Virtual Concatenation Research Articles

Eavesdropping-aware routing and spectrum allocation based on multi-flow virtual concatenation for confidential information service in elastic optical networks

Abstract The leakage of confidential information is one of important issues in the network security area. Elastic Optical Networks (EON) as a promising technology in the optical transport network is under threat from eavesdropping attacks. It is a great demand to support confidential information service (CIS) and design efficient security strategy against the eavesdropping attacks. In this paper, we propose a solution to cope with the eavesdropping attacks in routing and spectrum allocation. Firstly, we introduce probability theory to describe eavesdropping issue and achieve awareness of eavesdropping attacks. Then we propose an eavesdropping-aware routing and spectrum allocation (ES-RSA) algorithm to guarantee information security. For further improving security and network performance, we employ multi-flow virtual concatenation (MFVC) and propose an eavesdropping-aware MFVC-based secure routing and spectrum allocation (MES-RSA) algorithm. The presented simulation results show that the proposed two RSA algorithms can both achieve greater security against the eavesdropping attacks and MES-RSA can also improve the network performance efficiently.

Multi-core virtual concatenation scheme considering inter-core crosstalk in spatial division multiplexing enabled elastic optical networks

Spatial division multiplexing enabled elastic optical networks (SDM-EONs) are the potential implementation form of future optical transport networks, because it can curve the physical limitation of achievable transmission capacity in single-mode fiber and single-core fiber. However, spectrum fragmentation issue becomes more serious in SDM-EONs compared with simple elastic optical networks (EONs) with single mode fiber or single core fiber. In this paper, multi-core virtual concatenation (MCVC) scheme is first proposed considering inter-core crosstalk to solve the spectrum fragmentation issue in SDM-EONs. Simulation results show that the proposed MCVC scheme can achieve better performance compared with the baseline scheme, i.e., single-core virtual concatenation (SCVC) scheme, in terms of blocking probability and spectrum utilization.

Migration From Fixed to Flexible Grid Optical Networks With Sub-Band Virtual Concatenation

A novel strategy is presented to operate a mixed fixed/flexible grid optical network which may be used to gradually migrate from a fixed to a flexible mode of operation. Routing and spectrum allocation (RSA) in an optical network where fixed and flexible grids co-exist using a multi-path sub-band virtual concatenation (VCAT) or split spectrum (SS) technique is considered. Mixed integer linear programming models and an efficient heuristic algorithm based on spectrum window planes are proposed for the RSA optimization. The results obtained for the static traffic demand indicate that it is operationally more convenient to use the multi-path VCAT only by itself in a mixed grid optical network to guarantee performance comparable to that of the joint multi-path and single-path VCAT case. Network performance is also evaluated in terms of bandwidth blocking probability (BBP) under a dynamic traffic demand. Simulation results show that the multi-path VCAT scheme can efficiently utilize the overall spectrum resources with low blocking. The results of studies with both static and dynamic traffic demands also confirm that migration from a pure fixed grid optical network to a pure flexible grid will be desirable for better network capacity utilization.

Novel Elastic Optical Network Embedding Using Re-Optimized VCAT Framework Accompanied by Hitless PPSM Function

The elastic optical network (EON) provides fine-grained and orthogonal frequency slots for establishing the connection that will realize high-rate data transmission among data centers (DCs). With the implementation of cloud DCs (CDCs) and EON virtualization, achieving EON embedding (EONE) is essential, which includes two components: node mapping from the virtual machine to the CDC and link mapping from the virtual lightpath to fiber link(s). In particular, the link mapping must satisfy some rigid constraints in terms of spectrum continuity, consistency, and nonoverlapping, which may create spectrum fragments over fiber links. Thus, in this paper, we reoptimize the virtual concatenation (VCAT) framework accompanied by the hitless push-pull spectrum movement (PPSM) function when the common link mapping fails. Our design framework integrates spectrum movement with inverse multiplexing such that more EONE requests can be satisfied by performing effective spectrum defragmentation. We also optimize the number of subbands with a constrained buffer size to compensate the differential delay at the receiving end. The problem is formulated using the relaxed integer linear programming (ILP) model, and the corresponding heuristic tailored to four different service-sorting strategies is also designed. The simulation results verify the superiority of our method in terms of increasing the spectrum efficiency and reducing the blocking rate of EONE requests. This paper is the first work to focus on designing a reoptimized VCAT framework accompanied by the hitless PPSM function for the EONE that includes both node and link mapping processes rather than a simple spectrum defragmentation.

