Xiaoxue Gong

Multi-granularity and robust grooming in power- and port-cost-efficient IP over WDM networks

Previous studies on the power efficiency or port savings in IP over WDM networks have required explicit knowledge of the traffic between each network node pair and the resource assignment of each fiber link. However, it is difficult to estimate this information accurately in live networks, due to the inherent features of IP traffic, e.g., bursts, unpredictability, and variability. Furthermore, the granularity of the demands on an IP-level connection tends to be diverse, and the number of ports consumed in Optical Cross-Connects (OXCs) tends to grow due to the use of hybrid grooming (i.e., traffic grooming with an optical bypass) for power savings. Therefore, it is critical to achieve both power efficiency and port savings in realistic IP over WDM networks. In this paper, we investigate the problem of multi-granularity and robust grooming for power- and port-cost-efficient IP over WDM networks. First, a key parameter, the Multi-Granularity Power Ratio (MGPR), which is the sum of the different single-granularity power ratios, is proposed. Second, the MMPR (Minimizing Multi-granularity Power Ratio) method is used to compute the Traffic Distribution Vectors. Finally, we present the multi-granularity and robust grooming approach, called the Maximizing Hop First (MXHF) approach, where hybrid grooming is adopted to improve power efficiency and waveband merging is utilized to reduce the port cost. Simulation results demonstrate that the MXHF approach can achieve power efficiency and port savings comparing with state-of-the-art robust grooming methods.

Survivable power efficiency oriented integrated grooming in green networks

The wide interests in the power savings of IP over wavelength-division-multiplexing (WDM) optical networks have recently risen in both academic and industrial communities. In an effort to tackle this problem, the hybrid grooming (traffic grooming along with an optical bypass) approach has been presented to reduce the power consumed by the entire network infrastructure, including the transmission ports of routers and optical-electrical-optical (OEO) conversions. However, the related works pay little or no attention to the power consumed to ensure the resiliency of the overall network. Meanwhile, the power consumed by components used for establishing lightpaths is not simultaneously taken into account. One survivable network with the higher power efficiency thereby save more power with hybrid grooming, require the lower power consumption of establishing lightpaths and exhibit the shorter recovery time. For the first time, this paper proposes the evaluating models of both survivable power ratio and protection switching time. We subsequently compare two green and survivable grooming heuristics, known as Single-hop Survivable Grooming with considering Power Efficiency (SSGPE) and Multi-hop Survivable Grooming with considering Power Efficiency (MSGPE). Simulation results demonstrate that, MSGPE obtains the higher power efficiency and resiliency although it has the slightly higher time complexity in comparison to SSGPE. Furthermore, it is effective to exploiting waveband merging in our MSGPE to form integrated grooming for further port savings.

Optimization mechanisms in multi-dimensional and flexible PONs

The current Passive Optical Network (PON) has faced many challenges when heterogeneous access techniques and multiple resource multiplexing ways are involved. Thus, we require a unified control and management of time, spectrum and mode, which is a necessary standardization for PONs. For this end, the multi-dimensional and flexible PON (Mflexi-PON) will emerge as an ideal solution of supporting the heterogeneous access with different resource multiplexing ways. But a high-efficient Mflexi-PON has its own problem. In term of the physical layer of Mflexi-PONs, some signals include a series of orthogonal subcarriers, or transmission modes should have the orthogonal property. Once multiple subcarriers have the same phase, the instantaneous power of a signal will exceed the average value, thus leading to a high Peak-to-Average Power Ratio (PAPR). Furthermore, the signal or transmission mode must be kept strictly orthogonal so that it can be correctly demodulated by the receiver side, which results in the high sensitivity of frequency offset and phase noise. In addition, we need to solve these problems under various resource multiplexing approaches. Thus in this paper, we first review previous solutions for the next-generation PON and discuss some challenging issues for Mflexi-PONs. Next, some promising solutions are proposed for optimization mechanisms in this new networking paradigm, mainly including system architecture, MAC (Media Access Control) layer allocation of multi-dimensional resources, physical-layer performance improvement, and cross-layer optimization.

