Andrea Fumagalli

CORD: contention resolution by delay lines

The implementation of optical packet-switched networks requires that the problems of resource contention, signalling and local and global synchronization be resolved. A possible optical solution to resource contention is based on the use of switching matrices suitably connected with optical delay lines. Signalling could be dealt with using subcarrier multiplexing of packet headers. Synchronization could take advantage of clock tone multiplexing techniques, digital processing for ultra-fast clock recovery, and new distributed techniques for global packet-slot alignment. To explore the practical feasibility and effectiveness of these key techniques, a consortium was formed among the University of Massachusetts, Stanford University, and GTE Laboratories. The consortium, funded by ARPA, has three main goals: investigating networking issues involved in optical contention resolution (University of Massachusetts), constructing an experimental contention-resolution optical (CRO) device (GTE Laboratories), and building a packet-switched optical network prototype employing a CRO and novel signaling/synchronization techniques (Stanford University). This paper describes the details of the project and provides an overview of the main results obtained so far.

Multibuffer delay line architectures for efficient contention resolution in optical switching nodes

This paper proposes an efficient contention resolution switching architecture which can serve as the basis for all-optical switching nodes. The presented solution builds on fiber delay lines used as temporary optical storage and 2/spl times/2 space photonic switches, a solution principle also known as Quadro or switched delay lines (SDLs). The efficiency of SDLs is fundamentally linked to its storage capacity, i.e., the length of the fiber delay lines, while its cost depends on the number of 2/spl times/2 photonic switches, i.e., the number of stages in the switch. This work presents a solution that makes use of multibuffer fiber delay lines which allow multiple packets to be concurrently stored (propagated) on each line. With a novel switch control, it is shown that this solution increases the total storage capacity and significantly improves switch and network performance, without increasing the number of the 2/spl times/2 switches in the system, i.e., its cost.

Cooperative and Reliable ARQ Protocols for Energy Harvesting Wireless Sensor Nodes

One class of wireless sensor networks makes use of sensor nodes that recharge their batteries by harvesting energy from the surrounding environment. Being continuously recharged, the battery does not need to be replaced regularly and the sensor node is maintenance-free. A key module in such sensor network solutions is the data link automatic repeat request (ARQ) protocol, which must be designed to reliably deliver sensor nodes data at the minimum energy cost. With this objective in mind, two ARQ protocol classes are compared. In one class, each sensor node operates individually. In the other, the concept of cooperative communications is adopted, whereby neighboring sensor nodes help each other during the retransmission process. It is shown that the use of cooperative ARQ protocols in energy harvesting sensor networks enables sensor nodes to balance their energy consumption to match their own battery recharge rate. In turn, a balanced energy consumption-to-recharge rate ratio has the potential to improve the network throughput. Both classes of ARQ protocols are analyzed and compared. Estimated throughput gains are discussed under various network scenarios.

Differentiated reliability in optical networks: theoretical and practical results

This paper presents both theoretical and experimental studies carried on wavelength-division multiplexing (WDM) networks with arbitrary (mesh) topology that provide optical circuits with differentiated reliability (DiR). Reliability is obtained by means of a modified shared path protection (SPP) switching scheme-here referred to as SPP-DiR. As explained in the paper, SPP-DiR networks provide multiple degrees of circuit reliability that satisfy client-specific reliability requirements in a cost-effective way. The theoretical study first defines the problem of optimally designing SPP-DiR WDM networks. It then presents a time-efficient suboptimal algorithm that determines the routing and the reliability degree of each demand in the given traffic matrix by applying both the conventional SPP and the SPP-DiR scheme. When compared to dedicated path protection switching, results obtained for the pan-European network using the proposed algorithm indicate cost reductions of about 16% when SPP is applied, and up to 34% when SPP-DiR is applied. The experimental study describes the /spl Omega/ testbed-a WDM optical circuit-switched mesh network with an IP control plane-which is believed to be the first testbed ever built that makes use of the SPP-DiR scheme. Experimental results performed on the /spl Omega/ testbed report restoration times of the optical circuits-disrupted by a fiber fault-that are few tens of milliseconds.

