|
|
||
|
OPNET Technologies © 2008 OPNET Technologies, Inc. |
Research: Nowadays, the use of WLANs is on the increase mainly due to their low cost, their ease of deployment and, above all, by allowing the end users to freely move around within the area they cover. Another influential factor is the appearance in 1997 of the standard IEEE 802.11, with its subsequent revision and amendments that nowadays enables transmission speeds of up to 54 Mbps. The basic access function in IEEE 802.11 is the Distributed Coordination Function (DCF). DCF mode is easy to implement and suitable for most applications. However, it does not provide Quality of Service (QoS) support. As an alternative but optional solution the Point Coordination Function (PCF) can in turn be used. It is a centralized access method where a node, the Point Coordinator (PC), will poll in turn each station allowing it to transmit without having to compete in order to gain access to the channel. However PCF have too much limitations. The above open issues have led many researchers to design techniques to provide solutions for both operation modes, DCF and PCF, using traffic engineering principles with the objective of making a better use of the network resources. We have found and classified 26 techniques. First we distinguish between those techniques affecting the DCF and PCF. Various approaches have been used for both of them: the first approach is based on priorities, giving access preference to those stations that have been assigned higher priority. The second approach uses fair scheduling algorithms and shares the resources proportionally to a pre-assigned weight. Finally, a third approach (only in PCF) is based on maximizing the amount of flows whose QoS needs are covered. At the same time, the IEEE 802.11 task group E is working on the introduction of mechanisms which give QoS support. In the unapproved draft IEEE 802.11e a third function of coordination is added to DCF and PCF: the Hybrid Coordination Function (HCF). This new coordination function is obligatory for all stations and incorporates two new access mechanisms: the Enhanced Distributed Channel Access (EDCA) known in previous drafts as Enhanced DCF (EDCF) which, as its name suggests, sought to substitute DCF; and HCF Controlled Channel Access (HCCA), known in previous drafts as HCF. We intend to make a quantitative comparison among all the proposed techniques based on our classification using OPNET. We have not been able to use the evidence and evaluations carried out by their authors due to the different configurations used in each case. We intend too to implement new techniques using OPNET.
We have implemented several techniques that affect the DCF: - Techniques based on priorities using jamming signals ([8], [9], [10], [11] and [12]). References: [8] J.L. Sobrinho and A.S. Krishnakumar. "Real-time traffic over the IEEE 802.11 MAC", Bell Labs Technical Journal , vol. 1, num. 2, pp. 172-187, Autumn 1996 [9] J.L. Sobrinho and A.S. Krishnakumar, "Quality of service in ad hoc carrier sense multiple access wireless networks", IEEE Journal on Selected Areas in Communications , pp. 1353-1368, August 1999 [10] W.T. Chen, B.B. Jian, and S.C. Lo, "An Adaptive Retransmission Scheme with QoS Support for the IEEE 802.11 MAC Enhancement", Vehicular Technology Conference 2002 (VTC Spring 2002), Birmingham , Alabama , USA , May 2002 [11] J.P. Sheu, C.H. Liu, S.L. Wu and Y.C. Tseng, "A Priority MAC Protocol to Support Real-Time Multimedia Traffic in Ad Hoc Networks", Wireless Networks, vol. 10, num. 1, pp. 61-69, January 2004 [12] A. Banchs, X. Perez, M. Radimirsch and H. J. Stuttgen, "Service differentiation extensions for elastic and real-time traffic in 802.11 wireless LAN", IEEE Workshop on High Performance Switching and Routing , pp.245-249, 2001
Results: [1] F. Micó, P. Cuenca, L. Orozco-Barbosa, "QoS in IEEE 802.11 wireless LAN: current research activities", IEEE Canadian Conference on Electrical and Computer Engineering, vol. 1, pp 447-452, May 2004 [2] F. Micó, P. Cuenca, L. Orozco-Barbosa, "QoS Mechanisms for IEEE 802.11 wireless LANs", High Speed Networks and Multimedia Communications: 7th IEEE International Conference, HSNMC 2004, Lectures Notes in Computer Science, vol. 3079/2004, pp 609-623, July 2004
OPNET Technologies, Inc. is a leading provider of solutions for managing networks and applications. OPNET's best-in-class solutions address application troubleshooting, application monitoring, network monitoring, network configuration management, capacity management, and network simulation. OPNET’s solutions have been operationally proven in thousands of customer environments worldwide, including corporate and government enterprises, government and defense agencies, network service providers, and network equipment manufacturers. For more information about OPNET and its products, visit www.opnet.com
|
