A few years ago they used an star topology based on Frame-Relay networks. The circuits were about 128 or 256Kbps. Nowdays the has increased the capacity of transmission needed.
Now Telcos have MPLS networks and banks (and other clients) implements a VPN over this MPLS net.
In each office you can have xDSL or optic fiber, it depends of the transmission speed or if you need or not symmetric wideband.
Hope this help.
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(sorry for my english)