52 Software Networks
devices. There are no intermediary boxes or computing machines. The
signal is sent to the central datacenter exactly as it is. In other words,
there is no longer a network, i.e. no messages, no packets, no frames –
just a succession of radio signals.
In terms of cost, the centralized C-RAN system is certainly one of
the most affordable solutions on the market, because all the
intermediary machines are eliminated. However, this solution exhibits
the disadvantage of being centralized, and therefore requires all the
usual precautions for centralized environments to be exercised. For
example, the amount of resources in the different datacenters needs to
be doubled or even tripled. Another problem is the response time for
simple or local actions, such as inter-cell handover. If we assume there
is a distance of 300 km between the periphery and the center, the
propagation time there and back represents around 2 ms. In addition to
this propagation time, we also need to allow for the time taken to run
the control algorithms, and therefore reaction times of around 5 ms.
Most control applications can cope with values like these. However,
they are too long for simple actions and, above all, they are too costly
in terms of overall data rate.
The solution represented by the centralized C-RAN architecture is
certainly interesting, but there is a danger that it will be rejected in
developed countries whose infrastructure is ripe for a decentralization
of the datacenter. On the other hand, for developing countries where
there is very little infrastructure, the C-RAN represents a good
opportunity to gain direct access to 5G environments at a low cost.
This centralization may be compensated by a slight distribution on
the periphery, in which case we see the emergence of small Clouds
(known as Cloudlets) situated near to the relay antennas. This solution
is shown in Figure 3.3.
The second solution for the placement of the controllers is to build
them into regional Clouds. In this case, the controllers are situated at
the level of the company, or the DSLAM (Data Subscriber Line
Access Module), in a telecommunication network. Here, the
controllers only manage networks of limited size. This solution
www.it-ebooks.info
devices. There are no intermediary boxes or computing machines. The
signal is sent to the central datacenter exactly as it is. In other words,
there is no longer a network, i.e. no messages, no packets, no frames –
just a succession of radio signals.
In terms of cost, the centralized C-RAN system is certainly one of
the most affordable solutions on the market, because all the
intermediary machines are eliminated. However, this solution exhibits
the disadvantage of being centralized, and therefore requires all the
usual precautions for centralized environments to be exercised. For
example, the amount of resources in the different datacenters needs to
be doubled or even tripled. Another problem is the response time for
simple or local actions, such as inter-cell handover. If we assume there
is a distance of 300 km between the periphery and the center, the
propagation time there and back represents around 2 ms. In addition to
this propagation time, we also need to allow for the time taken to run
the control algorithms, and therefore reaction times of around 5 ms.
Most control applications can cope with values like these. However,
they are too long for simple actions and, above all, they are too costly
in terms of overall data rate.
The solution represented by the centralized C-RAN architecture is
certainly interesting, but there is a danger that it will be rejected in
developed countries whose infrastructure is ripe for a decentralization
of the datacenter. On the other hand, for developing countries where
there is very little infrastructure, the C-RAN represents a good
opportunity to gain direct access to 5G environments at a low cost.
This centralization may be compensated by a slight distribution on
the periphery, in which case we see the emergence of small Clouds
(known as Cloudlets) situated near to the relay antennas. This solution
is shown in Figure 3.3.
The second solution for the placement of the controllers is to build
them into regional Clouds. In this case, the controllers are situated at
the level of the company, or the DSLAM (Data Subscriber Line
Access Module), in a telecommunication network. Here, the
controllers only manage networks of limited size. This solution
www.it-ebooks.info