Wireless Network Design: Optimization Models and Solution ...

15 Major Trends in Cellular Networks and Corresponding Optimization Issues 363
network for mobile cellular communication, and the television content distribution
network. As all media is digitized and packetized for transmission, these infrastructures
are converging. Technologies such as adaptive optical core, Carrier Ethernet
Transport, IP and Layer 2, multilayer networking can help bring down the transport
costs [12].
With the massive increase in traffic, optical technology and fiber optics is clearly
required in the backbone, where traffic is aggregated. In addition, a medium- to long
term goal of many carriers is to deploy fiber in the last/first mile to enable the delivery
of robust multimedia services, e.g., IPTV, Video on Demand, and Triple/Quad
play. The main trends that can help improve the transport efficiency include [24]:
• The metro and access parts of today’s networks will converge into a single network.
An aggregation layer collects traffic from different sources and transfers it
to the photonic core
• Hybrid architecture having transparent islands connected by opaque nodes that
employ Optical/Electrical/Optical (OEO) conversion. Within the transparent islands
packet headers may be processed electronically, but payloads are switched
optically to minimize inefficient OEO conversions
• Further advances in the optical technology itself
• Flexible optical transport networks that can react quickly to external factors, such
as (rapid) traffic changes or changes of the physical infrastructure. High traffic
demand will result in the automatic addition of resources, either on a wavelength
or on sub-wavelength level. In the event of failure in the network, the traffic will
be automatically re-routed
• Packet-based architectures
• Long range transparent optical paths, enabled by more robust modulation techniques.
The optical paths can potentially be end-to-end, which leads to new architectural
approaches. For instance, network sites may be reduced, which can
help to decrease the costs
• Automatic Switched Optical Network (ASON) will provide automatic and selforganized
set-up and tear down of optical link requests.
While IP will be the common layer for applications, some of its functions and
protocols are not needed for the efficient transport of data. Instead, simpler packetbased
forwarding technologies, in combination with optical transport, will enable
the cost-efficient transmission of large data volumes. Carrier Ethernet is the Layer 2
technology that will provide the common layer for packet-based transport, and the
reduction of TCO will be achieved by an optimized split of functionality between
different layers.
Network architectures are migrating to a three-layer model: Optical at Layer 1,
Carrier Ethernet at Layer 2 and IP/MPLS at Layer 3. Optimizing the interaction
of these three layers, i.e., by applying the concept of multi-layer optimization, can
significantly reduce TCO. Multi-layer optimization means assigning functionality
and traffic processing to the layer where it is technically and economically optimal
[13].