Kishan,
I think you're looking for information on the Ethernet AUI (Attachment User Interface) port, not the AUX (Auxiliary) serial port next to the Console port. Am I right?
There many documents on Cisco's website detailing the pinouts of this port. But I my 18+ years of networking, I have never needed to know those details; it's a pretty standard 10-megabit interface. What you're probably after is how to use it.
To connect that interface to an Ethernet LAN, you used to attach an AUI cable to that port, and a bulky external Ethernet transceiver to the other end of the cable. These days it's more common to use a mini-transceiver, and attach it directly to the router (no cable required).
There are AUI transceivers for every type of Ethernet LAN cabling: coaxial, UTP, fiber. UTP is the most commonly used, followed by fiber. Allied Telesyn (http://www.alliedtelesyn.com) makes the AUI transceivers I see most often, but there are many other manufacturers out there. Go to any on-line reseller and search for "AUI transceiver" to see what's available.
Think of the AUI transceiver as a 10-megabit media converter: it converts the generic AUI port into the kind of Ethernet port you need -- UTP RJ-45, fiber ST, coaxial BNC, whatever.
Don't confuse the AUI with the MII (Media Independent Interface), which is like an AUI but for 100-megabit Fast Ethernet connections.
Hope this helps.
