Rauf Izmailov

Interference-aware IEEE 802.16 WiMax mesh networks

The IEEE 802.16 WiMax standard provides a mechanism for creating multi-hop mesh, which can be deployed as a high speed wide-area wireless network To realize the full potential of such high-speed IEEE 802.16 mesh networks, two efficient wireless radio resource allocation extensions were developed The objective of this paper is to propose an efficient approach for increasing the utilization of WiMax mesh through appropriate design of multi-hop routing and scheduling. As multiple-access interference is a major limiting factor for wireless communication systems, we adopt here an interference-aware cross-layer design to increase the throughput of the wireless mesh network. In particular, our scheme creates a tree-based routing framework, which along with scheduling is interference aware and results in a much higher spectral efficiency. Performance evaluation results show that the proposed interference-aware scheme achieves significant throughput enhancement over the basic IEEE 802.16 mesh network.

Performance of VoIP in a 802.11 Wireless Mesh Network

Performance in multihop wireless networks is known to degrade with the number of hops for both TCP and UDP traffic. For VoIP, the wireless network presents additional challenges as the perceived quality is dependent on both loss and delay. We investigate several methods to improve voice quality and present experimental results from an 802.11b testbed optimized for voice delivery. Use of multiple interfaces, path diversity and aggregation are shown to provide a combined improvement of 13 times in number of calls supported in our 15 node 802.11 mesh system. VoIP, multihop, mesh

Nonuniform waveband hierarchy in hybrid optical networks

Aggregation of individual wavelengths into wavebands for their subsequent switching and routing as a single group is an attractive way for scalable and cost-efficient optical networks. We analyze the implications of this waveband hierarchy for a single optical node by analyzing two issues: the proper selection of waveband sizes and the assignment of wavebands for a limited set of input-output patterns of traffic. We formulate a general model and propose optimal algorithmic solutions for both problems. The performance of resulting sets of nonuniform wavebands is studied for several representative cases (a single node, an optical ring network, an optical mesh network). The results demonstrate improved optical throughput and reduced cost of switching and routing when using nonuniform waveband hierarchy.

Hybrid hierarchical optical networks

Hybrid hierarchical optical cross-connects enhance the performance/cost ratio of optical networks by providing transparent (optical) switching of sets of wavelengths (wavebands) in addition to opaque (electrical) switching of individual wavelengths. As network bandwidth gets cheaper, and the performance bottleneck moves to switching nodes, these systems provide an attractive scalable solution for next-generation optical networks. We describe key technological components (including flexible nonuniform wavebands) of hybrid hierarchical optical cross-connects and discuss their performance/cost implications.

Path provisioning for service level agreements in Differentiated Services networks

We study the path provisioning as a mechanism to deliver service level agreements in IP Differentiated Services networks. There is no known polynomial time solution for this problem, so we propose and analyze (by simulations) several heuristic algorithms for solving the problem. As our simulations demonstrate, a centralized server consistently delivers a better performance than a distributed solution. We also show that the performance of one of the proposed algorithms, the greedy algorithm with backtracking, can be very close to the optimal one, while being computationally feasible.

QOS aggregation algorithms in hierarchical ATM networks

We propose a new private network-to-network interface (PNNI) aggregation algorithms for hierarchical ATM networks. Standard PNNI routing provides a scalable hierarchical routing capability to support a large ATM network, and its hierarchy mechanism can decrease the network complexity significantly. However, in order to support effective QoS-based routing across foreign subnetworks, the topology aggregation mechanism, representing the lower level network topology to higher level, becomes a key issue. PNNI specification defines general notions of this aggregation mechanism, leaving enough opportunities for subnetwork administrators to choose the amount of aggregated information that they advertise. So far, no feasible PNNI compliant algorithms have been proposed. We propose a new three step aggregation scheme to solve the problem. We evaluated the proposed scheme, based on large-scale simulations with different network topologies, traffic scenarios, and performance metrics. The proposed scheme delivers good network performance while significantly reducing the network complexity.

Fast replication in content distribution overlays

We present SPIDER-a system for fast replication or distribution of large content from a single source to multiple sites interconnected over Internet or via a private network. In order to exploit spatial diversity of the underlying network, SPIDER uses an overlay structure composed of dedicated transit nodes (TNs). The data transport mechanism in SPIDER leverages this overlay structure to provide a coordinated approach that minimizes the maximum time to replicate to all destination sites (the make span of content replication). In order to achieve this objective, SPIDER employs two orthogonal components: a) creation of multiple dynamic distribution trees using the transit nodes b) end-to-end reliable data transport with flow control on these trees by chaining point-to-point TCPs. We further present simulations based results to quantify benefits of tree construction algorithms in random topologies. We evaluate the real implementation of the SPIDER in Planet Lab and observe a 2-6 times speed up compared to different existing schemes.

Adaptive feedback control algorithms for large data transfers in high-speed networks

Two linear feedback control algorithms for handling and preventing congestion in broadband asynchronous transfer mode networks are proposed and analyzed. The fluid approximation model is described with a continuous-time system of delay-differential equations. The algorithms are asymptotically stable, and the transient processes are nonoscillatory. The control parameters are locally optimal (optimality is based on the asymptotic rate of convergence). The results of numerical experiments suggest that these parameters are globally optimal as well. >

Hierarchical routing in layered ring and mesh optical networks

We consider hierarchical optical networks with different granularities of paths (wavelengths and wavebands). We introduce classification layers for routing models in these networks (separated and integrated routing, homogeneous and heterogeneous networks, online and offline routing). We also propose and analyze two heuristic routing and aggregation algorithms (online and offline) to be used for homogeneous networks in the separate routing framework. The analysis is based on ring topology; its results are supported by simulations of large scale networks (Europe and USA). These simulations demonstrate a significant cost reduction achieved by employing hierarchical routing (from 33% in the online algorithm to almost 60% in the offline one).

Waveband routing and merging in hybrid optical networks

Hybrid hierarchical optical cross-connects leverages the benefits of both all-optical (OOO) and optical-electrical (OEO) switching for a cost-effective solution in future optical networks. The design goal using hybrid cross-connects is to minimize the sum of two cost metrics: OEO switching cost and OOO switching cost. This paper proposes two different waveband merging architectures and minimum cost routing and merging algorithms for offline traffic scenario. The simulation based results show that the proposed algorithms provide higher cost benefit as compared to existing algorithms that do not rely on waveband merging architecture.