Crosstalk‐aware cross‐core virtual concatenation in spatial division multiplexing elastic optical networks

Spatial division multiplexing elastic optical networks (SDM-EONs) will become the most important form of future optical transport networks, because it can break the physical limit of achievable capacity in single-mode and single-core fibre. However, spectrum fragmentation issue becomes more serious in SDM-EONs compared with in single EON. Crosstalk-aware cross-core virtual concatenation (CCVC) scheme is first proposed to solve the spectrum fragmentation issue in SDM-EONs. Simulation results show that CCVC can achieve lower blocking probability and higher spectrum utilisation compared with single-core virtual concatenation scheme.

Benefits of Sub-band Virtual Concatenation for Enhancing Availability of Elastic Optical Networks

Sub-band virtual concatenation (VCAT) technique can help improve spectrum utilization of an elastic optical network (EON). On the other hand, availability is an important service level agreement (SLA) criterion for an optical transport network. This paper evaluates how the sub-band VCAT technique can enhance the availability of an EON. A quadratic programming optimization model and an efficient heuristic algorithm are developed to maximize availability-weighted network bandwidth. Also, an allowed maximal differential delay (MDD) between different sub-paths that make up a VCAT connection is considered as a constraint, and the related availability-weighted network bandwidth is evaluated. Considering the limited spectrum capacity of each transponder, we also extend the model to assign spectra based on each independent transponder. Simulation results show that the sub-band VCAT technique can significantly increase average network availability of an EON compared to the case without VCAT (non-VCAT). A trend is also observed that with an increasing MDD, the average network availability increases, but saturates for a large MDD. In addition, the limitation of the available transponders at each node can become a bottleneck for provisioning the bandwidth between node pairs.

Dynamic Capacity Allocation in OTN Networks

A dynamic Optical Transport Network (OTN) has the advantage of being able to adjust the connection capacity on demand in order to respond to variations on traffic patterns or to network failures. This feature has the potential to reduce operational costs and at the same time to optimize networks resources. Virtual Concatenation (VCAT) and Link Capacity Adjustment Scheme (LCAS) are two techniques that when properly combined can be used to provide improved dynamism in OTN networks. These techniques have been previously standardized in the context of Next Generation SDH/SONET networks. VCAT is used to tailor the capacity of network connections according to service requirements, while LCAS can adjust dynamically that capacity in a hitless manner. This paper presents an overview of the application of VCAT/LCAS techniques in the context of OTN. It explains in detail how these techniques can be employed to resize the connection capacity and analyses its use in network protection solutions. Furthermore, a detailed analysis of the time delays associated with different operations is provided and its application to some reference networks is undertaken. The obtained results provide an idea about the time delays of the capacity adjustment processes and define potential scenarios for implementing VCAT/LCAS techniques.

Multi-flow virtual concatenation triggered by path cascading degree in Flexi-Grid optical networks

The Flexi-Grid optical networks can elastically allocate spectrum tailored for various bandwidth requirements. In the flexible architecture, routing and spectrum allocation (RSA) is the key problem is to assign spectral resources to accommodate traffic demands. However, spectrum continuity and contiguity constraints in Flexi-Grid optical networks may cause the network fragmentation issue and lead to poor spectrum utilization. In this paper, different from defragmentation methods, we propose multi-flow virtual concatenation (MFVC) in Flexi-Grid optical networks. MFVC can utilize spectral fragments effectively and decrease blocking probability without influencing the already existing active services or wasting additional spectrum resources. We also analyze the feasibility of MFVC and present a MFVC-enabled transponder and control model implementation. For estimating the distribution and size of available fragments on a path in advance, a split-multi-flow RSA heuristic algorithm (SMF) is proposed by introducing path cascading degree (PCD) based triggered mechanism according to the proposed model. Additionally, resource assignment scheme, guard band size, maximum number of split-flow and differential delay constraint are also considered into MFVC and the performances of the proposed algorithm can be demonstrated to improve the spectral utilization and greatly decrease blocking probability through extensive simulations.

