Analisa Performansi IEEE 802.11e WLAN untuk Mixed Traffic TCP-UDP dengan Menggunakan Mekanisme Adaptive Admission Control

ABSTRAKSI: Standard IEEE 802.11e Medium Access Control memberikan jaminan QoS untuk trafik multimedia dengan fungsi baru yang ditambahkan yaitu Hybrid Coordination Function (HCF). HCF menyediakan mekanisme akses secara terpusat yaitu HCCA dan secara terdistribusi yaitu EDCA. Mekanisme EDCA telah dipilih oleh sebagian besar vendor WLAN untuk diimplementasikan. Pada WLAN, mekanisme admission control sangat diperlukan terutama pada kondisi jaringan yang congested untuk membatasi trafik yang masuk sehingga performansi QoS dari flow yang sudah ada tetap terjamin dan medium dapat digunakan lebih optimal. Mekanisme admission control yang secara adaptif diperlukan untuk menyesuaikan dengan kondisi jaringan. Fuzzy logic dipilih sebagai mekanisme admission control karena kemampuannya untuk mengatasi situasi yang mengandung ketidakpastian (fuzzy) dan juga sangat mungkin diimplementasikan pada level MAC karena tidak serumit algoritma adaptasi lainnya seperti algoritma jaringan syaraf tiruan.Pada penelitian ini telah dibuat mekanisme admission control menggunakan fuzzy logic dengan menggunakan parameter network load dan collision rate untuk fungsi keanggotaannya, dan melibatkan perubahan parameter EDCA secara adaptif. Penelitian dilakukan pada kondisi trafik yang mixed antara TCP-UDP, dan jumlah trafik dibuat semakin meningkat. Uji performansi mekanisme admission control dilakukan dengan simulasi menggunakan Network Simulator NS2.Hasil penelitian menunjukkan bahwa pada kondisi jaringan yang congested, admission control berbasiskan fuzzy logic dan melibatkan perubahan parameter EDCA secara adaptif mengurangi packet loss pada trafik UDP dan meningkatkan throughput pada trafik TCP.Kata Kunci : IEEE 802.11e EDCA, performansi QoS, admission control, fuzzy logic, parameter EDCA, TCP-UDPABSTRACT: IEEE 802.11e Standard : Medium Access Control introduces new function wich called Hybrid Coordination Function to provide QoS guarantee for multimedia traffic. HCF provide two channel access mechanism : controlled channel access mechanism called HCCA and contention based channel access mechanism called EDCA. Most of WLAN vendor chooses EDCA as their MAC because its simplicity. In WLAN, especially in congested network, admission control is needed to limit new flow and guarantee QoS of existing flows.Therefore adaptive admission control is needed. Fuzzy logic is choosen as adaptive algorithm for admission control because its ability to handle fuzzy situation and its reability to be implemented in MAC layer.In this research, fuzzy based admission control model is presented and the model uses network load and collision rate as fuzzy membership and also includes tuning parameter EDCA adaptively. The research is done in mixed traffic TCP-UDP and performance is tested with simulation using Network Simulator NS-2.The result shows that in congested network, fuzzy based admission control will decrease packet loss of UDP traffic and increase throughput TCP traffic.Keyword: IEEE 802.11e EDCA, performansi QoS, admission control, fuzzy logic, EDCA parameter, TCP-UD

A Dynamic Multimedia User-Weight Classification Scheme for IEEE_802.11 WLANs

In this paper we expose a dynamic traffic-classification scheme to support multimedia applications such as voice and broadband video transmissions over IEEE 802.11 Wireless Local Area Networks (WLANs). Obviously, over a Wi-Fi link and to better serve these applications - which normally have strict bounded transmission delay or minimum link rate requirement - a service differentiation technique can be applied to the media traffic transmitted by the same mobile node using the well-known 802.11e Enhanced Distributed Channel Access (EDCA) protocol. However, the given EDCA mode does not offer user differentiation, which can be viewed as a deficiency in multi-access wireless networks. Accordingly, we propose a new inter-node priority access scheme for IEEE 802.11e networks which is compatible with the EDCA scheme. The proposed scheme joins a dynamic user-weight to each mobile station depending on its outgoing data, and therefore deploys inter-node priority for the channel access to complement the existing EDCA inter-frame priority. This provides efficient quality of service control across multiple users within the same coverage area of an access point. We provide performance evaluations to compare the proposed access model with the basic EDCA 802.11 MAC protocol mode to elucidate the quality improvement achieved for multimedia communication over 802.11 WLANs.Comment: 15 pages, 8 figures, 3 tables, International Journal of Computer Networks & Communications (IJCNC

Priority-Oriented Adaptive Control With QoS Guarantee for Wireless LANs.

In today’s wireless networks there is a great need for QoS, because of the time-bounded voice, audio and video traffic. A new QoS enhanced standard is being standardized by the IEEE 802.11e workgroup. It uses a contention free access mechanism called Hybrid Control Channel Access (HCCA) to guarantee QoS. However, HCCA is not efficient for all types of time-bounded traffic. This work proposes an alternative protocol which could be adapted in HCF (Hybrid Coordination Function). The Priority Oriented Adaptive Control with QoS Guarantee (POAC-QG) is a complete centralized channel access mechanism, it is able to guarantee QoS for all types of multimedia network applications, it enhances the parameterized traffic with priorities, and it supports time division access using slots. Furthermore, it instantly negotiates the quality levels of the traffic streams according to their priorities, supporting multiple streams to the best quality it can achieve. POAC-QG compared to HCCA, provides higher channel utilization, adapts better to the characteristics of the different traffic types, differentiates the traffic streams more efficiently using priorities, and generally exhibits superior performance

Spectrum Utilization and Congestion of IEEE 802.11 Networks in the 2.4 GHz ISM Band

Wi-Fi technology, plays a major role in society thanks to its widespread availability, ease of use and low cost. To assure its long term viability in terms of capacity and ability to share the spectrum efficiently, it is of paramount to study the spectrum utilization and congestion mechanisms in live environments. In this paper the service level in the 2.4 GHz ISM band is investigated with focus on todays IEEE 802.11 WLAN systems with support for the 802.11e extension. Here service level means the overall Quality of Service (QoS), i.e. can all devices fulfill their communication needs? A crosslayer approach is used, since the service level can be measured at several levels of the protocol stack. The focus is on monitoring at both the Physical (PHY) and the Medium Access Control (MAC) link layer simultaneously by performing respectively power measurements with a spectrum analyzer to assess spectrum utilization and packet sniffing to measure the congestion. Compared to traditional QoS analysis in 802.11 networks, packet sniffing allows to study the occurring congestion mechanisms more thoroughly. The monitoring is applied for the following two cases. First the influence of interference between WLAN networks sharing the same radio channel is investigated in a controlled environment. It turns out that retry rate, Clear-ToSend (CTS), Request-To-Send (RTS) and (Block) Acknowledgment (ACK) frames can be used to identify congestion, whereas the spectrum analyzer is employed to identify the source of interference. Secondly, live measurements are performed at three locations to identify this type of interference in real-live situations. Results show inefficient use of the wireless medium in certain scenarios, due to a large portion of management and control frames compared to data content frames (i.e. only 21% of the frames is identified as data frames)