Real-time support for HCCA function in IEEE 802.11e networks: a performance evaluation

The IEEE 802.11 standard for wireless networks has been recently enhanced with the IEEE 802.11e amendment which introduces Quality of Service support. It provides differentiation mechanisms at the Medium Access Control layer, using two additional access functions: the Enhanced Distributed Channel Access (EDCA) function and the HCF Controlled Channel Access (HCCA) function. Only the HCCA mechanism is suitable for serving traffic streams with real-time requirements such as multimedia applications and Voice Over IP. The IEEE 802.11e standard does not specify a mandatory HCCA scheduling algorithm, but it offers a reference scheduler as the guideline in the resources scheduling design.In this paper we analyze four HCCA alternative schedulers to the reference one. They offer real-time guarantees proposing different solutions to the request of QoS and real-time support expressed by the increasing diffusion of multimedia applications. A performance evaluation is conducted to show the main differences between the considered schedulers, including the reference one.The results show that under several scenarios there is not a unique best scheduler, but there exists a variety of solutions depending on the specified requirements. The conclusions of the paper offer some guidelines in the choice of the scheduler tailored for a particular scenario of interest

Quality of service provision for IP traffic over wireless local area networks

The rapid development and the high transmission rates attained by the Wireless Local Area Networks (Wireless LANs - WLANs) have established them as one of the most attractive choices for supporting alternative access to large 3rd generation networks (3G) like UMTS or metropolitan IP networks. The installation of WLANs in places with a dense mobile user population (i.e. hot-spots like malls, airports, hospitals etc.) relieves the traffic load towards the metropolitan networks while, at the same time, achieves an improved level of quality of service for the mobile users. The work in hand deals with the provision of guaranteed quality of service (QoS) to the users of a WLAN and the interworking between WLANs and the 3rd generation and IP networks. The provision of quality of service to WLAN users at a level at least equal to that offered by the metropolitan network is deemed as especially important since the objective is to offer the mobile users a uniform level of quality of service regardless of their current location. The work herein is divided into three main parts: i) Study and development of Wireless Adaptation Layer (WAL), a shim, transparent –both for the IP layer and the underlying WLAN- layer that supports the interworking of WLANs with IP networks and provides guaranteed QoS over WLANs by utilizing the QoS mechanisms of WAL. The focus of the study was on the architecture of WAL and the proposal of mechanisms that support the application of Differentiated Services (DiffServ) over WAL based on traffic classification and appropriate configuration of WAL module chains. The proposed architecture was evaluated through simulation studies. ii) Study of traffic scheduling algorithms for WLANs that are based on IEEE 80211e protocol, the extension of legacy IEEE 802.11 protocol for supporting guaranteed QoS over 802.11 WLANs. More specifically a new traffic scheduling algorithm for 802.11e called ARROW (Adaptive Resource Reservation Over Wireless) was developed and compared through simulation studies with two previously existing algorithms (namely Simple and SETT-EDD). Comparison and evaluation of the scheduling algorithms was performed with the use of simulation platform developed for this purpose. Following the initial version of ARROW, an extension named Prioritized ARROW (P-ARROW) was developed. P-ARROW introduced the prioritized treatment of specific traffic flows or traffic classes (e.g. flows of real time traffic). The performance of P-ARROW was also evaluated through simulation studies. iii) Study