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We present a novel strategy for the operation of a mixed fixed/flexible grid optical network which would be useful for the gradual migration from a fixed to a flexible mode of operation. Routing and spectrum allocation (RSA) in co-existing fixed/flexible grid optical networks with a multi-path sub-band virtual concatenation (VCAT) technique is considered. An integer linear programming (ILP) model and efficient heuristic algorithms based on k-shortest path (KSP) and spectrum window planes (SWPs) are proposed for the RSA optimization which minimizes the maximum number of frequency slots (FSs) used in the fiber link. Simulation studies are presented to show the efficiency of the proposed approaches.

An investigation on researches of technologies and applications tailored to optical-connection cloud data center networks (OCDCNs) is made in this article, moreover, the existing approaches of virtual network embedding (VNE) and future challenges are summarized for OCDCNs. Also, we propose a promising VNE solution in OCDCNs integrating both elastic optical networks and virtual concatenation technology.

The elastic optical network (EON) provides fine-grained and orthogonal spectrum slots for the establishment of the elastic connection using orthogonal frequency division multiplexing (OFDM). Currently, the EON interconnection has realized the high-rate transmission among data centers (DCs). With the implementation of cloud DCs (CDCs) and EON virtualization, it becomes very essential to achieve the elastic network embedding (ENE) that facilitates the resource sharing in inter-cloud-data-center networks. The ENE operation consists of two components, the virtual-node mapping from virtual machine to CDC and the virtual-link (VL) mapping from virtual lightpath to fiber link(s). Thus an ENE request can be satisfied only when those two mapping processes have completed successfully. But during the VL mapping, some rigid constraints must be satisfied, such as the spectrum continuity, etc. This makes the ENE operation create the spectrum fragments over fiber links, which results in the denial of requests. Thus in this paper, we take the virtual concatenation (VC) into account when the VL mapping fails. The problem is formulated using the relaxed integer linear programming (ILP) model, and we also design a VC-based heuristic. Simulation results have verified the superiorities of the VC scheme on increasing the spectrum utilization and reducing the blocking rate of ENE requests.

Orthogonal Frequency Division Multiplexing (OFDM) has recently been proposed as a modulation technique for optical networks due to its higher spectral efficiency and superior impairment tolerance. There have been extensive studies on routing and spectrum assignment (RSA) of the OFDM-based elastic optical network, of which most focus on a single route for each lightpath service. In this paper, we study the RSA problem for the elastic optical network considering the multi-path subband virtual concatenation (VCAT) technique that allows the sub-bands of a VCAT lightpath connection to be transmitted over different routes. We develop integer linear programing (ILP) models to optimally solve the problem. We evaluate the benefit of the multi-path sub-band VCAT technique for the RSA problem through comparing with the non-VCAT case. In addition, because of the limitation of synchronization in the sub-band VCAT technique, we set a maximal distance difference among the sub-band paths of a VCAT connection to evaluate how the limitation can impact the RSA performance. We find that the multi-path sub-band VCAT technique shows a stronger benefit in a network with a higher nodal degree.

The general frame size in an IEEE 802.11 wireless LAN environment is often much smaller than the specified MTU size. The small size of the frames increases the MAC layer traffic and can cause degradation in network performance. In this paper, we propose new IP packet concatenation methods that are able to merge two or more IP packets with same destination addresses into a MPDU. Our method provides a continuous monitoring of the channel state. If there are IP packets that can be concatenated, the concatenation is carried out at the same time as the channels are allocated to other nodes. At the receiving end, the data size of the received MPDU and the total length field in the IP header are compared to determine whether the received frame is concatenated or not. Our proposed method avoids any packet concatenation delay. When MAC layer traffic is low, our method provides a similar performance to existing wireless LANs. Our method can also improve the transmission performance as an increase in MAC layer traffic results in a decrease in the total traffic.

Providing the survivability in optical networks over wavelength-division multiplexing (WDM) is a critical concern. The design issue on WDM network is to minimize the buffer size and providing survivability based on differential delay and Multipath provisioning with the support of Virtual Concatenation (VC). In this paper, we propose the Shared Protection of the Largest Individual Traversed link (SPLIT) for survivable multipath and MFI (Multiframe Indicator) Buffer to reduce the buffer requirement at the receiver end of the VC with the help of minimized differential delay.

