Muhammad S. Javed

Circuits/Cutsets Duality and a Unified Algorithmic Framework for Survivable Logical Topology Design in IP-over-WDM Optical Networks

Given a logical topology G L and a physical topology G, the survivable logical topology design problem in an IP-over- WDM optical network is to map the logical links into lightpaths in G such that G L remains connected after the failure of any edge in G. In view of its fundamental nature and its practical importance, this problem has received considerable attention in the literature. The SMART algorithmic framework based on the circuits in G L is a novel and very significant contribution to this problem. Taking advantage of the dual relationship between circuits and cutsets in a graph, we first present in this paper the primal algorithm CIRCUIT-SMART (similar to SMART) and algorithm CUTSET-SMART that is dual of CIRCUIT-SMART and proofs of correctness of these algorithms. To guarantee survivability we add additional logical links called protection edges, if necessary. This investigation has provided much insight into the structural properties of solutions to this problem and the structure of survivable logical graphs. Specifically, we present a highly simplified version of CUTSET-SMART that always provides a survivable mapping as long as G is 3-edge connected, and a survivable logical topology structure. We also present algorithm INCIDENCE-SMART that uses incidence sets that are special cases of a cut. Two efficient heuristics, one based on maximum matching theory and the other based on both the primal and dual algorithms are also presented. Simulation results comparing the different algorithms in terms of computational time, protection capacity and survivability success rate are also presented.

Energy-efficient data broadcasting in mobile ad-hoc networks

Energy saving is the most important issue in wireless mobile computing due to power constraints on mobile units. Data broadcasting is the main method of information dissemination in wireless networks as its cost is independent of the number of mobile hosts receiving the information. A number of data broadcasting techniques have been proposed for mobile wireless networks, where servers have no energy restrictions, but little research has been done to address the issue of data broadcasting in mobile ad-hoc networks where both servers and clients are nomadic. In this paper, we propose two groups of broadcast scheduling algorithms called adaptive broadcasting and popularity based adaptive broadcasting that consider time constraints on requests as well as energy limitation on both servers and clients. We also present the simulation experiments that compare the algorithms.

Primal meets dual: A generalized theory of logical topology survivability in IP-over-WDM optical networks

The survivable logical topology mapping (SLTM) problem in an IP-over-WDM optical network is to map each link (u, v) in the logical topology (at the IP layer) into a lightpath between the nodes u and v in the physical topology (at the optical layer) such that failure of a physical link does not cause the logical topology to become disconnected. It is assumed that both the physical and logical topologies are 2-edge connected. For this problem Kurant and Thiran presented an algorithmic framework called SMART that involves successively contracting circuits in the logical topology and mapping the logical links in the circuits into edge disjoint lightpaths in the physical topology. In a recent work we presented a dual framework involving cutsets and showed that both these frameworks possess the same algorithmic structure. Algorithms CIRCUIT-SMART, CUTSET-SMART, CUTSET-SMART-SIMPLIFIED and INCIDENCE-SMART were also presented in. Effectiveness of both these frameworks as well as their robustness in providing survivability against multiple failures depends on the lengths of the cutset cover and circuit cover sequences on which they are based. To improve their effectiveness and robustness, in this paper we first introduce the concept of generalized cutset cover and generalized circuit cover sequences. We present an algorithm to get a generalized cutset (circuit) cover sequence from any given cutset (circuit) cover sequence. We then present GENCUTSET-SMART and GEN-CUTSET-SMART-SIMPLIFIED algorithms that remove some of the shortcomings of the dual framework of. We prove that there is a one-to-one correspondence between the set of generalized circuit cover sequences and the set of generalized cutset cover sequences. We then show that for each execution of GEN-CIRCUIT-SMART there exists an execution of GEN-CUTSET-SMART-SIMPLIFIED such that the groups of edges that they map into edge disjoint lightpaths are exactly the same. In other words, the distinction between the primal and dual methods disappears when they use generalized sequences. Preliminary simulation results confirm our expectation that GEN-CUTSET-SMART-SIMPLIFIED will perform better than CIRCUIT-SMART and CUTSET-SMART-SIMPLIFIED (when started with a circuit or a cutset sequence) in terms of number of additional protection edges to be added.

