Time-Domain Wavelength Interleaved Network Research Articles

The potential savings of SDN compliant sub-wavelength switching as a future carrier grade solution for the metropolitan network

Metropolitan area networks are currently challenged by a sharp increase of peak traffic demands, and would thus benefit from flexible network mechanisms able to ensure excellent Quality of Service (QoS) while limiting costs. In this paper, we evaluate the gain in Capital and Operational Expenditures (CAPEX and OPEX) brought by Time-domain Wavelength Interleaved Network (TWIN) thanks to a dynamic control plane implemented in a Software Defined Network (SDN) framework. The SDN compliant TWIN control plane attributes resources and activates the transmitters (Tx), receivers (Rx) and transceivers (TRx) according to traffic variations. The present paper first recaps how to dimension TWIN in terms of Tx, Rx or TRx to support a given traffic matrix. It is then shown that 20% resource over-provisioning allows to meet the metro level QoS requirements set by the Metro Ethernet Forum (MEF). Then, taking into account this over-provisioning value, a comparative study, assessing the OPEX and CAPEX savings for different configuration periods' duration (varying between 5 min and 6 h) is carried out. The obtained results show that the dynamic network re-configuration approach can bring some CAPEX savings and highly significant OPEX savings in a realistic metropolitan network scenario, even for rather large configuration periods (e.g. 1 h). Finally, using a control plane based on this configuration period, the CAPEX and OPEX for TWIN are compared with those for the current Optical Circuit Switching (OCS) transport technologies (both opaque and transparent). It is shown that TWIN CAPEX/OPEX savings are important even if the TWIN's Tx/Rx/TRx unit expenditure cost is many times more expensive than that of OCS.

Optimal Cost and Performance Evaluation of Various Protection Schemes for a Reliable All-Optical Subwavelength Switching Network

Abstract—In this paper, we study several alternatives of protection for a time-domain wavelength interleaved network (TWIN), an optical burst switching technology for transport networks with active edge nodes, passive core nodes, and time-slotted operation. The main difference between those alternatives concerns the degree of resource sharing (transmitters, receivers, and wavelengths). After an extended study on the protection challenges in TWIN, we distinguish three main protection schemes: totally shared protection, partially shared protection, and dedicated protection. We propose a network dimensioning comparison for the aforementioned schemes, based on linear programming formulation addressing the optimization of a used resource. In addition, we assess the ability of the proposed schemes to maintain network performance during the failure in terms of delay, jitter, and packet loss ratio. The obtained results show that the totally shared protection scheme outperforms the other schemes in terms of resource utilization with nonsignificant degradation of the performance and a prompt recovery time.

A new perspective on burst-switched optical networks

Recent experimental research in coherent detection has enabled 100G (or higher bit-rate) optical receivers to switch between wavelengths in less than a hundred nanoseconds. Such technologies enable a novel variant of the Time-domain Wavelength Interleaved Networks (TWIN) architecture in which fast tunable receivers replace tunable transmitters as the main switching elements in the otherwise passive optical network. Similar to TWIN, this architecture enables efficient sharing of 100G (or higher) wavelength rates among multiple destinations in metro networks or data centers where individual node-pairs may not need the full capacity of each wavelength. In this paper, we present the key elements of this novel variant of TWIN, discuss framing and scheduling efficiency, sub- and super-framing for TDM and packet data, as well as protection mechanisms. We also present the benefit of this approach relative to other optical network technologies. We conclude with an overview of the potential applications of this novel optical networking architecture.

