deploying and managing ip over wdm networks - Index of

62 Deploying and Managing IP over WDM Networks
physical representation of the network. Before wavelengths are set up, the management
system has to determine an appropriate route through the network that
complies with QoS and routing restrictions. Subsequently, the route is implemented
instructing the WDM network elements or EMSs to create the cross
connections.
One of the most important tasks that can be performed by the management
system of the network is to define the routes that the traffic will follow. In
WDM networks, where connections are supported by lightpaths, there are two
categories of wavelength routing:
1. Static routing. This applies to a network configuration where no wavelength
conversion is possible, which means that one wavelength is
required to connect both ends. Thus, the routing is fairly simple, and
the path through the network is predetermined.
2. Dynamic routing. This type of network is characterized by its ability
to perform wavelength conversions and thus does not require a single
wavelength to connect end points. Routing in this type of network is
also referred to as reconfigurable routing, and requires reconfigurability
of the WDM equipment such that a path can be computed to fulfill
the desired characteristics. Applying wavelength conversion, the
connection blocking probability is reduced.
Given the network topology and a set of end-to-end connection requests,
the routing and wavelength assignment (RWA) problem, studied by [8] and
others, defines the problem of determining a route and the wavelength assignment
for each route request, while at the same time minimizing the number of
the wavelengths. An important factor, besides the network capabilities, in the
RWA problem is what type of connection requests is issued. In case of static traffic,
the connection requests are known in advance, while in case of dynamic traffic,
connection requests arrive randomly. The RWA problem for static traffic
is also referred to as the static lightpath establishment (SLE) problem. In
general, the RWA problem is tightly coupled with the virtual (logical) topology
design. The latter resolves the connectivity between different nodes, taking into
consideration a set of restrictions like traffic demands matrices, nodal resources,
policy constraints, and overprovision constraints. However, it can be assumed
that the virtual topology design generally deals with long-term concerns, and
it provides input to the RWA problem. The RWA problem itself can be further
decomposed into two subproblems: route selection and wavelength
assignment.
The RWA problem is further complicated by different constraints,
such as: