Adnan Majeed | University of Baghdad (original) (raw)
Papers by Adnan Majeed
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BMJ, 2005
Responsible participation can make these initiatives work. Academics should submit their relevant... more Responsible participation can make these initiatives work. Academics should submit their relevant manuscripts to databases such as Relief Web. Moreover, we urge journals to submit the full text of all of their public health related articles to Relief Web, a policy which BioMed Central, an open access publisher, has pioneered, and has recently been joined by PLoS Medicine. The mass media could report more accurately on humanitarian situations. And funding agencies should look more favourably on evaluations of relief efforts and of the impact of their own responses. We do not seek to place blame upon the many agencies and NGOs that provide selfless and important care to the most vulnerable people in humanitarian crises. We understand that our proposal may be viewed as a challenge, and we recognise that it is impossible to make all reports available, particularly those about relief in political disasters. In exceptional circumstances, publishing a report that seemed to be censorious of a host country could place an organisation's staff or the population in danger or risk the expulsion of the agency. Indeed the head of the Sudan mission of Médecins Sans Frontières (MSF) was arrested in May 2005 and detained for releasing a report reporting sexual violence observed at MSF clinics. 10 We share a vision that everyone involved in making decisions about relief will be able to use evidence and knowledge generated by agencies and others. Archived evidence is a potent form of witness and testament for historical accountability and memory, and to achieve such an archive we have to collaborate. It is only a matter of time before another disaster will find us in disarray. Edward J Mills fellow
Wireless sensor networks (WSNs) have recently attracted a lot of interest due to the range of app... more Wireless sensor networks (WSNs) have recently attracted a lot of interest due to the range of applications they enable. Unfortunately, WSNs are exposed to numerous security threats that can adversely affect the success of important applications. Securing WSNs is challenging due to their unique nature as an application and a network, and due to their limited capabilities. In this paper, we argue that the WSN security research generally considers mechanisms that are modeled after and evaluated against abstract applications and WSN organizations. Instead, we propose that an effective solution for WSNs must be sensitive to the application and infrastructure. We propose an application-specific security context as the combination of a potential attacker's motivation and the WSN vulnerability. The vulnerability is a function of factors such as the sensor field, the WSN infrastructure, the application, protocols and system software, as well the accessibility and the observability of the WSN. To reduce the vulnerability, we argue that WSN design must balance traditional objectives such as energy efficiency, cost, and application level performance with security to a degree proportional to the attacker's motivation. We illustrate this argument via two example applications.
In timing analysis attackers study the transmission pattern of different nodes in a network with ... more In timing analysis attackers study the transmission pattern of different nodes in a network with the goal of extracting information about users, applications, or the structure of the network, even when the traffic is encrypted. Defeating timing analysis attacks requires expensive traffic mixing measures that equalize the transmission pattern at all nodes; such measures are especially expensive for battery operated wireless devices. In this paper, we first introduce TARP, a traffic mixing approach for defeating timing analysis tailored towards sensor networks. While TARP improves on traffic mixing approaches by combining multiple packets destined to different destinations in a single frame (amortizing packet overhead), traffic mixing remains expensive. To this end, we propose two techniques for improving the energy efficiency of TARP: (1) Using multi-path routing to exploit the available capacity engineered to defeat timing analysis; and (2) Adaptive transmission control to allow the transmission pattern to be adapted to the offered load without exposing the structure of the network. Furthermore, we define and explore the notion of relaxed timing analysis resilience where resilience is provided with a limited scope that is well defined in space and/or time. By controlling the scope to fit the application requirements, substantial savings in energy (or delay) can be achieved, while retaining desired levels of timing analysis resilience. Together, the proposed techniques significantly reduce the overhead of TARP, making timing analysis resilience more affordable for critical applications.