of interworking between WLANs and UMTS for the provision of guaranteed QoS for the mobile users that perform a handover from one network to the other. The focus was on how the QoS mechanisms of UMTS and WLANs can interwork and combine so as to offer guaranteed QoS service to the users that perform a handover. Moreover signalling exchange and signalling adaptation issues between UMTS and WLAN were also studied under the perspective of guaranteed QoS, while emphasis was put in the appropriate translation/mapping/conversion of the QoS parameters of the two networks so as to achieve a uniform and compatible QoS scheme. Then the scenarios of video and voice calls seamless handover were studied. The quantitative performance of the proposed handover mechanisms was evaluated through simulation studies.Η ταχεία ανάπτυξη και οι υψηλές ταχύτητες μετάδοσης και επιδόσεις έχουν καταστήσει τα Ασύρματα Τοπικά Δίκτυα (Wireless LANs – WLANs) έναν από τους ελκυστικότερους τρόπους εναλλακτικής πρόσβασης σε μεγάλα ασύρματα δίκτυα 3ης Γενεάς (3G) όπως το UMTS ή σε μητροπολιτικά IP δίκτυα. H εγκατάσταση των WLANs σε χώρους όπου υπάρχει μαζική παρουσία χρηστών (π.χ. εμπορικά κέντρα, αεροδρόμια, νοσοκομεία) αποσυμφορίζει την κίνηση προς το μητροπολιτικό δίκτυο ενώ παράλληλα εξασφαλίζει καλύτερη ποιότητα υπηρεσίας στους εξυπηρετούμενους χρήστες. Η παρούσα διατριβή ασχολήθηκε με την παροχή εγγυημένης ποιότητας υπηρεσίας στους χρήστες ενός WLAN αλλά και με την αλληλεπίδραση και τη διαλειτουργικότητα μεταξύ των WLANs και των δικτύων 3ης Γενεάς αλλά και των δικτύων IP. H παροχή εγγυημένης ποιότητας υπηρεσίας, τουλάχιστον ισότιμης με αυτή του μητροπολιτικού δικτύου, στους χρήστες του WLAN κρίνεται ιδιαίτερα σημαντική καθώς στόχος είναι οι χρήστες να απολαμβάνουν το επιθυμητό επίπεδο ποιότητας υπηρεσίας σε οποιοδήποτε σημείο και αν βρίσκονται. Η διατριβή χωρίζεται σε τρεις βασικές ενότητες: i) Μελέτη και ανάπτυξη του Επιπέδου Ασύρματης Προσαρμογής (Wireless Adaptation Layer - WAL), ενός ενδιάμεσου και διάφανου - τόσο για το επίπεδο IP όσο και για το WLAN- επιπέδου για αλληλεπίδραση των WLANs με δίκτυα IP και υποστήριξη εγγυημένης ποιότητας υπηρεσίας πάνω από τα WLANs με χρήση των μηχανισμών του WAL. Στα πλαίσια της διατριβής μελετήθηκε η αρχιτεκτονική του WAL και προτάθηκαν μέθοδοι υποστήριξης διαφοροποιημένων υπηρεσιών (DiffServ) πάνω από αυτό με χρήση κατάλληλων μηχανισμών κατηγοριοποίησης της κίνησης (traffic classification) και κατάλληλων συνδυασμών των οντοτήτων του WAL σε αλυσίδες (WAL module chains). ii) Μελέτη αλγορίθμων χρονοδρομολόγησης κίνησης (traffic scheduling) για WLANs βασισμένα στο πρωτόκολλο ΙΕΕΕ 802.11e που αποτελεί επέκταση του κλασσικού ΙΕΕΕ 802.11 πρωτοκόλλου για παροχή εγγυημένης ποιότητας υπηρεσίας πάνω από WLANs. Πιο συγκεκριμένα αναπτύχθηκε ένας νέος αλγόριθμος με το όνομα ARROW (Adaptive Resource Reservation Over Wireless) ο οποίος συγκρίθηκε με δύο υφιστάμενους αλγορίθμους (Simple, SETT-EDD). Η αξιολόγηση και η σύγκριση των αλγορίθμων έγινε με τη χρήση κατάλληλης πλατφόρμας προσομοίωσης. Μετά την αρχική έκδοση του ARROW αναπτύχθηκε και αξιολογήθηκε μια επέκταση του, ο αλγόριθμος Prioritized-ARROW (P-ARROW) o οποίος εισήγαγε επιπλέον την εκχώρηση προτεραιότητας σε συγκεκριμένες ροές (π.χ. ροές πραγματικού χρόνου). iii) Αλληλεπίδραση και Διαλειτουργικότητα των WLANs με το UMTS για παροχή εγγυημένης ποιότητας υπηρεσίας σε χρήστες που μεταπέμπονται από το ένα δίκτυο στο άλλο. Εξετάστηκε πώς οι μηχανισμοί παροχής εγγυημένης ποιότητας υπηρεσίας του UMTS και των WLANs μπορούν να αλληλεπιδράσουν και να συνδυαστούν ώστε να παράσχουν εγγυημένη ποιότητα υπηρεσίας στους μεταπεμπόμενους χρήστες. Εξετάστηκαν επίσης θέματα ανταλλαγής και προσαρμογής της σηματοδοσίας πάνω από το WLAN και το UMTS με έμφαση στην κατάλληλη μετάφραση/αντιστοίχηση/μετατροπή των παραμέτρων ποιότητας υπηρεσίας ώστε να επιτευχθεί η ομοιόμορφη παροχή εγγυημένης ποιότητας υπηρεσίας. Κατόπιν αναπτύχθηκαν και αξιολογήθηκαν ποσοτικά (μέσω προσομοίωσης) μηχανισμοί και σενάρια αδιάλειπτης μεταπομπής (από το UMTS προς το WLAN) ροών βίντεο και φωνής

