In this paper, a TDMA-based mechanism is proposed for IEEE 802.11 Wireless LANs. This mechanism p... more In this paper, a TDMA-based mechanism is proposed for IEEE 802.11 Wireless LANs. This mechanism prioritizes real-time traffic in IEEE 802.11 networks, allowing the coexistence of standard stations with modified (real-time) stations in the same network domain. The worst-case timing analysis of the TDMA-based mechanism shows that the service interval is upper-bounded, even when the communication medium is shared with timing unconstrained stations.
The IEEE 802.11e standard was published as an amendment to the original IEEE 802.11 standard. Thi... more The IEEE 802.11e standard was published as an amendment to the original IEEE 802.11 standard. This amendment is intended to provide differentiated levels of QoS to the supported applications. The 802.11e amendment incorporates an additional coordination function called hybrid coordination function (HCF) that uses both a contention-based channel access method, called the enhanced distributed channel access (EDCA) and a controlled channel access, referred to as the HCF controlled channel access (HCCA). Under the EDCA mechanism, it is a common assumption to consider the highest access category (voice) adequate to support real-time communication. In this paper, we analyze the timing behavior of the EDCA function, when it is used to support real-time traffic. Basically, we assess the behavior of the voice category in open communication environments (i.e., a communication environment subject to external disturbances) when this access category is used to transfer small sized packets, generated in periodic intervals. We show that the transmission opportunity (TXOP) mechanism included in the IEEE 802.11e amendment improves the system throughput, for the case of message streams with small packet sizes. However, the impact of external disturbances upon the transfer of real-time messages is highly relevant. For instance, the average access delay for the real-time messages is more than one order of magnitude larger when the external disturbance increases the network load from just 10% to 30%. Furthermore, both the number of packet losses and the average size of the MAC queues forecast an unacceptable number of deadline losses for the real-time message streams, even for intermediate load cases.
Currently there is a trend for the implementation of industrial communication systems on top of w... more Currently there is a trend for the implementation of industrial communication systems on top of wireless communications. However, keeping up with the timing constraints of real-time traffic in open medium environments is a hard task. The main source for complexity is that, if the set of communicating devices is not previously agreed, the timing constraints imposed by such devices cannot be predicted at the system setup time, nor can be effectively controlled at the system run-time. In this paper, we propose the VTP-CSMA architecture to deal with this problem. This architecture allows the coexistence of default IEEE 802.11e devices with real-time devices sharing the same communication medium, enabling the prioritization of real-time traffic. The proposed solution is based on the control of the medium access rights by means of a virtual token passing procedure (VTP), complemented by an underlying traffic separation mechanism that prioritizes realtime traffic over the traffic from default IEEE 802.11 stations. The simulation analysis shows that the VTP-CSMA architecture guarantees values for both the throughput and the average access delay that significantly improves the results obtained for default IEEE 802.11e stations operating under EDCA mode
Abstract In this paper, the enhanced collision resolution algorithm, referred as high priority bi... more Abstract In this paper, the enhanced collision resolution algorithm, referred as high priority binary exponential backoff (h-BEB) is analyzed. Such algorithm provides high priority traffic separation, enabling the support of real-time communication in shared Ethernet networks. It allows multiple Ethernet standard devices to coexist in the same network segment with one h-BEB enhanced station, imposing higher priority for the transfer of h-BEB related traffic. The simulation analysis shows that the h-BEB algorithm guarantees values for both the ...
In this paper, a TDMA-based mechanism is proposed for IEEE 802.11 Wireless LANs. This mechanism p... more In this paper, a TDMA-based mechanism is proposed for IEEE 802.11 Wireless LANs. This mechanism prioritizes real-time traffic in IEEE 802.11 networks, allowing the coexistence of standard stations with modified (real-time) stations in the same network domain. The worst-case timing analysis of the TDMA-based mechanism shows that the service interval is upper-bounded, even when the communication medium is shared with timing unconstrained stations.
The IEEE 802.11e standard was published as an amendment to the original IEEE 802.11 standard. Thi... more The IEEE 802.11e standard was published as an amendment to the original IEEE 802.11 standard. This amendment is intended to provide differentiated levels of QoS to the supported applications. The 802.11e amendment incorporates an additional coordination function called hybrid coordination function (HCF) that uses both a contention-based channel access method, called the enhanced distributed channel access (EDCA) and a controlled channel access, referred to as the HCF controlled channel access (HCCA). Under the EDCA mechanism, it is a common assumption to consider the highest access category (voice) adequate to support real-time communication. In this paper, we analyze the timing behavior of the EDCA function, when it is used to support real-time traffic. Basically, we assess the behavior of the voice category in open communication environments (i.e., a communication environment subject to external disturbances) when this access category is used to transfer small sized packets, generated in periodic intervals. We show that the transmission opportunity (TXOP) mechanism included in the IEEE 802.11e amendment improves the system throughput, for the case of message streams with small packet sizes. However, the impact of external disturbances upon the transfer of real-time messages is highly relevant. For instance, the average access delay for the real-time messages is more than one order of magnitude larger when the external disturbance increases the network load from just 10% to 30%. Furthermore, both the number of packet losses and the average size of the MAC queues forecast an unacceptable number of deadline losses for the real-time message streams, even for intermediate load cases.
Currently there is a trend for the implementation of industrial communication systems on top of w... more Currently there is a trend for the implementation of industrial communication systems on top of wireless communications. However, keeping up with the timing constraints of real-time traffic in open medium environments is a hard task. The main source for complexity is that, if the set of communicating devices is not previously agreed, the timing constraints imposed by such devices cannot be predicted at the system setup time, nor can be effectively controlled at the system run-time. In this paper, we propose the VTP-CSMA architecture to deal with this problem. This architecture allows the coexistence of default IEEE 802.11e devices with real-time devices sharing the same communication medium, enabling the prioritization of real-time traffic. The proposed solution is based on the control of the medium access rights by means of a virtual token passing procedure (VTP), complemented by an underlying traffic separation mechanism that prioritizes realtime traffic over the traffic from default IEEE 802.11 stations. The simulation analysis shows that the VTP-CSMA architecture guarantees values for both the throughput and the average access delay that significantly improves the results obtained for default IEEE 802.11e stations operating under EDCA mode
Abstract In this paper, the enhanced collision resolution algorithm, referred as high priority bi... more Abstract In this paper, the enhanced collision resolution algorithm, referred as high priority binary exponential backoff (h-BEB) is analyzed. Such algorithm provides high priority traffic separation, enabling the support of real-time communication in shared Ethernet networks. It allows multiple Ethernet standard devices to coexist in the same network segment with one h-BEB enhanced station, imposing higher priority for the transfer of h-BEB related traffic. The simulation analysis shows that the h-BEB algorithm guarantees values for both the ...
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