Andreas Kimsas

Reservation techniques in an OpMiGua node

An OpMiGua node integrates a packet switch for low priority traffic and a circuit switch for high priority traffic. Both traffic classes share the same input and output ports using time division multiplexing, but absolute priority is given to circuit switched packets. The circuit switched packets do not experience contention at output ports and are not subject to delay jitter; hence a guaranteed service class is created. Previous studies of OpMiGua nodes have used one of two reservation techniques to assure priority; either a time-window approach or a preemptive approach. This article introduces two new reservation techniques and investigates advantages and drawbacks associated with the four techniques. It is shown that each reservation technique is associated with specific loss mechanisms and methods to reduce their influence are proposed. Simulation results demonstrate that the choice of reservation technique is highly influenced by the relative share and length of high priority packets.

A Cross Layer Study of Packet Loss in All-Optical Networks

A crucial issue in all-optical networks is packet loss. In this paper we evaluate sources of packet loss, comparing impact of effects at the physical layer and at the network layer. The study is compiled for optical packet, burst and circuit switched networks. We provide an analytical model that evaluates packet loss due to bit errors using bit-error rate, packet length distribution and network size as parameters. Bit errors at the physical layer set a lower limit to the aggregate packet loss and for some scenarios it overshadows packet loss at the network layer. For applications applied in the Internet today, bit error requirements may be considerably alleviated as compared to those of synchronous digital hierarchy (SDH) systems without degrading the perceived quality of service for the end-user. By considering recommended packet loss rates for future Internet services we evaluate the usefulness of different techniques for reduced packet loss.

Improving performance in the OpMiGua hybrid network employing the network layer packet redundancy scheme

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.

Protection Using Redundancy in a Hybrid Circuit/Packet Node Design

A protection mechanism for use in OCS/OPS hybrid networks is proposed. Performance is compared for internally blocking and non-blocking switch fabrics. After protection switching, high-priority traffic is undisturbed while low-priority traffic is penalised

Hybrid packet/time slotted circuit switched scheme (HPTS)

In the OpMiGua hybrid network, whether packets follow a circuit or a packet path is decided on a packet-by-packet basis. Packets following a circuit are given absolute priority with no packet loss or jitter. Packets following a packet switched path are statistically multiplexed. Circuits are wavelength-paths in a Wavelength Routed Optical Network (WRON), resulting in bandwidth granularity of a wavelength. In this paper, we propose the HPTS scheme, enabling a higher granularity of the OpMiGua guaranteed service (GST) circuit paths by employing time-slots. Nodes sharing a wavelength path are allocated time-slots according to their bandwidth needs. Best effort traffic accesses unused bandwidth within any time-slot, enabling high bandwidth utilization. Finally, the proposed network schemepsilas compatibility with GMPLS is briefly discussed.

OBS vs. OpMiGua - A Comparative Performance Evaluation

Optical Burst Switching (OBS) and Optical Migration Capable Networks with Service Guarantees (OpMiGua) are two all-optical network architectures. In this paper we compare both by means of a quantitative performance evaluation based on simulations. In order to achieve a maximum of comparability both models are chosen as similar as possible and especially are fed with identical traffic. Results show differences regarding loss probabilities at which OpMiGua has a better performance.

Analysis of a Bufferless OpMiGua Node

This paper presents a closed form expression and a Markov model estimating packet loss in a bufferless hybrid circuit and packet switched OpMiGua node. Prior traffic analysis of hybrid network nodes are based on preemptive and queue-based priority mechanisms, however, in this article we focus on the time-window approach with its associated reservation induced blocking (RIB). A closed form expression for packet loss is found by minimizing the RIB and is proved to be asymptotically exact for increasing length of circuit packets. A Markov model accounting for the effect of RIB is proposed and simulation is used to determine its accuracy. For lower than 85% share of circuit switched traffic, the respective median and 95- percentile for the relative error equals 10% and 25%. Finally, when circuit packets are aggregated into bursts the total packet loss is reduced for sufficiently high share of circuit traffic. The mechanisms behind this performance gain are identified and methods to maximise its effect are proposed.

Performance Issues in Optical Burst/Packet Switching

This chapter summarises the activities on optical packet switching (OPS) and optical burst switching (OBS) carried out by the COST 291 partners in the last 4 years. It consists of an introduction, five sections with contributions on five different specific topics, and a final section dedicated to the conclusions. Each section contains an introductive state-of-the-art description of the specific topic and at least one contribution on that topic. The conclusions give some points on the current situation of the OPS/OBS paradigms.

Performance in a Failure Situation of an OpMiGua Packet Switch with Internal Blocking

Differentiated survivability is a crucial quality of service (QoS) issue in future optical networks. Traffic streams belonging to applications demanding high availability should not be disrupted by the recovery process initiated after a node-failure. A recent study suggested to protect high-priority traffic by exploiting the inherent redundancy in the all-optical OpMiGua node. This article compares performance of high and low priority traffic before and after partial node-failure. Simulations are performed for an internally blocking and an internally nonblocking node. The results provide insight to the underlying effects causing packet loss in an internally blocking OpMiGua node and gives directions to future work