IEEE 802.6 is a standard governed by the ANSI for Metropolitan Area Networks (MAN).
[1] It is an improvement of an older standard (also created by ANSI) which used the Fiber distributed data interface (FDDI) network structure.
The IEEE 802.6 standard uses the Distributed Queue Dual Bus (DQDB) network form.
DQDB is rated for a maximum of 160 km before significant signal degradation over fiberoptic cable with an optical wavelength of 1310 nm.
MANs are traditionally designed using Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH) or Asynchronous Transfer Mode (ATM).