Fabrice Poppe

Choosing the UMTS air interface parameters, the voice packet size and the dejittering delay for a voice-over-IP call between a UMTS and a PSTN party

We develop a methodology to set the VoIP application parameters (voice packet size and dejittering delay) and the UMTS air interface parameters in such a way that the quality of VoIP calls involving a UMTS party is ensured. We use analytical techniques to determine the delay and packet loss contributions of the various transmission stages crossed by the voice packet flow, and the E-model to predict the perceived quality. Our numerical results show that provided the parameters of the VoIP application and the UMTS air interface are chosen properly, UMTS access and the stringent delay and packet loss requirements of VoIP are reconcilable.

Guaranteeing quality of service to packetised voice over the UMTS air interface

A key feature of the air interface of the Universal Mobile Telecommunication System (UMTS) standardised by 3GPP is that its functionality can be tailored to the requirements of individual applications, In this paper we study how this flexibility can be exploited to meet the stringent delay and packet loss requirements of a voice-over-IP application (VoIP). We introduce an analytical model of the UMTS air interface that allows us to quantify the impact of the air interface parameters (power budget, interleaving span and channel coding rate) on the parameters that determine the perceived quality of VoIP calls (mouth-to-ear delay and packet loss probability). We use the model to explore the trade-offs that are inherent in the setting of the air interface parameters. The numerical results we present illustrate and quantify the trade-offs of bandwidth efficiency versus packet loss, and of packet loss versus packet delay. The latter trade-off is of particular importance for the feasibility of VoIP.

Quality-of-service differentiation and fairness in optical burst-switched networks

A mechanism that is often proposed for Quality-of-Service differentiation in Optical Burst-Switched networks is offset-time management. In this paper we identify and explain some undesired characteristics of this mechanism. The most important finding is that the burst drop probability differentiation that is attained for a given offset-time value strongly depends on the distribution of the burst durations. Hence control of the differentiation is difficult, since the distribution of burst durations is subject to changes all the time, depending on the traffic conditions at the edge of the OBS network. We also found that offset-time management slightly increases the unfairness within the lower priority classes, in the sense that longer bursts are dropped more frequently than shorter ones.

Choosing the Objectives for Traffic Engineering in IP Backbone Networks BAsed on Quality-of-Service Requirements

Objectives for traffic engineering in IP core networks can be different for different Quality-of-Service classes. In this paper we study the traffic engineering objectives for best-effort flows and for virtual leased line service flows. We propose mixed integer linear programming models that can be used for off-line centralized traffic engineering with label switched paths, and develop efficient algorithms for their approximate solution. We quantify the effect of the choice of the objective chosen for traffic engineering on the network performance, and assess the benefits of distributing the traffic between a single border node pair over multiple paths.

The impact of burstification on TCP throughput in optical burst switching networks

We focus on the optimal size a data burst (DB) should have in an Optical Burst Switching (OBS) network in the single wavelength link case. The optimality is understood in the sense of maximizing throughput under the assumption the traffic is TCP controlled. In such networks, packets are assembled into bursts containing several IP packets (burstification). A trade-off takes place between large and small DBs. The former leads to a degradation of throughput due to loss synchronization, a well known problem in TCP controlled traffic, whereas, the latter leads to overhead due to the guard-band intervals. To address the optimal DBs size problem, we use an estimate of throughput obtained through individual TCP connections sharing a common router. The effect on synchronization is thus taken into account. A classical optimization technique is then applied to the resulting goodput formula to determine, the optimal size. Besides, we also examine Fiber Delay Lines (FDL) modeling aspects.

Single-path traffic-engineering with explicit routes in a flat Differentiated Services network

In this paper, we present a scalable algorithm, capable of finding a single-path traffic-engineered solution for routing traffic in a Differentiated Services network by means of explicit paths. Additional supported features are preemption, fast restoration, with a choice of protection scheme, oversubscription and resource class affinity. The performance of the algorithm is demonstrated by means of statistical simulations on randomly generated network topologies.

Constrained shortest path first algorithm for lambda-switched mesh optical networks with logical overlay OCh/SP rings

We describe a constrained shortest path first (CSPF) routing algorithm for lambda-switched optical networks with logical overlay OCh/SP rings. Speed is definitely a requirement if the algorithm is to be used for lambda-switching, but several features of the network architecture complicate the routing problem. The algorithm we present in this paper meets the requirement of being fast. Moreover, the routing of a lightpath is based on a limited amount of link state information, which can be disseminated by a lightweight routing protocol. Our numerical results show that the performance of the algorithm does not improve significantly if the routing decisions are based on more detailed information about the configuration of the network.

Application of the Link Management Protocol to Discovery and Forwarding Adjacencies

The link management protocol (LMP) is used to maintain control channel connectivity, to verify the physical connectivity of data channels, to correlate link property information at both endpoints of a data link and to aggregate multiple data links into a single traffic engineering (TE) link. LMP also provides assistance in fault localization, both in opaque and transparent optical networks. In this paper, we show how LMP relates to the generalized multi-protocol label switching (GMPLS) suite of protocols and integrates into a distributed GMPLS control plane. We describe the role of LMP in two applications: data link (auto-)discovery and the establishment of forwarding adjacency label-switched paths (FA-LSPs) including their initiation, verification and bundling, and conclude that they can be built upon basic functions of LMP, namely control channel management, link verification and link property correlation.

Dynamic weights for OCSPF route computation in optical networks

In current routing algorithms for wavelength switched optical transport networks, based on the Open Constrained Shortest Path First (OCSPF) concept, the effects of traffic dynamicity (the fact that lightpaths (a.k.a. optical connections or optical LSPs) are continuously being set-up and torn down) are not taken into account. Therefore, in this study four new link metrics are proposed, each of which could be used to replace the current metrics being used. Two metrics are based on the average load ρ on a link during a given timeframe. Two other metrics are based on an estimate of the number of setup requests nbr that will be blocked during the lifetime of the lightpath that is being set up. It is shown that the former two link metrics (i.e. those based on ρ) significantly reduce the blocking probability compared to the case in which a constant link metric is used. The latter two metrics (i.e. those based on nbr) however perform only slightly better or even worse than the original algorithm. In addition, it is observed that by taking into account the traffic dynamicity using the average load on a link, the amount of sustainable demand can be increased by about 10% for a given blocking probability.

Capacity Efficiency of Distributed Path Restoration Mechanisms in Optical Mesh Networks

In this study the restoration performance of two closely related Sender/Chooser-based distributed path restoration protocols (both extensions of the Self-Healing Network (SHN) to path restoration) is compared. Some pathological situations in which these Sender/Chooser-based restoration algorithms perform suboptimally are identified and, where available, possible solutions are proposed. Built-in mechanisms to resolve contention between Sender/Chooser pairs were found to be very helpful. In addition, the performance of the distributed restoration algorithms studied was found to be close to its theoretical upper bound, suggesting that the pathological situations described may not be that important for real-life networks.