Question : Why Ring topology & not Star in optical ethernet MAN?

I am looking for support for why optical ring topology for MAN is better than star topology.  Or viceversa. It seems some people associate ethernet with Star, but carriers use rings? I can't find any information why? And does anybody know who is adopting MAN rings?

I'm especially hoping to find articles and statistics that support/explain these sorts of things. The only papers I find are on Mesh verses Ring topology, no mention of star anywhere? But perhaps I've been looking and looking in all the wrong places? Please help.

Cheers.

Answer : Why Ring topology & not Star in optical ethernet MAN?

What you are most likely refering to is SONET rings, most widely used by telco carriers. The other is FDDI rings, or TokenRing which is very different. The advantage of the ring is that it is usually a dual-ring in that if one path is cut, there is an alternate path. With a traditional star topology, there is only one path.

Sonet:
http://www.iec.org/tutorials/sonet/
http://www.nwfusion.com/edge/news/2000/1211edge.html

FDDI:
http://www.nswc.navy.mil/ITT/x3t12/FDDIFAQ.html
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/fddi.htm

Star vs Ring:
http://www.cisco.com/univercd/cc/td/doc/product/ismg/policy/ver23f/topodef/nwgdline.htm

Token Ring:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/tokenrng.htm