Hose-based VPNs offer greater bandwidth flexibility, as they allow traffic to and from a hose endpoint to be arbitrarily distributed across other endpoints. Existing studies on hose-based VPNs have primarily focused on VPN provisioning algorithms, while optimal capacity planning for hose-based VPN networks remains largely unexplored. Given budget constraints and forecasts of future bandwidth demands at VPN endpoints, the capacity planning problem requires the joint optimization of routing decisions and link capacity allocation. Although the problem can be formulated as a nonlinear programming model, its nonconvex nature makes direct solution computationally challenging. To address this issue, we reformulate the problem as a sequence of linear programming problems and develop a solution framework based on a water-filling algorithm. For any defined budget and relative tolerance, the proposed algorithm yields a near-optimal solution where the network expansion cost stays within the allowed margin. Numerical results demonstrate that the proposed approach efficiently solves the hose-based VPN capacity planning problem within practical computation time.

In this paper, we present the design of an in-band control plane system for P4 networks. The proposed in-band control plane performs automatic switch bootstrapping, network status monitoring, topology discovery and fast failover. The authentication and registration of newly connected switches are managed by the controller without manual intervention. The system can recover from any single link or single node failure in a short period of time. The recovery control paths for each single link and single node failure are prepared in advance. We propose an algorithm that takes recovery time into account for preplanning the recovery paths. In addition to handling any single failure, the proposed control plane is survivable even if there are multiple failures in the network. We implement an emulated network to evaluate the proposed control plane system. The experimental results show that the system successfully provides all the target functions.

Due to its wide range of applications, distributed beamforming (DB) has become one of the most popular study subjects in recent years. The critical problem of detecting distributed beamforming in achieving the carrier phase alignment at the receiver end. This paper presents an iterative algorithm that uses trial and error (TE) learning to attain phase alignment between the sending nodes that only requires 1-bit feedback from the receiver. This algorithm fits our case best, as the convergence speed is gained by obtaining the feedback information more competently than current solutions and improving the received signal strength (RSS) on the receiving end.

Network virtualization is a technology that enables multiple tenants to share a common physical network. A virtual network (VN) needs to have dedicated bandwidth and a priority differentiation capability to provide quality of service (QoS) for its serving flows. In this paper, we propose a traffic meter based on a multicolor marker (MCM) to fulfill both inter-VN and intra-VN QoS requirements. In our system, a VN's guaranteed bandwidth is dedicated to the VN, and the bandwidth is not influenced by the traffic generated from other VNs in the same physical network. In addition, the high-priority traffic of a VN can always achieve its needed bandwidth unless the total amount of high-priority traffic exceeds the VN's guaranteed bandwidth. This feature enables a network to provide independent QoS differentiation for each VN. Our MCM meters can be applied in two operation modes. In the remaining bandwidth nonsharing (RBNS) mode, the guaranteed bandwidth is treated as an upper bound for each VN, even if the network has unused capacity remaining. However, in the remaining bandwidth sharing (RBS) mode, the unused network capacity is shared among VNs so that a VN can use more than its guaranteed bandwidth. To validate our design, we implemented our MCM meter in P4 programmable switches. The experimental results on a testbed reveal that our design can accurately achieve bandwidth isolation and QoS differentiation for network virtualization in P4-based software-defined networking (SDN).

In this paper, we address the OpenFlow virtual network (VN) design problem. Unlike most of the existing approaches that directly performing bandwidth slicing on the physical networks, we take traffic uncertainly and statistical multiplexing into consideration. In our system, a user can specify the desired VN topology and the capacity for each virtual link (VL). The bandwidth descriptor for a VL consists of a pair of values for guaranteed bandwidth and upper limit bandwidth. Each user is guaranteed to own the guaranteed bandwidth at any moment without interferences from the bandwidth usages of the other users. Moreover, a user can successfully uses bandwidth up to its upper limit in short time with packet loss probability no more than a pre-defined value. This feature enables OpenFlow networks to provide QoS for network services with bursty traffic. We model this problem as a robust optimization program to jointly determine admission control for VN and routing for VL. We further present an approach for implementing the proposed design using commercial available OpenFlow switches. The performance of the proposed approach is evaluated through simulations and experiments. The results indicate that the proposed design can successfully tolerate traffic uncertainly in OpenFlow networks. Since the proposed approach can use bandwidth with high efficiency, it can admit more VNs than the one without taking statistical multiplexing into consideration.