Synchronous Digital Hierarchy (SDH) networks are wildly deployed by telecom service providers (SP) around the world. Conventionally, SDH network circuits have to be designed and provisioned beforehand. Circuit profiles, including capacity, circuit route, end points…, have to be assigned before service activations. Any attempt of network re-configuration caused by network failures or traffic congestions will lead to uncertain service interruption. To further increase network availability, SPs have to overbuild their networks or to assign backup route(s) for each critical circuit, which, however, is costly and inefficient. With the introduction of technologies such as Virtual Concatenation (VCAT) and Link Capacity Adjustment Scheme (LCAS) of Next generation SDH (NG-SDH), SPs are able to adjust their SDH circuits at various bandwidth granularities and to hitlessly increase or decrease bandwidth of each circuit. In this study, we propose an effective approach to locate overbuild bandwidth, failed circuits, as well as congested circuits based on real time traffic flow data and network alarm message. Then our approach reallocates overbuilt network bandwidth in responding to network failures or traffic congestions by exploiting the benefit of VCAT and LCAS. Our simulation results show that our approach can significantly improve network availability as well as network resource utilization with minimal cost.

Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) technology is now prevailing for its advantage of high spectrum efficiency. For the CO-OFDM-based networks, most of the existing studies are based on the assumption that all the sub-bands of a CO-OFDM optical channel are carried on the same route. For better network capacity utilization, the technique of Virtual Concatenation (VCAT) in the traditional Optical Transport Networks (OTN) can be applied to a CO-OFDM optical channel that is made up of multiple sub-bands. In this paper, we study the benefits of sub-band virtual concatenation for the CO-OFDM optical networks. We develop analytical models for a single node pair and a mesh network. Analytical results indicate that virtual concatenation can significantly improve the blocking performance compared to the case of without virtual concatenation, and moreover, such an improvement becomes more significant when the bandwidths of multiple VCAT sub-bands are allocated more evenly.

A potentially cost-effective approach for augmenting the transmission capacity in an optical transport network (OTN) consists of bundling several optical channels by means of an inverse-multiplexing strategy, e.g. virtual concatenation (VCAT). When VCAT is employed together with multipath routing, the differential delay between concatenated channels needs to be compensated via electrical buffering. To avoid installing large and costly high-speed buffers, this compensation can be dispersed throughout the intermediate path nodes. With this distributed scheme, each intermediate compensation operation requires an optical-electrical-optical (OEO) converter. Such converters, which are typically employed to allow electrical processing (e.g. signal regeneration, traffic switching/grooming, etc.), represent the largest contributor to the capital expenditures of an optical network. Hence, to save on OEO equipment and keep the network cost-effectiveness, we propose the novel approach of collocating the differential delay buffering and the regeneration on the same network element, enabling the implementation of distributed schemes with minimal link capacity levels, OEO count, and buffer size requirements. To effectively design an OTN network under these conditions, we also present a new multi-step optimization framework based on integer linear programming (ILP) modeling. To test our approach, emerging 100 Gb/s Ethernet services are established over two reference networks using virtually-concatenated 40 Gb/s channels. The correspondent results confirm that relevant OEO/regenerator count savings (ranging from 23% to 44%) can be attained with the collocated approach while the buffer sizes are maintained reasonably small. We also show that the end-to-end transmission latency is not affected by the adoption of this collocated strategy

The availability of novel communication services to telecom subscribers is creating a huge traffic growth over the underlying optical infrastructure. The expected high development costs of first generation 100 Gb/s equipment drives service providers to find alternative solutions for upgrading network capacity. Optical transport network (OTN) systems can use mature 10 Gb/s and 40 Gb/s equipment along with virtual concatenation (VCAT) to cost-effectively split and carry large data flows, such as the emerging 100 Gb/s Ethernet (100-GbE) signals. In addition, the combination of VCAT with multipath routing, in detriment of single-path forwarding, can improve load balancing, reducing the maximum capacity required per fiber link. However, the utilization of physical routes with distinct lengths introduces differential delay between the concatenated flows, which is typically compensated via buffering the flows in high-speed memories located at the destination node. These memories are very expensive, particularly when scaled to large sizes. Alternatively, distributed delay compensation architectures extend the compensation to the other path nodes, decreasing the individual size of memories. This paper proposes a multi-stage heuristic framework for optimizing the distributed compensation of inverse-multiplexed 100-GbE signals over OTN with the main objective of reducing the maximum buffer size per node while keeping capacity requirements to a minimum. The performance of the proposed framework, assuming execution time constraints, is compared to that of another heuristic method and an integer linear programming approach. The results obtained show that our framework reaches the optimal link load values, while outperforming both alternatives in reducing the buffer size.