ARROW: An efficient traffic scheduling algorithm for IEEE 802.11e HCCA

In this paper we present a novel traffic scheduling algorithm for IEEE 802.11e, referred to as ARROW(Adaptive Resource Reservation Over WLANs), which aims at providing improved performance for the support of multimedia traffic. The novel characteristic of this algorithm, compared to previous proposals, is that it performs channel allocations based on the actual traffic buffered in the various mobile stations, i.e., on the exact transmission requirements. This feature renders ARROW ideal for variable bit rate traffic. However, an enhancement is also presented that improves ARROW performance under constant bit rate traffic. The ARROW algorithm and its enhancement are discussed and evaluated against two other schedulers found in the open technical literature, namely the Simple Scheduler and SETT-EDD. Results from a detailed simulation model verify that ARROW provides much better channel utilization and considerably improved performance, in terms of mean delay and packet loss. © 2006 IEEE

A centralized approach to dynamic channel assignment in wireless ATM LANs

A centralized approach for Dynamic Channel Assignment (DCA) in wireless ATM system is presented. The proposed approach applies to structured wireless ATM LANs, where base stations act as hubs to offer wireless access to mobile units. An IntrAdomain DCA entity (IADCA) is introduced for the dynamic assignment of resources to the requesting base stations, taking into account mutual interference constraints and current resource usage. The IADCA entity is based on two different reservation disciplines and multiple assignment policies when candidate carriers are available. Simulation results for a number of scenarios are presented to assess the performance of the proposed approach

Supporting UMTS QoS in Wireless LANs

This paper focuses on how the UMTS Quality of Service (QoS) architecture can be supported in Wireless LANs (WLANs), deployed as alternative access networks to the UMTS core. More specifically, the paper addresses the provision of UMTS QoS over WLANs and proposes a solution based on the introduction of the Wireless Adaptation Layer (WAL). The WAL provides means for extending the UMTS QoS in WLAN environments, independently of the underlying WLAN technology. Moreover, the WAL configuration to support the provisioning of UMTS QoS is discussed. In this context, a mapping between UMTS QoS attributes and WAL modules is proposed and justified. © IFIP International Federation for Information Processing 2003

On the support of voice call continuity across UMTS and wireless LANs

In this paper, we address the architecture and the procedures that can enable voice call handover from UMTS to WLAN and we also study how efficiently the WLAN can support the voice calls transferred from UMTS. Our study is based on a practical simulation model that lets us quantify the maximum number of voice calls that can be handed over from UMTS to WLAN, subject to maintaining the same level of UMTS QoS and respecting some WLAN policies. In addition, several other voice call performance metrics are derived. Our results indicate that an IEEE 802.11e access point can support a limited number of voice calls handed over from UMTS, which depends primarily on the applied WLAN bandwidth sharing policy (i.e., how the bandwidth is shared between WLAN voice and data users) and the QoS requirements. The performance of the WLAN scheduling algorithm is also of paramount importance and in our study we consider the so-called ARROW scheduler. Although the simulation results are derived for a specific bandwidth sharing policy, they can readily be scaled and provide practical upper bounds for the number of UMTS voice calls that can be seamlessly admitted to a WLAN access point. Copyright © 2007 John Wiley & Sons, Ltd