Survivability and energy efficiency are in conflict with each other on network resources usage in IP networks. The basic principle to achieve high survivability is via provisioning backup paths over spare capacity. However, in designing an energy efficient network, the target is the opposite. In order to minimize energy consumption, routing and traffic engineering techniques are applied to aggregate flows so as to minimize network resource usage. The unused network devices are turned off for power saving. How to reduce power consumption while maintaining high survivability is quite a challenging task. In this paper, we first evaluate the survivability for an IP network using various IP fast reroute (IPFRR) schemes. The results indicate that NotVia IPFRR is one of the most suitable schemes for designing a survivable green IP network. Therefore, in this work, we focus on studying the active topology design and link weight assignment problem for energy efficient IP networks with NotVia IPFRR. We have formulated the problem as an integer linear programming problem and propose a Lagrangean relaxation-based approach to obtain a near optimal solution. The numerical results indicate that the proposed method is not only energy efficient but also has a 100% network survivability capability against any single node failure.

In this work, we address the Routing and Time slot Assignment (R&TA) problem in multi-hop PLC access networks. In our system, time is divided into fixed sized TDM cycles. Each cycle comprises a semi-dynamic bandwidth allocation period (SBAP) and a dynamic bandwidth allocation period (DBAP). The SBAP is used to provide each PLC CPE fixed bandwidth for providing bandwidth guaranteed services. It's a persistent bandwidth provisioning. The bandwidth of DBAP is shared by all of the nodes. This bandwidth is dynamically allocated to each node by a per cycle basis. We take spatial reuse and rate adaption into account. Our design also takes channel quality into consideration in determining the optimal multi-hop routing. We formulate the R&TA problem for the SBAP as an ILP model in which the objective function is to minimize the total bandwidth usage for supporting all bandwidth sensitive services in the network. Since this problem is an NP-hard problem, in order to reduce the computation time, we have developed a Lagrangean relaxation (LR) based algorithm to resolve the problem. For the DBAP part, we propose a token-based scheduling algorithm. Numerical results reveal that the proposed LR algorithm can obtain a near optimal solution in short computation time. For the DBAP part, the proposed token-based scheduling algorithm can provide high throughput especially it can provide excellent fairness for bandwidth sharing among all nodes.

IETF has defined IP fast reroute (IPFRR) schemes to enable IP networks with fast failover capability. Fundamentally, failure recovery is achieved by provisioning backup paths on standby network resources to provide traffic rerouting for bypassing a failed device. Unlike survivable network designs, the principle used in designing a green network is the opposite. To minimize energy consumption, traffic engineering techniques are applied to aggregate traffic flows on limited network resources. Thus, the unused network devices can be turned off or put on sleep mode to save power. How to reduce power consumption while maintaining high survivability is quite challenging. In this paper, we first evaluate the required number of active links for an IP network operating at its maximum survivability ratio. The results indicate that power saving is quite limited using standard IPFRR. We identify that this result comes from the inflexibility of IP routing using only one set of link metrics. To resolve this issue, we introduced RFC 4915 MTR into the design of a novel green IP network. The method we proposed uses only two routing configurations. Configuration 1 is used for routing traffic in the normal state and Configuration 2 is used to compensate Configuration 1 to enhance network survivability. We have formulated the problem as an integer linear programming problem and propose an optimization-based approach to obtain a solution. The numerical results indicate that the proposed method is not only energy efficient but also can provide 100% network survivability against any single link failure.

Network coding has been proven with the capability to improve the network bandwidth efficiency for multicast communications. Streaming based IPTV services provided by network operators match the paradigm of using network coding. However, the major research works in the literature focus on the selection of network codes under given routing paths. Few research work jointly considers routing and network coding together to obtain survivable multicast routing and minimum bandwidth provision. In this paper, we investigate this new research topic and propose mathematical models that can be used to obtain an optimal routing for survivable multicast communications against any single link/node failure. To clarify the gain from applying network coding, we also made performance comparisons between the network-coding-based protection schemes and those without using network coding. We observe that the network coding scheme holds the best performance for all cases we had simulated. The trade-offs between the network protection schemes with and without using network coding are also identified in this paper.