Lightpaths routing for single link failure survivability in IP-over-WDM networks

High speed all optical network is a viable option to satisfy the exponential growth of internet usage in the recent years. Optical networks offer very high bit rates and, by employing technologies like internet protocol over wavelength division multiplexing (IP-over-WDM), these high bit rates can be effectively utilized. However, failure of a network component, carrying such high speed data traffic can result in enormous loss of data in a few seconds and persistence of a failure can severely degrade the performance of the entire network. Designing IP-over-WDM networks, which can withstand failures, has been subject of considerable interest in the research community recently. Most of the research is focused on the failure of optical links in the network. This paper addresses the problem of designing IP-over-WDM networks that do not suffer service degradation in case of a single link failure. The paper proposes an approach based on the framework provided by a re- cent paper by M. Kurant and P. Thiran. The proposed approach can be used to design large survivable IP-over-WDM networks.

Prototype for wrapping and visualizing geo-referenced data in a distributed environment using XML technology

This paper proposes a prototype for integration and visualization of geo-referenced information (GRI) in a distributed environment in general and World Wide Web in particular. This prototype adopts a three-tier architecture and includes three main components: GRI wrapper for distributed GRI web sites, GRI integration mediator and client side visualization interface. In this prototype, XML is used as a communication protocol between distributed web sites that provide GRI and the mediator, and between the mediator and clients. Java Servlets are written to translate data in distributed websites into XML documents. Data in distributed websites can be stored in a flat file, relational database, object-oriented database or object-relational database. Java Servlet in the mediator server retrieves data from related distributed websites in an XML format upon a request from the client side, parses the retrieved XML documents, performs merge or other operations on the retrieved XML documents to build a new XML document and sends it to the client side. When the client side gets the requested data from the mediator server, it will parse the returned XML document and draw it inside the browser window by using a Java applet.

Logical topology augmentation for guaranteed survivability under multiple failures in IP-over-WDM optical network

The survivable logical topology mapping problem in an IP-over-WDM optical network is to map each link (u, v) in the logical topology (at the IP layer) into a lightpath between the nodes u and v in the physical topology (at the optical layer) such that failure of a physical link does not cause the logical topology to become disconnected. Kurant and Thiran [8] presented an algorithmic framework called SMART that involves successive contracting of circuits in the logical topology and mapping the logical links in the circuits into edge disjoint lightpaths in the physical topology. In a recent work [11] a dual framework involving cutsets was presented and it was shown that both these frameworks possess the same algorithmic structure. Algorithms CIRCUIT-SMART, CUTSET-SMART and INCIDENCE-SMART were also presented in [11]. All these algorithms suffer from one important shortcoming, namely, disjoint lightpaths for certain groups of logical links may not exist in the physical topology. Therefore, in such cases, we will have to augment the logical graph with new logical links to guarantee survivability. In this paper we address this augmentation problem. We first show that if a logical topology is a chordal graph then it admits a survivable mapping as long as the physical topology is 3-edge connected and the logical topology is 2-edge connected. We identify one such chordal graph. We then show how to embed this chordal graph on a logical topology to guarantee survivability. We also show how this augmentation approach can be generalized to guarantee survivability under multiple failures.

Logical Topology Design for IP-over-WDM Networks: A Hybrid Approach for Minimum Protection Capacity

The problem of designing high capacity and high bit rate IP-over-WDM networks, which can provide uninterrupted service in the presence of network equipment failures, continues to attract significant interest from the research community. An IP-over-WDM network implements Internet Protocol (IP) directly over physical WDM network by establishing lightpaths using IP routers, optical crossconnects (OXC) and optical fibers. Generally an optical fiber carries several lightpaths and all of them get disconnected, if the fiber carrying them fails. Such failures can quickly impact the performance of the entire network. If IP routers can find paths to all the nodes in the network, then the network can continue to provide service without significant performance degradation. This can be achieved by reserving network resources (protection) or provisioning the network with some additional capacity (restoration). Such networks are usually called survivable networks. In this paper, we propose four algorithms based on SMART framework proposed by Kurant and Thiran, and a hybrid approach by Shenai and Sivalingam. The algorithms use a combination of protection and restoration mechanisms to make IP-over-WDM networks survivable such that the protection capacity required is not significant.