Wanjun Huang

Finding a simple path with multiple must-include nodes

This paper presents an algorithm to find a simple path in the given network with multiple must-include nodes in the path. The problem of finding a path with must-include node(s) can be easily found in some special cases. However, in general, including multiple nodes in the simple path has been shown to be NP-Complete. This problem may arise in network areas such as forcing the route to go through particular nodes, which have wavelength converter (optical), have monitoring provision (telecom), have gateway functions (in OSPF) or are base stations (in MANET). In this paper, a heuristic algorithm is described that follows divide and conquer approach, by dividing the problem in two subproblems. It is shown that the algorithm does not grow exponentially in this application and initial re-ordering of the given sequence of must-include nodes can improve the result. The experimental results demonstrate that the algorithm successfully computes near optimal path in reasonable time.

Cooperative Data Center Selection for Optimal Service Performance: An ILP Formulation

Cross layer optimization is well-known to offer certain cost and performance advantages when designing and operating data networks [1]. It is reasonable to anticipate similar advantages when applying such optimizations across the network layer and the application layer too. In this paper, the authors define one optimization problem whereby the service-to-hosting data center mapping is performed taking into account the available resources in both the data center (CPU cycles) and network (bandwidth) subsystems. The objective function of the optimization problem accounts for the amount of both CPU cycles and bandwidth, which are assigned to each requested service, with the assumption that the users Quality of Experience (QoE) strictly depends only on these two factors. The problem is formulated using ILP and its numerical results are discussed to gain insights into the potential QoE gains that might result from using this cross layer (cooperative) resource assignment technique.

Routing and wavelength assignment computed jointly for a given set of multicast trees reduces the total wavelength conversion

A significant drawback when establishing multicast optical trees (light-tree) using lambda channels in wavelength division multiplexing (WDM) network is the potentially large amount of wavelength converters (WCs), which are required when the wavelength continuity constraint cannot be satisfied across each light-tree. Prior works address this challenge by solving the routing and wavelength assignment (RWA) problem for each individual light-tree sequentially, to locally minimize the number of WCs required by each light-tree. In this paper, the authors intend to solve the RWA problem for a group of light-trees with the objective of globally minimizing the number of WCs that are required to support the entire group of multicast requests. The rationale for using the proposed RWA solution is that a joint solution of the RWA problem across the whole set of requested multicast trees may significantly reduce the number of WCs overall.

Multicast tree computation in networks with multicast incapable nodes

Multicast transmission offers a bandwidth efficient solution for delivering media content to multiple destinations over the Internet. However, in many existing networks, some (if not all) nodes do not support multicast, i.e., they cannot create multiple outgoing flows with one incoming data flow. In this paper, the authors propose an algorithm for multicast tree computation in networks with multicast incapable nodes. Paths that originate at the source and traversing all destinations are computed first; if such paths cannot be found, destinations are partitioned into subsets and traverse paths are computed over each subset, which is executed recursively until feasible trees can be built based on traverse paths found or no further partition is possible. Two procedures for traverse path computation are presented and their respective advantages are discussed, in terms of both complexity and solution optimality. The algorithm is also shown to be very effective in finding multicast trees even if only a few multicast capable nodes exist in the network.

The PlaNet-PTN Module: a Single Layer Design Tool for Packet Transport Network

PlaNet is a multilayer network planning tool developed at the University of Texas at Dallas. This paper illustrates some of the features of PlaNet-PTN, one of the modules available in the PlaNet tool. PlaNet-PTN can be used to design and plan a single layer packet transport network (PTN). Quality of protection, routing constraints, minimization of the network equipment cost, and user’s desired run time of the tool are just some examples of the features available in PlaNet. As shown in the paper, the PlaNet-PTN planning module is able to provide, among others, optimization of Label Switched Path (LSP) routes, link capacity placement, node and link equipment configuration.

Digital subcarrier optical networks (DSONs)

This paper describes an energy efficient and data rate flexible network transport solution to achieve sub-wavelength circuit provisioning between edge node pairs. Sub-wavelength circuits are obtained by concatenating spectrally efficient digital subcarrier channels along the network path, with each subcarrier frequency carrying only a fraction of the wavelength bandwidth. By reserving one or more such subcarrier frequencies along a path connecting two edge nodes, a dedicated end-to-end sub-wavelength circuit is provisioned. At intermediate nodes, incoming frequencies are switched to outgoing frequencies via a specially designed frequency selective switch or cross-connect, described in a companion paper [7]. The power consumption required to switch subcarrier frequencies across the network is estimated to be a fraction of the power dissipated by currently available transport solutions, e.g., optical transport network (OTN) and multiprotocol label switching transport profile (MPLS-TP).