In Multi Hop Wireless Networks (MHWNs), nodes act both as end-hosts as well as intermediate route... more In Multi Hop Wireless Networks (MHWNs), nodes act both as end-hosts as well as intermediate routers. When communication occurs, these nodes form chains between different sources and destinations. Researchers have studied how these chains behave, discovering that MAC level interactions play a major role in determining their performance. In this paper, we extend this analysis to study how TCP connections, which involve bidirectional flows, behave over wireless chains. First, we break down and examine the types of chains that occur most frequently in TCP configurations and classify them by the nature of the MAC level interactions that arise in each. We then show that the throughput of TCP over a wireless chain is greatly affected by the type of interactions within the chain. Finally, we show the implications of the MAC level interactions on network performance: specifically, route instability and number of retransmissions.
In CSMA networks, there is a significant overhead associated with each packet including header ov... more In CSMA networks, there is a significant overhead associated with each packet including header overhead and contention overhead. The high overhead problem is exacerbated because some of these overheads are required to be at the lowest data rate to ensure that all contending nodes can compete fairly. For applications where packets are small, such as Voice over IP (VOIP), this means that a majority of the available transmission time is wasted on overhead. Packet aggregation is one of the techniques that has been proposed to amortize the per-transmission overhead over multiple aggregated packets. However, existing heuristics are limited, often not considering multi-rate wireless MAC, or operation in a WLAN environment. In this paper, we first formulate the problem of optimal aggregation for a multi-rate CSMA MAC protocol and show that it is NP-Hard. We then propose two heuristics that solve the aggregation problem for multi-rate WLANs. The first, which we call Data Rate based Aggregation protocol (DRA), divides packets in the MAC queue into groups based on the data rate they are to be transmitted at. The algorithm aggregates packets in the same group and broadcasts the aggregated frame at the data rate of that group. Empirically, DRA achieves several fold increase in throughput compared to basic aggregation. DRA also achieves up to a 200% increase in the number of VoIP calls supported by a single 802.11g AP compared to using state of the art aggregation protocols. The second heuristic, which we call Data Rate based Aggregation with Selective Demotion (DRA-SD), enables cross data rate aggregation. Through preliminary evaluation, we show that selectively demoting packets can further improve performance.
Proceedings of the 9th ACM international symposium on Mobility management and wireless access, 2011
Wireless Home Networks (WHNs) suffer from the rate anomaly problem which leads to network perform... more Wireless Home Networks (WHNs) suffer from the rate anomaly problem which leads to network performance deterioration. We observe that transmitting bandwidth intensive traffic, such as a video stream, over low data rate links can affect the end-to-end delays of co-existing high data rate traffic. Based on this observation, we propose modifications to the WHN setup. This paper suggests the use
Wireless Communications and Mobile Computing, 2008
... nodes can claim the false proximity to the sink to attract packets, considerably increase the... more ... nodes can claim the false proximity to the sink to attract packets, considerably increase the clock ... APPLICATION-DRIVEN APPROACH TO SECURING WSNs ... propose a trust and reputation management scheme in WSNs with minimal delay and energy/bandwidth consumption. ...
