A distributed MAC scheme supporting voice services in mobile ad hoc networks

Future mobile ad hoc networks are expected to support voice traffic. The requirement for small delay and jitter of voice traffic poses a significant challenge for medium access control (MAC) in such networks. User mobility presents unique difficulties in this context due to the associated dynamic path attenuation. In this paper, a MAC scheme for mobile ad hoc networks supporting voice traffic is proposed. With the aid of a low‐power probe prior to DATA transmissions, resource reservation is achieved in a distributed manner, thus leading to small packet transmission delay and jitter. The proposed scheme can automatically adapt to dynamic path attenuation in a mobile environment. Statistical multiplexing of on/off voice traffic can also be achieved by partial resource reservation for off voice flows. Simulation results demonstrate the effectiveness of the proposed scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

A fast‐convergent fairness scheme for resource allocation in RPR networks

In this paper, we propose a fast‐convergent fairness scheme in IEEE 802.17 resilient packet ring (RPR) networks. In the proposed scheme, each station could rapidly approach fair rate by estimating the number of unbounded flows at each link. In addition, the fast‐convergent scheme could prevent rate oscillations in the RPR aggressive mode scheme under unbalanced traffic. The estimation mechanism is simple and scalable since it is stateless without per‐flow management. Through analytical and simulation evaluations our scheme was found to be stable and speedy when compared with 802.17 RPR fairness scheme or the proposed distributed virtual‐time scheduling in rings scheme. Our scheme could allocate bandwidth fairly and smoothly among flows and achieve high utilization at the same time in the RPR network. Copyright © 2008 John Wiley & Sons, Ltd.     

Slot allocation strategies for delay sensitive traffic support in asynchronous ad hoc wireless networks

Supporting real‐time traffic in ad hoc wireless networks is considered as a challenging problem. Existing bandwidth reservation mechanisms assume a TDMA environment where achieving time synchronisation is expensive in terms of resources. Heuristics that exist for slot allocation schemes assume a CDMA over TDMA model in order to alleviate the presence of hidden terminals. Slot allocation strategies in the presence of hidden terminals assume significance in a single channel system for supporting delay sensitive traffic. In this paper, we propose three heuristics for the slot allocation process in asynchronou single channel multihop wireless networks in the presence of hidden terminals. The heuristics we propose are the early fit reservation (EFR), minimum bandwidth‐based reservation (MBR) and position‐based hybrid reservation (PHR). The EFR heuristic assigns bandwidth link‐by‐link in the forward path. The MBR heuristic allocates bandwidth to the links in the increasing order of free conn‐slots. The PHR heuristic assigns bandwidth for every link proportional to its position in the path. Simulation studies show that EFR performs better in terms of delay characteristics. MBR provides better call blocking performance at the cost of high end‐to‐end delay. PHR provides a better delay performance compared to MBR and better call blocking performance comparedto EFR. Copyright © 2004 John Wiley & Sons, Ltd.     

An unslotted multichannel channel‐access protocol for distributed direct‐sequence networks

A multichannel reservation-based channel-access protocol is investigated in this paper. The available system bandwidth is divided into distinct frequency channels. Under the protocol, one channel (the control channel) is used to exchange reservation messages and the remaining channels (the traffic channels) are used for information-bearing traffic. The performance of this scheme is compared to that of a single-channel reservation-based protocol. A simple contention-based slotted-Aloha protocol is also considered. Performance results take into account the effects of multiple-access interference on acquisition and packet errors. Results show that the reservation-based approach is advantageous under conditions of high traffic. In addition, a pacing mechanism that mitigates multiple-access interference and promotes fairness is described, and results are presented that demonstrate its effectiveness. This revised version was published online in June 2006 with corrections to the Cover Date.     

