Traffic differentiation in dense collision-free WLANs using CSMA/ECA

Abstract

The ability to perform traffic differentiation is a promising feature of the current Medium Access Control (MAC) in Wireless Local Area Networks (WLANs). The Enhanced Distributed Channel Access (EDCA) protocol for WLANs proposes up to four Access Categories (AC) that can be mapped to different traffic priorities. High priority ACs are allowed to transmit more often than low priority ACs, providing a way of prioritising delay sensitive traffic like voice calls or video streaming. Further, EDCA also considers the intricacies related to the management of multiple queues, virtual collisions and traffic differentiation. Nevertheless, EDCA falls short in efficiency when performing in dense WLAN scenarios. Its collision-prone contention mechanism degrades the overall throughput to the point of starving low priority ACs, and produce priority inversions at high number of contenders.Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA/ECA) is a compatible MAC protocol for WLANs which is also capable of providing traffic differentiation. Contrary to EDCA, CSMA/ECA uses a contention mechanism with a deterministic backoff technique which is capable of constructing collision-free schedules for many nodes with multiple active ACs, extending the network capacity without starving low priority ACs, as experienced in EDCA. This work analyses traffic differentiation with CSMA/ECA by describing the mechanisms used to construct collisionfree schedules with multiple queues. Additionally, evaluates the performance under different traffic conditions and a growing number of contenders. Furthermore, it introduces a way to eliminate Virtual Collisions (VC), which also contribute to the throughput degradation in EDCA WLANs. Simulation tests are performed using voice and video packet sources that emulate commonly used codecs. Results show CSMA/ECA outperforming EDCA in different commonly-found scenarios with higher number of users, including when both MAC protocols coexist in the same WLAN.

Target Wake Time: Scheduled Access in IEEE 802.11ax WLANs

“…The most simple approach is to allocate TWT sessions in which only transmissions from certain ACs are allowed, thus instead of setting TWT sessions per station they would be set by the pair AC-station. Although conceptually very different, the scheduled access defined in CSMA with Enhanced Collision Avoidance (CSMA/ECA) for multiple ACs [8] can provide inspiration to dynamically schedule TWT sessions supporting different priorities.…”

Traffic Differentiation in Dense WLANs with CSMA/ECA-DR MAC Protocol

“…In traffic differentiation, delay-sensitive access categories (AC) require frequent transmissions and hence shorter transmission intervals (and CW sizes). However, among the deterministic backoff values computed by Algorithm 1 (i.e., 3, 7, 15, 31, 63, 127, 255, 511), 15 is divisible by 3 (AC[VO], the voice AC, in 2 This algorithm is borrowed from [1] and adapted to traffic differentiation using ECA-DR.…”

“…Thus, a station can compute P cc to choose the proper CW when it is supposed to reset its backoff stage. In Algorithm 1, ECA-DR uses P cc to estimate the NAC and choose the proper CW (1) between two consecutive transmissions of a station if the first transmission results in a collision by computing the backoff stage increae value (lines 20) and (2) where the station has to reset its backoff stage (line 30 and line 34).…”

“…We extend [2] to implement ECA-DR in the COST simulator [14]. Simulations are carried out in a single hop scenario where all stations are in transmission range of each other and the channel is assumed to have no errors.…”

“…AC[VO] is chosen based on Internet Low Bit Rate Codec (iLBC) with silent detection (payload of 38 bytes with 20 ms intervals). For more information about the detail of Voice and Video codecs, we refer the readers to [2]. In saturated settings, MAC queues Simulations are based on 10 repetitions with different seeds that simulate 60 seconds of different protocols (i.e., ECA and ECA-DR).…”