The emerging context-aware applications relying on the wireless networking, require the availabil... more The emerging context-aware applications relying on the wireless networking, require the availability of network services that provide even simple notions of context as position and identity. In the last few years several localization and tracking systems for indoor environment have been proposed. However, these systems are often very expensive since they require the installation of dedicated infrastructures of sensors based on radio, ultrasound or infrared technologies, to determine the user position. This paper aims to propose and analyze a novel indoor localization and tracking system based on the Bluetooth technology. This is a short-range, low complexity and low cost wireless technology that supports explicit device discovery services. The proposed localization system fully integrates these device discovery procedures into the infrastructure-based network of Bluetooth access points that provides the wireless connectivity inside a building. This design approach guarantees a cost-effective solution for the positioning service implementation. In this paper we have extensively investigated through simulative analysis the performances of the proposed localization system, showing that it has a negligible overhead, still providing a timely update of user location.
We present a procedure to evaluate the parameters of the LEAP (linear bounded arrival processes) ... more We present a procedure to evaluate the parameters of the LEAP (linear bounded arrival processes) traffic characterisation when a stochastic model of considered traffic flow is available. The procedure, based on an equivalent queuing system, has been applied to a VoIP (voice over IP) scenario in a DiffServ (differentiated services) network architecture. In particular, we consider the characterisation of a traffic flow composed by the aggregation of telephone sources with VAD (voice activity detection), where each one has been modelled by a fluidic on-off process with exponentially distributed sojourn times in each state. For testing the goodness of our approach we have carried out discrete events simulations, which have highlighted the accuracy of the proposed procedure in the considered scenario
We address the throughput analysis of high-speed IEEE 802.11b WLANs from both an analytical and a... more We address the throughput analysis of high-speed IEEE 802.11b WLANs from both an analytical and a simulative perspective. Specifically, we derive the throughput formula for the RTS/CTS access method of the p-persistent IEEE 802.11b MAC protocol. The accuracy of the proposed model is exhaustively validated via simulation results. By exploiting our formulas, we derive the theoretical upper bound for the throughput performance of the IEEE 802.11b protocol. Our analytical and simulative results indicated that the RTS/CTS mechanism produces very limited advantages in the standard IEEE 802.11 networks with respect to the basic access when no hidden stations are present. Finally, we extend a distributed backoff-tuning strategy firstly proposed for the basic access method, and we validate its effectiveness to approach closely the throughput limit of the IEEE 802.11b protocol.
The paper focuses on two emerging technologies for constructing a Mobile ad hoc network: IEEE 802... more The paper focuses on two emerging technologies for constructing a Mobile ad hoc network: IEEE 802.11 and Bluetooth. The IEEE 802.11 standard is a good platform to implement a single-hop ad hoc network because of its extreme simplicity. Furthermore, multi-hop networks covering areas of several square kilometers could be built by exploiting the IEEE 802.11 technology. On smaller scales, technologies like Bluetooth can be exploited (perhaps in combination with the 802.11-type technology) to build ad-hoc wireless Personal Area Networks, i.e. networks that connect devices placed inside a circle with radius of 10 meters. The paper presents with a tutorial style the architectures and protocols of IEEE 802.11 and Bluetooth. In addition, a discussion on the performance of these two technologies is presented. Specifically, we focus on the Medium Access Control (MAC) protocol adopted by the two technologies and we analyze both the protocol efficiency (channel utilization) and the response time.
AbstractWireless technologies in the LAN environment are becoming increasingly important. The IEE... more AbstractWireless technologies in the LAN environment are becoming increasingly important. The IEEE 802.11 is the most mature technology for Wireless Local Area Networks ( WLANs). The limited bandwidth and the finite battery power of mobile computers represent one of ...
This paper develops an analytical framework to model the interaction between TCP and 802:11 MAC p... more This paper develops an analytical framework to model the interaction between TCP and 802:11 MAC proto- col over a WLAN, when concurrent TCP downlink and uplink connections are active. Assuming a TCP advertised window equal to one, we formulate a Markov model to characterize the dynamic network contention level, dened as the expected number of wireless stations having at least
... A simple protocol for the dynamic tuning of the backoff mechanism in IEEE 802.11 networks. ..... more ... A simple protocol for the dynamic tuning of the backoff mechanism in IEEE 802.11 networks. ... optimal average backoff window size) equals the average backoff of the p-persistent IEEE 802.11 ... Finally, to avoid harmful fluctuations of the p-value, we utilize a smoothing factor, and ...
