Minimum-Storage Regenerating (MSR) codes have emerged as a viable alternative to Reed-Solomon (RS) codes as they minimize the repair bandwidth while they are still optimal in terms of reliability and storage overhead. Although several MSR constructions exist, so far they have not been practically implemented mainly due to the big number of I/O operations. In this paper, we analyze high-rate MDS codes that are simultaneously optimized in terms of storage, reliability, I/O operations, and repair-bandwidth for single and multiple failures of the systematic nodes. The codes were recently introduced in [1] without any specific name. Due to the resemblance between the hashtag sign # and the procedure of the code construction, we call them in this paper HashTag Erasure Codes (HTECs). HTECs provide the lowest data-read and data-transfer, and thus the lowest repair time for an arbitrary sub-packetization level α, where α ≤ r⌈k/r⌉, among all existing MDS codes for distributed storage including MSR codes. The repair process is linear and highly parallel. Additionally, we show that HTECs are the first high-rate MDS codes that reduce the repair bandwidth for more than one failure. Practical implementations of HTECs in Hadoop release 3.0.0-alpha2 demonstrate their great potentials.

Bufferless network operation is favorable in many application domains such as industrial networks, on-chip networks and optical packet switching (OPS). The main challenge with zero buffers is the avoidance or handling of contention; indeed, many domain-specific contention resolution techniques have been proposed in the literature. In this paper, we propose a generic combined forward error correction (FEC) and network coding (NC) scheme, which mitigates the negative impact of contentions at the network layer. Specifically, we present a case study for OPS utilizing FEC at the ingress node and NC at an intermediary optical packet switch to reduce packet loss due to contention. Our analysis shows that if used in a smart way, our mechanism can reduce decoding error and packet loss with multiple orders of magnitude while adhering to buffering limitations and meeting delay requirements. We believe that such a combined coding scheme has the potential to be utilized both in OPS (data center and core networks) and other networks where (near-)zero buffers are required.

This paper presents the Coded Packet Transport (CPT) scheme, a novel transport mechanism for Optical Packet/Burst Switched (OPS/OBS) networks. The CPT scheme exploits the combined benefits of source coding by erasure codes and path diversity to provide efficient means for recovering from packet loss due to contentions and path failures, and to provide non-cryptographic secrecy. In the CPT scheme, erasure coding is employed at the OPS/OBS ingress node to form coded packets, which are transmitted on disjoint paths from the ingress node to an egress node in the network. The CPT scheme allows for a unified view of Quality of Service (QoS) in OPS/OBS networks by linking the interactions between survivability, performance and secrecy. We provide analytical models that illustrate how QoS aspects of CPT are affected by the number of disjoint paths, packet overhead and processing delay.

This paper addresses contention resolution in optical switching fabrics exploiting Parametric Wavelength Converters (PWCs). Being a PWC able to perform simultaneous wavelength conversions, it can be employed to replace many single-channel wavelength converters, thus saving in the number of expensive optical components. Recently a switching fabric employing FixedWavelength Converters (FWCs), providing relevant cost savings compared to previous proposals, has been presented. The drawback is that it requires a high number of FWCs. For this reason, here new solutions based on PWCs instead of FWCs for such an architecture are proposed. Resulting switching fabrics are compared in terms of loss performance and cost. Simulation results outline that fabrics based on PWCs allow to save devices while obtaining the same performance as architectures using FWCs. They also prove how cost benefits are obtained in many switch configurations.

Communication networks have to provide a high level of resilience in order to ensure sufficient Quality of Service for mission-critical services. Currently, dedicated 1+1 path protection is implemented in backbone networks to provide the necessary resilience. On the other hand, there are several possible realization strategies for 1+1 path protection functionality (1PPF), utilizing both diversity- and network coding. In this paper we consider the cost aspects of the different realization strategies. We evaluate the cost of providing 1PPF both analytically and empirically in realistic network topologies. Our results show that both diversity and network coding can provide 1PPF with reduced cost compared to traditional 1+1 path protection, even in case of short paths and strict coding restrictions. Specifically, the network coding scheme could be used as a cost-efficient and potentially all-optical realization of 1PPF.

The optical migration-capable network with service guarantees hybrid network is a time-divided packet/circuit hybrid network offering absolute performance guarantees and high resource utilisation. Guaranteed service traffic (GST) follows lightpaths receiving absolute priority over statistically multiplexed (SM) traffic. Transmission resources are fully shared by interleaving SM and GST packets, but packet-switched SM packets experience contention, resulting in a packet loss that should be minimised. This article explores a novel bufferless network approach where the performance of the SM class is satisfied by applying packet-level forward error correction (FEC). Two implementation strategies are proposed: RedSM transmitting redundancy packets as SM traffic and RedGST transmitting redundancy packets as low-priority GST traffic. The performance of the schemes is explored analytically and by simulation. For uniform traffic loads, the RedGST scheme shows the best performance of the two, but even at 60% load the RedSM scheme shows packet loss rates (PLRs)close to 10−5. Simulations with non-uniform traffic loads illustrate the importance of selecting the optimal redundancy ratio; the failure to do so results in up to two orders of magnitude increase in PLR for the RedGST scheme. A much higher tolerance for traffic variations is the main benefit for the RedSM scheme. In view of the results, both schemes are attractive alternatives to buffered contention resolution techniques.

Optical Packet/Burst Switching (OPS/OBS) has emerged as a promising candidate for the next-generation all-optical network scenario. A crucial issue in OPS/OBS networks is how to provide packet loss rate (PLR) differentiation at the network layer. In this paper we propose a novel PLR differentiation scheme that utilizes network layer packet redundancy in order to isolate service classes in an OPS/OBS network. We derive an analytical model of the proposed scheme based on reduced load Erlang fix-point analysis. A numerical evaluation shows that the isolation degree between the service classes is dependent on the amount of redundancy, system load and share of high priority traffic.

This papers reports the advances in optical core networks research coordinated in the framework of the e- photon/ONe and e-photon/ONe+ networks of excellence.