Luciano Lenzini

Quality of service support in IEEE 802.16 networks

During the last few years, users ail over the world have become more and more accustomed to the availability of broadband access. This has boosted the use of a wide variety both of established and recent multimedia applications. However, there are cases where it is too expensive for network providers to serve a community of users. This is typically the case in rural and suburban areas, where there is slow deployment (or no deployment at all) of traditional wired technologies for broadband access (e.g., cable modems, xDSL). In those cases, the most promising opportunity rests with broadband wireless access technologies, such as the IEEE 802.16, also known as WiMAX. One of the features of the MAC layer of 802.16 is that it is designed to differentiate service among traffic categories with different multimedia requirements. This article focuses on mechanisms that are available in an 802.16 system to support quality of service (QoS) and whose effectiveness is evaluated through simulation

Channel Assignment Strategies for Multiradio Wireless Mesh Networks: Issues and Solutions

Next-generation wireless mobile communications will be driven by converged networks that integrate disparate technologies and services. The wireless mesh network is envisaged to be one of the key components in the converged networks of the future, providing flexible high- bandwidth wireless backhaul over large geographical areas. While single radio mesh nodes operating on a single channel suffer from capacity constraints, equipping mesh routers with multiple radios using multiple nonoverlap- ping channels can significantly alleviate the capacity problem and increase the aggregate bandwidth available to the network. However, the assignment of channels to the radio interfaces poses significant challenges. The goal of channel assignment algorithms in multiradio mesh networks is to minimize interference while improving the aggregate network capacity and maintaining the connectivity of the network. In this article we examine the unique constraints of channel assignment in wireless mesh networks and identify the key factors governing assignment schemes, with particular reference to interference, traffic patterns, and multipath connectivity. After presenting a taxonomy of existing channel assignment algorithms for WMNs, we describe a new channel assignment scheme called MesTiC, which incorporates the mesh traffic pattern together with connectivity issues in order to minimize interference in multi- radio mesh networks.

Performance Evaluation of the IEEE 802.16 MAC for QoS Support

The IEEE 802.16 is a standard for broadband wireless communication in metropolitan area networks (MAN). To meet the QoS requirements of multimedia applications, the IEEE 802.16 standard provides four different scheduling services: unsolicited grant service (UGS), real-time polling service (rtPS), non-real-time polling service (nrtPS), and Best Effort (BE). The paper is aimed at verifying, via simulation, the effectiveness of rtPS, nrtPS, and BE (but UGS) in managing traffic generated by data and multimedia sources. Performance is assessed for an IEEE 802.16 wireless system working in point-to-multipoint (PMP) mode, with frequency division duplex (FDD), and with full-duplex subscriber stations (SSs). Our results show that the performance of the system, in terms of throughput and delay, depends on several factors. These include the frame duration, the mechanisms for requesting uplink bandwidth, and the offered load partitioning, i.e., the way traffic is distributed among SSs, connections within each SS, and traffic sources within each connection. The results also highlight that the rtPS scheduling service is a very robust scheduling service for meeting the delay requirements of multimedia applications

Metropolitan Area Networks

With the continued success of Local Area Networks (LANs) there has been an increasing demand to extend their capabilities. This need has given rise to Metropolitan Area Networks (MANs), which through the use of fibre-optic technology offer much higher data rates over much greater distances. This volume presents a detailed, self-contained account of the state the art in high-speed LANs and MANs, with a particular focus on the two available standards, FDDI and DQDB. Special attention is given to the analysis of quality of service provided at the Medium Access Control (MAC) level, and to emerging techniques for performance evaluation (including M/G/1-tyoe models, rare event simulation and polling methods).

A methodological approach to an extensive analysis of DQDB performance and fairness

A distributed queue dual bus media access control (DQDB MAC) protocol state machine is described. The DQDB mathematical models and the tools used for their solution are introduced. The workload characterization is shown, and fairness metrics and performance indexes are defined. An analysis in underload and overload conditions is described, and the influence of the DQDB internal mechanisms is discussed. The asymptotic analysis is reported. DQDB behavior at higher speeds is analyzed. >

QoS provided by the IEEE 802.11 wireless LAN to advanced data applications: a simulation analysis

