Claudio Cicconetti

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

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

An SDN-Based Network Architecture for Extremely Dense Wireless Networks

Telecommunications networks are undergoing major changes so as to meet the requirements of the next generation of users and services, which create a need for a general revised architectural approach rather than a series of local and incremental technology updates. This is especially manifest in mobile broadband wireless access, where a major traffic increase is expected, mostly because of video transmission and cloud-based applications. The installation of a high number of very small cells is foreseen as the only practical way to achieve the demands. However, this would create a struggle on the mobile network operators because of the limited backhaul capacity, the increased energy consumption, and the explosion of signalling. In the FP7 project CROWD, Software Defined Networking (SDN) has been identified as a solution to tame extreme density of wireless networks. Following this paradigm, a novel network architecture accounting for MAC control and Mobility Management has been proposed, being the subject of this paper.

CROWD: An SDN Approach for DenseNets

Traffic demands in mobile networks are expected to grow substantially in the next years, both in terms of total traffic volume and of bit-rate required by individual users. It is generally agreed that the only possible solution to overcome the current limitations is to deploy very dense and heterogeneous wireless networks, which we call DenseNets. However, simply scaling down existing networks by orders of magnitude, as required to fulfill traffic forecasts, is not possible because of the following constraints: i) the bottleneck would shift from the Radio Access Network (RAN) to the backhaul, ii) control overhead, especially related to mobility management, would make the network collapse, iii) operational costs of the network would be unbearable due to energy consumption and maintenance/optimisation. In this paper, Software Defined Network (SDN) for mobile networks is claimed as the paradigm shift necessary to tackle adequately the above challenges. A novel architecture is proposed, which supports DenseNets made of overlapping LTE and WLAN cells connected to the core network via a reconfigurable backhaul.

FEBA: a bandwidth allocation algorithm for service differentiation in IEEE 802.16 mesh networks

In wireless mesh networks, the end-to-end throughput of traffic flows depends on the path length, i.e., the higher the number of hops, the lower becomes the throughput. In this paper, a fair end-to-end bandwidth allocation (FEBA) algorithm is introduced to solve this problem. FEBA is implemented at the medium access control (MAC) layer of single-radio, multiple channels IEEE 802.16 mesh nodes, operated in a distributed coordinated scheduling mode. FEBA negotiates bandwidth among neighbors to assign a fair share proportional to a specified weight to each end-to-end traffic flow. This way traffic flows are served in a differentiated manner, with higher priority traffic flows being allocated more bandwidth on the average than the lower priority traffic flows. In fact, a node requests/grants bandwidth from/to its neighbors in a round-robin fashion where the amount of service depends on both the load on its different links and the priority of currently active traffic flows. If multiple channels are available, they are all shared evenly in order to increase the network capacity due to frequency reuse. The performance of FEBA is evaluated by extensive simulations. It is shown that wireless resources are shared fairly among best-effort traffic flows, while multimedia streams are provided with a differentiated service that enables quality of service.

A downlink data region allocation algorithm for IEEE 802.16e OFDMA

IEEE 802.16e specifies a connection-oriented centralized medium access control (MAC) protocol, based on time division multiple access (TDMA), which adds mobility support to the MAC protocol defined by the IEEE 802.16 standard for fixed broadband wireless access. To this end, orthogonal frequency division multiple access (OFDMA) is specified as the air interface. In OFDMA, the MAC frame extends over two dimensions: time, in units of OFDMA symbols, and frequency, in units of logical sub-channels. The base station (BS) is responsible for allocating data into the MAC frames so as to meet the quality of service (QoS) guarantees of the admitted connections of the mobile stations (MSs). This is done on a frame-by-frame basis by defining the content of map messages, which advertise the position and shape of data regions reserved for transmission to/from MSs. We refer to the latter operation as data region allocation. In this paper, we propose a sample data region allocation algorithm (SDRA), and we evaluate its performance by means of Monte Carlo analysis. The effectiveness of SDRA is assessed in several scenarios, involving mixed voice over IP (VoIP) and best effort MSs, different modulations, and frequency re-use plans.

