Providing for QoS Maintenance in Wireless IP Environments Nikos Passas ∗ , Evangelos Zervas † , George Hortopan ∗ , and Lazaros Merakos ∗ ∗ Dept. of Informatics and Telecommunications † Dept. of Electronics University of Athens TEI-Athens Panepistimiopolis, Ilisia Egaleo 15784 Athens, Greece 12210 Athens, Greece Email: {passas,hortopan,merakos}@di.uoa.gr Email: zervas@ee.teiath.gr Abstract— A flow rejection algorithm for the dynamic RSVP (dRSVP) is proposed. dRSVP is an enhanced version of RSVP, aiming at providing dynamic Quality of Service (QoS) support in a variable bandwidth environment through guarantees of ranges of bandwidth instead of specific values. Flow rejection occurs when the channel quality decreases to a level that even the minimum bandwidth requirements per flow cannot be fulfilled. The proposed algorithm aims at significantly improving the flow dropping probability, without affecting the bandwidth utilization. Its operation is based on setting priority classes and rejecting the minimum required number of flows per class, in order to guarantee QoS to the remaining. Both mathematical analysis and simulation results show that the overall flow rejection probability can be significantly reduced. I. I NTRODUCTION Next generation networks are expected to rely on the Internet Protocol (IP) as their fundamental instrument for data transmission. Besides basic accommodation of data, guarantees for specific Quality of Service (QoS) should be provided, implied by the use of advanced network applications, such as voice and video-conference. On the other hand, next generation networks will incorporate a wide range of access systems, including both wired and wireless. Especially wireless local area networks (WLANs) are becoming more and more popular and tend to replace in many cases the traditional wired LANs [1], [2]. To interwork with wired IP networks, WLANs have to incorporate QoS mechanisms for fixed IP, such as Integrated Services (IntServ) [3], which is mainly targeted for access systems. The Resource Reservation Protocol (RSVP) [4], [5] is the most popular signalling protocol in IntServ for requesting QoS per flow and setting up reservations end-to-end upon admission. This approach is problematic in wireless links, due to the variable available bandwidth they provide, as a result of factors such as interference, fading and node movement. To address this problem, RSVP extensions and modifications have been proposed in the literature, and one of the most promising ones is the so-called dynamic RSVP (dRSVP) [6]. dRSVP modifies the existing RSVP standard, in order to request ranges of QoS instead of specific values. In case the channel quality falls to a level that not even the lowest values can be guaranteed for the admitted flows, the network has to reject one or more of them to maintain QoS to the rest. One of the key components of dRSVP over wireless, in terms of performance, is the flow rejection algorithm. The initial proposal [6] describes a simple algorithm that discards randomly a number of flows, to reduce the total bandwidth requirements below the offered limit. In this paper, we pro- pose a more sophisticated flow rejection algorithm, trying to significantly improve the performance of dRSVP, especially in terms of flow dropping probability. With minor adjustments, the same algorithm can also be used in RSVP over wireless as well. To show and measure the performance improvement, we use both mathematical analysis and simulations. The paper is organized as follows. Section II briefly dis- cusses prior work on dRSVP, to give the background. In section III, the proposed flow rejection algorithm is described in detail. The mathematical analysis of section IV shows that the proposed algorithm outperforms the original algorithm under all traffic and channel conditions. Moreover, in section IV a simulation model and results are presented to assess the performance improvement attained by the proposed algorithm. Finally, section V presents our conclusions. II. DESCRIPTION OF DRSVP RSVP was designed to enable hosts and routers to commu- nicate with each other in order to setup the necessary states for Integrated Services support. RSVP defines a communication “session” to be a data flow with a particular destination and transport layer protocol, identified by the triplet (destination address, transport-layer protocol type, destination port num- ber). Its operation only applies to packets of a particular session, and therefore every RSVP message must include details of the session to which it applies [4]. In the rest of the paper, the term “flow” is equivalent to “RSVP session”. The RSVP protocol defines seven types of messages, of which the PATH and RESV messages carry out the basic operation of resource allocation [5]. In contrast to the stable links used in fixed networks, band- width of wireless links is subject to variations due to factors, such as interference, fading, and node movement, which cause