Optimized Parallel Transmission in OTN/WDM Networks to Support High-Speed Ethernet With Multiple Lane Distribution

The emerging high-speed Ethernet is expected to take full advantage of the currently deployed optical infrastructure, i.e., optical transport network over wavelength division multiplexing (OTN/WDM) networks. Parallel transmission is a viable option towards this goal, as exemplified by several IEEE and ITU-T standards. The optical virtual concatenation protocol in the OTN layer defined in ITU-T G.709 enables high-speed Ethernet signals to be decoupled into low rate virtual containers. The multiple lane distribution layer defined in IEEE 802.3ba facilitates the optical parallel transmission by stripping Ethernet signals into multiple low rate lanes which can be mapped onto optical channels. In this paper, we propose a new optimization framework for parallel transmission in OTN/WDM networks to support high-speed Ethernet. We formulate the parallel transmission optimization as an integer linear programming problem encompassing three sub-problems: parallel wavelength routing and assignment, usage of electronic buffering for skew compensation, and bufferless parallel transmission. To reduce computational complexity, we deploy multi-objective evolutionary optimization. The numerical results show that parallel transmission in OTN/WDM networks is feasible, and optimal solutions can be obtained with minimum resource consumption and bufferless system design.

VCAT synchroniser-reduction of buffer size in VCAT enabled next generation SDH networks

Next generation synchronous digital hierarchy is a popular transport technology for integrated voice and data communication. It typically uses virtual concatenation (VCAT) for dynamic bandwidth management. This paper discusses different issues related to VCAT. Paper mainly focuses on the differential delay that occurs as all the VCAT members traverse through different path to reach the destination. These streams do not reach the destination at the same time and thus incur differential delay. Buffers are provided at the receiver to compensate for differential delay. The larger the differential delay, the larger is the buffer requirement at the receiver. Differential delay/buffer size can be reduced by proper routing of the traffic. In the existing receiver circuits, all incoming streams are allocated the same buffer space, specifying the maximum differential delay it can compensate. This results in a large buffer requirement. To overcome this limitation, this paper proposes a novel scheme of allocating buffers dynamically to all the streams. To achieve this, differential delay between the streams is computed by extracting the multiframe indicator and then as per the delay, each stream is allocated buffer space from a common buffer pool. The common buffer pool consists of a number of buffer modules. The size of each module is equal to the frame size for the specific virtual channel, and the size of the common buffer pool is architecture dependent. Sixty per cent reduction in the buffer requirement is predicted using this scheme, at the receiver. For functional verification of the concept, a hardware circuit is designed. Copyright © 2011 John Wiley & Sons, Ltd.

Optimized Routing and Buffer Design for Optical Transport Networks Based on Virtual Concatenation

