If the hub fails then everything connected to it is down. This is like if you were to burn down the phone company's central office, then anyone connected to it wouldn't be able to make any phone calls. The ring topology looks the same as the star, except that it uses special hubs and ethernet adapters. Difficult to troubleshoot, network changes affect many users, failure affects many users. Mesh topologies are combinations of the above and are common on very large networks.
Crosstalk is overflow from an adjacent wire.
There is also a maximum of 30 computers per segment. Plenum grade is resistant to fire and does not emit poisonous gasses when burned. A transceiver with a vampire tap penetrates the core of the cable. From the transceiver a DB-15 connector plugs into the AUI port on a given device. Optic cabling has an built in security as you can't intercept data as you can with other cable mediums.