Dynamic hybrid grooming based on power efficiency in green IP over WDM networks

Due to the rapid growth of various applications, the network devices scale and complexity are significantly increased. Meanwhile, to deal with the burst IP traffic, the network devices need to provide continuous services, which will result in the excessive power consumption. Meanwhile, with the development of IP network and intelligent optical switch network, the backbone network tends to be an IP over wavelength-division-multiplexing (WDM) network. Therefore, it has attracted wide interests in both academic and industrial communities to build power-efficient (i.e., green) IP over WDM network, where we can switch several IP-level requests as one unit in the WDM optical layer. This method is called hybrid grooming and it requires less component power than that of electronic IP routers in the IP layer. Under this hybrid approach, the traffic grooming multiplexes many IP-level requests into a high-capacity lightpath; meanwhile the reduction in power consumed by optical-electrical-optical conversions is achieved through optical bypass. However, the power consumed by components used to establish lightpaths should also be considered. One network with the higher power efficiency not only saves more power followed by hybrid grooming but also requires the lower power consumption of establishing lightpaths. In this paper, to improve the power efficiency of dynamic IP over WDM network, we design two kinds of Wavelength Integrated Auxiliary Graphs (WIAGs), each of which contains one Virtual Topology Layer and multiple Wavelength-Plane Layers. Based on WIAGs, we propose two heuristic algorithms named single-hop grooming with considering power efficiency and multi-hop grooming with considering power efficiency (MGPE) since grooming is NP-hard. Simulation results demonstrate that MGPE obtains the higher power efficiency, although it has the slightly higher time complexity; the power efficiency mainly depends on the kind of grooming strategy (single- or multi-hop) we use while the increasing number of available transceivers in each node cannot improve the power efficiency, although it can make blocking probability decrease.

Virtual Network Embedding for Collaborative Edge Computing in Optical-Wireless Networks

As an open integrated environment deployed with wired and wireless infrastructures, the smart city heavily relies on the wireless-optical broadband access network. Smart home data are usually sent to neighbor optical network units (ONUs) through front-end wireless mesh networks (WMNs) and finally reach the optical line terminal (OLT) for decision making via the passive optical network (PON) backhaul. To reduce backhaul bandwidth saturated by this conventional approach, smart edge devices (EDs) should be deployed at sensors and ONUs so that collaborative edge computing can be performed in front-end WMNs. Moreover, the cooperation of EDs at different ONUs is also promising for computing tasks that cannot be handled within front-end WMNs due to the local bottleneck, leading to collaborative edge computing in the PON backhaul. In this paper, network virtualization is utilized to support the coordination of computing and network resources. We also describe the relationship between virtual networks and requirements of computing tasks for substrate resources. First, a graph-cutting algorithm is employed to embed as many virtual networks as possible onto the common network infrastructure in front-end WMNs, aiming at minimizing the total transmitting power. Next, we transform impossibly embedded virtual networks into new ones that must be processed through the PON backhaul where the wavelength consumption will be optimized. Simulations results demonstrate that 1) the total transmitting power assigned for nodes is effectively reduced using the graph-cutting algorithm if all computing tasks can be solved by front-end WMNs; 2) otherwise, our method accepts more virtual networks with the improvement ratio of 77%, through the PON backhaul. In addition, there is a good match between the algorithm result and the optimal number of consumed wavelengths per optical fiber cable.

Green Provisioning of Many-to-Many Sessions Over WDM Optical Networks

In a many-to-many session, a participant distributes and receives traffic flows to/from all others in the same session. It is desirable to achieve both high resource utilization and low power consumption when such sessions are provisioned. In wavelength division multiplexing (WDM) optical networks, traffic grooming has been widely applied as the key technology for aggregating sessions to improve resource utilization. However, the current many-to-many grooming approaches, the lightpath circle and hubbed light-tree, do not make an effort to reduce the power consumption of many-to-many sessions. In this paper, we formulate the green routing and aggregation of many-to-many sessions problem and prove its NP-completeness. For problem solving in WDM optical networks, we apply a rational combined method of lightpaths. Both an integer linear programming-based approach and a novel graph-based heuristic are devised. We further provide an illustrative comparison between our heuristic and the existing benchmarks in terms of power consumption. Extensive simulation results demonstrate that, compared with the benchmarks, our heuristic improves the average power efficiency in the range of 13-19%.

