Packet aggregation in multi-rate wireless LANs

Abstract

Abstract-In CSMA networks, there is a significant overhead associated with each packet including header overhead and contention overhead. The high overhead problem is exacerbated because some of these overheads are required to be at the lowest data rate to ensure that all contending nodes can compete fairly. For applications where packets are small, such as Voice over IP (VOIP), this means that a majority of the available transmission time is wasted on overhead. Packet aggregation is one of the techniques that has been proposed to amortize the per-transmission overhead over multiple aggregated packets. However, existing heuristics are limited, often not considering multi-rate wireless MAC, or operation in a WLAN environment. In this paper, we first formulate the problem of optimal aggregation for a multi-rate CSMA MAC protocol and show that it is NP-Hard. We then propose two heuristics that solve the aggregation problem for multi-rate WLANs. The first, which we call Data Rate based Aggregation protocol (DRA), divides packets in the MAC queue into groups based on the data rate they are to be transmitted at. The algorithm aggregates packets in the same group and broadcasts the aggregated frame at the data rate of that group. Empirically, DRA achieves several fold increase in throughput compared to basic aggregation. DRA also achieves up to a 200% increase in the number of VoIP calls supported by a single 802.11g AP compared to using state of the art aggregation protocols. The second heuristic, which we call Data Rate based Aggregation with Selective Demotion (DRA-SD), enables cross data rate aggregation. Through preliminary evaluation, we show that selectively demoting packets can further improve performance.

Dynamic frame aggregation scheduler for multimedia applications in IEEE 802.11n networks

“…Table I highlights the major performance analysis of aggregation scheme sorted by reported works. Although this mechanism improves the average throughput as it was confirmed by Jibukumar et al [33] and Majeed and Abu-Ghazaleh [34], it has a negative effect on the delay performance of some applications. This is due to two reasons.…”

“…For the studied schedulers, we can draw the following conclusions: Schedulers based on AC priority give highest performance for voice flows, while video flows must wait in the queue for further transmissions. This was the case of proposed schedulers in . Schedulers based on deadline packet transmission improve network performance by reducing packet rejection, as it was proposed by Majeed and Abu‐Ghazaleh . Schedulers that consider QoS requirements of different applications are the most appropriate for multimedia applications. This was the case of scheduler elaborated by .…”

“…This was the case of proposed schedulers in [39][40][41]. (ii) Schedulers based on deadline packet transmission improve network performance by reducing packet rejection, as it was proposed by Majeed and Abu-Ghazaleh [34]. (iii) Schedulers that consider QoS requirements of different applications are the most appropriate for multimedia applications.…”

“…In fact, reducing the protocol overheads is an important approach to improve the throughput as an upper limit on throughput exists. For example, adopting a packet aggregation algorithm in increases by a factor of seven the number of calls that can be supported for VoIP applications; in improves the throughput by a factor of 2.5 times; and in achieves a 200 per cent improvement in the throughput.…”

New RTP Packet Payload Shrinking Method to Enhance Bandwidth Exploitation Over RTP Protocol

“…These heuristics have improved the number of synchronous VoIP calls by up to 200%, when using a single 802.11g Access Point, and lessens WLAN delays. Therefore, the suggested method has highly improved the bandwidth saving ratio [14].…”