BMJ, 2009
On 5 May I arrived at my south London general practice to discover that I was at the “epicentre” ... more On 5 May I arrived at my south London general practice to discover that I was at the “epicentre” of the H1N1 outbreak in the UK.1 Two local schools had been closed because of diagnosed cases of swine flu among their pupils. However, by the time the new cases of swine …
BMJ, 1996
has recently been confirmed in the Nurses' Health Study,9 and the results of a secondary preventi... more has recently been confirmed in the Nurses' Health Study,9 and the results of a secondary prevention study (heart and oestrogen/ progestin replacement study) are expected in 1999. Doctors and managers are understandably concerned about the cost implications of widespread use of lipid lowering treatment. However, a cost minimisation analysis of the 4S study's data concluded that the reduced use of hospital services that would result from use of simvastatin in a similar group of patients in the United States would offset most of the cost of treatment.'0 Cost effectiveness of expensive drug treatments such as the statins depends on risk of ischaemic heart disease. A cost effectiveness study based on the findings of the 4S study estimated that simvastatin treatment of men aged 55-64 who have suffered a myocardial infarction would cost ;6000 per life year saved, whereas it would cost £361 000 per life year saved for women aged 45-54 with angina." Consideration of the direct costs to health services of morbidity from ischaemic heart disease or the indirect costs of mortality or morbidity to
BMJ, 2005
European research area. ERC debate. www.cordis.lu/era/concept.htm (accessed 10 May 2005). 9 Europ... more European research area. ERC debate. www.cordis.lu/era/concept.htm (accessed 10 May 2005). 9 European Commission. ESFRI-European strategy forum on research infrastructures. www.cordis.lu/era/esfri_home.htm (accessed 10 May 2005). 10 Kuh D, Ben-Shlomo Y. A life course approach to chronic disease epidemiology.
BMJ, 2002
... Little PS,; Williamson I. .Controversies in management: Are antibiotics appropriate for sore ... more ... Little PS,; Williamson I. .Controversies in management: Are antibiotics appropriate for sore throats? ... NI-CO WORK ON THE MOST REMOTE INHABITED ISLAND IN THE WORLD ISLAND DOCTOR(S) REQUIRED FOR TRISTAN DA CUNHA STARTING MAY 2012 (24 Nov 2011); ...
BMJ, 2011
Fielden states: “A small number of people working within the BMA, such as catering staff, are emp... more Fielden states: “A small number of people working within the BMA, such as catering staff, are employed and paid by external contractors. As such, …
BMJ, 2001
Health authority has no power Editor-Majeed's editorial on the referral of Dr Peter Mansfield to ... more Health authority has no power Editor-Majeed's editorial on the referral of Dr Peter Mansfield to the General Medical Council is flawed as he assumes that Worcestershire Health Authority has power in managing its responsibility for a successful public health immunisation campaign. 1 It is precisely because the authority is impotent as a public statutory public body that it asked the GMC to intervene.
Annals of Internal Medicine, 2005
TO THE EDITOR: The U.S. Preventive Services Task Force (USPSTF) recommended screening for abdomin... more TO THE EDITOR: The U.S. Preventive Services Task Force (USPSTF) recommended screening for abdominal aortic aneurysms (AAAs) with ultrasonography only in male smokers 65 to 75 years of age. Other subsets were excluded in part because of good evidence that screening and early treatment result in important harms, including an increased number of surgeries with associated morbidity and mortality, and psychological harms (1). I question the evidence regarding harms. First, the companion review on this topic by Fleming and colleagues (2) concluded that screening does not appear to be associated with significant physical or psychological harms. Second, the harm related to morbidity and mortality of unnecessary operations requires an unstated assumption that small AAAs identified by screening would be inappropriately repaired before they reached a size of substantial rupture risk. The members of the USPSTF do not provide evidence for this assumption, nor do they indicate the magnitude of this effect on their conclusions. In fact, evidence from randomized trials of AAA screening indicates that more than 90% of subsequent elective AAA repairs were performed at recommended size criteria (3). The USPSTF made separate recommendations for men on the basis of smoking, even though randomized trials favor screening for all men (2). To do so, the USPSTF relied on separate analyses of AAA prevalence, based on risk factors such as smoking. Clearly, screening is more cost-effective if the screened population has a higher prevalence of AAA, so the impact of smoking is an important consideration. It is unclear, however, why the USPSTF did not evaluate women on the basis of smoking history. Female smokers have the same AAA prevalence as male nonsmokers (1.9% for 3-cm AAAs [4]), yet they were bundled into a grade D recommendation against screening for all women while male smokers received a neutral grade C recommendation. I do not believe that risk factor analysis should be differentially applied on the basis of sex. Finally, it is disappointing that the USPSTF ignored the importance of a family history of AAA in its overall recommendations. Most studies have found that first-degree relatives of patients with AAA have a much higher prevalence of small AAAs (25% to 43% in brothers, 6% to 16% in sisters [5]) than the 5.9% prevalence in male smokers (4), for whom the USPSTF issued a grade B recommendation for screening. I believe that the USPSTF recommendations were too conservative in not recommending AAA screening for all men older than age 64 years, for female smokers in this age group, and for men or women in this age group whose sibling or parent had an AAA. The Society for Vascular Surgery and the Society for Vascular Medicine and Biology have recommended more comprehensive screening that reflects these concerns (6).
