**3.2.2 Dynamic wavelength allocation**

By creating multiple wavelengths in a common fiber infrastructure, the capabilities of this infrastructure can be extended into an additional dimension. This wavelength dimension can implement independent communication planes between nodes. For example, interconnections in this plane can be asynchronous, have different quality-of-service requirements, and can transport signals with widely differing characteristics. By using the WDM technique, the access network can: 1) separate services; 2) separate service providers; 3) enable traffic routing; 4) provide higher capacity; 5) improve scalability. For assignment of wavelengths to channels the system may follow different scenarios such as: a) static allocation; b) semi-static allocation; c) dynamic allocation, (Urban et al., 2009).

The static wavelength multiplexing scheme sets a virtual P-to-P topology up between two nodes of the network. However, the rapid growth in access network traffic requires flexible and adaptive planning of the wavelength allocation to each different channel or wired and wireless service to avoid congestion resulting from variable data rates demanded or to guaranteed data traffic transportation or services to/from the end-users. By using adaptive wavelength allocation deliverable services will be more cost-effective on the same network and the vast potential bandwidth of fiber optical networks will be more fully exploited. By assigning the wavelength dynamically at the Optical Network Unit (ONU), with flexible wavelength routing, the access network capabilities can be considerably enhanced. This configuration allows setting up a new wavelength channel before breaking down the old one. Alternatively, it may use wavelength tuneable transmitters and receivers, which can in

lead to a convergence to high bandwidth provision for both fixed and mobile users in a single, low-cost transport platform, This can be accomplished by using the developed hybrid optical and wireless networks, which not only can transmit signals received wirelessly over fiber at the BS, but also simultaneously provide services received over fiber

By creating multiple wavelengths in a common fiber infrastructure, the capabilities of this infrastructure can be extended into an additional dimension. This wavelength dimension can implement independent communication planes between nodes. For example, interconnections in this plane can be asynchronous, have different quality-of-service requirements, and can transport signals with widely differing characteristics. By using the WDM technique, the access network can: 1) separate services; 2) separate service providers; 3) enable traffic routing; 4) provide higher capacity; 5) improve scalability. For assignment of wavelengths to channels the system may follow different scenarios such as: a) static

The static wavelength multiplexing scheme sets a virtual P-to-P topology up between two nodes of the network. However, the rapid growth in access network traffic requires flexible and adaptive planning of the wavelength allocation to each different channel or wired and wireless service to avoid congestion resulting from variable data rates demanded or to guaranteed data traffic transportation or services to/from the end-users. By using adaptive wavelength allocation deliverable services will be more cost-effective on the same network and the vast potential bandwidth of fiber optical networks will be more fully exploited. By assigning the wavelength dynamically at the Optical Network Unit (ONU), with flexible wavelength routing, the access network capabilities can be considerably enhanced. This configuration allows setting up a new wavelength channel before breaking down the old one. Alternatively, it may use wavelength tuneable transmitters and receivers, which can in

allocation; b) semi-static allocation; c) dynamic allocation, (Urban et al., 2009).

to wireless the end users.

Fig. 9. WDM over a passive optical network.

**3.2.2 Dynamic wavelength allocation** 

principle, address any wavelength in a certain range. The network management and control system commands to which downstream and to which upstream wavelength channel each ONU transceiver is switched. By issuing these commands from a central station, the network operator actually controls the virtual topology of the network, and thus is able to allocate the networks resources in response to the traffic at the various ONU sites. By changing the wavelength selection at the ONUs, the network operator can adjust the system's capacity allocation in order to meet the local traffic demands at the ONU sites.

In this scenario, as soon as the traffic to be sent upstream by an ONU grows and does not fit anymore within its wavelength channel, the network management system can command the ONU to be allocated another wavelength channel, in which sufficient free capacity is available. Obviously, this dynamic wavelength reallocation process reduces the system's blocking probability, i.e. it allows the system to handle more traffic without blocking and thus it can increase the revenue of the operator from a given pool of communication resources at the central station.