... Nevertheless, the commercial deployment of community networks is still in its infancy. ... Mo... more ... Nevertheless, the commercial deployment of community networks is still in its infancy. ... Moreover, many commercial mesh networks rely on direc-tional antennas for increased range, but Roofnet nodes use mainly omnidirectional antennas to reduce the per-node costs. ...
The paper concerns device discovery in multi-hop networks of Bluetooth devices. We start from the... more The paper concerns device discovery in multi-hop networks of Bluetooth devices. We start from the observation that forming a Bluetooth scatternet (i.e., a multi-hop wireless topology) requires each pair of neighboring nodes to have a “symmetric” knowledge of each other, i.e., if node u knows node v then node v knows node u. We investigate the use of the Bluetooth procedures for device discovery (inquiry procedures) in order to guarantee the needed symmetric knowledge for scatternet formation. Through the use of simulations we observed that despite the long time required for each node to become aware of the presence of all its neighbors, the Bluetooth topologies obtained by using the devices discovered after just 6 seconds are connected. The average number of neighbors of each node and the average route length are also consistently close to the values that we would obtain if all the neighbors of a device were discovered.
This paper describes the results of the first ns2-based comparative performance evaluation among ... more This paper describes the results of the first ns2-based comparative performance evaluation among four major solutions presented in the literature for forming multi-hop networks of Bluetooth devices (scatternet formation). The four protocols considered in this paper are BlueTrees [1], BlueStars [2], BlueNet [3] and the protocol presented in [4] which proposes geometric techniques for topology reduction combined with cluster-based scatternet formation. We implemented the operations of the four protocols from device discovery to scatternet formation. By means of a thorough performance evaluation we have identified protocol parameters and Bluetooth technology features that affect the duration of the formation process and the properties of the produced scatternet. We have investigated how possible modifications of the BT technology (e.g., backoff duration, possibility for a BT inquirer to identify itself) make device discovery more efficient for scatternet formation in multi-hop networks. We have then discussed implementation concerns for each of the selected protocols. Finally, we have analyzed the protocols overhead as well as the effect of the different protocols operations on key metrics of the generated scatternets, which includes the time needed for forming a scatternet, the number of its piconets, the number of slaves per piconet, the number of roles assumed by each node and the scatternet route lengths.
The channel utilization of 802.11-based wireless local area networks has been studied extensively... more The channel utilization of 802.11-based wireless local area networks has been studied extensively from an analytical perspective. However, these studies consider wireless networks formed by saturated stations that transmit UDP-like traffic to randomly selected destinations. This model cannot be easily applied to hot spots since: i) the majority of Internet applications are based on the TCP protocol; ii) the TCP traffic is rate-controlled and the TCP flow control mechanisms impede the stations to saturate; and iii) the users’ traffic is either sent towards or received from the access point. This paper is the first to provide an analytical model of the channel utilization in hot spots when there are M users which use TCP connections to download traffic from the Internet. Specifically, in this work we analytically investigate the complex interaction of the TCP flow control mechanisms and MAC collision avoidance techniques in 802.11b-based hot spot networks. We validate our model by means of simulations, and we exploit it to provide thorough reasons of the following counter-intuitive observations: i) the channel utilization is almost independent of the number of TCP connections; ii) on average the access point contends with few users for the channel bandwidth.
We evaluate the performance of a new protocol for scatternet formation in Bluetooth multihop netw... more We evaluate the performance of a new protocol for scatternet formation in Bluetooth multihop networks. The protocol implements the three fundamental steps to scatternet. formation, namely, device discovery, piconet formation and piconet interconnection. A Bluetooth extension to ns2, the VINT project simulator, has been developed to address all the details pertinent to scatternet formation.. The performance evaluation allows us to assess the impact of the device discovery duration over the scatternet formation process, to evaluate the time for the protocol to generate a connected scatternet, and to investigate metrics that pertain to the "quality" of the scatternet, such as the average number of piconets, the average number of slaves per piconets, the average number of roles assumed by each node and the average length of the routes between any two Bluetooth devices.