Traffic analysis in Multi-hop Wireless Networks can expose the structure of the network allowing ... more Traffic analysis in Multi-hop Wireless Networks can expose the structure of the network allowing attackers to focus their efforts on critical nodes. For example, jamming the only data sink in a sensor network can cripple the network. We propose a new communication protocol that is part of the MAC layer, but resides conceptually between the routing layer and MAC, that is resilient to traffic analysis. Each node broadcasts the data that it has to transmit according to a fixed transmission schedule that is independent of the traffic being generated, making the network immune to time correlation analysis. The transmission pattern is identical, with the exception of a possible time shift, at all nodes, removing spatial correlation of transmissions to network strucutre. Data for all neighbors resides in the same encrypted packet. Each neighbor then decides which subset of the data in a packet to forward onwards using a routing protocol whose details are orthogonal to the proposed scheme. We analyze the basic scheme, exploring the tradeoffs in terms of frequency of transmission and packet size. We also explore adaptive and time changing patterns and analyze their performance under a number of representative scenarios.
... The transmission pattern is identical, with the exception of a possible time shift, at all no... more ... The transmission pattern is identical, with the exception of a possible time shift, at all nodes, removing spatial correlation of ... against traffic analysis. These are discussed in chapter 3. ... Typically, the routing protocol sets up paths to allow the collection of the data from individual ...
Restricted access! Kindly consult the site administrator.
BMJ, 2005
Responsible participation can make these initiatives work. Academics should submit their relevant... more Responsible participation can make these initiatives work. Academics should submit their relevant manuscripts to databases such as Relief Web. Moreover, we urge journals to submit the full text of all of their public health related articles to Relief Web, a policy which BioMed Central, an open access publisher, has pioneered, and has recently been joined by PLoS Medicine. The mass media could report more accurately on humanitarian situations. And funding agencies should look more favourably on evaluations of relief efforts and of the impact of their own responses. We do not seek to place blame upon the many agencies and NGOs that provide selfless and important care to the most vulnerable people in humanitarian crises. We understand that our proposal may be viewed as a challenge, and we recognise that it is impossible to make all reports available, particularly those about relief in political disasters. In exceptional circumstances, publishing a report that seemed to be censorious of a host country could place an organisation's staff or the population in danger or risk the expulsion of the agency. Indeed the head of the Sudan mission of Médecins Sans Frontières (MSF) was arrested in May 2005 and detained for releasing a report reporting sexual violence observed at MSF clinics. 10 We share a vision that everyone involved in making decisions about relief will be able to use evidence and knowledge generated by agencies and others. Archived evidence is a potent form of witness and testament for historical accountability and memory, and to achieve such an archive we have to collaborate. It is only a matter of time before another disaster will find us in disarray. Edward J Mills fellow
Wireless sensor networks (WSNs) have recently attracted a lot of interest due to the range of app... more Wireless sensor networks (WSNs) have recently attracted a lot of interest due to the range of applications they enable. Unfortunately, WSNs are exposed to numerous security threats that can adversely affect the success of important applications. Securing WSNs is challenging due to their unique nature as an application and a network, and due to their limited capabilities. In this paper, we argue that the WSN security research generally considers mechanisms that are modeled after and evaluated against abstract applications and WSN organizations. Instead, we propose that an effective solution for WSNs must be sensitive to the application and infrastructure. We propose an application-specific security context as the combination of a potential attacker's motivation and the WSN vulnerability. The vulnerability is a function of factors such as the sensor field, the WSN infrastructure, the application, protocols and system software, as well the accessibility and the observability of the WSN. To reduce the vulnerability, we argue that WSN design must balance traditional objectives such as energy efficiency, cost, and application level performance with security to a degree proportional to the attacker's motivation. We illustrate this argument via two example applications.
