It only goes to half duplex if you connect more than 1 switch to a giga-stack GBIC. We have two gigastacks per 3550 switch and we do some diasy chaining with them. This keeps the links at full duplex. I group my switches into groups of 3 and then plug the the top and bottom into our core switch. This way, no switch has more than 2 hops to the core.
[ CORE SWITCH ]
| |
| |
[ TOP 3550 ] G1 G2 |
/ |
[ MID 3550 ] G1 G2 |
/ |
[ BOT 3550 ] G1 G2----
I let spanning tree decide whitch switch the middle unit will communicate through. You do need extra GBICS, but you can find them on ebay for really cheap. Depending on the closet, I could have as many as 4 of these setups.