The emergence of new telematic applications and services is creating significant growth in the traffic carried over the optical transport network (OTN). One potential cost-effective approach for satisfying these demands consists in applying inverse-multiplexing techniques, such as virtual concatenation (VCAT). In this context, efficient load balancing can be achieved by exploiting multipath routing at the cost of introducing differential delay in the concatenated circuits. This effect can be compensated through appropriate delay compensation techniques (e.g., electrical buffering), which can act either in a centralized way with the buffering at the end nodes, or by distributing the differential delay throughout the intermediate nodes. In order to properly solve the routing and differential delay compensation distribution problem in the OTN, we propose two novel methods: a dual-step integer linear programming (ILP) model and a tabu search multi-stage heuristic. These strategies are compared with our two former proposals consisting of a single-step ILP model and an iterative search heuristic. The four solutions are further expanded to consider the possibility of using homogeneous or heterogeneous VCAT. The performance of these optimization methods is examined in two network topologies assuming that 100 Gb/s Ethernet streams are carried over 40 Gb/s channels (homogeneous case) or over a mixed combination of 40 Gb/s and 10 Gb/s channels (heterogeneous case) in the OTN. The results obtained show that, as expected, the smallest buffering requirements are obtained by both ILP models, with the dual-step version exhibiting also a significant reduction in the number of optical-to-electrical and electrical-to-optical operations used for intermediate compensation. In addition, the novel tabu search framework is able to surpass our former heuristic by simultaneously leveraging minimum link capacities and reducing the buffer sizes.

Survivable Multipath Provisioning With Differential Delay Constraint in Telecom Mesh Networks

Survivability is a critical concern in modern telecom mesh networks because the failure of a network element may cause tremendous data and revenue loss in such networks using high-capacity optical fibers employing wavelength-division multiplexing (WDM). Multipath provisioning is a key feature of next-generation SONET/SDH networks (which can be used on top of optical WDM), and they can support virtual concatenation (VCAT); thus, multipath provisioning can significantly outperform single-path provisioning in resource efficiency, service resilience, and flexibility. However, in multipath provisioning, differential delay is an important constraint that should be considered. We investigate survivability of service paths based on differential-delay constraint (DDC) and multipath provisioning together in telecom backbone mesh networks. We propose the Shared Protection of the Largest Individual Traversed link (SPLIT) method for survivable multipath provisioning and present a DDC-based algorithm for multipath routing subject to DDC. We also compare the DDC-based algorithm with the K shortest link-disjoint paths (KDP) algorithm, using SPLIT, under dynamic service requests. We find that exploiting link-disjoint paths is very efficient for survivable multipath provisioning, and our algorithm is resource-efficient, has low signaling overhead, and has fast fault recovery for survivable multipath provisioning with DDC. For a 5-ms DDC, our algorithm can decrease the bandwidth blocking ratio (BBR) significantly in typical U.S. backbone networks.

New Approach to Reliable Multipath Provisioning

We study the problem of reliably provisioning traffic in high-capacity backbone mesh networks supporting virtual concatenation (VCAT). Traditional approaches handled reliability requirements using full protection, which offers high assurance but can be costly. We take a less expensive approach by offering an expected bandwidth, rather than an absolute amount, but at lower costs than full-protection approaches. We propose a new routing algorithm that uses minimum-cost flow to find efficient collections of paths that satisfy traffic requests for expected bandwidth. We find that in most realistic network settings, paths are reliable enough so that only few additional network resources are required to compensate for the bandwidth loss incurred from possible network failures. We compared our approach to a previous algorithm under both a uniform setting, with symmetric traffic distribution and equal edge capacities, and in a more realistic setting with asymmetric traffic and differing edge capacities. Results show that our algorithm is an attractive approach in both settings, and much more effective than the previous scheme. We also compare our approach to a full-protection approach. Results show that by using fewer network resources, our algorithm is able to satisfy significantly more traffic requests than full protection. Thus, when full protection is not crucial, using our routing approach should be beneficial.

FPGA Implementation of Cross Virtual Concatenation Transmitter/ Receiver for Data Transmission over Next Generation SDH Systems