In timing analysis attackers study the transmission pattern of different nodes in a network with ... more In timing analysis attackers study the transmission pattern of different nodes in a network with the goal of extracting information about users, applications, or the structure of the network, even when the traffic is encrypted. Defeating timing analysis attacks requires expensive traffic mixing measures that equalize the transmission pattern at all nodes; such measures are especially expensive for battery operated wireless devices. In this paper, we first introduce TARP, a traffic mixing approach for defeating timing analysis tailored towards sensor networks. While TARP improves on traffic mixing approaches by combining multiple packets destined to different destinations in a single frame (amortizing packet overhead), traffic mixing remains expensive. To this end, we propose two techniques for improving the energy efficiency of TARP: (1) Using multi-path routing to exploit the available capacity engineered to defeat timing analysis; and (2) Adaptive transmission control to allow the transmission pattern to be adapted to the offered load without exposing the structure of the network. Furthermore, we define and explore the notion of relaxed timing analysis resilience where resilience is provided with a limited scope that is well defined in space and/or time. By controlling the scope to fit the application requirements, substantial savings in energy (or delay) can be achieved, while retaining desired levels of timing analysis resilience. Together, the proposed techniques significantly reduce the overhead of TARP, making timing analysis resilience more affordable for critical applications.
In Multi Hop Wireless Networks (MHWNs), nodes act both as end-hosts as well as intermediate route... more In Multi Hop Wireless Networks (MHWNs), nodes act both as end-hosts as well as intermediate routers. When communication occurs, these nodes form chains between different sources and destinations. Researchers have studied how these chains behave, discovering that MAC level interactions play a major role in determining their performance. In this paper, we extend this analysis to study how TCP connections, which involve bidirectional flows, behave over wireless chains. First, we break down and examine the types of chains that occur most frequently in TCP configurations and classify them by the nature of the MAC level interactions that arise in each. We then show that the throughput of TCP over a wireless chain is greatly affected by the type of interactions within the chain. Finally, we show the implications of the MAC level interactions on network performance: specifically, route instability and number of retransmissions.
In CSMA networks, there is a significant overhead associated with each packet including header ov... more In CSMA networks, there is a significant overhead associated with each packet including header overhead and contention overhead. The high overhead problem is exacerbated because some of these overheads are required to be at the lowest data rate to ensure that all contending nodes can compete fairly. For applications where packets are small, such as Voice over IP (VOIP), this means that a majority of the available transmission time is wasted on overhead. Packet aggregation is one of the techniques that has been proposed to amortize the per-transmission overhead over multiple aggregated packets. However, existing heuristics are limited, often not considering multi-rate wireless MAC, or operation in a WLAN environment. In this paper, we first formulate the problem of optimal aggregation for a multi-rate CSMA MAC protocol and show that it is NP-Hard. We then propose two heuristics that solve the aggregation problem for multi-rate WLANs. The first, which we call Data Rate based Aggregation protocol (DRA), divides packets in the MAC queue into groups based on the data rate they are to be transmitted at. The algorithm aggregates packets in the same group and broadcasts the aggregated frame at the data rate of that group. Empirically, DRA achieves several fold increase in throughput compared to basic aggregation. DRA also achieves up to a 200% increase in the number of VoIP calls supported by a single 802.11g AP compared to using state of the art aggregation protocols. The second heuristic, which we call Data Rate based Aggregation with Selective Demotion (DRA-SD), enables cross data rate aggregation. Through preliminary evaluation, we show that selectively demoting packets can further improve performance.
