Abstract
The wavelength division multiplexing passive optical network (WDM-PON) is a natural path forward to satisfy demands of optical network operators to develop valuable converged optical metropolitan and access networks. For effective utilization of possible transmission capacities, available wavelengths must be carefully designed for their utilization. Therefore, some principles of wavelength allocation and scheduling methods are characterized and specified. For ensuring the network reliability, efficient traffic protection mechanisms must be implemented. Simultaneously, different equipment in remote nodes can be installed. Therefore, different WDM-PON network designs with traffic protection securing are analyzed and compared. Protection possibilities for various network parts and elements are characterized and optical power budgets are evaluated and optimized. Finally, a research of the DWA algorithms can be realized using functionalities of selected wavelength scheduling methods. Moreover, the wavelength transmission capacity characterizing can be simultaneously determined.
TopIntroduction
In the design of optical telecommunication networks, it is necessary to take into account various parameters and characteristics, for example network type, utilized technology, distance for the signal transmission, network traffic protection, mutual interconnection between network components, network control and many others (Róka, 2014), (Róka, 2019). The idea for utilizing multiple wavelength channels in metropolitan and access optical networks is well known (Róka, 2003). This chapter is focusing on the realistic design of the Wavelength Division Multiplexing - Passive Optical Network (WDM-PON) from a viewpoint of its interconnecting scheme. First, an in-depth survey of existing methods and algorithms is presented. Subsequently, basics of the main protocol are introduced and main wavelength allocation categories - static and dynamic - are particularly presented. Next, various WDM-PON network designs are analyzed with regard to the traffic protection securing. For this aim, passive optical components are mainly considered and a protection of another control element and access part is characterized. Finally, optical power budget possibilities for various WDM-PON network designs are optimized. Simultaneously, a deployment environment for dynamic wavelength algorithms is introduced and main functionalities of wavelength scheduling techniques are summarized.
There are certain basic variants of WDM-PON architectures (Grobe, 2008), (Róka, 2015) varying in utilization of the wavelength routing - Broadcast-and-Select (B&S), Arrayed Waveguide Grating (AWG), Spectrum Slicing (SS). Except fundamental changes in the Optical Line Terminal (OLT) equipment (WDM transmitters, circulators), real WDM-PON network implementations could include several stages of splitting points, allowing the topology to be scalable with a number of users connected using the Optical Network Terminal (ONT) equipment. There are various approaches that have been proposed for implementing in WDM-PON networks (Abbas, 2016), also different architectural options (Mahloo, 2014) varying in the Remote Node (RN) equipment (power splitter, array wavelength grating) are defined. In presented WDM-PON network designs, an attention is paid to only passive components in the RN location based on extensive utilization.
For current Time Division Multiplexing - Passive Optical Network (TDM-PON) networks, one of main tasks is increasing the effective utilization of the determined transmission capacity on the available wavelength used in the upstream direction of data transmitting. This can be achieved using advanced dynamic bandwidth allocation algorithms compared to a unified Time Division Multiple Access (TDMA) approach. For near-future WDM-PON networks, a corresponding task is increasing the effective utilization of the transmission capacity on available wavelengths used in both downstream and upstream directions for data transmitting. Investigating appropriate dynamic wavelength allocation algorithms is very difficult and complex process. As its integrated part, a wavelength scheduling process must be carefully designated and analyzed. Therefore, wavelength allocation and scheduling methods must be considered for various WDM-PON network designs before their real implementations. It must be stressed that first and foremost passive optical components are focused. However, a task of active optical components is likewise important. For example, optical sources (light-emitting diodes and lasers) in WDM-PON networks and their resulting performance analysis in terms of improvements as well as limitations is very interesting topic.
Key Terms in this Chapter
Bandwidth Allocation: A process of assigning time slots to different ONU units for the upstream direction in common TDM-PON networks; the frequency bandwidth of the optical fiber is a finite resource with a need for the effective allocation process.
Network Design: An iterative process, encompassing topological design, network-synthesis, and network-realization, for creating new telecommunications networks satisfying needs of the operator and subscribers.
Power Splitter: A device used in the optical network for coupling optical signals from various input branches into one output optical signal to the common OLT terminal and for splitting an optical signal from one input into various output branches for distribution to different ONT terminals; one of the most important passive devices in the optical fiber link.
Optical Add-Drop Multiplexor: A device used in wavelength-division multiplexing systems for multiplexing, switching and routing different lightpath channels into or out of a single-mode optical fiber; a type of optical node generally used for the formation and the construction of optical telecommunications networks.
Traffic Protection: Any protection scheme used in different network architectures for protecting data traffic against inevitable failures on service providers’ network/fibers/nodes; any failure occurred at any point along the path will cause nodes to move/pick the data traffic to/from a new route.
WDM-PON: A passive optical network with utilization of the WDM principle on a physical layer with assigning different multiple wavelengths for separate ONU units.
Wavelength Scheduling: A process of arranging, controlling and optimizing wavelengths used for data transmitting between for different OLT and ONT terminals in future WDM-PON networks; it is an important tool for creating and effective utilization of the wavelength transmission capacity.
Optical Power Budget: An allocation of the available optical power (launched into a given optical fiber by a given source) among various loss-producing mechanisms in order to ensure adequate optical power levels available at the receiver side.
Wavelength Allocation: A process of assigning wavelengths to different OLT and ONT terminals for downstream and upstream directions in future WDM-PON networks; the wavelength band of the optical fiber is a finite resource with a need for the effective wavelength allocation process.