In order to mitigate the greenhouse effects and reduce environmental pollution, energy saving has become an important issue in designing the next generation Internet. Shutting down the network devices carrying light loads and redirecting their traffic flows to other routes is a way to decrease energy consumption. An energy efficient network has to dynamically determine the optimal active links to adapt itself to network traffic changes. However, in current IP networks, shutting down and/or turning on links would trigger link state routing protocols to reconverge to a new topology. Since the convergence time would take tens of seconds, routing table inconsistencies among routers would result in network disconnection and even worse, generating traffic loops during the convergence interval. In this paper, we propose a comprehensive solution to resolve such problems. The contribution of the paper is presented in three parts. First, we propose a distributed energy-aware link management algorithm to dynamically determine the link states for a router. Routers performing the algorithm obtain a pair of high and low thresholds in order to compare flow amount to determine the link states. Those thresholds are automatically adapted to network traffic so that network load and power saving are balanced. The second contribution of the paper comes from the flows being immediately redirected to their new next hop nodes when a link's state is changed. We borrow link metric from link state routing protocols to determine potential for each node pair. The potential is used to determine loop free next hop routing nodes. This technique enables us to redirect flows on the fly without suffering from long convergence of link state routing protocols. The third contribution of the work comes from our proposal of an optimization model to determine a link metric and a most power saving network topology. The obtained link metric is used in our distributed link management algorithm to determine node potential. We have evaluated the performance of the proposed algorithm through extensive simulations. The numerical results reveal that the proposed distributed link management algorithm can effectively save network energy in three benchmark networks.

As a failure occurs, the affected traffic is quickly rerouted to backup paths for a network performing a fast protection scheme. Such a prompt reaction is aimed to reduce the damages caused by a failure. However, in some cases, the rerouted traffic may cause congestion along the backup paths which would lead to more packet losses than purely discarded affected flows. In this paper, we propose a load-balanced fast local protection scheme called Non-Weighted Interface Specific Routing (NISR) for determining the working and backup routing tables of IP routers. We jointly consider protection switching time, network survivability, and traffic load distribution together in the proposed scheme. In NISR, once a failure occurs, only the nodes adjacent to a failure divert affected traffic to backup paths. This local reaction process guarantees fast protection switching and reduces failure recovery time. Unlike the conventional IP routing, our approach relaxes the shortest path routing in computing working and backup routing tables. Most importantly, each interface in a router has its own routing tables. Combining the interface specific routing with the shortest path relaxation provides greater routing flexibility to enhance network survivability and load balancing. We formulate this as a mixed integer programming problem in which the traffic load on the most congested link is to be minimized. Since this problem is intractable by its NP-hard nature, we further decompose it into several sub-problems which are solved optimally and their solutions combined to provide a solution to the original problem. We perform experiments on some benchmark networks and compare the proposed scheme to several well-known schemes (including LFA, ECMP, OSPF, and NLB) on survivability ratio, link load distribution, and average path length for both normal and failure states. Through numerical results, we delineate that the proposed scheme achieves a sub-optimal solution, which is better for its high survivability and load balancing at the expense of slightly raising the average path hop count.

In order to reduce the greenhouse effects and environmental pollution, energy saving has become important in designing next the generation networks. Shutting down the network devices carrying light loads and redirecting the traffic flows to other routes is a way to decrease network energy consumption. Since traffic demands among node pairs vary in different time periods, the energy efficient network design is to determine the optimal network topologies for them. However, in current IP network, flows are governed by shortest path routing, thus purely determining the network topology is not enough. A set of link weight metric has to be derived in company with the network topology such that the flows on the active links can meet the physical capacity constraints. Although applying adaptive network topology could save energy consumption, however, the lack of stringent synchronization among routers would cause undesired loops during the transient period of topology changes. Removing routing images inconsistent among routers to prevent loops is a critical issue in energy efficient network and this issue is still not yet considered in the green network design. In this paper, we propose a comprehensive approach that determines network topology and link metric for each time period. Traffic engineering is considered in our design such that flows going on the energy aware network are within a predetermined percentage of the link capacity such that no congestion occurs in a statistical manner. To avoid accurate synchronization among routers, we propose using RFC 4915 Multi-Topology Routing, to resolve the transient loop problem. By controlling the update sequence in MTR, there is no transient loop during the period of topology changes. We formulate an integer linear programming to jointly determine this multi-topology and link weight assignment problem. Due to its NP-hard property, we propose an efficient algorithm, termed Lagrangean Relaxation and Harmonic Series (LR&HS) heuristic. Numerical results demonstrate that the proposed LR&HS approach outperforms the other approaches on four benchmark networks and provides up to 35%-50% energy saving in our experimental cases.