The increasing traffic demand resulting from the widespread use of information and communication technologies is impelling network operators to upgrade the capacity of their existing transport network facilities. Recent advances in the scientific community have led to the first developments in serial 100 Gb/s technology that could provide an adequate solution for solving the capacity expansion problem. Nevertheless, given the complexity of 100 Gb/s transceiver equipment, the initial costs may refrain early adoption of the technology, leading carriers to invest in more cost-effective alternatives. Embedded in the optical transport network (OTN) functionality portfolio, traffic grooming and virtual concatenation can be exploited in order to optimally combine 40 Gb/s and 100 Gb/s equipment for supporting mixed line rate (MLR) demands. Hence, this work proposes an optimization framework for designing optical transport infrastructures with the objective of minimizing the network costs directly related to transceiver and regenerator equipment. The framework models the problem via an integer linear programming formulation that takes into account the relative cost, the maximum optical reach, and the capacity of each optical interface, as well as the optical channel limit per fiber link. As a result, the proposed method is able to select the equipment type and the routing path for each connection which correspond to the most cost-effective solution satisfying the 100G and 40G service demands.

Exploiting inverse-multiplexing in optical transport networks (OTN) leads to a cost-effective network design based on legacy 10 Gbps or 40 Gbps equipment to support next-generation services, e.g., 100 Gbps Ethernet. The inclusion of multipath routing permits to better balance the load and avoid problematic capacity bottlenecks. However, with diverse-path routing the inverse-multiplexed connections may arrive at the destination node with differential delay. Such effect needs to be mitigated by buffering the early-arriving connections until synchronization is achieved and the original signal can be adequately reconstructed. One of the main design issues on inverse-multiplexed networking consists in routing the demands in such way that the buffer sizes are minimized and the load balancing maximized. In this context, centralized or distributed solutions may be adopted. The latter option considers that buffering at intermediate path nodes results in smaller buffer dimensions per node. However, existing literature in this topic has systematically neglected the limited availability of expensive optical-to-electrical and electrical-to-optical converters necessary to buffer the transit signals. OTN architectures typically dispose of such elements when signal regeneration is performed. Hence, it makes sense to promote the buffering-regeneration collocation to limit network expenditures. For this reason, this work proposes a set of integer linear programming formulations for planning OTN networks using inverse-multiplexed traffic in a scenario where the distribution of the differential delay compensation takes into account the presence of regeneration equipment. As a result, we observe that our methodologies are capable of reaching a satisfactory compromise by minimizing the regenerator count while attaining small buffer sizes.

In this paper, we investigate the design and performance of multi-path routing in optical wavelength division multiplexed (WDM) networks, that support traffic grooming. A circuit-switched network is considered, where connection requests arriving to the network have to be allotted an end-to-end path carrying the requested bandwidth. Traffic grooming implies that the capacity of a wavelength on a fiber link (e.g. OC-48) will be shared among several lower capacity connections (e.g. OC-3). In order to increase the network performance in terms of improved blocking probability and also to support survivable operation, a connection is split into multiple smaller sub-streams and carried on multiple sub-paths from source to destination. This is based on the Virtual Concatenation (VCAT) mechanisms used in SONET/SDH networks. One important constraint is that the differential delay among the sub-paths should be limited (e.g. 25 ms, 45 ms, etc.). In this paper, we consider mechanisms for splitting a connection request while maintaining the differential delay constraint. In particular, we study two schemes: even splitting of connection bandwidth among the constituent sub-paths; and uneven splitting of connection bandwidth. The work also considers sub-paths that are not necessarily link-disjoint. The performance analysis shows that the uneven splitting mechanism can substantially improve performance in terms of blocking probability (and other metrics) compared to the even splitting mechanism.