Cross Virtual Concatenation is the new technique proposed for bandwidth efficient transmission of data over SDH networks. SDH networks came into existence for reliable voice transmission. As the demand of data traffic grew in wide area networks, new technologies were developed and standardized for data transmission over SDH networks. The technologies used namely, GFP (generic framing procedure), VCAT (virtual concatenation) and LCAS (link capacity adjustment scheme) enable network operator to provide integrated voice and data services over their legacy SDH infrastructure. Data packets are encapsulated using framing protocols GFP. VCAT is a process of distributing the GFP framed data payload in number of virtual channels of same capacity forming a Virtually Concatenated Group (VCG). LCAS is used for dynamic bandwidth allocation. LCAS enhances the VCAT scheme with hitless in service addition and removal of VC's to/from the VCG.VCAT combines homogeneous virtual channels together which in some cases limits the performance of VCAT. This paper describes the implementation of new concatenation technology named cross virtual concatenation (CVC), which combines heterogeneous VC's together to utilize the SDH bandwidth more efficiently. CVC implementation requires only end node equipments to be upgraded as VCG members travel through the link similar to the conventional VCAT. This paper proposes FPGA implementation of transmitter and receiver circuits for 100 Mbps Ethernet data transmission over next Generation SDH systems using CVC, where two types of VC's namely VC-3 and VC-12 are used for data transmission. Total Transmission delay is calculated as 125 μs. There is no complexity added at the receiver side due to this delay. The receiver is designed for 32 ms differential delay compensation which can be increased up to maximum 256 ms by increasing the buffer size at the receiver.

Survivable Multipath Traffic Grooming in Telecom Mesh Networks With Inverse Multiplexing

We investigate the survivable traffic grooming problem with inverse multiplexing in telecommunication mesh networks employing next-generation SONET/SDH and WDM. With the support of virtual concatenation, a connection of any bandwidth can be provisioned as several subconnections (i.e., inverse multiplexed) over diverse paths. Therefore, it is important to efficiently groom and protect these low-speed subconnections onto high-capacity wavelength channels, considering the typical constraints. We propose and investigate the characteristics of survivable multipath traffic grooming with protection-at-connection and protection-at-lightpath levels for grooming connections with shared pro- tection, subject to the constraints of the inverse-multiplexing factor, differential-delay constraint, and grooming ports. Since this problem is NP-complete, we propose effective heuristics using a novel analytical model. Our results show that (1) the network performance, in metrics of bandwidth blocking ratio and resource overbuild, can be notably improved by exploiting the inverse-multiplexing capability, (2) tight constraints have negative impact on performance, (3) protection-at-connection performs better in most cases of multipath provisioning when the constraints are not too tight, and (4) protection-at-lightpath achieves better performance when the number of grooming ports is moderate or small.

Adaptive Reliable Multipath Provisioning in Survivable WDM Mesh Networks

We investigate the problem of adaptive reliable multipath provisioning in next-generation backbone mesh networks employing optical wavelength-division multiplexing (WDM) and channelization techniques such as synchronous optical network/synchronous digital hierarchy (SONET/SDH) and supporting virtual concatenation (VCAT). VCAT enables multipath provisioning, but also introduces differential delay at destination nodes. How to guarantee service availability, using multipath provisioning, and meet the differential-delay constraint (DDC) is an important problem. We introduce the notation M:N(m) for multipath provisioning where a service path for a connection is set up with M primary paths and N backup paths, where each path has a fraction of the bandwidth of the connection, and (m) in this notation denotes “multipath.” With M:N(m) provisioning schemes, we develop an analytical model to analyze the end-to-end connection availability for the full bandwidth request. We propose two types of bandwidth migration methods, which can be implemented by a link-capacity adjustment scheme (LCAS) protocol of next-generation SONET/SDH, to optimize resource usage. Based on the M:N(m) analytical model, we develop an adaptive heuristic algorithm to provision a connection subject to the DDC while satisfying its service-level agreement (SLA). We show that, for end-to-end connection-availability-guaranteed service, multipath provisioning can achieve much better network performance than traditional single-path provisioning. With bandwidth migration, we can further improve multipath provisioning performance.

Value-added services in next-generation SONET/SDH networks

Advances in next-generation SONET/SDH have introduced novel features for generic protocol framing/encapsulation, virtual concatenation, inverse multiplexing, dynamic circuit adjustment, and so on. In turn, these provisions have enabled much improved multi-tiered service provisioning and are viewed very favorably by carriers, particularly incumbents. This article looks at this evolved framework with a particular focus on value-added services creation. Results from a sample performance evaluation study also are presented to quantify some of the achievable gains.

