For some reason the Avocent doesn't uses the Cisco Rollover cable and it uses some DB9 (serial pinout) and since it's RJ45 to RJ45 from
Make your own cable and don't buy that expensive adapter from Avocent


Here is the pinout for the crimping a straight cable

RJ45 Cisco Console cable RJ45 end:						
Pin 1: or/wh	(RTS)
Pin 2: or		(DTR)
Pin 3: gr/w		(TXD)
Pin 4: bl		(GND)
Pin 5: bl/w		(GND)
Pin 6: gr		(RXD)
Pin 7: br/w		(DSR)
Pin 8: br		(CTS)

Avocent Serial RJ45 end:
Pin 1: br		(RTS)
Pin 2: or		(DSR)
Pin 3: *br		(DCD)(You can connected it but it's not needed)
Pin 4: gr/w		(RXD)
Pin 5: gr		(TXD)
Pin 6: bl/w		(GND)
Pin 7: br/w		(DTR)
Pin 8: or/w		(CTS)



** If you are using it with Telnet Server mode. On your telnet client side make sure it is set to speed of: 9600 for trasmit and recieve.
(on putty click on Connection -> Data and -> Terminal speeds.  Set that to 9600,9600.   you have to do this or it won't work properly, this basically matches the speed of the server and cisco)
* You will also need to set the port on the AvoCent side to 9600 8N1 now flow control (the standard setting that ciso uses)