Abstract
Recently Andrew et al. proposed the TCP Evaluationsuite to provide a common test suite for researchers designingnew TCP extensions and AQM mechanisms. It defines networktopologies, simulation scenarios i.e. traffic characteristic as well asevaluation parameters to provide a common testbed for all newenhancements. The presented remarks determine the essentialfeatures of a simulation environment for different solutions incommon networks.Following the introduction of a standardized TCP benchmarkwe propose several improvements to the TCP-targeted test suitewhich allow WiMAX environment evaluation. Some specificimplementation issues can significantly influence the efficiencyof the applied solutions. For instance the current WiMAXtechnology is based on time division duplex (TDD) and the sizeof TDD burst influences TCP protocol efficiency. Moreover, thescheduling mechanism implemented in a base station (BS) andin subscriber stations (SS) should provide Quality of Service(QoS) which influences overall network performance. Also the bidirectionaltraffic requires an efficient and adequate schedulingmechanism.This paper aims at proposing requirements for a commonWiMAX Evaluation Suite. The authors depict the limitations ofthe mentioned TCP benchmark and suggest the basic WiMAXtopology as well as the scenarios and the output parametersthat allow comparing: TCP protocols, scheduling algorithms andQoS requirements fulfillment in a simulator. Moreover we pointout the comparison criteria for particular aspects of WiMAXtechnologies.
I. INTRODUCTION
The next-generation wireless technology - WiMAX is designedto enable high-speed, mobile Internet access to the widearray of devices. It delivers low-cost, open networks as wellas solution for the efficient transmission with QoS (Qualityof Service) support. One of the most important part of thisarchitecture is the Scheduling Algorithm and it is not definedby the IEEE 802.16 standard but left open for vendors toimplement, in order to satisfy QoS requirements.Recently Andrew et al. [1] proposed the TCP Evaluationsuite to provide a common test suite for researchers thatare designing new TCP extensions. It defines the networktopologies, scenarios and evaluation parameters the authorsbelieve to be crucial for an overall protocol assessment. Theidea that stands behind this undertaking is to offer a commontool that enables different protocol comparison. We believe,that a similar suite, designed for the WiMAX environmentevaluation is needed. More, such a suite would probably needto focus not only on the TCP comparison, but also on thescheduling algorithms and their interaction with the ServiceFlow level buffer management schemes.The Network Simulator 2 (NS-2) provides support forsimulating various network protocols, including TCP and UDP,the routing algorithms and MAC protocols over the wiredand wireless networks (IEEE 802.11). However, it does notprovide a native WiMAX implementation. Several WiMAXmodules were proposed and developed by third party organisations,notably by the National Institute of Standardsand Technology [2] and the Computer Networks Laboratory(LRC), Institute of Computing, UNICAMP [3]. Unfortunatelythey lack the comprehensive support for the advanced, QoSawarescheduling algorithms. We aim at creating a ns-2 basedtestbed for the WiMAX environment. We selected the NISTmodel for creation of our evaluation suite, basing on ouropinion on its scalability. This paper describes the criteriataken into account during the development of the suite (sectionII). The changes and improvements performed in the NISTWiMAX module have been briefly described in section III.The proposed scenarios and topologies are presented in sectionIV.
II. THE 802.16-SPECIFIC EVALUATION PARAMETERS
In comparison to 802.11 WLAN networks, WiMAX playsmuch bigger role in large scale operator networks. The maincause for this situation is that WiMAX was originally designedfor the last mile deployment in MANs. Moreover, the 802.16estandard enhancement was designed to support mobile communicationat vehicular speed which requires not only a robusthand-off support but also power saving and sleep mode toextend the life of the mobile devices.A key feature of the WiMAX technology is that it is a connectionoriented technology, which provides a strong supportfor QoS management. This fact introduces many new problemsinto the already difficult realm of the network simulation, asboth the wireless media and QoS specific aspects need to beconsidered during the model design. We believe, that a specialmeasure should be imposed with the election of the mostimportant factors for the WiMAX evaluation. In particular, weindicate the specific conditions, that were taken into accountduring the development of the universal benchmark tool:• Most WiMAX implementations are based on the timedivision duplex (TDD). Such environments were provedto influence the TCP protocol efficiency


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