Marco Listanti

Architectural and technological issues for future optical Internet networks

This article reports a review of the most significant issues related to network architectures and technologies which will enable the realization of future optical Internet networks. The design of such networks has to take into consideration the peculiar characteristics of Internet traffic. Several architectures have been proposed to provide optical networking solutions, based on wavelength-division multiplexing and compatible with the IP world. These architectures are presented briefly, and the main advantages and drawbacks are discussed. Furthermore, advanced network architectures are reported. In particular, two network paradigms are illustrated and discussed: the optical transparent packet network and optical burst switching. Finally, the key technologies are illustrated.

Is green networking beneficial in terms of device lifetime

This article analyzes the impact that sleep mode (SM)-based green strategies have on the reliability performance of optical and cellular network elements. First, we consider a device in isolation (i.e., not plugged into a network in operation), showing how operational temperature and temperature variations, both introduced by SM, impact its lifetime. We then evaluate, from an operational cost perspective, the impact of these lifetime variations, showing that some devices are critical, that is, their achievable energy savings might not cover the potential additional reparation costs resulting from being put in SM too frequently. Moreover, we present a model for evaluating the impact of SM on the lifetime of a device plugged into an operational network. The analysis considers two case studies (one based on the optical backbone and one on cellular networks) showing that the lifetime of a device is influenced by both the hardware parameters, which depend on the specific design of the device, and the SM parameters, which instead depend on the energy-efficient algorithm used, the network topology, and the traffic variations over time. Our results show that (i) the changes in the operational temperature and the frequency of their variation are two crucial aspects to consider while designing a SM-based green strategy, and (ii) the impact of a certain SM-based strategy on the lifetime of network devices is not homogeneous (i.e., it can vary through the network).

Definition and performance evaluation of a low-cost/high-capacity scalable integrated OTN/WDM switch

Digital reconfigurable optical add-drop multiplexer systems are characterized by optical-electrical-optical (OEO) conversion of wavelength division multiplexing line wavelengths and by an electronic switching providing wavelength routing. The recent implementation of monolithically integrated large-scale photonic integrated circuits (PICs) in indium phosphide of terabit capacity cross-point switches and of high-capacity optical transport network (OTN) processor chips has allowed not only a considerable reduction in cost and power consumption of the OEO conversion stage but has also enabled the integration, in the same hardware, of OTN sub-wavelength switching and wavelength switching. To reduce the switching fabric complexity, we propose and investigate the structure of a scalable switch core composed of a space switching fabric routing only signals at a higher rate (high-order optical channel data unit (ODU)) and by OTN time-space switching fabrics switching both signals at a lower rate (low-order ODU) and a higher rate (high-order ODU). The lower hardware complexity of the proposed switching fabric is to be paid with a sub-flow blocking that we have investigated by introducing an analytical model validated by simulation. The blocking performance is evaluated as a function of the main switch and traffic parameters and under some traffic aggregation and routing policies. We show that in some traffic scenarios the blocking probability can reach a value of 10-8 if suitable resource management policies are adopted.

Integrated OTN/WDM switching architecture equipped with the minimum number of OTN switches

In packet-optical integrated transport nodes for metropolitan networks, the wavelength data rate of the transponders has increased quickly to 10, 40, and 100 Gbps to reduce the cost of the transported bit. Meanwhile, the majority of the client data rate in routers and packet switches are still operating at 1, 2.5, and 10 Gbps. In this scenario, the introduction of optical transport network (OTN) switching technology enables an efficient wavelength bandwidth utilization and reduces the number of wavelengths, leading to reduced network costs. It has been shown that the use of integrated OTN/WDM switch architecture is cost effective because it reduces the number of short-reach client interfaces. The OTN/WDM also reduces the rack space and the power consumption compared to an architecture that uses a reconfigurable optical add-drop multiplexer and a separate standalone OTN switch or one that uses back-to-back muxponder connections to perform manual grooming. We introduce and investigate the performance of a new integrated OTN/WDN switching architecture in which the number of OTN switches is minimized. We propose an analytical model for the evaluation of the switch-blocking probability when two different OTN switch assignment policies are used. We show how the number of OTN switches can be reduced if a suitable dimensioning procedure is performed and depending on the traffic percentage needing OTN switching. As an example, if traffic is less than 45%, then the new proposed OTN/WDM switching architecture allows for 25% savings in OTN switching resources in the case of a switch with 4 input/output lines, 48 wavelengths, and 12 × 12 OTN switches.

Implementing energy-aware algorithms in backbone networks: A transient analysis

In this work we study the impact of energy-aware routing algorithms on IP backbone networks, focusing on the routing protocol transients due to network reconfiguration. We first propose the Green Partial Exportation (GPE) algorithm, which is fully compatible with the OSPF protocol and targets the reduction of the number of changed paths in the network; we also realize a green software router by integrating GPE in the Quagga routing suite. Then we define an experimental methodology to evaluate the effects of a green routing strategy on the network behavior, in terms of delay increase and packet loss. Finally, we evaluate our solution on an emulated testbed from a national telecom operator. Our results show a maximum increment of 320 ms for the RTT and a packet loss of 1.45% during the network transients. Moreover, GPE can be safely applied in the network with a time granularity of less than one minute.