Bandwidth Balancing in Multi-Channel IEEE 802.16 Wireless Mesh Networks

In wireless mesh networks, the end-to-end throughput of traffic flows depends on the path length, i.e. the higher the number of hops, the lower becomes the throughput. In this paper, a Fair End-to-end Bandwidth Allocation (FEBA) algorithm is introduced to solve this problem. FEBA is implemented at the Medium Access Control (MAC) layer of single-radio, multiple channels IEEE 802.16 mesh nodes, operated in a distributed coordinated scheduling mode. FEBA negotiates bandwidth among neighbors to assign a fair share to each end-to-end traffic flow. This is carried out in two steps. First, bandwidth is requested and granted in a round-robin fashion where heavily loaded links are provided with a proportionally higher amount of service than the lightly loaded links at each round. Second, at each output link, packets from different traffic flows are buffered in separate queues which are served by the Deficit Round Robin (DRR) scheduling algorithm. If multiple channels are available, all of them are shared evenly in order to increase the network capacity due to frequency reuse. The performance of FEBA is evaluated by extensive simulations and is shown to provide fairness by balancing the bandwidth among traffic flows.

An integrated framework for enabling effective data collection and statistical analysis with ns-2

The Network Simulator 2 (ns-2) is an open source tool for network simulation. When planning for large-scale simulation experiments, an efficient and flexible data collection and a statistically sound output data analysis are important aspects to keep in mind. Unfortunately, ns-2 offers little support for data collection, and statistical analysis of the simulation results is most often performed offline, using either home made code or available packages, which are not integrated with ns-2. In this paper we describe two complementary contributions: the first one consists of a set of C++ modules, that allow a flexible and efficient data collection; the second one is a software framework, which is fully integrated with ns-2, that performs all the operations required to carry out simulation experiments in a statistically sound way. Our framework allows a user to significantly reduce the postprocessing overhead and to save simulation time, especially with large-scale simulations. Our code is publicly available at [3].

Design and performance analysis of the Real-Time HCCA scheduler for IEEE 802.11e WLANs

This paper presents a new scheduling algorithm, called Real-Time HCCA (RTH), devised to support Quality of Service (QoS) at the flow level in an IEEE 802.11e network using the Hybrid Coordinator Function (HCF) Controlled Channel Access (HCCA) function. RTH separates online activities which take place at the frame transmission timescale, from offline activities which take place at the flow lifetime timescale. Complex computations are relegated to offline activities, while online tasks are kept as simple as possible. More specifically, at admission control time, RTH computes a periodic schedule based on the well-known Earliest Deadline First algorithm for 802.11e Traffic Streams (TSs). In doing so, the Stack Resource Policy is applied to account for non-pre-emptability of frame transmissions. Furthermore, the parameters are configured so as to reduce the MAC overhead due to polling uplink TSs. On the other hand, online scheduling is enforced simply by reading the pre-computed schedule, at little or no computational cost. RTH performance is assessed in terms of the admission control limit and of the amount of channel capacity that is left for contention-based access. Under both criteria, RTH is shown to outperform the sample scheduler proposed in IEEE 802.11e.

G-PaMeLA: A divide-and-conquer approach for joint channel assignment and routing in multi-radio multi-channel wireless mesh networks

The performance of Multi-Radio Multi-Channel Wireless Mesh Networks (MRMC-WMNs) based on the IEEE 802.11 technology depends significantly on how the channels are assigned to the radios and how traffic is routed between the access points and the gateways. In this paper we propose an algorithmic approach to this problem, for which, as far as we know, no optimal polynomial time solutions have been put forward in the literature. The core of our scheme consists of a sequential divide-and-conquer technique which divides the overall Joint Channel Assignment and Routing (JCAR) problem into a number of local optimization sub-problems that are executed sequentially. We propose a generalized scheme called Generalized Partitioned Mesh network traffic and interference aware channeL Assignment (G-PaMeLA), where the number of sub-problems is equal to the maximum number of hops to the gateway, and a customized version which takes advantage of the knowledge of the topology. In both cases each sub-problem is formulated as an Integer Linear Programming (ILP) optimization problem. An optimal solution for each sub-problem can be found by using a branch-and-cut method. The final solution is obtained after a post-processing phase, which improves network connectivity. The divide-and-conquer technique significantly reduces the execution time and makes our solution feasible for an operational WMN. With the help of a detailed packet level simulation, the G-PaMeLA technique is compared with several state-of-the-art JCAR algorithms. Our results highlight that G-PaMeLA performs much better than the others in terms of packet loss rate, collision probability and fairness among traffic flows.