As a failure occurs, the affected traffic is quickly switched to backup paths for a network performing a fast IP rerouting. However, the rerouted traffic may cause congestion along the backup paths that would result in more packet losses than purely discarded the affected flows. In this paper, we take the concept of interface specific forwarding (ISF) to provide more flexibility in determining load balanced traffic rerouting. This problem is formulated as an Integer Linear Programming (ILP) problem, in which network survivability and traffic load distribution are jointly considered and the traffic load on the most congested link is to be minimized. Since this is an NP-hard problem, we further decompose it into several sub-problems which are solved optimally and their solutions are combined to provide an approximate solution to the ILP problem. The numerical results delineate that the proposed scheme achieves high survivability, load balancing and lesser bandwidth consumption at the expense of slightly raising the average path hop count.

In this paper, we present the access and control design of a high-performance optical packet-switched WDM metro ring network (HOPSMAN). HOPSMAN has been designed for networks and nodes to be unconstrained by the number of wavelengths. It includes a handful of nodes that are equipped with fast optical slot erasers making bandwidth reusable and achieving greater bandwidth efficiency. In essence, HOPSMAN incorporates a versatile medium access control (MAC) scheme, which embodies efficient and fair bandwidth allocation in accordance with a quota being exerted probabilistically. The quota is analytically derived with the number of slot-eraser-nodes taken into account. The scheme also employs a new notion of credit to regulate flexible access of remaining bandwidth that is suitable for the metro environment with bursty traffic. With the MAC scheme, HOPSMAN is shown to achieve exceptional throughput, delay, and fairness performance under a wide range of traffic settings via simulation results.

In this paper, we investigate delay constrained multicast routing for supporting QoS guaranteed point to multi-point communications in IP over WDM networks. To achieve high bandwidth utilization, packets coming from different multicast connections are groomed and carried together over a single wavelength. Lightpath scheme is adopted in this paper that unicast lightpath is provisioned to support the multicast traffic in the IP network. Hop count constraint is introduced to deal with and queueing delay from traffic grooming. The challenge of the problem comes not only from considering delay constrained multicast routing but also WDM lightpath routing and wavelength assignment (RWA). We formulated the problem as an integer optimization problem in which the revenue from admitting multicast groups is to be maximized. The problem constraints include hop count constraint for end-to-end QoS requirements, tree constraint for multicast routing, IP link capacity and WDM fiber link capacity constraints, and wavelength continuity constraint. We apply Lagrangean relaxation technique to perform constraint relaxation and propose optimization-based heuristics (LGR) to tackle this problem. We draw performance comparisons between the LGR and the minimum hop (MH) heuristics. Numerical results demonstrate that LGR outperforms MH algorithm under all experimental cases.

Multigranular optical WDM network aims to reduce network cost by grouping multiple wavelengths and then switching those wavelengths together at waveband or fiber levels. To configure such multi-granular network, we have two choices-homogeneous network and heterogeneous network. The former applies only a single type of optical cross connect (OXC) while the latter allows different types of OXCs. Due to the demands varies and change asymmetrically geographically, networks with heterogeneous OXC nodes is especially suitable for placing best switching types at different location. In this paper, we aim at the design of an algorithm to solve the network planning problem in optical network with heterogeneous multi- granularity OXCs. The planning program determines not only the switching granularity for each node but also determine the routing and wavelength assignments to satisfy the given demands. The contributions of the paper are four folded. First, we propose a graph model to represent the OXC node. The transformed graph simplifies the representation of node structure and helps to model the problem. Secondly, we propose a mathematical formulation to model the network planning problem as an ILP problem. Thirdly, a Lagrangean relaxation based heuristic algorithm is proposed to obtain a near optimal solution. Fourthly, we studied the impact of waveband size on network cost. This work reveals that the waveband size plays a crucial factor. The proposed algorithms can determine the optimal number of waveband size.

