13.6 Optical Switching Architectures
547
10 -1
10 -3
10 -4
10 -2
0.1
0.2 0.3 0.4
0.5 0.6 0.7
0.8 0.9
Wavelength utilization efficiency ρ
Blocking probability
Without
wavelength
conversion
With
wavelength
conversion
F = 20 wavelengths
H = 10 hops
Fig. 13.31 Packet blocking probabilities with and without wavelength conversion for the case of
20 wavelengths and 10 hops
use of wavelength blocking can be expensive in large networks if it is applied to all
WDM channels and at all nodes.
13.6.3 Methodologies for Wavelength Routing
To send information quickly and reliably across a network, service providers use
various techniques to establish a circuit-switched lightpath between communicating
end equipment. An OXC is a key element to set up express paths through intermediate nodes for this process. Because an OXC is a large complex switch, it is
used in extended mesh backbone networks, where there is a heavy volume of traffic
between nodes, to connect equipment such as SONET/SDH terminals, IP routers,
and ROADMs. In such a network the lightpath normally is set up for long periods
of time. Depending on the desired service running between distant nodes, this time
connection can range from minutes to months and even longer.
Lightpaths running from a source node to a destination node may traverse many
fiber link segments along the route. At intermediate points along the connection
route, the lightpaths may be switched between different links, and sometimes the
lightpath wavelength may need to be changed when entering another link segment.
As noted in Sect. 13.6.2, this wavelength conversion is necessary if two lightpaths
entering some segment happen to have the same wavelength.
The process of establishing a lightpath is called by various names, such as wavelength routing, optical circuit switching, or lightpath switching. The more popular
terms are wavelength routing and wavelength routed network (WRN). Many different
static and dynamic approaches have been proposed and implemented for establishing
a lightpath. Because a method for setting up a lightpath requires deciding which path
to traverse and what wavelength to use, it involves a routing and wavelength assignment (RWA) procedure. In general the RWA problem is fairly complex and special
software algorithms have been developed for solving it [33–35].
547
10 -1
10 -3
10 -4
10 -2
0.1
0.2 0.3 0.4
0.5 0.6 0.7
0.8 0.9
Wavelength utilization efficiency ρ
Blocking probability
Without
wavelength
conversion
With
wavelength
conversion
F = 20 wavelengths
H = 10 hops
Fig. 13.31 Packet blocking probabilities with and without wavelength conversion for the case of
20 wavelengths and 10 hops
use of wavelength blocking can be expensive in large networks if it is applied to all
WDM channels and at all nodes.
13.6.3 Methodologies for Wavelength Routing
To send information quickly and reliably across a network, service providers use
various techniques to establish a circuit-switched lightpath between communicating
end equipment. An OXC is a key element to set up express paths through intermediate nodes for this process. Because an OXC is a large complex switch, it is
used in extended mesh backbone networks, where there is a heavy volume of traffic
between nodes, to connect equipment such as SONET/SDH terminals, IP routers,
and ROADMs. In such a network the lightpath normally is set up for long periods
of time. Depending on the desired service running between distant nodes, this time
connection can range from minutes to months and even longer.
Lightpaths running from a source node to a destination node may traverse many
fiber link segments along the route. At intermediate points along the connection
route, the lightpaths may be switched between different links, and sometimes the
lightpath wavelength may need to be changed when entering another link segment.
As noted in Sect. 13.6.2, this wavelength conversion is necessary if two lightpaths
entering some segment happen to have the same wavelength.
The process of establishing a lightpath is called by various names, such as wavelength routing, optical circuit switching, or lightpath switching. The more popular
terms are wavelength routing and wavelength routed network (WRN). Many different
static and dynamic approaches have been proposed and implemented for establishing
a lightpath. Because a method for setting up a lightpath requires deciding which path
to traverse and what wavelength to use, it involves a routing and wavelength assignment (RWA) procedure. In general the RWA problem is fairly complex and special
software algorithms have been developed for solving it [33–35].