Reducing cell loss in banyan based ATM switching fabrics

In this paper, we propose a new technique for reducing cell loss in multi‐banyan‐based ATM switching fabrics. We propose a switch architecture that uses incremental path reservation based on previously established connections. Path reservation is carried out sequentially within each banyan but multiple banyan planes can be concurrently reserved. We use a conflict resolution approach according to which banyans make concurrent reservation offers of conflict‐free paths to head of the line cells waiting in input buffers. A reservation offer from a given banyan is allocated to the cell whose source‐to‐destination path uses the largest number of partially allocated switching elements which are shared with previously reserved paths. Paths are incrementally clustered within each banyan. This approach leaves the largest number of free switching elements for subsequent reservations which has the effect of reducing the potential of future conflicts and improves throughput. We present a pipelined switch architecture based on the above concept of path‐clustering which we call path‐clustering banyan switching fabric (PCBSF). An efficient hardware that implements PCBSF is presented together with its theoretical basis. The performance and robustness of PCBSF are evaluated under simulated uniform traffic and ATM traffic. We also compare the cell loss rate of PCBSF to that of other pipelined banyan switches by varying the switch size, input buffer size, and traffic pattern. Copyright © 2001 John Wiley & Sons, Ltd.     

Data traffic‐based analysis of delay and energy consumption in cognitive radio networks with and without resource reservation

A new opportunistic cross‐layer MAC protocol involving channel allocation and packet scheduling for cognitive radio networks is proposed. Cognitive radio allows secondary users (SUs) to exploit the available portions of the licensed spectrum bands without interfering with primary users. In particular, we consider a cognitive radio system, where SUs are equipped with two transceivers: a control transceiver and a software‐defined radio transceiver. Data traffic characteristics of SUs are considered to ameliorate system performance. So, we propose a mechanism of resource reservation to improve QoS requirements that favors successful SUs to transmit data during x time slots without interfering with primary users. The key novelty of this paper is giving priority for SUs with important data traffic and which frequently solicits data channels to transmit for the remaining time of the ongoing time slot and for the next time slots directly after checking the channel availability. We develop a new analytical model to evaluate delay parameter for two scenarios with and without resource reservation and we then investigate the impact of those scenarios on the energy consumption. We show through simulations that cognitive radio performances increase noticeably with the proposed scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

End-to-end bandwidth allocation scheme for voice traffic support over MANETs

Multimedia and real-time applications require bandwidth guarantees, which can be achieved by resource reservation. However, bandwidth reservation in ad-hoc networks is a very challenging task due to the instability of radio channels, node mobility and lack of coordination between mobile nodes. Most proposed reservation protocols focus on point-to-point reservations, and only a few work has been done to propose an efficient end-to-end reservation scheme. In this paper, we propose a reservation scheme called End-to-end reservation scheme for voice and data traffic support (EERV). The basic component of our protocol is a handshake mechanism which has the role to establish point-to-point reservations, and to ensure consistency of reservations between neighbor nodes. Both data and voice sources are allowed to establish reservations with priority given to voice sources. This reservation scheme is extended to support the reservation and release of resources along a path in cooperation with the routing layer. Our reservation scheme is based on DSR, a well-known reactive routing protocol. Mobility of nodes and node failure cause frequent reservation breakages resulting in significant performance degradation. In order to resolve this issue we propose a reservation loss detection and reservation recovery mechanisms. We achieved intensive simulations to evaluate the performance of our protocol. Simulation results show the effectiveness of this protocol.     

Integrated video and voice transmission using packet reservation multiple access

This paper proposes a new protocol for the integration of voice and video transmission over the packet reservation multiple access (PRMA) system that is a modification of reservation‐ALOHA protocol. We focus on low bit‐rate video applications like video conferencing and visual telephony for wireless communications. The ITU–T H.263 standard provides a solution to the need for low bit‐rate video compression under 64 kbytes/s. The proposed protocol assumes that each voice terminal follows a traffic pattern of talk spurts and silent gaps with fixed permission probability (p=0.3), and each video terminal has the higher permission probability (p=1) to access the available slot based on ITU–T H.263 standard. Again, we present a ‘pseudo‐reservation’ scheme to release slots reserved by video terminals according to the contents of each video transmission buffer, and the active voice terminals can temporarily access the additional slots to improve the performance without sacrificing the video capacity of the system. The packet dropping probability of the active voice terminals and bandwidth utilization of the system are superior to the original PRMA, as indicated in simulation results. Copyright © 2001 John Wiley & Sons, Ltd.     