Proceedings of the 9th ACM international symposium on Mobility management and wireless access, 2011
Wireless Home Networks (WHNs) suffer from the rate anomaly problem which leads to network perform... more Wireless Home Networks (WHNs) suffer from the rate anomaly problem which leads to network performance deterioration. We observe that transmitting bandwidth intensive traffic, such as a video stream, over low data rate links can affect the end-to-end delays of co-existing high data rate traffic. Based on this observation, we propose modifications to the WHN setup. This paper suggests the use
Wireless Communications and Mobile Computing, 2008
... nodes can claim the false proximity to the sink to attract packets, considerably increase the... more ... nodes can claim the false proximity to the sink to attract packets, considerably increase the clock ... APPLICATION-DRIVEN APPROACH TO SECURING WSNs ... propose a trust and reputation management scheme in WSNs with minimal delay and energy/bandwidth consumption. ...
BMJ, 2009
On 5 May I arrived at my south London general practice to discover that I was at the “epicentre” ... more On 5 May I arrived at my south London general practice to discover that I was at the “epicentre” of the H1N1 outbreak in the UK.1 Two local schools had been closed because of diagnosed cases of swine flu among their pupils. However, by the time the new cases of swine …
BMJ, 1996
has recently been confirmed in the Nurses' Health Study,9 and the results of a secondary preventi... more has recently been confirmed in the Nurses' Health Study,9 and the results of a secondary prevention study (heart and oestrogen/ progestin replacement study) are expected in 1999. Doctors and managers are understandably concerned about the cost implications of widespread use of lipid lowering treatment. However, a cost minimisation analysis of the 4S study's data concluded that the reduced use of hospital services that would result from use of simvastatin in a similar group of patients in the United States would offset most of the cost of treatment.'0 Cost effectiveness of expensive drug treatments such as the statins depends on risk of ischaemic heart disease. A cost effectiveness study based on the findings of the 4S study estimated that simvastatin treatment of men aged 55-64 who have suffered a myocardial infarction would cost ;6000 per life year saved, whereas it would cost £361 000 per life year saved for women aged 45-54 with angina." Consideration of the direct costs to health services of morbidity from ischaemic heart disease or the indirect costs of mortality or morbidity to
BMJ, 2005
European research area. ERC debate. www.cordis.lu/era/concept.htm (accessed 10 May 2005). 9 Europ... more European research area. ERC debate. www.cordis.lu/era/concept.htm (accessed 10 May 2005). 9 European Commission. ESFRI-European strategy forum on research infrastructures. www.cordis.lu/era/esfri_home.htm (accessed 10 May 2005). 10 Kuh D, Ben-Shlomo Y. A life course approach to chronic disease epidemiology.
BMJ, 2002
... Little PS,; Williamson I. .Controversies in management: Are antibiotics appropriate for sore ... more ... Little PS,; Williamson I. .Controversies in management: Are antibiotics appropriate for sore throats? ... NI-CO WORK ON THE MOST REMOTE INHABITED ISLAND IN THE WORLD ISLAND DOCTOR(S) REQUIRED FOR TRISTAN DA CUNHA STARTING MAY 2012 (24 Nov 2011); ...
BMJ, 2011
Fielden states: “A small number of people working within the BMA, such as catering staff, are emp... more Fielden states: “A small number of people working within the BMA, such as catering staff, are employed and paid by external contractors. As such, …
BMJ, 2001
Health authority has no power Editor-Majeed's editorial on the referral of Dr Peter Mansfield to ... more Health authority has no power Editor-Majeed's editorial on the referral of Dr Peter Mansfield to the General Medical Council is flawed as he assumes that Worcestershire Health Authority has power in managing its responsibility for a successful public health immunisation campaign. 1 It is precisely because the authority is impotent as a public statutory public body that it asked the GMC to intervene.