IEEE 802.11 is a Media Access Control (MAC) protocol which has been standardized by IEEE for Wireless Local Area Networks (WLANs). The IEEE 802.11 MAC protocol offers two types of services to its users: synchronous and asynchronous. This paper presents an in‐depth analysis, by simulation, of the asynchronous part alone. The analysis is performed by considering station data traffic patterns (hereafter advanced data traffic) which have a very similar shape to traffic generated by WWW applications. We carried out the simulation by taking into consideration two classes of scenarios: balanced and unbalanced. In the former class each station has the same offered load while in the latter class a specific station is more loaded than the others. Our conclusion is that the IEEE 802.11 MAC protocol performs satisfactorily for both classes of scenarios, although performance measures with advanced traffic are worse than the corresponding performance measures with Poissonian traffic. Furthermore, we broadened our analysis to include higher medium capacities than those planned (i.e., 1 and 2 Mbit/sec) up to 10 Mbit/sec. This part of the analysis shows that the IEEE 802.11 MAC protocol is not adequate to work at speeds planned for the forthcoming ATM Wireless LAN.

Tight end-to-end per-flow delay bounds in FIFO multiplexing sink-tree networks

Aggregate scheduling has been proposed as a solution for achieving scalability in large-size networks. However, in order to enable the provisioning of real-time services, such as video delivery or voice conversations, in aggregate scheduling networks, end-to-end delay bounds for single flows are required. In this paper, we derive per-flow end-to-end delay bounds in aggregate scheduling networks in which per-egress (or sink-tree) aggregation is in place, and flows traffic is aggregated according to a FIFO policy. The derivation process is based on Network Calculus, which is suitably extended to this purpose. We show that the bound is tight by deriving the scenario in which it is attained. A tight delay bound can be employed for a variety of purposes: for example, devising optimal aggregation criteria and rate provisioning policies based on pre-specified flow delay bounds.

A genetic approach to joint routing and link scheduling for wireless mesh networks

Wireless mesh networks are an attractive technology for providing broadband connectivity to mobile clients who are just on the edge of wired networks, and also for building self-organized networks in places where wired infrastructures are not available or not deemed to be worth deploying. This paper investigates the joint link scheduling and routing issues involved in the delivery of a given backlog from any node of a wireless mesh network towards a specific node (which acts as a gateway), within a given deadline. Scheduling and routing are assumed to be aware of the physical interference among nodes, which is modeled in the paper by means of a signal-to-interference ratio. Firstly, we present a theoretical model which allows us to formulate the task of deriving joint routing and scheduling as an integer linear programming problem. Secondly, since the problem cannot be dealt with using exact methods, we propose and use a technique based on genetic algorithms. To the best of our knowledge, these algorithms have never been used before for working out these kinds of optimization problems in a wireless mesh environment. We show that our technique is suitable for this purpose as it provides a good trade-off between fast computation and the overall goodness of the solution found. Our experience has in fact shown that genetic algorithms would seem to be quite promising for solving more complex models than the one dealt with in this paper, such as those including multiple flows and multi-radio multi-channels.

Tradeoffs between low complexity, low latency, and fairness with deficit round-robin schedulers

Deficit Round-Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the presence of variable length packets. The main attractive feature of DRR is its simplicity of implementation: in fact, it can exhibit O(1) complexity, provided that specific allocation constraints are met. However, according to the original DRR implementation, meeting such constraints often implies tolerating high latency and poor fairness. In this paper, we first derive new and exact bounds for DRR latency and fairness. On the basis of these results, we then propose a novel implementation technique, called Active List Queue Method (Aliquem), which allows a remarkable gain in latency and fairness to be achieved, while still preserving O(1) complexity. We show that DRR achieves better performance metrics than those of other round-robin algorithms such as Pre-Order Deficit Round-Robin and Smoothed Round-Robin. We also show by simulation that the proposed implementation allows the average delay and the jitter to be reduced.

MAC protocols for wideband wireless local access: evolution toward wireless ATM

The wireless local area network (WLAN) and wireless ATM are emerging technologies for wideband wireless local access. Two standards, IEEE 802.11 and ETSI HIPERLAN type 1, are currently available for WLAN; the standardization process of wireless ATM, involving, among others, the wireless ATM Group of the ATM Forum and the broadband radio access networks project of the ETSI, is ongoing and related standards are expected to be released by mid-1999. This article focuses on the MAC protocol aspects of wireless local access networks. It first investigates, from a traffic performance point of view, the MAC protocol of the IEEE 802.11 and ETSI HIPERLAN type 1 standards, and then verifies to what extent these MAC protocols are suitable for wireless ATM. The analysis is then extended by considering a new MAC protocol, dynamic slot assignment (DSA++), which has been designed to explicitly support ATM technology over the radio interface. DSA++ is a candidate for the ETSI HIPERLAN type 2 standard, a developing ETSI standard for wireless ATM.