On the effectiveness of alternative paths in QoS routing

We propose a routing strategy in which connection requests with specific bandwidth demands can be assigned to one of several alternative paths connecting the source to the destination. The primary goal of this multiple‐path approach is to compensate for the inaccuracy of the knowledge available to routing nodes, caused by the limited frequency of link state (LS) information exchanges. We introduce a collection of K‐shortest path routing schemes and investigate their performance under a variety of traffic conditions and network configurations. We subsequently demonstrate that K‐shortest path routing offers a lower blocking probability in all scenarios and more balanced link utilization than other routing methods discussed in the literature. With our approach, it is possible to reduce the frequency of link state exchanges, and the incurred bandwidth overhead, without compromising the overall performance of the network. Based on the proposed routing scheme, we investigate different link state dissemination algorithms, which are aimed at reducing the communication overhead by prioritizing the scope and differentiating the qualitative content of LS update messages. Copyright © 2004 John Wiley & Sons, Ltd.     

Improving handoff performance by utilizing ad hoc links in multi-hop cellular systems

Handoff performance is a critical issue for mobile users in wireless cellular networks, such as GSM networks, 3G networks, and next generation networks (NGNs). When ad hoc mode is introduced to cellular networks, multi-hop handoffs become inevitable, which brings in new challenging issues to network designers, such as how to reduce the call dropping rate, how to simplify the multi-hop handoff processes, and how to take more advantage of ad hoc mode for better resource management, and most of these issues have not been well addressed as yet. In this paper, we will address some of the issues and propose a scheme, Ad-hoc-Network–Embedded handoff Assisting Scheme (ANHOA), which utilizes the self-organizing feature of ad hoc networks to facilitate handoffs in cellular networks and provide an auxiliary way for mobile users to handoff across different cells. Moreover, we also propose a scheme enabling each BS to find the feasible minimum reservation for handoff calls based on the knowledge of adjacent cells’ traffic information. Due to the use of multi-hop connections, our scheme can apparently alleviate the reservation requirement and lower the call blocking rate while retaining higher spectrum efficiency. We further provide a framework for information exchange among adjacent cells, which can dynamically balance the load among cells. Through this study, we demonstrate how we can utilize ad hoc mode in cellular systems to significantly improve the handoff performance.     

An energy‐efficient node‐scheduling scheme for wireless sensor networks based on minimum dominating sets

One of the major requirements for new wireless sensor networks is to extend the lifetime of the network. Node‐scheduling techniques have been used extensively for this purpose. Some existing approaches rely mainly on location information through global positioning system (GPS) devices for designing efficient scheduling strategies. However, integration of GPS devices with sensor nodes is expensive and increases the cost of deployment dramatically. In this paper we present a location‐free solution for node scheduling. Our scheme is based on a graph theoretical approach using minimum dominating sets. We propose a heuristic to extract a collection of dominating sets. Each set consists of a group of working nodes which ensures a high level of network coverage. At each round, one set is responsible for covering the sensor field while the nodes in other sets are in sleep mode. We evaluate our solution through simulations and discuss our future research directions. Copyright © 2008 John Wiley & Sons, Ltd.     

A short ID‐based proxy signature scheme

The notion of identity‐based proxy signature with message recovery feature has been proposed to shorten identity‐based proxy signatures and improve their communication overhead because signed messages are not transmitted with these kinds of signatures. There are a few schemes for this notion: the schemes of Singh and Verma and Yoon et al. Unfortunately, Tian et al., by presenting two forgery attacks, show that Singh and Verma scheme is not secure, and also, the scheme of Yoon et al. does not support provable security. The contributions of this paper are twofold. First, we review the scheme by Yoon et al. and discuss why it does not have message recovery property, and consequently, it is not short. Second, we propose a short identity‐based proxy signature scheme with the help of message recovery property and show that it is secure under computational Diffie–Hellman assumption in the random oracle model. Furthermore, our scheme is more efficient than (as efficient as) previous identity‐based proxy signatures. Copyright © 2014 John Wiley & Sons, Ltd.     

