Modeling of a distributed access protocol for an ATM satellitesystem: an algorithmic approach

An algorithmic model for the performance evaluation of the medium access control (MAC) protocol for a satellite system in an asynchronous transfer mode (ATM) environment is presented. This model allows analysis of general load configurations and yields the mean value of the performance parameters (e.g. queue lengths and access delays). The model is based on a computer-oriented approach, and the characterization of the key model variables is obtained by means of an iterative procedure. A comparison of the model analysis results to those obtained by a simulative approach shows a satisfactory matching     

An Architecture for Differentiated Protection Against Single and Double Faults in GMPLS

In the context of an optical network GMPLS can be used to provide network robustness to faults through end-to-end path protection techniques. In this paper, we present a dynamic distributed model supporting five different classes of protection, including protection against single and double fault, with and without sharing of backup bandwidth. Beyond link and node failures we also consider protection against shared risk link group (SLRG) failure. In this paper, we briefly describe the protection model and the underlying algorithms for route selection and backup bandwidth sharing. After that we face the following issue: Which subset out of the five possible protection classes is convenient for an operator to support on the same network infrastructure? To answer this question it is fundamental to have a clear view of the trade-offs between the costs and the performances associated to each class. To achieve that we carried out an extensive performance analysis by means of simulations. For each protection class, we evaluated two fundamental performance metrics: the recovery probability under multiple faults, and the average per-demand resource usage. On the basis of such results, we are able to identify some basic guidelines driving the choice of the more convenient subset of protection classes to be implemented within a single network.     

Resources sharing in optical packet switches with limited-range wavelength converters

This paper compares selected optical packet switching architectures that use the wavelength conversion technique to solve the packet contention problem. The architectures are equipped with shared and limited-range wavelength converters (LRWCs). This paper focuses on two architectures: the shared per node (SPN) and the shared per output fiber (SPOF) architectures, in which the wavelength converters are SPN and output fiber, respectively. Packet loss probability is expressed as a function of the number of wavelength converters used, by means of analytical models validated by simulations. The analytical results show how the use of a reduced number of LRWCs with small range allows the switch to obtain the same performances of an architecture equipped with all of the wavelength converters and using a full wavelength conversion.     

Analysis and dimensioning of switchless networks for single-layeroptical architecture

The “switchless” all-optical network is an alternative networking approach being developed in the framework of the ACTS project named SONATA, which aims to provide a future single layer, advanced transport architecture on a national scale. The single hop, shared access network employs time and wavelength agility (a WDMA/TDMA scheme), using fast tunable transmitters and receivers, to set up individual customer connections through a single wavelength router (suitably replicated for resilience). The dimensioning of this type of network is one of the main tasks for the design of networks serving a certain number of customers, connected together by means of passive optical networks (PONs). This paper reports an analytical model which allows the network dimensioning according to some relevant design parameters: the number of customers per PON, the number of PONs, the offered traffic per single user (either considering residential or business user), and the required system performance expressed in terms of blocking probability. Furthermore, relevant issues related to the dimensioning of switchless networks are discussed and some results achieved for relevant network scenarios are reported, to assess the feasibility of the system concept     

Amplification effects of the send rate of TCP connection through an optical burst switching network

This paper investigates support for TCP RENO flows in an Optical Burst Switching (OBS) network. In particular we evaluate the TCP send-rate, i.e., the amount of data sent per time unit taking into account the burst assembly mechanism at the edge nodes of the OBS network and burst loss events inside the network. The analysis demonstrates an interesting phenomenon, that we call correlation benefit. This phenomenon is introduced by the aggregation mechanism and can give rise, in some conditions, to a significant increase in the TCP send-rate. These results are obtained by means of an analytical model, based on a Markovian approach, and have been validated via an intensive simulation campaign.     

Optimal Routing for Protection and Restoration in an Optical Network

In this paper we provide a centralized method for optimally selecting the set of active and backup paths in an optical transport network in the cases of shared-path restoration and 1:1 protection schemes. We provide novel mixed integer linear programming (MILP) formulations for both the schemes, for a network with full wavelength conversion capability. The given formulations are not restricted to consider single link failures: the concept of fault event is introduced to handle the possibility that multiple links go simultaneously under fault. The optimization objective includes the total capacity requirement plus an additional term related to the active paths reliability. We use a simple decomposition heuristic to support the resolution process. The optimization is solved for various sample scenarios in order to evaluate the resource saving achieved with the shared-path restoration scheme. The impact of different factors such as topology, traffic demand and structure of failures on the resource saving is analyzed. Also, we provide guidelines about handling differentiated levels of protection within the framework of the proposed formulations.     

Input wavelength conversion in optical packet switches

This letter analyzes an architecture for optical packet switches in which the wavelength converters are shared per input line (SPIL). The architecture performance are evaluated by means of an analytical model and are compared with those of an optical packet switch architecture in which the wavelength converters are shared per output line (SPOL). The obtained results show that in both balanced and unbalanced traffic scenarios the proposed architecture allows for a remarkable saving in terms of number of converters. In some cases this saving can reach 50%.     

Performance evaluation of optical cross connect architectures underan efficient wavelength assignment

In this letter we evaluate the performance of optical cross connect (OXC) architectures with wavelength conversion capability and in which the number of wavelength converters (WCs) is optimized by means of WC sharing. Dimensioning models of WCs are proposed and the number of WCs is evaluated according to an efficient wavelength assignment that allows to obtain a high saving of WCs     

Advantages of Hybrid Input/output Wavelength Conversion in Optical Packet Switches

In this paper, we propose a new Optical Packet Switching Architecture referred to as Shared Per Input/Output Line (SPIOL) in which Wavelength Converters, used to solve output packet contentions, are shared per input and per output line. In this architecture, packets needing conversion can be wavelength translated by converters placed on output lines or by converters placed on input lines. We introduce and discuss the analytical and simulation models we used to evaluate the performance of the architecture in question when a simple control algorithm, referred to as Random Algorithm, is adopted. The proposed architecture performance is compared to that of two other architectures referred to as Shared Per Input Line (SPIL) and Shared per Output Line (SPOL), which share converters per output line only and per input line only, respectively. The comparison is carried out under symmetric and asymmetric traffic scenarios. The obtained results show that in some cases the SPIOL architecture allows for a saving in the order of 20% and 30% with respect to the SPIL and SPOL architectures, respectively.     

Packet loss in a bufferless optical WDM switch employing sharedtunable wavelength converters

We propose an architecture for a bufferless packet optical switch employing the wavelength dimension for contention resolution. The optical packet switch is equipped with tunable wavelength converters shared among the input lines. An analytical model Is proposed in order to determine the number of converters needed to satisfy prefixed packet loss probability constraints. This analytical model very accurately fits with simulations results. A sensitivity analysis of the required number of converters as a function of the main system parameters (number of input and output lines, number of wavelengths, …) and traffic parameters has been carried out. Making use of the introduced dimensioning procedure we have observed that the proposed architecture allows a saving in terms of employed number of converters with respect to the other architectures proposed in literature. Such a saving can reach about 95% of the number of converters