Flexible optical channel data unit (ODUflex) is a new technique in the optical transport network (OTN) used to replace virtual concatenation (VCAT). For packet clients, it will be advantageous while ODUflex has the capability of hitless resizing like link capacity adjustment scheme (LCAS). A novel scheme is proposed in the paper for this purpose. The proposed scheme designs the new overhead (OH) and new protocol to achieve ODUflex hitless resizing. Moreover, it can be easily implemented in practical application.

Dynamic resource distribution of General Multi-protocol Label Switch (GMPLS) network provides an appropriate technology for Data-intensive transmission. This technique can support the application of optical virtual concatenation (OVC) which uses a group of wavelengths to transmit a large scale data in parallel. With RESV-TE protocol, optical channels of OVC can be easily established in GMPLS network. A novel contention resolution for RSVP-TE protocol extension was proposed to relieve the resource contention on the process of channel establishment. It can diminish the backward blocking probability by redistributing resource to the Label Switch Path (LSP) request which is closer to source.

In this paper, a novel wavelength assignment scheme called the WASDT (Wavelength Assignment Scheme for Data-intensive Transmission) is proposed in GMPLS based WDM Network. The WASDT is designed for the dataintensive transmission with the Optical Virtual Concatenation (OVC) technology. The novel scheme takes the data-intensive connection as a high priority connection and sends messages to all nodes before and after the data-intensive connections have reserved the resource. In our simulation, the results show that the WASDT can effectively reduce the probability of the wavelength collision with the data-intensive connections.

The use of inverse-multiplexing with diverse-path routing techniques in transport networks is expected to satisfy the traffic demands at the expense of lower capacity requirements. However, when the traffic between two nodes is routed over multiple paths, the different flows have different arrival times at the destination node. In order to compensate for this difference, known as differential delay, data has to be temporarily buffered in this node. Eventually, the size of the high-speed buffers involved may expand beyond acceptable figures, resulting in a cost increase that may even cancel the advantages attained with these techniques, in terms of network capacity. As an alternative to compensating for the delay only at the end-node, the use of distributed schemes can enable the reduction of the maximum buffer size per node, while preserving the capacity savings from diverse-path routing. Hence, this paper presents a novel model for optimizing the differential delay compensation across the network, when inverse-multiplexed diverse-path routing is employed. In order to quantify its gains, the framework is applied in the routing of 100 Gb/s Ethernet signals over high-speed optical transport networks (OTN) using virtually concatenated 40 Gb/s optical channel data units (ODUs). In the two reference network topologies evaluated, the buffer reduction obtained varied from 67% to more than 90%.

Stimulated by the remarkable packet traffic growth, the transport of 100 Gb/s Ethernet (100-GbE) services is to become a reality in a near future. To provide a smooth and cost-efficient network evolution, inverse-multiplexing techniques can be employed to carry the high-capacity data streams. In this context, the Virtual Concatenation (VCAT) protocol, available in Optical Transport Network (OTN) systems, represents the most adequate solution to decompose the 100-GbE signal into logical containers of 10 Gb/s and 40 Gb/s. With VCAT, each container can be independently routed throughout the network under several distribution paradigms, such as the classical single-path and multipath schemes, and the alternative degraded-service approach. In the network architecture considered, each routing path is required to be transmitted over an optical channel at the underlying WDM layer. Hence, in this work, we provide an optimization framework for solving the resource provisioning problem for 100-GbE at both OTN and WDM layers. Linear Programming based heuristics are proposed for routing the containers and dimension the capacity required at the OTN level. In particular, solutions for single-path, multipath, and degraded-service routing are described and evaluated in a reference network topology. The optimization procedures are also extended to resolve the wavelength assignment problem at the physical WDM layer. With this optimized multilayer architecture, the capacity gains resulting from the adoption of multipath strategies over single-path are properly evaluated and demonstrated. In addition, it is shown that the implications of using diverse-routing over the WDM layer have a minor impact in the capacity savings.

