Farid Farahmand

GeoSpray: A geographic routing protocol for vehicular delay-tolerant networks

Vehicular networks are characterized by a highly dynamic network topology, and disruptive and intermittent connectivity. In such network environments, a complete path from source to destination does not exist on the most part of the time. Vehicular delay-tolerant network (VDTN) architecture was introduced to deal with these connectivity constraints. VDTN assumes asynchronous, bundle-oriented communication, and a store-carry-and-forward routing paradigm. A routing protocol for VDTNs should make the best use of the tight resources available in network nodes to create a multi-hop path that exists over time. This paper proposes a VDTN routing protocol, called GeoSpray, which takes routing decisions based on geographical location data, and combines a hybrid approach between multiple-copy and single-copy schemes. First, it starts with a multiple-copy scheme, spreading a limited number of bundle copies, in order to exploit alternative paths. Then, it switches to a forwarding scheme, which takes advantage of additional contact opportunities. In order to improve resources utilization, it clears delivered bundles across the network nodes. It is shown that GeoSpray improves significantly the delivery probability and reduces the delivery delay, compared to traditional location and non location-based single-copy and multiple-copy routing protocols.

A layered architecture for Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Network (VDTN) is a new network architecture based on the concept of Delay Tolerant Networks (DTN). It aims to be an architecture that handles non-real time applications at low cost, under unreliable conditions, enabling connectivity in diverse scenarios, using vehicles to carry data between terminal nodes. For example, it can be applied in rural and remote areas, or in emergency scenarios. This paper proposes a layered architecture for VDTNs, using out-of-band signaling, based on the separation of the control plane and data plane. It presents the layers interactions and the envisioned protocols required at each layer. The paper provides a deep understanding of the characteristics of VDTN and reveal some design issues in its modeling, leading to insights for future theoretic study and protocol design.

Traffic Grooming in Green Optical Networks

Compared to energy-awareness research in wireless and copper networks, less attention has been given to energy awareness in optical counterparts. In this paper, we introduce energy-aware traffic grooming problems for optical networks. We show that by looking further into the modular physical architecture of a node during request allocations, we can significantly reduce the number of active components and, hence, total energy consumption in the network, especially when traffic load is low. Since energy usage is an important element of operational expenditure (OPEX), this approach provides the financial motivation for service providers along with the desired environmental motivation. We present auxiliary graph based heuristics and justify our cases compared to traditional approaches with simulation results.

Multicast traffic grooming in wavelength-routed WDM mesh networks using dynamically changing light-trees

In this paper, we address the online multicast traffic grooming problem in wavelength-routed wavelength division multiplexing (WDM) mesh networks with sparse grooming capability. We develop a multicast dynamic light-tree grooming algorithm (MDTGA) that can support multihop traffic grooming by taking advantage of light-trees. In this algorithm, a light-tree can be dropped, branched, and extended when a route is to be established for a new request; a light-tree can also be contracted when some branches carry no effective traffic after requests depart from the network. The difficulty of the algorithm lies in the dynamic characteristic of light-trees. We implement MDTGA on a new auxiliary-graph model. For the purpose of comparison, we also implement a lightpath-based grooming algorithm by putting a constraint on the optical-splitting capability of the nodes. Through extensive simulations, we find that MDTGA has much better performance than the lightpath-based algorithm.

Energy-Efficient Translucent Optical Transport Networks With Mixed Regenerator Placement

Translucent networks utilize sparse placements of optical-electronic-optical (O/E/O) 3R (reamplification, reshaping, and retiming) regenerators to improve the cost effectiveness and energy efficiency of wavelength-routed optical transport networks. In this paper, we show that the energy cost of a translucent network can be further reduced by leveraging the energy efficiency of all-optical 2R (reamplification and reshaping) regenerators. We propose a translucent network infrastructure that uses all-optical 2R regenerators to partially replace O/E/O 3R regenerators and implements mixed regenerator placements (MRP). We first consider the problem of MRP along a single given path, and propose three path-based impairment-aware MRP algorithms, based on periodic placement, genetic algorithm (GA), and ant colony optimization (ACO). We then address the offline network planning problem and develop a heuristic algorithm. By incorporating with one of the proposed MRP algorithms, the heuristic can achieve joint optimization of MRP and routing and wavelength assignment for high energy efficiency. We design simulations to compare the performance of different offline network planning scenarios and to see which one can provide the best balance between quality of transmission and energy cost. Simulation results show that the algorithm achieves 58.91-73.62% saving on regeneration energy, compared to the traditional scheme without all-optical 2R regenerators. The results also indicate that the joint optimization using the MRP-GA obtains the best network planning in terms of energy efficiency. Finally, we address the problem of online provisioning, and propose several algorithms to serve dynamic lightpath requests in translucent networks with MRP, and implement them in simulations to compare their performance in terms of blocking probability. Simulation results indicate that the online provisioning algorithm that utilizes the combination of the MRP-GA and a multiple MRP scheme achieves the lowest blocking probability.

Improving Vehicular Delay-Tolerant Network Performance with Relay Nodes

Vehicular Delay-Tolerant Networking (VDTN) is an extension of the Delay-Tolerant Network (DTN) architecture concept to transit networks. VDTN architecture handles non-real time applications, exploiting vehicles to enable connectivity under unreliable scenarios with unstable links and where an end-to-end path may not exist. Intuitively, the use of stationary store-and-forward devices (relay nodes) located at crossroads where vehicles meet them and should improve the message delivery probability. In this paper, we analyze the influence of the number of relay nodes, in urban scenarios with different numbers of vehicles. It was shown that relay nodes significantly improve the message delivery probability on studied DTN routing protocols.

Supporting QoS with look-ahead window contention resolution in optical burst switched networks

Optical burst switching (OBS) has been proposed as a competitive hybrid switching technology to support the next-generation optical Internet. This paper addresses the problem of contention in OBS networks and introduces a new contention resolution algorithm called look-ahead window contention resolution (LCR) that can also support service differentiation. Simulation results show that the performance of LCR is competitive to existing contention resolution mechanisms in terms of reducing burst loss.

Efficient online traffic grooming algorithms in WDM mesh networks with drop-and-continue node architecture

As high capacity all-optical networks and WDM technologies advance and merge together, aggregating low-speed traffic streams onto high-speed wavelengths becomes more critical. Efficient aggregation techniques, known as traffic grooming, allow higher bandwidth utilization and can reduce request blocking probability. These algorithms can also result in lower network cost in terms of electronic switching. In this paper we focus on traffic grooming in WDM mesh networks with dynamic traffic patterns. We offer two new grooming concepts called lightpath dropping and lightpath extension. These concepts are based on an alternative node architecture in which incoming optical signals can be dropped at a node, while optically continuing to the next node. Based on these concepts, we develop several grooming algorithms and study them under various network objectives. We also compare their performance with previously proposed lightpath-based grooming algorithms. Through extensive simulation results we show that our proposed approaches lead to lower request blocking probability and lower average number of logical hops when the number of transceivers per node is limited.

Energy-awareness in dynamic traffic grooming

We introduce an energy-efficient traffic grooming scheme for promoting greener optical networks. The scheme considers a modular node architecture, reuses already active components during request allocations, and conserves total energy consumption in the network.

Look-ahead window contention resolution in optical burst switched networks

We introduce a new contention resolution algorithm called look-ahead window contention resolution (LCR). This unique contention resolution approach can be used in conjunction with a scheduling technique to reduce the packet loss in an optical burst switched network. We analyze the performance of LCR by means of simulations and compare it with other major existing contention resolution policies.