Digital subcarrier cross-connects (DSXCs)

Digital subcarrier cross-connect (DSXC) is a circuit switching node which offers bandwidth flexibility, improved transmission performance, and electric power efficiency in transport networks. In contrast to the time division multiplexing-based optical transport network (OTN) architectures, DSXC makes use of frequency division multiplexing to perform cross-connection operation of individual subcarrier channels, which can be established to provide end-to-end dedicated circuits with flexible data rates between edge node pairs. By leveraging digital subcarrier multiplexing (DSCM), spectral guard-bands between adjacent channels are not necessary in DSXC, thus yielding good bandwidth efficiency when multiplexing subcarrier channels onto the same wavelength. In addition, digital signal processing (DSP) algorithms can be implemented to perform compensation of fiber transmission impairments in the electronic domain, thus ensuring good signal integrity. As discussed in this paper, the power consumption needed by DSXC to perform subcarrier channel cross-connection operations is estimated to be approximately one third of that required by todays OTN digital cross-connects. As illustrated in a companion paper [1] multiple DSXCs can be arranged together to build digital subcarrier optical networks (DSONs), which is a promising energy efficient alternative to currently available transport network solutions, e.g., OTN/SONET/SDH/MPLS-TP. This paper introduces the concept, the basic building blocks and the key functionalities of DSXC.

The PlaNet-OTN module: A double layer design tool for optical transport networks

PlaNet is a multilayer network planning tool designed and developed at the University of Texas at Dallas. This paper illustrates some of the features of PlaNet-OTN, one of the modules available in the PlaNet tool. PlaNet-OTN can be used to design and plan an optical transport network (OTN), which is comprised of two layers: wavelength division multiplexing (WDM) layer, which deals with wavelength allocation and routing of WDM services, and optical transport network (OTN) layer, which deals with optical data unit (ODU) equipment provisioning and routing of ODU services. Features of the PlaNet-OTN module include: multiple protection schemes and routing constraints for both WDM and ODU services, network equipment cost minimization, load balancing of traffic, and user-controlled run time of the optimization process. As shown in this paper, the PlaNet-WDM and OTN layers and optimizing equipment usage, hence reducing the cost of the whole network.

Digital subcarrier optical networks and cross-connects

This paper describes a rate flexible network transport solution to achieve sub-wavelength circuit provisioning between edge node pairs. Sub-wavelength circuits are obtained by concatenating spectrally efficient digital subcarrier channels along the network path, with each subcarrier frequency carrying only a fraction of the wavelength bandwidth. By reserving one or more such subcarrier frequencies along a path connecting two edge nodes, a dedicated end-to-end sub-wavelength circuit is provisioned. At an intermediate node, incoming frequencies are switched to outgoing frequencies via a cross-bar electronic circuit switch or cross-connect. By performing digital subcarrier multiplexing DSCM using CMOS based advanced digital signal processing DSP algorithms, spectral guard-bands between adjacent channels are not necessary, thus yielding good bandwidth efficiency when multiplexing multiple subcarrier channels onto the same wavelength.Compared to current TDM based transport network solutions, e.g., OTN/SONET/SDH, the described solution offers the unique advantage of implementing two key transport functionalities in the same DSP system, which is capable of 1 performing compensation of fiber transmission impairments in the electronic domain to ensure good signal integrity, and 2 multiplexing demultiplexing subcarrier channels after before add/drop and switching circuit operations. Because of this design advantage, system complexity and fabrication of the network equipment are ameliorated, possibly leading to tangible cost and electric power consumption reductions.

Coupling wavelength assignment in bidirectional lightpath: Is it worth the extra cost?

The introduction of end-to-end (multi hop) optical circuits (lightpaths) is often seen as the natural extension of a point-to-point (single hop) wavelength division multiplexing (WDM) transmission system, spanning across optical cross-connect nodes. Conventionally, a bidirectional lightpath (whether single or multi hop) comprises two lambda channels in fibers with opposite directions of signal propagation, which are assigned the same wavelength. This constraint is referred to as identical wavelength in bidirectional lightpath (IWBL). While IWBL is a natural and historical choice in point-to-point system, the authors are going to demonstrate that IWBL may unnecessarily increase the number of wavelength converters (WCs), which are required to establish lightpaths in the WDM network when the wavelength continuity constraint cannot be met. In the study, the IWBL constraint is relaxed, thus allowing the assignment of two distinct wavelengths to the same lightpath, one for each direction. A wavelength assignment (WA) algorithm is designed to both take advantage of the IWBL constraint relaxation and minimize the required number of WCs to establish a given set of lightpaths. The algorithm is then applied to a number of network topologies. The outcome is quite surprising, in that the amount of WC reduction obtained by relaxation of the IWBL constraint may be significant under certain conditions.