Optical Packet Switching (OPS) has been envisioned as a prominent future optical networking technology for datacentric IP over Wavelength Division Multiplexing (WDM) networks, or optical Internet. Such OPS technology however raises significant transport and Quality of Service (QoS) challenges due to technological limitations. To circumvent OPS limitations, we have proposed a new Optical Coarse Packet Switching (OCPS) paradigm, which uses in-band-controlled per-burst switching and advocates traffic control enforcement to achieve high packet-loss performance and differentiated services. Based on OCPS, we have constructed an experimental IP-over-WDM network, referred to as OPSINET. OPSINET consists of two major types of nodes-edge routers, and Optical Label Switched Routers (OLSRs), and is facilitated with an out-of-band Generalized Multi-protocol Label Switching (GMPLS) control network. In this paper, we first introduce the OCPS paradigm. We then present the architecture of OPSINET, describe the in-band header/payload modulation technique, and detail the operations of the edge routers, OLSRs, and GMPLS control.

In this paper, we propose an efficient approximation approach, called Lagrangean relaxation with heuristics (LRH), aimed to resolve routing and wavelength assignment (RWA) for multi-granularity WDM networks facilitating fiber, waveband, and lambda switching capabilities. The task is first formulated as a combinatorial optimization problem in which the bottleneck link utilization is to be minimized. The LRH approach performs constraint relaxation and derives a lower-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LRH approach employs a new heuristic algorithm to arrive at a near-optimal upper-bound solution. With lower and upper bounds, we delineate the performance of LRH with respect to accuracy and convergence speed under different parameter settings. We further draw comparisons between LRH and a typical linear programming (LP) approach via experiments over the widely-used NSFNET and three randomly generated networks. Numerical results demonstrate that LRH outperforms the LP approach in both accuracy and computational time complexity particularly for larger sized networks.

Optical wavelength-division multiplexed (WDM) networks often include optical cross-connects with multigranularity switching capability, such as switching on a single lambda, a waveband, or an entire fiber basis. In addition, it has been shown that routing and wavelength assignment (RWA) in an arbitrary mesh WDM network is an NP-complete problem. In this paper, we propose an efficient approximation approach, called Lagrangean relaxation with heuristics (LRH), aimed to resolve RWA in multigranularity WDM networks particularly with lambda and fiber switches. The task is first formulated as a combinatorial optimization problem in which the bottleneck link utilization is to be minimized. The LRH approach performs constraint relaxation and derives a lower-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LRH approach employs a new heuristic algorithm to arrive at a near-optimal upper-bound solution. With lower and upper bounds, we conduct a performance study on LRH with respect to accuracy and convergence speed under different parameter settings. We further draw comparisons between LRH and an existing practical approach via experiments over randomly generated and several well-known large sized networks. Numerical results demonstrate that LRH outperforms the existing approach in both accuracy and computational time complexity, particularly for larger sized networks.

For WDM networks with multi-granularity switching, optical tunnel allocation (OTA) deals with the real-time establishment of optical tunnels between optical nodes through various optical multi-granularity switching devices. OTA is in principle a dynamic routing and wavelength assignment (RWA) problem with multi-granularity switching devices taken into account. In this paper, we propose a novel approximation approach, called Lagrangean relaxation with heuristics (LRH), aimed to resolve RWA considering both fiber and lambda switches. Such RWA is first formulated as a combinatorial optimization problem in which the bottleneck link utilization is to be minimized. To tackle the problem, the LRH approach performs constraint relaxation and derives a lower-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LRH approach employs a new heuristic algorithm to arrive at a near-optimal upper-bound solution. Through numerical results and comparisons, we delineate that the LRH approach achieves a near-optimal solution, which is profoundly tight to its lower bound, at the expense of low computational time complexity.

In this paper, we study several backup path building schemes for a multicast tree in self-healing ATM networks. Point-to-point link and path restoration schemes are extended and modified for point-to-multipoint connection in ATM networks. Three spare capacity sharing strategies are discussed. Among these strategies, one is directly from point-to-point restoration schemes and the other two take advantage of the tree structure of point-to-multicast connection to further increase the utilization of spare capacity. By applying different sharing strategies, we develop several link based and path based restoration schemes. These restoration schemes are formulated as combinatorial optimization problems in which the objective functions are the minimization of bandwidth usage and the constraints are required to satisfy the survivability and physical limitations. The backup bandwidth usage, the average restoration time (ART) and the average processing nodes (APN) are the three performance metrics considered in the paper. By evaluating these performance metrics, we conclude that the new proposed link based restoration scheme, Link Scheme 2, which takes advantage of the tree structure of a multicast connection has the best performance.