Sven Wiethölter, Christian Hoene
The IEEE 802.11 standard supports two MAC mechanisms, the Distributed Coordination Function (DCF) and the Point Coordination Function (PCF). These mechanisms are considered to be insufficient for achieving a reasonable quality in scenarios with high background load. Thus, QoS enhancements are vividly studied and evaluated. The QoS enhancements developed by the IEEE 802.11e WG have been under design for several years. The amendment to the 802.11 standard was finally approved and published in November 2005. Basically, IEEE 802.11e introduces two additional MAC modes: the Enhanced Distributed Channel Access (EDCA) and the HCF Controlled Channel Access (HCCA), which have been derived from their earlier versions EDCF (Enhanced Distributed Channel Function) and HCF (Hybrid Coordination Function) of previous drafts.
On this web page, we present an open-source, verified simulation model of IEEE 802.11e's EDCF / EDCA mode for the network simulator (ns-2.26 / ns-2.28). We verified the model by comparing it with previous results, which have been published by Stefan Mangold et al. The 802.11e EDCA model is an easy adaptable, modular and documented solution. We added the contention free bursting (CFB) to our model, which allows the transmission of a train of small packets without intermediate contention. Sometimes CFB is also denoted as TXOP bursting.
Our simulation model is based on the ns-802.11 DCF model. Actually, it extends the wireless and mobility code, which has been developed in the CMU Monarch project. We removed a couple of bugs in the legacy model and expanded the queues as well as the MAC with its timer model into a multi-dimensional MAC. The bug description, a short introduction into the model implementation and its verification can be found here. Additionally, we provide a patch for the legacy 802.11 model of ns-2.28 that can be downloaded here. It includes all fixes to the bugs described in the technical report (TKN-03-019).
The EDCA model lacks the HCCA, the block ACK mechanism, any management mechanisms like Association/Reassociation, Authentication/Deauthentication. In addition, no superframe structure with Beacon frames and no power-saving methods are supported.
The RTS/CTS mechanism, which is included in the legacy ns-802.11 model, has never been tested and verified. Therefore we do not recommend to use RTS/CTS without reviewing the code in detail.
We recommend to use the EDCA model for ns-2.28, since the older version is not compliant to the final 802.11e amendment. An installation instruction is included in the readme file.
- Patch for 802.11 model (ns-2.28)
Technical Report TKN-03-019, Sven Wiethölter, Christian Hoene, "Design and Verification of an IEEE 802.11e EDCF Simulation Model in ns-2.26", Telecommunication Networks Group, Technische Universität Berlin, November 2003. (PDF)
Technical Report TKN-04-11, Sven Wiethölter, Christian Hoene, Adam Wolisz, "Perceptual Quality of Internet Telephony over IEEE 802.11e Supporting Enhanced DCF and Contention Free Bursting", Telecommunication Networks Group, Technische Universität Berlin, September 2004. (PDF)
Technical Report TKN-06-003, Sven Wiethölter, M. Emmelmann, Christian Hoene, Adam Wolisz "TKN EDCA Model for ns-2", Telecommunication Networks Group, Technische Universität Berlin, June 2006. (PDF)
Publications refering to this model
Alessandro Andreadis, Giuliano Benelli, and Riccardo Zambon, „Evaluation of QoS Support for Multimedia Traffics in IEEE 802.11e “, in Proc. of SoftCOM, Split-Dubrovnik, Croatia, September 2006.
M. Thottan and M. C. Weigle, „Impact of 802.11e EDCA on Mixed TCP-based Applications“, in Proc. of the International Wireless Internet Conference (WICON), Boston, August 2006.
A. Banchs and L. Vollero, „Throughput analysis and optimal configuration of 802.11e EDCA“, Computer Networks, Volume 50, Issue 11, pp. 1749-1768, August 2006.
Yi-Wen Lan, Jui-Hung Yeh, Jyh-Cheng Chen, and Zi-Tsan Chou, „Performance Enhancement of IEEE 802.11e EDCA by Contention Adaption“, VTC 2005-Spring, Stockholm, Sweden.
C. Bettstetter, C. Prehofer, and A. Wolisz, "A Performance Comparison of QoS Approaches for Ad Hoc Networks: 802.11e versus Distributed Resource Allocation", In Proc. of European Wireless 2005, Nicosia, Cyprus, April 2005.
Carlos Calafate, Pietro Manzoni, Manuel Malumbres, "Supporting soft real-time services in MANETs using distributed admission control and IEEE 802.11e technology", 10th IEEE Symposium on Computers and Communications (ISCC 2005), June 27-30, 2005, La Manga del Mar Menor, Cartagena, Spain.
Carlos T. Calafate, Pietro Manzoni, Manuel P. Malumbres. "On the Interaction Between IEEE 802.11e and Routing Protocols in Mobile Ad-Hoc Networks," 13th Euromicro Conference on Parallel, Distributed and Network-Based Processing (PDP'05), pp. 110-117, 2005.
L. Scalia, I. Tinnirello, “Differentiation mechanisms for heterogeneous traffic integration in IEEE 802.11 networks," BroadWin 2004, October 2004, San Jose, USA.
Carlos T. Calafate, M. P. Malumbres, Pietro Manzoni, "Assessing the effectiveness of IEEE 802.11e in multi-hop network environments", 12th Annual Meeting of the IEEE / ACM International Symposium on Modeling, Analysis, and Simulation of Computer and Telecommunication Systems (MASCOTS), October 5-7 2004, Volendam The Netherlands.
Douglas J. Leith, Peter Clifford: Using the 802.11e EDCF to Achieve TCP Upload Fairness over WLAN Links. WiOpt 2005: 109-118
Ken Duffy, David Malone and Douglas J. Leith, „Modeling the 802.11 distributed coordination function in non-saturated conditions,“ to appear IEEE Communications Letters (2005).
Lu Yang, “P-HCCA: A New Scheme for Real-time Traffic with QoS in IEEE 802.11e Based Networks,” APAN Network Research Workshop 2004 .
Andrea Alfieri, „Simulazione del modello Enhanced Distributed Coordination Function (EDCF) tramite NS-2“, Thesis, UNIVERSITA’ DEGLI STUDI DI PARMA, Italy, 2005.
If you use our model, please send us a brief email with a reference to your publication.
If you have any questions please mail them to the sourceforge.net or the ns-2 mailing list. We are sorry to announce that we are not going to answer any emails regarding 802.11e anymore.
IEEE 802.11e HCCA simulation using the Network Simulator 2 by the Computer Networking Group of the University of Pisa
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