Bluetooth is an emerging technology for constructing adhoc wirelessPersonal Area Networks (WPANs)... more Bluetooth is an emerging technology for constructing adhoc wirelessPersonal Area Networks (WPANs). In this paper we analyze aninnovative scheduling algorithm for asynchronous data trafficspecifically tailored to the Bluetooth characteristic. Thisalgorithm, named Efficient Double-Cycle (EDC), dynamically adaptsthe polling frequency to the traffic conditions. By considering ascenario where a Bluetooth master is used as wireless access pointto the Internet, we show that
There is a vast literature on the throughput analysis of the IEEE 802.11 media access control (MA... more There is a vast literature on the throughput analysis of the IEEE 802.11 media access control (MAC) protocol. However, very little has been done on investigating the interplay between the collision avoidance mechanisms of the 802.11 MAC protocol and the dynamics of upper layer transport protocols. In this paper, we tackle this issue from an analytical, simulative, and experimental perspective.
AbstractIn this letter we deal with the characterization and computation of the value, say opt, ... more AbstractIn this letter we deal with the characterization and computation of the value, say opt, corresponding to the max-imum protocol capacity in -persistent carrier-sense multiaccess (CSMA) protocols. The contribution of this letter is twofold. First, we give an analytical ...
The paper focuses on one of the emerging technologies for constructing a Mobile ad hoc network: B... more The paper focuses on one of the emerging technologies for constructing a Mobile ad hoc network: Bluetooth. Bluetooth can be exploited on small scales, to build ad hoc wireless Personal Area Networks (WPAN), i.e., networks that connect devices placed inside a circle with radius of 10 m. The Bluetooth technology is just starting to appear on the market and its architecture and protocols are not widely known. For this reason, the first part of the paper contains a tutorial-oriented description of the Bluetooth architecture and protocols. In addition, in the paper we extensively discuss the performance of this technology by investigating, through simulation, the main performance figures: the protocol efficiency (channel utilization), the response time, and the system power (i.e., the ratio between throughput and delay). Specifically, the performance analysis focuses on the algorithms for scheduling the transmissions in a Bluetooth network. The Bluetooth Specification indicates a Round Robin scheduler as possible solution, that is each slaves is polled in a consecutive order. For this reason, we first study in depth the performance figures of a Bluetooth network with a Round Robin scheduler. Our results point out the inefficient Bluetooth behavior under asymmetric traffic conditions. To solve this problem we propose and analyze an innovative scheduling algorithm specifically tailored to the Bluetooth characteristic. This algorithm, named efficient double-cycle (EDC), dynamically adapts the polling frequency to the traffic conditions. A performance study indicates that our EDC scheduler always outperforms the Round Robin scheduler.
The emerging context-aware applications relying on the wireless networking, require the availabil... more The emerging context-aware applications relying on the wireless networking, require the availability of network services that provide even simple notions of context as position and identity. In the last few years several localization and tracking systems for indoor environment have been proposed. However, these systems are often very expensive since they require the installation of dedicated infrastructures of sensors based on radio, ultrasound or infrared technologies, to determine the user position. This paper aims to propose and analyze a novel indoor localization and tracking system based on the Bluetooth technology. This is a short-range, low complexity and low cost wireless technology that supports explicit device discovery services. The proposed localization system fully integrates these device discovery procedures into the infrastructure-based network of Bluetooth access points that provides the wireless connectivity inside a building. This design approach guarantees a cost-effective solution for the positioning service implementation. In this paper we have extensively investigated through simulative analysis the performances of the proposed localization system, showing that it has a negligible overhead, still providing a timely update of user location.
We present a procedure to evaluate the parameters of the LEAP (linear bounded arrival processes) ... more We present a procedure to evaluate the parameters of the LEAP (linear bounded arrival processes) traffic characterisation when a stochastic model of considered traffic flow is available. The procedure, based on an equivalent queuing system, has been applied to a VoIP (voice over IP) scenario in a DiffServ (differentiated services) network architecture. In particular, we consider the characterisation of a traffic flow composed by the aggregation of telephone sources with VAD (voice activity detection), where each one has been modelled by a fluidic on-off process with exponentially distributed sojourn times in each state. For testing the goodness of our approach we have carried out discrete events simulations, which have highlighted the accuracy of the proposed procedure in the considered scenario
We address the throughput analysis of high-speed IEEE 802.11b WLANs from both an analytical and a... more We address the throughput analysis of high-speed IEEE 802.11b WLANs from both an analytical and a simulative perspective. Specifically, we derive the throughput formula for the RTS/CTS access method of the p-persistent IEEE 802.11b MAC protocol. The accuracy of the proposed model is exhaustively validated via simulation results. By exploiting our formulas, we derive the theoretical upper bound for the throughput performance of the IEEE 802.11b protocol. Our analytical and simulative results indicated that the RTS/CTS mechanism produces very limited advantages in the standard IEEE 802.11 networks with respect to the basic access when no hidden stations are present. Finally, we extend a distributed backoff-tuning strategy firstly proposed for the basic access method, and we validate its effectiveness to approach closely the throughput limit of the IEEE 802.11b protocol.
