Maximizing bandwidth use in ring Provider Backbone Bridging
networks  Whether or not bandwidth remains unused when building
a ring Provider Backbone Bridging (PBB) network depends on a
couple of factors. IP expert Ivan Pepelnjak explains.  When
building a ring Provider Backbone Bridging (PBB) network, is
half the bandwidth unused unless there's a break in the loop?
As always, the correct answer is, "It depends." In this
particular case, it depends on the control-plane loop-prevention
algorithms (a loop in a bridged network usually causes a total
network meltdown).  If you're using traditional spanning tree
algorithm (in any incarnation, including MSTP), one of the links
in the ring will be blocking (almost identical to the break in
the ring), so you'll lose the bandwidth of that link and have a
lot of traffic flowing across suboptimal paths.  If you use PBB-
Traffic Engineering, you can engineer your paths according to
your needs. Unless you use true 1:1 protection backed up with
stringent Quality of Service