Packet Collision Probability Research Articles

Slot Synchronization of a WDM Packet-Switched Slotted Ring

In this paper, we present two different strategies of slot synchronization in wavelength-division-multiplexing (WDM) packet-switched slotted-ring networks. Emphasis is given to the architecture behind the WDM optical network demonstrator over rings (WONDER) project, which is based on tunable transmitters and fixed receivers. The WONDER experimental prototype is currently being developed at the laboratories of Politecnico di Torino. In the former strategy, a slot-synchronization signal is transmitted by the master station on a dedicated control wavelength; in the latter, slave nodes achieve slot synchronization aligning on data packets that are received from the master. The performance of both synchronization strategies, particularly in terms of packet-collision probability, was evaluated by simulation. The technique based on transmitting a timing signal on a dedicated control wavelength achieves better performance, although it is more expensive due to the need for an additional wavelength. However, the technique based on aligning data packets that are received from the master, despite attaining lower timing stability, still deserves further study, particularly if limiting the number of wavelengths and receivers is a major requirement. Some experimental results, which were measured on the WONDER prototype, are also shown. Measurement results, together with theoretical findings, demonstrate the good synchronization performance of the prototype.

A Dual-Tone DMAC Protocol for Mobile Ad Hoc Networks

Ad hoc DMAC protocols have been proposed to improve spatial reuse, but directional transmissions have the problem of deafness. In the ToneDMAC protocol [9], an omnidirectional out-of-band tone after transmitting DATA or ACK mitigates deafness, but cannot prevent the interference packets caused by retransmissions to node in deafness. In this paper, we propose a dual-tone DMAC protocol with the out-of-band start-tone and stop-tone. In the proposed MAC protocol, a start-tone prevents retransmissions to node in deafness and decreases the packet collision probability. Throughput performance of the proposed MAC protocol is confirmed by simulations using Qualnet ver. 3.8 simulator.

A Novel Random Backoff Algorithm to Enhance the Performance of IEEE 802.11 DCF

The Probability Distribution of Slot Selection (PDoSS) of IEEE 802.11 DCF is extremely uneven, which makes the packet collision probability very high. In this paper, we propose a novel RWBO+BEB backoff algorithm for 802.11 DCF to make the PDoSS even and thus decrease the packet collision probability. A Markov model is built for analyzing RWBO+BEB's PDoSS and saturation throughput. The model's correctness is validated by simulation. The performance of RWBO+BEB is also evaluated by simulation in terms of PDoSS, saturation throughput, packet collision probability and packet delay. The simulation results indicate that RWBO+BEB can decrease the packet collision probability to a large extent, utilize the channel more efficiently, and make the packet delay jitter much lower comparing to 802.11 DCF. Moreover, we analyze the relation of saturation throughput and packet collision probability to walking probability (pd) and contention windows (w), respectively. The analysis indicates that RWBO+BEB has a remarkable feature: its saturation throughput keeps high, and packet collision probability keeps very low (which under 0.1) in a large range of pd and w, this allows us to configure pd and w more flexibly.

QOLSR, QoS routing for ad hoc wireless networks using OLSR

AbstractThis paper describes a novel quality‐of‐service (QoS) routing protocol for ad hoc networks based on the OLSR protocol. Our protocol, QOLSR, is designed for wireless networks with stationary or moving nodes, where each node is equipped with 802.11 wireless card. The goal of our protocol is not only to find a route from a source to a destination, but an optimal route that satisfies the end‐to‐end QoS requirement, often given in terms of bandwidth or delay. We present an analytical model to compute the average delay and permissible throughput on links using the IEEE 802.11 medium access protocol and considering correlations and interferences between nodes. This model takes into account packet's collision probability, node's MAC queuing and service times based on the IEEE 802.11 binary exponential backoff algorithm and the events underneath its operation. Afterwards, our protocol assigns weights to individual links based on the average delay and bandwidth metrics of packets over the link. We present a distributed algorithm for multiple QoS requirements to find the source destination optimal paths in terms of bandwidth and delay using the known partial network topology available on each node. However, these optimal paths in partial network topology are not optimal paths in the whole ad hoc network. We show that this problem is due to the heuristic for the selection of MPRs used in OLSR. We propose innovative heuristics for the selection of MPRs based on QoS measurements that allow QOLSR to find optimal paths on the known partial topology having the same bandwidth performances that those on the whole network. The performance evaluation of our protocol in both static and dynamic ad hoc networks is extensively investigated. Mathematical analysis and simulation results show that the QOLSR protocol yields better performance compared to the best‐effort OLSR protocol and significantly improves throughput by using our proposed heuristic. Copyright © 2005 AEIT.

Collision Avoidance and Recovery for Multicast Communications in Ad Hoc Networks

The basic carrier sense multi-access control scheme for multicast communications in wireless ad hoc networks suffers from the well know hidden terminal problem. The data packet collision probability is relatively high, and the packet delivery ratio is sensitive to the network topology, nodes distribution and traffic load. In this paper, we generalize the virtual carrier sense collision avoidance approach to reduce packet collisions in multicast communications. The sender and receivers exchange RTS and CTS packets to reserve the channel. When more than one receivers reply with CTS packets, the sender will detect an expected collision which may be interpreted as a valid clear-to-send signal provided the collision satisfies the given timing requirements. Together with a receiver-initiated local recovery mechanism, the reliability and packet delivery ratio can be improved to close to 100%.