The paper focuses on two emerging technologies for constructing a Mobile ad hoc network: IEEE 802... more The paper focuses on two emerging technologies for constructing a Mobile ad hoc network: IEEE 802.11 and Bluetooth. The IEEE 802.11 standard is a good platform to implement a single-hop ad hoc network because of its extreme simplicity. Furthermore, multi-hop networks covering areas of several square kilometers could be built by exploiting the IEEE 802.11 technology. On smaller scales, technologies like Bluetooth can be exploited (perhaps in combination with the 802.11-type technology) to build ad-hoc wireless Personal Area Networks, i.e. networks that connect devices placed inside a circle with radius of 10 meters. The paper presents with a tutorial style the architectures and protocols of IEEE 802.11 and Bluetooth. In addition, a discussion on the performance of these two technologies is presented. Specifically, we focus on the Medium Access Control (MAC) protocol adopted by the two technologies and we analyze both the protocol efficiency (channel utilization) and the response time.
AbstractWireless technologies in the LAN environment are becoming increasingly important. The IEE... more AbstractWireless technologies in the LAN environment are becoming increasingly important. The IEEE 802.11 is the most mature technology for Wireless Local Area Networks ( WLANs). The limited bandwidth and the finite battery power of mobile computers represent one of ...
This paper develops an analytical framework to model the interaction between TCP and 802:11 MAC p... more This paper develops an analytical framework to model the interaction between TCP and 802:11 MAC proto- col over a WLAN, when concurrent TCP downlink and uplink connections are active. Assuming a TCP advertised window equal to one, we formulate a Markov model to characterize the dynamic network contention level, dened as the expected number of wireless stations having at least
... A simple protocol for the dynamic tuning of the backoff mechanism in IEEE 802.11 networks. ..... more ... A simple protocol for the dynamic tuning of the backoff mechanism in IEEE 802.11 networks. ... optimal average backoff window size) equals the average backoff of the p-persistent IEEE 802.11 ... Finally, to avoid harmful fluctuations of the p-value, we utilize a smoothing factor, and ...
... Nevertheless, the commercial deployment of community networks is still in its infancy. ... Mo... more ... Nevertheless, the commercial deployment of community networks is still in its infancy. ... Moreover, many commercial mesh networks rely on direc-tional antennas for increased range, but Roofnet nodes use mainly omnidirectional antennas to reduce the per-node costs. ...
The paper concerns device discovery in multi-hop networks of Bluetooth devices. We start from the... more The paper concerns device discovery in multi-hop networks of Bluetooth devices. We start from the observation that forming a Bluetooth scatternet (i.e., a multi-hop wireless topology) requires each pair of neighboring nodes to have a “symmetric” knowledge of each other, i.e., if node u knows node v then node v knows node u. We investigate the use of the Bluetooth procedures for device discovery (inquiry procedures) in order to guarantee the needed symmetric knowledge for scatternet formation. Through the use of simulations we observed that despite the long time required for each node to become aware of the presence of all its neighbors, the Bluetooth topologies obtained by using the devices discovered after just 6 seconds are connected. The average number of neighbors of each node and the average route length are also consistently close to the values that we would obtain if all the neighbors of a device were discovered.
This paper describes the results of the first ns2-based comparative performance evaluation among ... more This paper describes the results of the first ns2-based comparative performance evaluation among four major solutions presented in the literature for forming multi-hop networks of Bluetooth devices (scatternet formation). The four protocols considered in this paper are BlueTrees [1], BlueStars [2], BlueNet [3] and the protocol presented in [4] which proposes geometric techniques for topology reduction combined with cluster-based scatternet formation. We implemented the operations of the four protocols from device discovery to scatternet formation. By means of a thorough performance evaluation we have identified protocol parameters and Bluetooth technology features that affect the duration of the formation process and the properties of the produced scatternet. We have investigated how possible modifications of the BT technology (e.g., backoff duration, possibility for a BT inquirer to identify itself) make device discovery more efficient for scatternet formation in multi-hop networks. We have then discussed implementation concerns for each of the selected protocols. Finally, we have analyzed the protocols overhead as well as the effect of the different protocols operations on key metrics of the generated scatternets, which includes the time needed for forming a scatternet, the number of its piconets, the number of slaves per piconet, the number of roles assumed by each node and the scatternet route lengths.
