Weekly Seminar: “Collision-free WLANs: from concepts to working protocols”
Collisions are a main cause of throughput degradation in wireless local area networks. The current contention mechanism used in the IEEE 802.11 networks is called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). It uses a binary exponential backoff technique to randomize each contender attempt of transmitting, effectively reducing the collision probability. Nevertheless, CSMA/CA relies on a random backoff that while effective and fully decentralized, in principle is unable to completely eliminate collisions, therefore degrading the network throughput as more contenders attempt to share the channel. To overcome these situations, Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA/ECA) is able to create a collision-free schedule in a fully decentralized manner using a deterministic backoff after successful transmissions. Hysteresis and Fair Share are two extensions of CSMA/ECA to support a large number of contenders in a collision-free schedule. CSMA/ECA offers better throughput than CSMA/CA and short-term throughput fairness. We will describe CSMA/ECA and its extensions. In addition, we provide the first evaluation results of CSMA/ECA with non-saturated traffic, and its performance when coexisting with CSMA/CA nodes. Furthermore, we present a mechanism to leverage the impact of channel errors and the addition/withdrawal of nodes over collision-free schedules. Finally, the experimental results on throughput and lost frames from a CSMA/ECA implementation using commercial hardware and open-source firmware are presented.
Luis Sanabria-Russo is a Networking and Communications engineer from Universidad Tecnológica del Centro, Venezuela. He got his MSc. in Advanced Sciences of Modern Telecommunications from Univesitat de Valencia, Spain, and received his PhD in Information and Communications Technologies from Universitat Pompeu Fabra, Barcelona. With a background mostly related to routing and switching, his interest now turned to Software Defined Network abstractions to different layers of the communication stack. He is currently exploring ways of leveraging network-wide metrics and to provide centralized traffic engineering and QoS capabilities to IoT deployments, both at the sensor and gateway tiers. He is part of the Communications Technologies Division at CTTC.