The abstract MAC layer

A diversity of possible communication assumptions complicates the study of algorithms and lower bounds for radio networks. We address this problem by defining an Abstract MAC Layer. This service provides reliable local broadcast communication, with timing guarantees stated in terms of a collection of abstract delay functions applied to the relevant contention. Algorithm designers can analyze their algorithms in terms of these functions, independently of specific channel behavior. Concrete implementations of the Abstract MAC Layer over basic radio network models generate concrete definitions for these delay functions, automatically adapting bounds proven for the abstract service to bounds for the specific radio network under consideration. To illustrate this approach, we use the Abstract MAC Layer to study the new problem of Multi-Message Broadcast, a generalization of standard single-message broadcast, in which any number of messages arrive at any processes at any times. We present and analyze two algorithms for Multi-Message Broadcast in static networks: a simple greedy algorithm and one that uses regional leaders. We then indicate how these results can be extended to mobile networks.Cisco Systems, Inc.Lehman Brothers (1993-2008)CUNY (A New MAC-Layer Paradigm for Mobile Ad-Hoc Networks)National Science Foundation (U.S.) (NSF Award Number CCF-0726514)National Science Foundation (U.S.) (NSF Award Number CNS-0715397

The Cost of Global Broadcast Using Abstract MAC Layers

We analyze greedy algorithms for broadcasting messages throughout a multi-hop wireless network, using a slot-based model that includes message collisions without collision detection. Our algorithms are split formally into two pieces: a high-level piece for broadcast and a low-level piece for contention management. We accomplish the split using abstract versions of the MAC layer to encapsulate the contention management. We use two different abstract MAC layers: a basic non-probabilistic one, which our contention management algorithm implements with high probability, and a probabilistic one, which our contention management algorithm implements precisely. Using this approach, we obtain the following complexity bounds: Single-message broadcast, using the basic abstract MAC layer, takes time O(D log(n/epsilon) log(Delta)) to deliver the message everywhere with probability 1 - epsilon, where D is the network diameter, n is the number of nodes, and Delta is the maximum node degree. Single-message broadcast, using the probabilistic abstract MAC layer, takes time only O((D + log(n/epsilon)) log(Delta)). For multi-message broadcast, the bounds are O((D + k' Delta) log(n/epsilon) log(Delta)) using the basic layer and O((D + k' Delta log(n/epsilon)) log(Delta)) using the probabilistic layer,for the time to deliver a single message everywhere in the presence of at most k' concurrent messages

Multi-message broadcast with abstract MAC layers and unreliable links

We study the multi-message broadcast problem using abstract MAC layer models of wireless networks. These models capture the key guarantees of existing MAC layers while abstracting away low-level details such as signal propagation and contention.We begin by studying upper and lower bounds for this problem in a standard abstract MAC layer model---identifying an interesting dependence between the structure of unreliable links and achievable time complexity. In more detail, given a restriction that devices connected directly by an unreliable link are not too far from each other in the reliable link topology, we can (almost) match the efficiency of the reliable case. For the related restriction, however, that two devices connected by an unreliable link are not too far from each other in geographic distance, we prove a new lower bound that shows that this efficiency is impossible. We then investigate how much extra power must be added to the model to enable a new order of magnitude of efficiency. In more detail, we consider an enhanced abstract MAC layer model and present a new multi-message broadcast algorithm that (under certain natural assumptions) solves the problem in this model faster than any known solutions in an abstract MAC layer setting.United States. Air Force Office of Scientific Research (FA9550-13-1-0042)Ford Motor Company. University Research ProgramNational Science Foundation (U.S.) (Grant CCF-1320279)National Science Foundation (U.S.) (Grant CCF-0939370)National Science Foundation (U.S.) (Grant CCF-1217506)National Science Foundation (U.S.) (Grant CCF-AF-0937274)MIT Center for Wireless Networks and Mobile Computin

Decomposing Broadcast Algorithms Using Abstract MAC Layers

In much of the theoretical literature on global broadcast algorithms for wireless networks, issues of message dissemination are considered together with issues of contention management. This combination leads to complicated algorithms and analysis, and makes it difficult to extend the work to more difficult communication problems. In this paper, we present results aimed at simplifying such algorithms and analysis by decomposing the treatment into two levels, using abstract "MAC layer" specifications to encapsulate contention management. We use two different abstract MAC layers: the basic layer of Kuhn, Lynch, and Newport, and a new probabilistic layer. We first present a typical randomized contention-management algorithm for a standard graph-based radio network model and show that it implements both abstract MAC layers. Then we combine this algorithm with greedy algorithms for single-message and multi-message global broadcast and analyze the combinations, using both abstract MAC layers as intermediate layers. Using the basic MAC layer, we prove a bound of O(D log(n / epsilon) log(Delta)) for the time to deliver a single message everywhere with probability 1 - epsilon, where D is the network diameter, n is the number of nodes, and Delta is the maximum node degree. Using the probabilistic layer, we prove a bound of O((D + log(n/epsilon)) log(Delta)), which matches the best previously-known bound for single-message broadcast over the physical network model. For multi-message broadcast, we obtain bounds of O((D + k Delta) log(n/epsilon) log(Delta)) using the basic layer and O((D + k Delta log(n/epsilon)) log(Delta)) using the probabilistic layer, for the time to deliver a message everywhere in the presence of at most k concurrent messages.Author Lynch's research is supported by AFOSR contract FA9550-08-1-0159 and NSF grants CCF-0726514, CNS-0715397, CCF-0937274, and NSF-PURDUE-STC Award 0939370-CCF. Author Kowalski's research is supported by the Engineering and Physical Sciences Research Council [grant numbers EP/G023018/1, EP/H018816/1]