The channel utilization of 802.11-based wireless local area networks has been studied extensively... more The channel utilization of 802.11-based wireless local area networks has been studied extensively from an analytical perspective. However, these studies consider wireless networks formed by saturated stations that transmit UDP-like traffic to randomly selected destinations. This model cannot be easily applied to hot spots since: i) the majority of Internet applications are based on the TCP protocol; ii) the TCP traffic is rate-controlled and the TCP flow control mechanisms impede the stations to saturate; and iii) the users’ traffic is either sent towards or received from the access point. This paper is the first to provide an analytical model of the channel utilization in hot spots when there are M users which use TCP connections to download traffic from the Internet. Specifically, in this work we analytically investigate the complex interaction of the TCP flow control mechanisms and MAC collision avoidance techniques in 802.11b-based hot spot networks. We validate our model by means of simulations, and we exploit it to provide thorough reasons of the following counter-intuitive observations: i) the channel utilization is almost independent of the number of TCP connections; ii) on average the access point contends with few users for the channel bandwidth.
We evaluate the performance of a new protocol for scatternet formation in Bluetooth multihop netw... more We evaluate the performance of a new protocol for scatternet formation in Bluetooth multihop networks. The protocol implements the three fundamental steps to scatternet. formation, namely, device discovery, piconet formation and piconet interconnection. A Bluetooth extension to ns2, the VINT project simulator, has been developed to address all the details pertinent to scatternet formation.. The performance evaluation allows us to assess the impact of the device discovery duration over the scatternet formation process, to evaluate the time for the protocol to generate a connected scatternet, and to investigate metrics that pertain to the "quality" of the scatternet, such as the average number of piconets, the average number of slaves per piconets, the average number of roles assumed by each node and the average length of the routes between any two Bluetooth devices.
Bluetooth is an emerging technology for constructing adhoc wirelessPersonal Area Networks (WPANs)... more Bluetooth is an emerging technology for constructing adhoc wirelessPersonal Area Networks (WPANs). In this paper we analyze aninnovative scheduling algorithm for asynchronous data trafficspecifically tailored to the Bluetooth characteristic. Thisalgorithm, named Efficient Double-Cycle (EDC), dynamically adaptsthe polling frequency to the traffic conditions. By considering ascenario where a Bluetooth master is used as wireless access pointto the Internet, we show that
There is a vast literature on the throughput analysis of the IEEE 802.11 media access control (MA... more There is a vast literature on the throughput analysis of the IEEE 802.11 media access control (MAC) protocol. However, very little has been done on investigating the interplay between the collision avoidance mechanisms of the 802.11 MAC protocol and the dynamics of upper layer transport protocols. In this paper, we tackle this issue from an analytical, simulative, and experimental perspective.
AbstractIn this letter we deal with the characterization and computation of the value, say opt, ... more AbstractIn this letter we deal with the characterization and computation of the value, say opt, corresponding to the max-imum protocol capacity in -persistent carrier-sense multiaccess (CSMA) protocols. The contribution of this letter is twofold. First, we give an analytical ...
The paper focuses on one of the emerging technologies for constructing a Mobile ad hoc network: B... more The paper focuses on one of the emerging technologies for constructing a Mobile ad hoc network: Bluetooth. Bluetooth can be exploited on small scales, to build ad hoc wireless Personal Area Networks (WPAN), i.e., networks that connect devices placed inside a circle with radius of 10 m. The Bluetooth technology is just starting to appear on the market and its architecture and protocols are not widely known. For this reason, the first part of the paper contains a tutorial-oriented description of the Bluetooth architecture and protocols. In addition, in the paper we extensively discuss the performance of this technology by investigating, through simulation, the main performance figures: the protocol efficiency (channel utilization), the response time, and the system power (i.e., the ratio between throughput and delay). Specifically, the performance analysis focuses on the algorithms for scheduling the transmissions in a Bluetooth network. The Bluetooth Specification indicates a Round Robin scheduler as possible solution, that is each slaves is polled in a consecutive order. For this reason, we first study in depth the performance figures of a Bluetooth network with a Round Robin scheduler. Our results point out the inefficient Bluetooth behavior under asymmetric traffic conditions. To solve this problem we propose and analyze an innovative scheduling algorithm specifically tailored to the Bluetooth characteristic. This algorithm, named efficient double-cycle (EDC), dynamically adapts the polling frequency to the traffic conditions. A performance study indicates that our EDC scheduler always outperforms the Round Robin scheduler.
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