Next-generation SONET/SDH technologies namely, Generic Framing Procedure(GFP), Virtual Concatenation (VCAT) and Link Capacity Adjustment Scheme (LCAS) enable network operators to provide integrated data and voice services over their legacy SONET/SDH infrastructure to generate new revenue. VCAT is a inversing multiplexing technology used to break the GFP framed data payload such that it can be mapped into SDH frame. It groups arbitrary number of virtual containers to achieve the desired data rate. The number of virtual containers forms a group named virtual containers group (VCG). Individual member of VCG can traverse through any path to reach the destination and all VCs are combined at the destination as per the MFI (Multiframe Indicator) and Sequence Number written in the control packet of the SDH frame. As all the VCG members are routed independently, they do not reach the destination at the same time. These streams thus incur differential delay. Buffers are provided at the receiver to compensate differential delay and combine the streams for generating the data signal. More the differential delay more 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 allotted fixed and equal buffer size, specifying maximum differential delay it can compensate. This results in large amount of buffer requirement and wastage of buffer as all the streams do not suffer same differential delay. To overcome this limitation, this paper proposes a novel scheme of allotting buffers dynamically to all the streams. To achieve this, differential delay between the streams is computed by extracting the MFI and then as per the delay, each stream is allotted buffer from a common buffer pool. The common buffer pool size is network architecture dependent. This scheme drastically reduces the buffer requirement at the receiver. For functional verification of the concept hardware circuit is designed. The circuit accepts three VC-3 streams, calculates the differential delay, allots buffers as per the delay and finally outputs synchronized streams compensating the differential delay.

In this paper, we investigate problems related to optical wavelength division multiplexing (WDM) networks that use the virtual concatenation (VCAT) mechanism of synchronous optical network (SONET) technology. VCAT, an end-to-end mechanism, allows SONET based optical WDM networks to carry traffic in finer granularity via multiple paths or a single path with multiple wavelengths. The benefits include efficient utilization of link capacity and implicit partial link failure protection if link-disjoint paths are used. However, multi-path routing causes differential delay among constituent paths and requires high-speed buffer capacity at receiving nodes. In this paper, we propose four route selection methods to study the tradeoffs of VCAT's traffic splitting feature. The performance analysis is conducted using a discrete-event simulation model. Optical WDM grooming networks under dynamic traffic demand are considered. The simulation results quantify the costs and benefits of using the VCAT mechanism in SONET based optical WDM networks. The simulation results confirm the benefits of carrying traffic in finer granularity. MP and SPMW consistently outperform the traditional SPSW method by 50 percent and 90 percent respectively in blocking performance. In the event of a link failure, the implicit protection ratio increases as connections use more link-disjoint paths. The results also show that differential delay, which is the cost of VCAT's multi-path routing, increases as the number of link-disjoint paths increases.

Layer 1 Virtual Private Networks (L1VPN) is a type of VPN that utilizes optical networks to implement VPN technologies and has the potential to deliver optical services at reduced cost. Network providers and content providers will be able to deploy applications that contain materials such as high definition video, audio, and high quality graphics for which high bandwidth is required directly into the layer 1 network. Next generation SONET utilizes virtual concatenation (VCAT) to split a circuit into multiple smaller circuits and is expected to improve network utilization. However, there is a time delay limit that VCAT requires for it to split and combine the circuits without jeopardizing the content of the stream. We associate this time limit as the quality of service (QoS) the L1VPN network needs to meet in implementing VCAT in multi-domain environment. In this paper, QoS implementation is taken into consideration in order to achieve optimal network utilization when network performance is measured. The results show that VCAT implementation in multidomain environment with QoS consideration improve the network performance.

Optical virtual concatenation (OVC) is a promising technique for data-intensive, latency-sensitive and large-scale applications. In this paper, we present an OVC-based network architecture and key technologies for achieving virtual bulk-data transmission with a group of wavelengths. To offset the relative delay-difference among the grouped optical channels (wavelengths), a dynamic detection and compensation mechanism based on 40-Gb/s/ch OTN physical-layer multiframe architecture is proposed and discussed in detail. Using recently developed OVC hardware, 40-Gb/s/ch parallel transmission is demonstrated for the first time, and system performance is evaluated.