Wavelength-reuse in optical time-slotted networks

An all-optical approach to achieve finer bandwidth granularity is to time division multiplex low capacity circuits on each wavelength channel and switch time–wavelength slots optically within the network. One such time-slotted network proposed in the literature is the Time Domain Wavelength Interleaved Network (TWIN), which eliminates slot switching within the network by using a non-reconfigurable core and an intelligent edge utilizing a fast tunable laser to emulate fast switching. In contrast to the TWIN, an optical time-slotted network which incorporates slot-switching within the network is the Time Wavelength Switched Network (TWSN), wherein the Time Wavelength Space Routers (TWSRs) are configured to change their routing pattern on a time-slot basis. The TWIN network assigns a unique wavelength to each node in the network and thus requires a total of W = N wavelengths for an N -node network. We call such a TWIN network as an unconstrained TWIN network. In this paper, we first provide integer linear programs and heuristic algorithms to solve the scheduling problem for a static traffic matrix (of connections) for both, the unconstrained TWIN and the TWSN networks and also compare their performances under a dynamic traffic scenario. To address the problem of scalability of the unconstrained TWIN network, we propose to design a wavelength-constrained (i.e., W < N ) TWIN network with no switching (TWIN-NS) by using a multicasting strategy. We also propose a variant of the TWIN network which possesses switching capabilities only at the edge nodes (TWIN-ES). Overall, this paper compares both versions of the TWIN networks to the TWSN network and investigates the benefits of having a reconfigurable core as opposed to a non-reconfigurable one.

High-Capacity Time-Domain Wavelength Interleaved Networks

Time-domain wavelength interleaved network (TWIN) is an elegant and cost-effective all-optical network designed by a group of researchers in Bell Labs. It emulates fast optical switching via fast tunable lasers at the network edge, so it does not need optical switching and buffering in the network core. TWIN can be upgraded to provide larger capacity by using more receivers at the nodes, where capacity is the aggregate data rate supported by the network. In this paper, we focus on making this upgrade resource-effective. Specifically, we exploit and optimize wavelength reuse so that the resulting network, called <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">high-capacity</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TWIN</i> (HC-TWIN), can better utilize its available resources to provide larger capacity while retaining the appealing advantages of TWIN. We formulate the problem of optimizing HC-TWIN, prove its NP-hardness, and design an efficient three-stage algorithm to solve it. Simulation results demonstrate that 1) HC-TWIN can provide larger capacity by realizing larger degree of wavelength reuse and 2) the three-stage algorithm can find optimal or close-to-optimal solutions.

Design and performance of randomized schedules for time-domain wavelength interleaved networks

Time-domain wavelength interleaved networking (TWIN) is an optical mesh network architecture in which each edge node has one (or more) tunable lasers to transmit fixed-length bursts to various destinations and one (or more) burst-mode receivers capable of decoding each burst intended to it. In this architecture, the interior nodes route each burst independently and passively based on the wavelength of the burst. Network scheduling is thus a critical component that arbitrates burst transmissions from sources to destinations so that conflicts are either avoided or minimized, and wavelength division multiplexing (WDM) transport capacity is efficiently utilized. However, in access or metro networks, which lend themselves naturally to the TWIN mesh architecture, centralized network scheduling would be cumbersome. We consider a distributed mechanism that performs scheduling of bursts to further simplify TWIN mesh architectures. In one realization, each source randomly assigns non-overlapping time slots within a frame for its transmissions. In another realization, each destination grants random but non-overlapping time slots to sources for transmissions. In neither scheme is there any coordination across sources and destinations. We present an analytical formulation of these schemes and investigate their performance under two broad types of traffic: dynamic traffic and semi-dynamic traffic. For dynamic traffic, the analytical results show that for offered load close to 100 percent of capacity, there is 63 percent efficiency for the destination-based mechanism and 37 percent efficiency for the source-based mechanism. When end-to-end demands are semi dynamic, we show through simulations that the destination-based random schedules can achieve over 90 percent efficiency even for offered loads close to 100 percent. These results indicate that the proposed distributed schemes, though exceedingly simple, provide acceptable efficiency comparable to that realized by computation-intensive centralized schedulers irrespective of propagation delays and applicable to any kind of network traffic.

