Dynamic bandwidth allocation with optimal wavelength switching in TWDM-PONs

Abstract

Time and wavelength division multiplexed passive optical networks (TWDM-PONs) have been widely considered as one of the next evolutionary steps of optical access networks. A variety of algorithms exists that explore the problem of scheduling and wavelength assignment in TWDM-PONs. These algorithms, however, allow unlimited switching of wavelengths. In reality, wavelength switching increases guard bands due to the tuning and the switching time of components, limiting channel utilization and increasing packet delays. We propose a novel dynamic bandwidth allocation (DBA) algorithm for TWDM-PON that minimizes the performance degradation due to excessive wavelength switching.Keywords: Dynamic Bandwidth Allocation, Passive Optical Networks, and TDMA/WDMA PON. INTRODUCTIONThe continuous growth of bandwidth intensive applications like high-definition internet video, file sharing and video conferencing requires a concurrent growth in bandwidth capacities, which can be achieved by bringing an optical fibre closer to an end user, leading to the fibre-to-the-home (FTTH) technology. A promising and widely adopted FTTH technology is a passive optical network (PON). The PON has a tree topology and consists of an optical line terminal (OLT) in a central office, passive splitters/combiners in a remote node (RN) and a number of optical network units (ONU) at a user side. The PON technology can be implemented in a variety of ways, and time and wavelength division multiplexed PON (TWDM-PON) has been adopted by FSAN as the primary candidate of the next generation PON solution. TWDM-PON combines the expansion in capacity deposited by WDM with the inherent resource granularity of a TDM PON. TWDM-PON requires a dynamic bandwidth allocation (DBA) algorithm that dynamically assigns wavelengths and time slots to the ONUs. These DBAs are also known as upstream scheduling and wavelength assignment (USWA) algorithms.TWDM-PON is realized with a tuneable laser in each ONU. There exist several types of tuneable lasers: the slowest can switch between wavelengths in times ranging from several seconds to a few microseconds, whereas the fastest can switch in nanoseconds. Unfortunately, fast tuneable lasers are very costly and energy consuming, and thus would not be available for access networks. Thus, most often the ONUs will be equipped with lasers having long tuning times (at least tens of microseconds) and the DBA algorithms must take into account the performance degradation inherent to the long tuning and switching times. In addition, completely static allocation of wavelengths is also inefficient. This entails designing a DBA algorithm that switches wavelengths optimally in accord with the laser tuning times.Current state-of-the-art DBA algorithms, like earliest finish last transmission time (EFT), do not take into account the tuning and the switching time of lasers (and receivers), leading to a very high wavelength switching at ONUs. A very high switching leads to a high switching latency, which degrades the DBA performance. From exte...

Energy efficient DBA algorithms for TWDM-PONs

“…This new design dimension can be further extended over EFT/LFT algorithms. In paper [8], we proposed EFT with optimal switching (EFT-OS) algorithm that adapts the wavelength switching to the laser tuning times, and thus obtains a high performance.…”

“…For the details about EFT-OS, we refer the readers to [8]. In STWA-OS, we use a separate time and wavelength-scheduling algorithm; the algorithms are disjoint in upstream and downstream direction.…”

Performance Analysis of Dynamic Wavelength Allocation Algorithm for TWDM PON with Inexpensive ONUs

“…TWDM PON can vary the number of active wavelengths. Also TWDM PON can change the upstream and downstream wavelengths of an ONU [1][2][3][4]8].…”

Two-Stage Resource Allocation to Improve Utilization of Synchronous OFDM-PON Supporting Service Differentiation

“…A time-and wavelength-division multiplexed PON (TWDM-PON) that combines the expansion of capacity by wavelengthdivision multiplexing (WDM) with stacked XG-PONs was chosen as a major solution for 40-gigabit-capable PONs (NG-PON2) [2]. It has been focused upon to provide a total of 40 Gbits/s on four downstream wavelengths (or 80 Gbits/s on eight wavelengths) and 2.5 Gbits/s or 10 Gbits/s on each of four upstream wavelengths (or each of eight wavelengths) [2]- [4]. Concurrently, as one of the post-NG-PON2 candidates, the orthogonal frequency-division multiplexing PON (OFDM-PON) has received a significant amount of attention over the past few years.…”