50 Software Networks
this scenario, the solution sends the control data to local or regional
datacenters. Finally, the last example of architecture consists of
positioning the control as close as possible to the user in femtoClouds. The advantages are clearly the very short response time, the
agility of the solution because of the possibility of changing the virtual
machines used in the femto-datacenters and the addition of a form of
network intelligence very close to the user. The disadvantage here is
that the solution involves widespread distribution of the information,
with all the complications that this can entail to perform controls,
which, obviously, will not take place locally.
Figure 3.1. Scenarios for the placement of a controller
The three main solutions described above can be combined, with
two levels or even all three levels, acting simultaneously, certain
virtual machines may be migrated to the femto-datacenter, whilst
others remain in a central or regional datacenter.
If we examine the first scenario, it represents a highly centralized
system on a large Cloud with several high-capacity datacenters. These
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