Flexible bandwidth modification in packet switched networks is very important in the support of a BoD service. Virtual concatenation (VCAT) and link capacity adjustment scheme (LCAS) technology is widely used in time division multiplexing (TDM) networks to provide the dynamic bandwidth modification for circuit connection. This paper discusses how to deploy the VCAT/LCAS technology with the help of general multiprotocol label switching (GMPLS) signalling to provide the dynamic bandwidth modification in the packet switched networks for a BoD service. Especially the GMPLS CALL which is initiated from a customer edge (CE) node is introduced to trigger the negotiation process of the configuration parameters of both provider's edge (PE) nodes, and provides the Ethernet service or other packet service.

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.

Digital virtual concatenation allows service transmission of high-bandwidth services over existing WDM infrastructures. Results are presented showing 40 Gb/s service transmission over a 2000 km link with 65 ps peak PMD, and over a 8,477 km trans-oceanic network.

Deskew function using OTU3 multiframe identification is demonstrated. Master-slave type deskew method with simple configuration is proposed to realign skewed parallel data. Skew is successfully compensated.

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 by ITU 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 VCpsilas to/from the VCG. VCAT combines homogeneous virtual containers(VCpsilas) 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 VCpsilas 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. In this paper transmitter and receiver circuits are designed to transmit and receive 100Mbps Ethernet data using CVC, where two types of VCpsilas namely VC-3 and VC-12 are used for data transmission. The functionality of the circuit is tested using Modelsim Simulator using VHDL. Total Transmission delay is calculated as 125us and proved that, there is no complexity added at the receiver side due to this delay. The receiver is designed for 32ms differential delay compensation which can be increased up to maximum 256ms by increasing the buffer size at the receiver.

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 SONET/SDH, and supporting virtual concatenation (VCAT). With VCAT, a connection request can be split, diversely routed, and inversely multiplexed on to multiple paths, a feature that has many advantages over conventional single-path provisioning, such as improved reliability, load balancing, etc. However, these diversely routed traffic components are subject to the differential delay constraints (DDC), which could be limited by the destination node's delay-compensation capability, network operations, administration, maintenance, and provisioning (OAM&P), or connection quality-of-service (QoS). We introduce a new 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 may have a fraction of the bandwidth of the connection, and (m) in this notation denotes "multipath'. We present the flexibility and benefits of multipath provisioning and develop an analytical model to analyze the connection availability under M : N (m) provisioning schemes. We propose two types of bandwidth migration methods, which can be implemented by link- capacity adjustment scheme (LCAS) protocol of next-generation SONET/SDH, to optimize resource usage. We develop two adaptive heuristic algorithms to provision a connection subject to DDC while satisfying its service-level agreement (SLA). We show that, for end-to-end connection-availability-guaranteed service, multi- path provisioning can achieve better network performance than traditional single-path provisioning. With bandwidth migration, we can further improve the performance.

We study the problem of reliably provisioning traffic in high-capacity backbone mesh networks supporting virtual concatenation (VCAT). VCAT enables a connection to be inversely multiplexed on to multiple paths, a feature that has many advantages over conventional single-path provisioning. We propose improved routing algorithms which use minimum- cost flow to find efficient collections of paths that satisfy the traffic requests. We first investigate the performance of our scheme under a uniform setting with symmetric traffic distribution and equal link capacities. We then apply our algorithm in a more realistic setting with asymmetric traffic and differing link capacities. Our algorithm is effective in both the uniform and non-uniform settings, and is much more effective than previously proposed schemes. Our study in the non-uniform setting is significant as it gives insight into the performance of our algorithm under more realistic scenarios.

We propose a model for differential-delay compensation and two approaches for provisioning survivable service on Data-over-SONET/SDH networks with virtual concatenation. Our approaches optimize the resource subject to the constraint of differential-delay compensation.

In this paper we propose a unified model for dynamic bandwidth adaptation in future transport networks. It acts as an umbrella for both next generation SONET/SDH (NG-SONET/SDH) and even more general, networks with a GMPLS control plane. We adapt bandwidth in discrete steps by exploiting features of virtual concatenation and bundled links, respectively. Applying our model, we demonstrate its advantage in providing improved service quality in comparison to a scheduled provisioning scheme. We evaluate the adaptation granularity to provide a required quality of service for typical IP network traffic behavior in the access network. Furthermore we quantify in depth the impact of increasing access bandwidth at the network edge on signaling load in a transport network.