RWBO(pd w): A Novel Backoff Algorithm for IEEE 802.11 DCF

The Probability Distribution of Slot Selection (PDoSS) of IEEE 802.11 DCF is extremely uneven, which makes the packet collision probability very high. In this paper, the authors explore how to make the stations select the slots uniformly, and give an RWBO(pd, w) algorithm for 802.11 DCF to make the PDoSS even and decrease the packet collision probability. A Markov model is given to analyze the PDoSS of RWBO(pd, w). The performance of RWBO(pd, w) is evaluated by simulation in terms of saturation throughput and packet collision probability. The simulation results indicate that RWBO(pd, w) can decrease the packet contention probability to a large extent, and utilize the channel more efficiently as compared to the 802.11 DCF. Moreover, the relation between saturation throughput and walking probability (pd), the relation between saturation throughput and contention windows (w), the relation between packet collision probability and walking probability (pd), and the relation between packet collision probability and contention windows (w) are analyzed. The analysis indicates that RWBO(pd, w) has some remarkable features: its saturation throughout keeps high and packet collision probability keeps very low (under 0.1) in a large range of pd and w, which allow users to configure pd and w more flexibly.

Soft real-time communication over ethernet with adaptive traffic smoothing

Due to the low price and robustness resulting from its wide acceptance and deployment, Ethernet has become an attractive candidate for real-time control networks. However, it is difficult to build a real-time control network using the standard Ethernet because the Ethernet MAC protocol-1-persistent CSMA/CD protocol-may cause unpredictable access delay. When both real-time and nonreal-time packets are concurrently transported over an ordinary Ethernet, real-time (RT) packets from a node may experience a large delay due to 1) contention with nonRT packets in the local node where they originate and 2) collision with RT and nonRT packets from the other nodes. To resolve this problem, we design, implement, and evaluate an adaptive traffic smoother. Specifically, we design two adaptive traffic smoothers, one at the kernel level and the other at the user level. The kernel-level traffic smoother is installed between the IP layer and the Ethernet MAC layer for better performance, and the user-level traffic smoother is installed on top of the transport layer for better portability. The kernel-level traffic smoother first gives RT packets priority over nonRT packets in order to eliminate contention within the local node. Second, it smoothes nonRT traffic so as to reduce collision with RT packets from the other nodes. This traffic smoothing can dramatically decrease the packet-collision probability on the network. The traffic smoother, installed at each node, regulates the node's outgoing nonRT traffic to maintain a certain rate. In order to provide a reasonable nonRT throughput while providing probabilistic delay guarantees for RT traffic, the nonRT traffic-generation rate is allowed to adapt itself to the underlying network load condition. Our implementation of the traffic smoother requires only a minimal change in the OS kernel without any modification to the current standard of Ethernet MAC protocol or the TCP or UDP/IP stack. The traffic smoother has been implemented on the Linux OS and is shown to reduce the RT message deadline-miss ratio up to two orders of magnitude under a heavily loaded condition, while the nonRT throughput drops only by half. For better portability, we also implemented and evaluated a user-level traffic smoother on top of the transport layer. Moreover, we emulate a switch using a kernel-level traffic smoother to evaluate the performance of traffic smoother in a switched Ethernet environment that can scale to a large control network.

Performance of wireless networks with hidden nodes: a queuing-theoretic analysis

Hidden nodes are a fundamental problem that can potentially affect any wireless network where nodes cannot hear each other. Although the hidden node problem is well known, so far only few papers have quantified its effects in a comprehensive manner. This paper represents a first step towards getting a quantitative insight into the impact of hidden nodes on the performance of wireless networks. We first carry out an exact queuing-theoretic analysis for a 4-node segment and derive analytical expressions for the probability of packet collision, the mean packet delay, and the maximum throughput, based on a model that closely follows the IEEE 802.11 standard. We then extend the analysis and provide an approximation for a general linear topology that is asymptotically exact at low load. Finally, we perform detailed simulations to validate our analytical results and show their applicability to predict the performance of IEEE 802.11 networks with hidden nodes. The simulation and analysis closely match. Moreover, they reveal that the impact of hidden nodes propagates through the network causing some nodes to saturate at load as low as 15% of the capacity.

Interference Mitigation in Asynchronous Slow Frequency Hopping Bluetooth Networks

In asynchronous slow frequency hopping Bluetooth networks, packet collisions diminish the total link throughput. However, interference mitigation capability can reduce packet losses due to collisions. In this paper, an interference cancelling dual decision feedback (IC-DDF) Bluetooth receiver is proposed and its performance is evaluated for slow fading indoor channels. In addition to the bit error rate (BER) performance, the system level performance is evaluated by using the packet error rate (PER). To integrate the BER performance into the PER performance, a new geometric interpretation of packet error rate is introduced that uses an ensemble average of the received carrier to interference ratio (CIR). Also, a generalized packet collision probability is derived to analyze total link throughput.

Performance of Aloha channels under self-similarinput

The authors perform a trace-driven simulation experiment to analyse the performance of the Aloha channel under self-similar input. The real traffic trace is obtained by recording four days worth of data in the UCB campus network. The Aloha channel is assumed to carry delay-sensitive, non-bandwidth-intensive traffic, such as that generated by a Telnet client, which presents self-similarity features. The authors' findings show a significant increase in normalised throughput and a drop in packet collision probability in comparison with the Poissonian case.