Performance evaluation of integrated OTN/WDM metropolitan networks in static and dynamic traffic scenarios

The introduction of optical transport network (OTN) switching technology in metropolitan networks enables efficient wavelength bandwidth utilization and reduces the number of wavelengths, leading to reduced network costs. It has been shown that the use of integrated OTN/WDM switch architecture is cost effective because it reduces the number of short-reach client interfaces and the rack space compared to an architecture that uses a reconfigurable optical add-drop multiplexer and a separate standalone OTN switch or one that uses back-to-back muxponder connections to perform manual grooming. We have proposed an integrated OTN/WDM switch that allows for significantly lower complexity and cost at the price of relaxing the nonblocking ideal performance requirements normally applied to this kind of switch. In this paper we investigate the impact that the switch blocking has on the network performance in static and dynamic scenarios. We formulate the routing problem in the integrated OTN/WDM network as an integer linear problem and develop an efficient heuristic to evaluate the blocking performance in a static traffic scenario. We study the blocking degradation of the proposed switch in the case of some metropolitan networks, and we show how higher blocking occurs in networks having a larger average node degree. We also show that the degradation of two orders of magnitude in blocking probability occurring under a dynamic traffic scenario can be mitigated with the introduction of a spatial speedup equal to 1.5.

Trade-off between power and bandwidth consumption in a reconfigurable xhaul network architecture

The increasing number of wireless devices, the high required traffic bandwidth, and power consumption will lead to a revolution of mobile access networks, which is not a simple evolution of traditional ones. Cloud radio access network technologies are seen as promising solution in order to deal with the heavy requirements defined for 5G mobile networks. The introduction of the common public radio interface (CPRI) technology allows for a centralization in BaseBand unit (BBU) of some access functions with advantages in terms of power consumption saving when switching off algorithms are implemented. Unfortunately, the advantages of the CPRI technology are to be paid with an increase in required bandwidth to carry the traffic between the BBU and the radio remote unit (RRU), in which only the radio functions are implemented. For this reason, a tradeoff solution between power and bandwidth consumption is proposed and evaluated. The proposed solution consists of: 1) handling the traffic generated by the users through both RRU and traditional radio base stations (RBS) and 2) carrying the traffic generated by the RRU and RBS (CPRI and Ethernet flows) with a reconfigurable network. The proposed solution is investigated under the lognormal spatial traffic distribution assumption. After proposing resource dimensioning analytical models validated by simulation, we show how the sum of the bandwidth and power consumption may be minimized with the deployment of a given percentage of RRU. For instance we show how in 5G traffic scenarios this percentage can vary from 30% to 50% according to total traffic amount handled by a switching node of the reconfigurable network.

Lifetime awareness in backbone networks with sleep modes

We investigate the problem of managing the lifetime of links in IP backbone networks exploiting a sleep mode (SM) state. In particular, the SM duration tends to increase the lifetime, while the frequency of power state transitions tends to decrease it. After optimally formulating the problem of limiting the impact on the link lifetime when SMs are applied, we propose an online heuristic, called AFA, to practically solve it. Our solution performs SMs decisions at each time slot, without requiring the knowledge of future traffic (which may be an unrealistic assumption). We test the performance of AFA on a realistic case study, by comparing it against two algorithms energy-aware. Results show that AFA outperforms the other algorithms in terms of lifetime performance, while allowing devices to be put in SMs.

The Power of SDN to Improve the Estimation of the ISP Traffic Matrix Through the Flow Spread Concept

Traffic matrix estimation in communication network is a long standing problem for its intrinsic difficulty and potential benefit to a vast number of network optimization and management functions. We address the improvement of the traffic matrix estimation by means of selected traffic flow measurements, besides the easily obtained link load measurements. The key contribution of this paper is the definition and assessment of an effective criterion, based on the flow spread parameter, to identify the flows to be measured that reduce the estimation error most. It turns out that a small percentage of flows are enough to drive the estimation error an order of magnitude lower than the one obtained with the classical solution solely based on link load measurements. Our algorithm, referred to as flow spread-based algorithm (FSBA), is also able to distribute measurement tasks fairly among network nodes, taking into account the available forwarding tables space. We also show that FSBA outperforms the state-of-the-art similar approaches. A detailed discussion on how the observation of the desired flows can be performed is done as well, by addressing the SDN paradigm. This is in fact a rapidly growing concept that enables individual flow measurements, though for only a limited number of flows to be practical with current technology.

Modeling the Impact of Power State Transitions on the Lifetime of Cellular Networks

We consider the effect of power state transitions on the lifetime of Base Stations (BSs) in a cellular network. In particular, we take into account the impact of putting in sleep mode the BS, and also the change of the radiated power. When the BS reduces its power consumption, its lifetime tends to increase, as a consequence of the temperature reduction. However, the change in the power state triggers a negative effect which instead tends to reduce the BS lifetime. We therefore propose a model to evaluate the BS lifetime considering the two aforementioned effects, triggered either by the application of a sleep mode state or a change in the radiated power. Our results, obtained over a representative case study, indicate that the BS lifetime may be negatively affected when power state transitions take place. Therefore, we argue that the lifetime should be considered in the process of deciding how and when to change from a power state to another one.