Lambda-on-demand, optical virtual concatenation, and a novel user-network interface-based restoration are proposed to manage parallel lambdas toward achieving assured quality-of-service terabit networks. A successful demonstration of these technologies is described when employing bandwidth-intensive visualizing applications.

As a very successful technology, Ethernet has now dominated the data transmission in LAN. However, some inborn defects, like the lack of guaranteed quality of services (QoS), restricts the maximum scope of Ethernet. Utilizing SDH/SONET, a technology for transmitting data over long distance, to overcome such limit is one promising solution. This solution termed Ethernet over SDH/SONET (EOS) combines the simplicity and affordability of Ethernet with the reliability and scalability of SDH/SONET. In this paper, the design and implementation of an EOS chip, which maps Ethernet frames into SONET/SDH payloads using both standard concatenation and virtual concatenation, is put forward. Several problems encountered during the implementation and their solutions are also discussed. The validity of the design has been proved by thorough functional simulation and FPGA verification

Ethernet over SONET (EoS) is a popular approach for interconnecting geographically distant Ethernet segments using a SONET transport infrastructure. It typically uses virtual concatenation (VC) for dynamic bandwidth management. The aggregate SONET bandwidth that supports a given EoS system is obtained by "concatenating" a number of virtual channels (VCs), which together form a virtually concatenated group (VCG). This aggregate bandwidth can be increased on demand by adding one or more VCs to the existing VCG. The new VC must be selected such that its end-to-end delay is within a certain range that reflects the delays of all existing VCs in the VCG and the available memory buffer of the EoS system. Algorithmically, the problem of selecting such a VC becomes that of finding a path in a graph network that is bounded by an upper and lower bounds. In this paper, we first prove that the TSCP problem is NP-complete. We then propose a new solution for it based on the "backward-forward" search approach. We show that this solution is much more efficient than the previously proposed MLW-KSP algorithm. We then consider the TSCP problem under inaccurate link information, in which the delay and available bandwidth for each link are taken as random variables. The problem is now formulated as that of finding the most probable path that satisfies the upper and lower delay constraints. We consider two cases. In the first case, we assume that the link delays are random but the link bandwidths are exact. We then consider the more general case where both the link delays and bandwidths are random. Heuristic solutions are presented for both cases. Simulations are conducted to evaluate the performance of the proposed algorithms and to demonstrate the advantages of the probabilistic path selection approach over the classic trigger-based approach.

This white paper explores enhancements to existing metro architectures that can serve as a catalyst for a broader modernization and optimization of incumbent carriers' service infrastructures. Included in this white paper are strategies for the optimal use of existing capital resources, and pragmatic migration steps to ease and facilitate network evolution. With the gradual adoption of new and more intelligent networking technologies, incumbent carriers can accelerate migration toward the more dynamic and data-centric service architectures that will fuel future network growth and increase competitive differentiation. These service architectures must support the cost-effective deployment of new service offerings such as gigabit Ethernet over SDH. Key technology enablers for these agile network architectures, including optical routing and signaling, virtual concatenation (VC: G.707), link capacity adjustment scheme (LCAS: G.7042) and generic framing procedure (GFP: G.7041), are also discussed.

Advances in next-generation SONET/SDH technologies have enabled many new service provisioning paradigms. A key addition is the inverse multiplexing feature which enables the splitting of connection demands across SONET/SDH domains. This paper presents a novel tiered survivability scheme that leverages this feature to support multiple levels of service survivability and achieve higher load carrying capability and service resiliency. Detailed simulation performance analysis results are also presented along with conclusions and directions for future work.

Advances in next-generation SONET/SDH along with GMPLS control have enabled many new service provisioning capabilities. A key paradigm is the new Layer 1 virtual private network (L1 VPN) framework, which allows clients to directly provision their own services without deploying expensive infrastructures. This paper proposes a novel L1 VPN resource management scheme for virtual concatenation-enabled nextgeneration SONET/SDH networks. The scheme is fully compatible with both centralized and distributed control frameworks and allows for dynamic resource sharing. Detailed performance analysis results are also presented.