Location-Recommendation-Aware Virtual Network Embedding in Energy-Efficient Optical-Wireless Hybrid Networks Supporting 5G Models

Given the possibility of ubiquitous 5G wireless access, location data bridge the gap between the physical world and digital online social networking services and also reflect user preferences and even interdependence among users. Owing to this interdependence, the advertiser can push corresponding products to users according to location recommendations, i.e., advertisement targeting. To achieve this mobile cloud computing service, after moving the computing capacity away from end devices to data centres (DCs), the converged infrastructure integrating optical metro and ubiquitous wireless access technologies is proposed in accordance with the 5G model. To minimize energy consumption, we propose a novel design framework of location-recommendation-aware virtual network embedding. This design framework determines the interdependency among user groups so that we can embed the virtual networks owned by user groups with a high interdependence into the same DC of the substrate optical-wireless hybrid infrastructure. Thus, the adviser can locally push the corresponding products to user groups at a single DC instead of consuming a large amount of energy to build inter-DC paths. The simulation results show that our design framework has greater energy efficiency and more profitable advertisement targeting compared with the benchmark, and the result of our heuristic is very close to the upper bound.

SPM-Improved Transmission Performance of Software-Reconfigurable IMDD PONs Based on Digital Orthogonal Filtering

Extensive explorations are undertaken of the feasibility of utilizing self-phase modulation (SPM) to mitigate the channel fading effect associated with digital-orthogonal-filtering-enabled software-reconfigurable intensity-modulation direct-detection passive optical networks (PONs). A comprehensive theoretical model is developed and subsequently verified, based on which numerical simulations are undertaken to investigate the effectiveness of the effects of both SPM and adaptive channel power loading in maximizing the signal transmission capacity of each individual channel in the aforementioned PON systems. It is shown that, for the channel experiencing the worst channel fading effect, the SPM effect can enhance its transmission capacity by a factor as large as 2, and a further 45% transmission capacity improvement is also obtainable when adaptive channel power loading is applied. The signal transmission capacity improvement enabled by the coexistence of these two effects increases almost linearly with transmission distance. The research work not only provides a new means for dynamically manipulating the signal transmission capacity of each individual channel, but also allows the utilization of low-cost optical components without comprising the overall PON system performance.

Novel multi-band DFT-spread OFDM-PON systems based on intensity modulation and direct detection for cloud computing

Passive optical network (PON) has become a preferable access technique for cloud computing due to its elastic bandwidth capacity and transmission stability. In particular, the orthogonal frequency division multiplexing PON based on intensity modulation and direct detection (IM/DD OFDM-PON) has gained extensive attention since it is a cost- and spectral-efficient system, while for the traditional IM/DD OFDM-PON, the use of OFDM could lead to the high peak-to-average power ratio (PAPR), and it is impossible to satisfy the different QoS degrees required by ONUs under a cloud environment. Thus in this paper, we design a novel multi-band discrete Fourier transform (DFT)-spread IM/DD OFDM-PON. The DFT-spread is utilized to reduce the PAPR; meanwhile, a multi-band power allocation and bit loading are achieved to satisfy the different degrees of QoS requirement owned by ONUs. The simulation results show that our system has the better performance of PAPR reduction compared with the traditional IM/DD OFDM-PON; meanwhile, the different QoS degrees of all ONUs are guaranteed.

System performance analysis of time-division-multiplexing passive optical network using directly modulated lasers or colorless optical network units

Abstract. As a promising technology for broadband communication, passive optical network (PON) has been deployed to support the last-mile broadband access network. In particular, time-division-multiplexing PON (TDM-PON) has been widely used owing to its mature technology and low cost. To practically implement TDM-PONs, the combination of intensity modulation and direct detection is a very promising technique because it achieves cost reduction in system installation and maintenance. However, the current intensity-modulation and direct-detection TDM-PON still suffers from some problems, which mainly include a high-power penalty, detrimental Brillouin backscattering (BB), and so on. Thus, using directly modulated lasers (DMLs) and colorless optical network units (ONUs), respectively, two intensity-modulation and direct-detection TDM-PON architectures are proposed. Using VPI (an optical simulation software developed by VPIphotonics company) simulators, we first analyze the influences on DML-based intensity-modulation and direct-detection TDM-PON (system 1) performances, which mainly include bit error rate (BER) and power penalty. Next, the BB effect on the BER of the intensity-modulation and direct-detection TDM-PON that uses colorless ONUs (system 2) is also investigated. The simulation results show that: (1) a low-power penalty is achieved without degrading the BER of system 1, and (2) the BB can be effectively reduced using phase modulation of the optical carrier in system 2.