Cross-virtual concatenation for Ethernet-over-SONET/SDH networks

Ethernet-over-SONET/SDH (EoS) is a popular approach for interconnecting geographically distant Ethernet segments using a SONET/SDH transport infrastructure. It typically uses virtual concatenation (VC) for dynamic bandwidth management. The aggregate SONET/SDH bandwidth for a given EoS connection is obtained by “concatenating” a number of equal-capacity virtual channels. Together, these virtual channels form a virtually concatenated group (VCG). In this article, we introduce a new concatenation technique, referred to as cross-virtual concatenation (CVC), which involves the concatenation of virtual channels of heterogeneous capacities. We show that CVC can be implemented through a simple upgrade at the end node, thus utilizing the existing legacy SDH infrastructure. By employing CVC for EoS systems, we show that the SDH bandwidth can be harvested more efficiently than in conventional VC. We consider two problems associated with routing CVC connections: the connection establishment problem and the connection upgrade problem. The goal of the first problem is to compute a set of paths between two EoS end systems such that a total bandwidth demand and a constraint on the differential delay between the paths are satisfied. Among all feasible sets, the one that consumes the least amount of network bandwidth is selected. For this problem, we develop an integer linear program (ILP) and an efficient algorithm based on the sliding-window approach. For the connection upgrade problem, the goal is to augment an existing set of paths so as to increase the aggregate bandwidth, while continue to meet the differential-delay constraint. We model this problem as a flow-maximization problem with a constraint on the delay of the virtual channels with positive flow. We then consider the problem of path selection under imprecise network state information. Simulations are conducted to demonstrate the advantages of employing CVC and to evaluate the performance of the proposed algorithms.

On Provisioning in Dual-Node Interconnected SONET/SDH Rings

SONET/SDH is historically the dominant telecom transport infrastructure for backbone networks, and it is optimized for reliable delivery of voice and private-line services. Efficient utilization of the existing infrastructure through novel methods and algorithms can lead to higher revenue, which is attractive for network operators. In this study, we examine a network of inter-connected SONET/SDH rings that use dual-node interconnection employing the drop-and-continue facility, which is the de-facto standard for interworking SONET/SDH protection architectures. We develop an efficient algorithm for provisioning in such a network while keeping fragmentation of capacity low and taking into account the various constraints imposed by the underlying physical layer. We examine the case of dual-node-interconnected ring networks employing both contiguous and virtual concatenation (a next-generation SONET/SDH architecture), and as expected, we discover that provisioning higher-bandwidth connections with virtual concatenation offers significant improvement. The stringent time-slot alignment and contiguity constraints imposed by contiguous concatenation are further compounded by the constraints imposed by the ring interworking architecture, and virtual concatenation allows capacity to be used more efficiently.

Bandwidth virtualization enables long-haul WDM transport of 40 Gb/s and 100 Gb/s services

This article describes how bandwidth virtualization can enable transmission of ultra-high bandwidth 40 Gb/s and 100 Gb/s services over existing optical transport networks independently of the underlying network infrastructure. An overview of the technology alternatives available to enable high-bandwidth service transport is provided, along with a discussion of the relative merits of different approaches. The authors describe how wavelength division multiplexing, using large- scale photonic integrated circuits combined with the use of a digital virtual concatenation mapping protocol, can be used to enable decoupling of 40 Gb/s and 100 Gb/s service provisioning from the underlying optical link engineering, thereby enabling bandwidth virtualization. Real-world implementation examples of bandwidth virtualization are provided, including 40 Gb/s service transmission over a 2000-km fiber link with 65 ps of peak PMD, a field trial of 40 Gb/s service transmission over an 8477-km trans-oceanic network, and finally a field trial of a pre-standard 100 gigabit Ethernet service transmission over a 4000-km terrestrial long-haul network.