.
I have now confirmed this behavior with the Avaya docs:
The G450 provides LAN services through the fixed LAN ports on the chassis front panel for the connection of external LAN switches or local data devices. The LAN ports are connected to the internal LAN switch and support HP auto-MDIX, which automatically detects and corrects the polarity of crossed cables. This results in simplified LAN installation and maintenance.
The moral of this story? In a dispute, confirm everything your vendor says with objective tests and hard documentation.