Annals of Internal Medicine, 2005
TO THE EDITOR: The U.S. Preventive Services Task Force (USPSTF) recommended screening for abdomin... more TO THE EDITOR: The U.S. Preventive Services Task Force (USPSTF) recommended screening for abdominal aortic aneurysms (AAAs) with ultrasonography only in male smokers 65 to 75 years of age. Other subsets were excluded in part because of good evidence that screening and early treatment result in important harms, including an increased number of surgeries with associated morbidity and mortality, and psychological harms (1). I question the evidence regarding harms. First, the companion review on this topic by Fleming and colleagues (2) concluded that screening does not appear to be associated with significant physical or psychological harms. Second, the harm related to morbidity and mortality of unnecessary operations requires an unstated assumption that small AAAs identified by screening would be inappropriately repaired before they reached a size of substantial rupture risk. The members of the USPSTF do not provide evidence for this assumption, nor do they indicate the magnitude of this effect on their conclusions. In fact, evidence from randomized trials of AAA screening indicates that more than 90% of subsequent elective AAA repairs were performed at recommended size criteria (3). The USPSTF made separate recommendations for men on the basis of smoking, even though randomized trials favor screening for all men (2). To do so, the USPSTF relied on separate analyses of AAA prevalence, based on risk factors such as smoking. Clearly, screening is more cost-effective if the screened population has a higher prevalence of AAA, so the impact of smoking is an important consideration. It is unclear, however, why the USPSTF did not evaluate women on the basis of smoking history. Female smokers have the same AAA prevalence as male nonsmokers (1.9% for 3-cm AAAs [4]), yet they were bundled into a grade D recommendation against screening for all women while male smokers received a neutral grade C recommendation. I do not believe that risk factor analysis should be differentially applied on the basis of sex. Finally, it is disappointing that the USPSTF ignored the importance of a family history of AAA in its overall recommendations. Most studies have found that first-degree relatives of patients with AAA have a much higher prevalence of small AAAs (25% to 43% in brothers, 6% to 16% in sisters [5]) than the 5.9% prevalence in male smokers (4), for whom the USPSTF issued a grade B recommendation for screening. I believe that the USPSTF recommendations were too conservative in not recommending AAA screening for all men older than age 64 years, for female smokers in this age group, and for men or women in this age group whose sibling or parent had an AAA. The Society for Vascular Surgery and the Society for Vascular Medicine and Biology have recommended more comprehensive screening that reflects these concerns (6).
Traffic analysis in Multi-hop Wireless Networks can expose the structure of the network allowing ... more Traffic analysis in Multi-hop Wireless Networks can expose the structure of the network allowing attackers to focus their efforts on critical nodes. For example, jamming the only data sink in a sensor network can cripple the network. We propose a new communication protocol that is part of the MAC layer, but resides conceptually between the routing layer and MAC, that is resilient to traffic analysis. Each node broadcasts the data that it has to transmit according to a fixed transmission schedule that is independent of the traffic being generated, making the network immune to time correlation analysis. The transmission pattern is identical, with the exception of a possible time shift, at all nodes, removing spatial correlation of transmissions to network strucutre. Data for all neighbors resides in the same encrypted packet. Each neighbor then decides which subset of the data in a packet to forward onwards using a routing protocol whose details are orthogonal to the proposed scheme. We analyze the basic scheme, exploring the tradeoffs in terms of frequency of transmission and packet size. We also explore adaptive and time changing patterns and analyze their performance under a number of representative scenarios.
... The transmission pattern is identical, with the exception of a possible time shift, at all no... more ... The transmission pattern is identical, with the exception of a possible time shift, at all nodes, removing spatial correlation of ... against traffic analysis. These are discussed in chapter 3. ... Typically, the routing protocol sets up paths to allow the collection of the data from individual ...