Complexity of Wavelength Assignment in Optical Network Optimization

We study the complexity of a set of design problems for optical networks. Under wavelength division multiplexing (WDM) technology, demands sharing a common fiber are transported on distinct wavelengths. Multiple fibers may be deployed on a physical link. Our basic goal is to design networks of minimum cost, minimum congestion and maximum throughput. This translates to three variants in the design objectives: 1) MIN-SUMFIBER: minimizing the total cost of fibers deployed to carry all demands; 2) MIN-MAXFIBER: minimizing the maximum number of fibers per link to carry all demands; and 3) MAX-THROUGHPUT: maximizing the carried demands using a given set of fibers. We also have two variants in the design constraints: 1) CHOOSEROUTE: Here we need to specify both a routing path and a wavelength for each demand; 2) FIXEDROUTE: Here we are given demand routes and we need to specify wavelengths only. The FIXEDROUTE variant allows us to study wavelength assignment in isolation. Combining these variants, we have six design problems. Previously we have shown that general instances of the problems MIN-SUMFIBER-CHOOSEROUTE and MIN-MAXFIBER-FIXEDROUTE have no constant-approximation algorithms. In this paper, we prove that a similar statement holds for all four other problems. Our main result shows that MIN-SUMFIBER-FIXEDROUTE cannot be approximated within any constant factor unless NP-hard problems have efficient algorithms. This, together with the previous hardness result of MIN-MAXFIBER-FIXEDROUTE, shows that the problem of wavelength assignment is inherently hard by itself. We also study the complexity of problems that arise when multiple demands can be time-multiplexed onto a single wavelength (as in time-domain wavelength interleaved networking (TWIN) networks) and when wavelength converters can be placed along the path of a demand.

Performance analysis of a novel traffic scheduling algorithm in slotted optical networks

This paper considers the scheduling problem in a new slotted optical network called Time-Domain Wavelength Interleaved network (TWIN). The TWIN architecture possesses interesting properties, which may offer solutions for next-generation optical networks. Besides, better Quality of Service (QoS) could be achieved in TWIN by minimizing two parameters: queueing delay and delay variance. However, to the best of our knowledge, most of the existing scheduling algorithms in TWIN ignored consideration of QoS and focused mainly on maximizing the throughput. In this paper, we formulate the scheduling problem into an Integer Linear Programming (ILP) problem and propose a novel heuristic – Destination Slot Set (DSS) algorithm to solve it fast and efficiently. Besides, we derive an analytical model for TWIN and investigate the performance of DSS in it. By means of simulations, we demonstrate that our analytical model approximates the TWIN network very well; moreover, DSS incurs smaller queueing delay and delay variance, which ensures better QoS.

Providing deterministic quality of service in slotted optical networks

This paper proposes an efficient framework for deterministic service guarantees in slot-based optical networks. The framework uses the combination of a control plane and a data plane to solve the complex problem of capacity allocation, slot-matching and traffic scheduling. The control plane implements admission control and capacity allocation to source-destination node pairs and the data plane handles traffic aggregation, buffering, and scheduling. We propose an efficient algorithm in the control plane for slot collision-resolution. In the data plane, we present a comprehensive aggregation and scheduling mechanism that realizes Service Curves assurance. We use the Time-Domain Wavelength Interleaved Network (TWIN) architecture for the proof of concept and conduct extensive simulations to assess the performance of the algorithm and scheduling mechanism.

Scheduling bursts in time-domain wavelength interleaved networks

A time-domain wavelength interleaved network (TWIN) (Widjaja, I. et al., IEEE Commun. Mag., vol.41, 2003) is an optical network with an ultrafast tunable laser and a fixed receiver at each node. We consider the problem of scheduling bursts of data in a TWIN. Due to the high data rates employed on the optical links, the burst transmissions typically last for very short times compared with the round trip propagation times between source-destination pairs. A good schedule should ensure that: 1) there are no transmit/receive conflicts; 2) propagation delays are observed; 3) throughput is maximized (schedule length is minimized). We formulate the scheduling problem with periodic demand as a generalization of the well-known crossbar switch scheduling. We prove that even in the presence of propagation delays, there exist a class of computationally viable scheduling algorithms which asymptotically achieve the maximum throughput obtainable without propagation delays. We also show that any schedule can be rearranged to achieve a factor-two approximation of the maximum throughput even without asymptotic limits. However, the delay/throughput performance of these schedules is limited in practice. We consequently propose a scheduling algorithm that exhibits near optimal (on average within /spl sim/7% of optimum) delay/throughput performance in realistic network examples.