Byzantine Consensus in Abstract MAC Layer

This paper studies the design of Byzantine consensus algorithms in an asynchronous single-hop network equipped with the “abstract MAC layer” [DISC09], which captures core properties of modern wireless MAC protocols. Newport [PODC14], Newport and Robinson [DISC18], and Tseng and Zhang [PODC22] study crash-tolerant consensus in the model. In our setting, a Byzantine faulty node may behave arbitrarily, but it cannot break the guarantees provided by the underlying abstract MAC layer. To our knowledge, we are the first to study Byzantine faults in this model. We harness the power of the abstract MAC layer to develop a Byzantine approximate consensus algorithm and a Byzantine randomized binary consensus algorithm. Both of our algorithms require only the knowledge of the upper bound on the number of faulty nodes f, and do not require the knowledge of the number of nodes n. This demonstrates the “power” of the abstract MAC layer, as consensus algorithms in traditional message-passing models require the knowledge of both n and f. Additionally, we show that it is necessary to know f in order to reach consensus. Hence, from this perspective, our algorithms require the minimal knowledge. The lack of knowledge of n brings the challenge of identifying a quorum explicitly, which is a common technique in traditional message-passing algorithms. A key technical novelty of our algorithms is to identify “implicit quorums” which have the necessary information for reaching consensus. The quorums are implicit because nodes do not know the identity of the quorums – such notion is only used in the analysis

New contention resolution schemes for WiMAX

Abstract—The use of Broadband Wireless Access (BWA) technology is increasing due to the use of Internet and multimedia applications with strict requirements of end–to–end delay and jitter, through wireless devices. The IEEE 802.16 standard, which defines the physical (PHY) and the medium access control (MAC) layers, is one of the BWA standards. Its MAC layer is centralized basis, where the Base Station (BS) is responsible for assigning the needed bandwidth for each Subscriber Station (SS), which requests bandwidth competing between all of them. The standard defines a contention resolution process to resolve the potential occurrence of collisions during the requesting process. In this paper, we propose to modify the contention resolution process to improve the network performance, including end–to–end delay and throughput

Classification of Smart Home Applications’ Requirements for the MAC Layer

Abstract—Smart homes and Wireless Home Automation Networks (WHAN) face several challenges in terms of cost, scalability, reliability, delay, energy consumption and many others. Smart homes typically have huge number of communicating devices. Efficient management of network resources is a major challenge in such environments. This paper provides insights on how to improve the MAC layer in smart home networks to fulfil the requirements of the different smart home applications. It provides a classification of the different smart home applications and identifies the main requirements and challenges regarding the MAC layer in this environment. It also provides insights for MAC protocols designers by highlighting the main issues in designing MAC schemes for smart home environment. Based on the analysis, the paper highlights adaptability as the most critical and challenging feature for smart home MAC protocols

MAC Design for Analog Network Coding

Most medium access control mechanisms discard collided packets and consider interference harmful. Recent work on Analog Network Coding (ANC) suggests a different approach, in which multiple interfering transmissions are strategically scheduled. The received collisions are collected and then used in a decoding process, such as the ZigZag decoding process, where the packets involved in the collisions are extracted. In this paper, we present an algebraic representation of collisions and describe a general approach to recovering collisions using ANC. To study the eect of using ANC on the performance of MAC layers, we develop an ANC-based algorithm that implements an abstract MAC layer service, as defined in [1, 2], and analyze its performance. This study proves that ANC can significantly improve the performance of MAC layer services, in terms of probabilistic time guarantees for packet delivery. We illustrate how this improvement at the MAC layer can translate into faster higher-level algorithms, by analyzing the time complexity of a multiple-message network-wide broadcast algorithm that uses our ANC-based MAC service

Adaptive delayed channel access for IEEE 802.11n WLANs

Abstract— In this paper we investigate potential benefits that an adaptive delayed channel access algorithm can attain for the next-generation wireless LANs, the IEEE 802.11n. We show that the performance of frame aggregation introduced by the 802.11n adheres due to the priority mechanism of the legacy 802.11e EDCA scheduler, resulting in a poor overall performance. Because high priority flows have low channel utilization, the low priority flows throughputs can be amerced further. By introducing an additional delay at the MAC layer, before the channel access scheduling, it will retain aggregate sizes at higher numbers and consequently a better channel utilization. Also, in order to support both UDP and TCP transport layer protocols, the algorithm’s operational conditions are kept adaptive. The simulation results demonstrate that our proposed adaptive delayed channel access outperforms significantly the current 802.11n specification and non-adaptive delayed channel access

Fault-Tolerant Consensus with an Abstract MAC Layer

In this paper, we study fault-tolerant distributed consensus in wireless systems. In more detail, we produce two new randomized algorithms that solve this problem in the abstract MAC layer model, which captures the basic interface and communication guarantees provided by most wireless MAC layers. Our algorithms work for any number of failures, require no advance knowledge of the network participants or network size, and guarantee termination with high probability after a number of broadcasts that are polynomial in the network size. Our first algorithm satisfies the standard agreement property, while our second trades a faster termination guarantee in exchange for a looser agreement property in which most nodes agree on the same value. These are the first known fault-tolerant consensus algorithms for this model. In addition to our main upper bound results, we explore the gap between the abstract MAC layer and the standard asynchronous message passing model by proving fault-tolerant consensus is impossible in the latter in the absence of information regarding the network participants, even if we assume no faults, allow randomized solutions, and provide the algorithm a constant-factor approximation of the network size