L. Mason, T. Drwiega, and J. Yan (Eds.): ITC 2007, LNCS 4516, pp. 386–397, 2007. © Springer-Verlag Berlin Heidelberg 2007 Performance Optimization of Single-Cell Voice over WiFi Communications Using Quantitative Cross-Layering Analysis Fabrizio Granelli 1 , Dzmitry Kliazovich 1 , Jie Hui 2 , and Michael Devetsikiotis 3 1 DIT – University of Trento, Via Sommarive 14, I-38050 Trento, Italy {granelli,klezovic}@dit.unitn.it 2 Intel – Communication Technology Lab, Portland, Oregon, USA Jie.Hui@intel.com 3 ECE – North Carolina State University, Raleigh, NC 27695-7911, USA mdevets@ncsu.edu Abstract. Cross-layer design has been proposed to optimize the performance of networks by exploiting the inter-relation among parameters and procedures at different levels of the protocol stack. This may be particularly beneficial in wireless scenarios, and for quality-of-service support. This paper proposes a quantitative study of cross-layer performance optimization for Voice over WiFi communications, which enables design engineers to analyze and quantify inter- layer dependencies and to identify the optimal operating point of the system, by using cost-benefit principles. Furthermore, insight gained on the problem en- ables the proposal of design principles for a Call Admission Control scheme able to enhance the overall system performance by limiting the number of users in the system and signalling to the active terminals of the proper parameter set- tings to optimize overall performance. Keywords: Cross-Layer design, metamodeling, VoIP over WiFi. 1 Introduction The layering principle has been long identified as a way to increase the interoperabil- ity and to improve the design of telecommunication protocols, where each layer offers services to adjacent upper layers and requires functionalities from adjacent lower ones. Standardization of such protocol stacks in the past enabled fast development of interoperable systems, but at the same time limited the performance of the overall ar- chitecture, due to the lack of coordination among layers. This issue is particularly relevant for wireless networks, where the very physical nature of the transmission medium introduces several performance limitations (including time-varying behavior, limited bandwidth, severe interference and propagation environments) and thus, se- verely limits the performance of protocols (e.g. TCP/IP) designed for wired networks. To overcome these limitations, a modification of the layering paradigm has been proposed, namely, cross-layer design, or “cross-layering.” The core idea is to