OBS offers exactly that, by separating the control and the data
in the physical space, that is, the control information and the data propagate discretely in
different designated channels, and maybe with different data rates. OBS also separates the
control and the data in time, that is, the control packet is transmitted at an offset time prior
to its corresponding data. In the buffer-less core nodes, the offset time is to compensate for
both processing and configuration time, needed respectively by the control unit to process
the control information and the switching-fabric to be configured.
Figure 1 shows some of the main components of an OBS network. There are two types
of nodes, edge (ingress/egress) nodes and core nodes. In the edge nodes, network traffic
is collected from access networks and assembled into macro data units called data bursts
(DBs). Core nodes serve as transit nodes at the core network. Their main task is to switch
bursts (data) all-optically without any conversion or processing. The switching fabrics are
configured according to the control information contained in the Burst Control Packets
(BCPs), which are transmitted as reservation requests at an offset time ahead of their corresponding
data bursts.
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