FDDI/CDDI is a dual ring token ring bus, with 4470 MTU byte packets, it has 802.-- frames. DEC had a mode where you turned the token off and used it for ptp full duplex. I didn't know about the ptp thing. That's nifty. A cisco FDDI-PA can talk both in a 7500 or old 7200 (the VXR don't support the FDDI cards but the VIP does ). I don't think there ever was a CDDI PA.. Sol.Stupi.SE that has a CDDI interface has a media converter from copper to fiber and then it plus in to a old 7200... -P