Service providers are starting to offer next-generation E-Line (point-to-point) and E-LAN (multipoint-to-multipoint) Ethernet services over their existing SONET/SDH networks. While Ethernet typically is "best-effort", these emerging services are expected to be "carrier-class" with strict bandwidth guarantees. Consequently, spanning tree creation, critical to any Ethernet network is fundamentally changed; each tree hop now needs to have sufficient capacity to meet the requisite bandwidth demands. In this paper, we introduce the bandwidth-endowed spanning tree (BEST) problem. Unlike the polynomial complexity of standard spanning tree algorithms, BEST is NP-complete, raising questions about the scalability of these services. We propose offline and online algorithms and study their performance using extensive simulations. We show that leveraging the Virtual Concatenation protocol (ITU-T G.707) is key to practical algorithms that are both effective and efficient. Inspite of the theoretical hardness, the online algorithms we propose are a good match to "optimal", offline integer programming benchmarks, demonstrating the viability of next-generation Ethernet services.

We investigate the problem of reliable multi-path provisioning of traffic in high-capacity optical backbone mesh networks, e.g., next-generation SONET/SDH networks supporting virtual concatenation (VCAT). VCAT enables a connection to be inversely multiplexed on to multiple paths. As a result, a connection can be provisioned more flexibly, and such a multi-path provisioning approach may lead to significantly improved performance over the conventional single-path provisioning approach. This multi-path provisioning approach may also be applicable to other mesh networks such as those employing optical wavelength-division multiplexing (WDM) and multi-protocol label switching (MPLS), where the bandwidth of a connection to be provisioned exceeds the available capacity on any path based on current network state. We propose effective multi-path bandwidth as the metric to provision a connection on to multiple paths while satisfying its reliability requirements (measured in terms of availability). We show that effective multi-path bandwidth provides more flexibility and lower blocking probability without the cost and complexity associated with traditional protection schemes developed for optical WDM and MPLS networks.

We consider the problem of minimizing the differential delay in a virtually concatenated Ethernet over SONET (EoS) system by suitable path selection. The link capacity adjustment scheme (LCAS) enables network service providers to dynamically add STS-n channels to or drop them from a virtually concatenated group (VCG). A new STS-n channel can be added to the VCG provided that the differential delay between the new STS-n channel and the existing STS-n channels in the VCG is within a certain bound that reflects the available memory buffer supported by the EoS system. We model the problem of finding such a STS-n channel as a constrained path selection problem where the cost of the required (feasible) path is constrained not only by an upper bound but also by a lower bound. We propose two algorithms to find such a path. Algorithm I uses the well-known k-shortest-path algorithm. Algorithm II is based on a modified link metric that linearly combines the original link weight (the link delay) and the inverse of that weight. The theoretical properties of such a metric are studied and used to develop a highly efficient heuristic for path selection. Simulations are conducted to evaluate the performance of both algorithms in terms of the miss rate and the execution time (average computational complexity)

This paper proposes an optical local area network that can transmit terabit-class bulk-data with low latency in a dynamic manner. A group of wavelengths is assigned to bulk-data transmission according to the latency requirement, and parallel WDM signals are transmitted with bit-phase synchronization mechanism after fast provisioning.

We propose effective multi-path bandwidth to provision a connection onto multiple paths while satisfying its availability requirement in next-generation SONET/SDH networks supporting virtual concatenation. Our proposal achieves lower blocking compared to the conventional single-path approach.

We introduce a novel scheme that flexibly distributes the differential delays in virtual concatenation (VCAT) paths in SONET/SDH networks. We show that this increases the utilization of the network in carrying dynamic traffic and reduces the total buffer requirements.

This paper addresses the issue of reliable transport of emerging data services in Ethernet over SONET (EoS) networks that require protection guarantees beyond standard best effort delivery. We argue that the current consensus of using Ethernet spanning tree and a SONET 1+1 protection, while providing reliability, is an inefficient use of resources. Instead, we claim that EoS opens novel opportunities for protection heretofore unavailable in other environments. In particular, the deployment of virtual concatenation and LCAS protocols enables "route splitting", creating a fundamentally new routing paradigm for circuit-switched environments. We propose a scheme called PESO, appropriate for EoS, with innovative routing, failure notification and switching components. More importantly, it is competitive with SONET protection without its 100% bandwidth overhead. We also suggest a enhancement in LCAS that can further improve PESO'S switching time. PESO leverages the underlying protocols, making it extremely attractive to implement and use in practice.