Survivable networks based on optimal routing and WDM self-healing rings

The design of survivable all-optical networks based on self-healing WDM rings (SHR/WDM) to provide 100% protection from any single link failure requires the joint solution of three sub-problems. These are the ring cover of the mesh topology (the RC sub-problem), the routing of working lightpaths between node pairs to support traffic demands (the WL sub-problem) and the selection of the SHR/WDM spare wavelengths for the protection of every link traffic (the SW subproblem). This paper presents an integer linear programming (ILP) formulation of the problem of minimizing the total wavelength mileage (/spl lambda/-miles) required to support a set of given traffic demands in a given network topology using SHR/WDM employing 1:N line protection mechanism (the WRL problem). This formulation allows to jointly and optimally solve the three subproblems, and yields up to 15% reduction of the total /spl lambda/-miles required by existing solutions that separately resolve the sub-problems. A simplified sub-optimal solution of the WRL problem is also provided, that yields results few percent worse than the optimal solution and that is tractable for networks whose size is on the order of the pan-European network, i.e., 19 nodes.

Shared path protection with differentiated reliability

The authors (Fumagalli and Tacca (2001)) introduced the concept of differentiated reliability (DiR) applied to dedicated path protection (DPP) switching in wavelength division multiplexing (WDM) rings. By means of the DiR concept, a network can be designed to provide multiple degrees of reliability and efficiently satisfy the user-specific requirements, yet minimizing the network total cost. This paper extends the DiR concept to the case of shared path protection (SPP) switching in arbitrary (mesh) topology, the so called SPP-DiR. A time efficient algorithm is proposed to determine the primary and backup path of each demand in both conventional SPP and SPP-DiR (WDM) networks. When compared to DPP, results obtained for the pan-European network by using the proposed algorithm indicate cost reductions of about 16% when SPP is applied, and up to 34% when SPP-DiR is applied.

Delay models of single-source single-relay cooperative ARQ protocols in slotted radio networks with Poisson frame arrivals

In conventional (noncooperative) automatic repeat request (ARQ) protocols for radio networks, the corrupted data frames that cannot be correctly decoded at the destination are retransmitted by the source. In cooperative ARQ protocols, data frame retransmissions may be performed by a neighboring node (the relay) that has successfully overheard the sources frame transmission. One advantage of the latter group of ARQ protocols is the spatial diversity provided by the relay. The first delay model for cooperative ARQ protocols is derived in this paper. The model is analytically derived for a simple set of retransmission rules that make use of both uncoded and coded cooperative communications in slotted radio networks. The model estimates the delay experienced by Poisson arriving frames, whose retransmissions (when required) are performed also by a single relay. Saturation throughput, data frame latency, and buffer occupancy at both the source and relay are quantified and compared against two noncooperative ARQ protocols.

Quadro-Star: a high performance optical WDM star network

This paper proposes an original approach to controlling WDM Passive optical stars, termed queuing arrivals for delayed reception operation (Quadro). In WDM stars the fundamental problem of receiver conflicts leads to severe performance degradation. In current solutions conflicts are prevented by scheduling transmissions or resolved by retransmissions. Both approaches waste bandwidth and involve electronic processing and buffering. The proposed approach is conceptually different in introducing a local conflict resolution mechanism at each receiver incorporating delay lines. This solution brings optical star networks a step closer to an all-optical realization. In addition, it allows an almost total utilization of the channels, as obtainable until now only by TDM control. Contrary to TDM, however, the proposed solution does not suffer performance degradation under heterogeneous traffic conditions and increasing number of nodes. It is thus unique in offering the potential of an all-optical solution providing at the same time high throughput, low delay, small buffer requirements, and robustness under all traffic conditions. >

Local and global handovers for mobility management in wireless ATM networks

This article deals with the problem of virtual circuit (VC) management in wireless ATM (W-ATM) networks with mobile user terminals. In W-ATM networks, a VC terminating at a mobile user may require dynamic reestablishment during the short time span necessary for terminal handover due to its movement from one (macro)cell to another. The VC reestablishment procedure has to ensure in-sequence and loss-free delivery of the ATM cells containing user data. After a classification of the solutions proposed so far in the literature, a novel technique for the dynamic reestablishment of VCs in W-ATM networks is described, and its performance is evaluated through simulation. The proposed technique allows for a progressive upgrade of the fixed part of the ATM network and for the incremental introduction of user terminal mobility.

A deterministic approach to the end-to-end analysis of packet flows in connection-oriented networks

We analyze the worst-case behavior of general connection-oriented networks, with first-in-first-out (FIFO) queueing policy, forwarding packets along an arbitrary system of routes. A worst-case bound is proven for the end-to-end queueing delay and buffer size needed to guarantee loss-free packet delivery, given that sources satisfy a given source rate condition. The results are based on a novel deterministic approach and help in reconciling the discrepancy between the unstable worst-case behavior of FIFO-based networks and their good practical performance.