Over the past few decades, wireless local area networks (WLANs) have been widely deployed for data communication in indoor environments such as offices, houses, and airports. In order to fairly and efficiently use the unlicensed frequency band that Wi-Fi devices share, the devices follow a set of channel access rules, which is called a wireless medium access control (MAC) protocol. It is known that wireless devices following the 802.11 standard MAC protocol, i.e. the distributed coordination function (DCF), suffer from packet collisions when multiple nodes simultaneously transmit. This significantly degrades the throughput performance. Recently, several studies have reported access techniques to reduce the number of packet collisions and to achieve a collision free WLAN. Although these studies have shown that the number of collisions can be reduced to zero in a simple way, there have been a couple of remaining issues to solve, such as dynamic parameter adjustment and fairness to legacy DCF nodes in terms of channel access opportunity. Recently, In-Band Full Duplex (IBFD) communication has received much attention, because it has significant potential to improve the communication capacity of a radio band. IBFD means that a node can simultaneously transmit one signal and receive another signal in the same band at the same time. In order to maximize the performance of IBFD communication capability and to fairly share access to the wireless medium among distributed devices in WLANs, a number of IBFD MAC protocols have been proposed. However, little attention has been paid to fairness issues between half duplex nodes (i.e. nodes that can either transmit or receive but not both simultaneously in one time-frequency resource block) and IBFD capable nodes in the presence of the hidden node problem.

BFT consensus algorithms can ensure the consistency of distributed systems where nodes may behave arbitrarily due to faults or intentional malicious actions. However, most of the practical BFT consensus algorithms are leader-based. In an adversarial network, leader-based BFT consensus algorithms exhibit vulnerabilities and lack resilience. Byzantine leaders can pose a potential threat to the system; firstly, malicious leaders can actively downgrade the processing speed of handling proposals, thereby diminishing the system’s overall performance. Secondly, they can determine the submission order of received requests, which can be fatal in specific decentralized financial systems. Additionally, external attackers can compromise the system’s stability by conducting DDoS attacks on leader nodes, frequently triggering view changes and potentially causing the system to lose liveness altogether. We present BFT Baxos, a more robust and resilient BFT consensus protocol that equips a BFT random exponential backoff mechanism to ensure each node has the egalitarian right to propose. Employing random exponential backoff as a replacement for leader election eliminates the potential malicious actions of Byzantine leaders and prevents external attackers from conducting targeted DDoS attacks on the leader node within systems. We implemented and evaluated our BFT Baxos prototype. Our results indicate that BFT Baxos exhibits good performance and scalability in low-concurrency scenarios. Additionally, we illustrated the functioning of BFT Baxos even in extremely adverse network conditions by subjecting it to random DDoS attacks. / BFT-konsensusalgoritmer är utformade för att säkerställa konsistensen i distribuerade system där noder kan agera godtyckligt, antingen på grund av fel eller avsiktliga skadliga handlingar. Dock är de flesta praktiska BFT-konsensusalgoritmerna baserade på ledare. I en fientlig nätverksmiljö uppvisar ledar-baserade BFT-konsensusalgoritmer sårbarheter och brist på motståndskraft. Bysantinska ledare kan utgöra en potentiell hot mot systemet; för det första kan skadliga ledare aktivt sänka behandlingshastigheten för hantering av förslag och därigenom minska systemets totala prestanda. För det andra kan de bestämma ordningen för inskickning av mottagna begäranden, vilket kan vara ödesdigert i vissa decentraliserade finansiella system. Dessutom kan externa angripare kompromettera systemets stabilitet genom att genomföra DDoS-attacker mot ledarnoder, vilket ofta utlöser vynändringar och potentiellt orsakar att systemet förlorar livskraft helt och hållet. Vi presenterar BFT Baxos, en mer robust och motståndskraftig BFT-konsensusprotokoll som utrustar en BFT slumpmässig exponentiell backoff-mekanism för att säkerställa att varje nod har rätten att föreslå på ett egalitärt sätt. Genom att använda slumpmässig exponentiell backoff som ett alternativ till ledarval eliminerar det inte bara möjliga skadliga handlingar från bysantinska ledare utan förhindrar även externa angripare från att genomföra riktade DDoS-attacker mot ledarnoden inom system. Vi implementerade och utvärderade vår BFT Baxos-prototyp. Våra resultat visar att BFT Baxos uppvisar god prestanda och skalbarhet i scenarier med låg samtidighet. Dessutom illustrerade vi funktionen av BFT Baxos även under extremt ogynnsamma nätverksförhållanden genom att utsätta den för slumpmässiga DDoS-attacker.