In‐band bootstrapping in database‐driven multi‐hop cognitive radio networks

Database‐driven approach has emerged recently as an alternative or supplement for spectrum sensing for cognitive radio networks (CRNs). Within database‐driven CRNs, master devices obtain spectrum information by direct connection to a spectrum database, while slave devices can only access spectrum information indirectly via masters. The in‐band approach completely based on primary spectrum channels can be used, which eliminates the need for out‐of‐band connections and eases the adoption of the database‐driven spectrum sharing. In this paper, we study the in‐band bootstrapping process for database‐driven multi‐hop CRNs, where master/slave devices form a multi‐hop networks, and slaves need multi‐hop communications to obtain spectrum information from the master during bootstrapping. We start with the basic design of in‐band bootstrap protocol, whose performance is unsatisfactory of protocol overhead and bootstrap time. Then we propose 2 enhancements: first, we incorporates the recursive fractional spectrum information query scheme to reduce protocol overhead; then we propose the prefetch scheme to reduce the bootstrap time. According to the analysis and simulation results, our proposed protocols can greatly improve the performance: the recursive fractional spectrum information query enhancement reduces up to 40% of the overhead, the prefetch enhancement reduces more than 20% of the bootstrap time.     

Performance comparison of end‐to‐end and on‐the‐spot traffic‐aware techniques

Traffic‐aware routing protocols have recently received considerable attention. This has been motivated by the role that it could play in extending the network's lifetime (or operational time) as it target the reservation of node's power and better utilisation of channel bandwidth, which could lead to performance improvement in terms of important performance metrics including throughput and end‐to‐end delay. Traffic‐aware techniques can be classified into two categories, namely end‐to‐end and on‐the‐spot, based on the way of establishing and maintaining routes between any source and destination. Although there has been much work on both categories, there has been no comparative performance study of the two approaches. To the best of our knowledge, this is the first work that carries out such a performance comparison. To this end, we have adapted our traffic‐aware technique namely load density to suggest a new ‘on‐the‐spot’ traffic‐aware technique. The main reason for doing this adaptation is to ensure that the comparison between the two approaches is fair and realistic. The study will reveal the main performance characteristics of the two approaches under various traffic and network conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

An improved anonymous multi‐receiver identity‐based encryption scheme

Anonymous receiver encryption is an important cryptographic primitive. It allows a sender to use the public identities of multiple receivers to encrypt messages so that only the authorized receivers or a privileged set of users can decrypt the messages, and the identities of the receivers are not revealed. Recently, Zhang et al. proposed a novel anonymous multi‐receiver encryption scheme and claimed that their scheme could realize the receiver's identity privacy. Unfortunately, in this paper, we pointed out that the scheme by Zhang et al. did not achieve the anonymity of the receiver identity after analyzing the security of the scheme. At the same time, we give the corresponding attack. After analyzing the reason to produce such attacks, a novel anonymous multi‐receiver encryption scheme is given to achieve the anonymity of the receiver's identities. And we formally prove that the proposed scheme is semantically secure for confidentiality and receiver identities’ anonymity. The security of the scheme is based on decisional bilinear Diffie‐Hellman problem. Compared with the scheme by Zhang et al., Fan et al., Wang et al., and Chien et al., our scheme is shown to be better performance and robust security. To the best of our knowledge, our scheme is most efficient in terms of computational cost and communication overhead. Copyright © 2013 John Wiley & Sons, Ltd.     

HeS‐CoP: Heuristic switch‐controller placement scheme for distributed SDN controllers in data center networks

Software‐defined networking (SDN) has been widely researched and used to manage large‐scale networks such as data center networks (DCNs). An early stage of SDN controller experienced low responsiveness, low scalability, and low reliability. To solve these problems, distributed SDN controllers have been proposed. The concept of distributed SDN controllers distributes control messages among multiple SDN controllers. However, distributed SDN controllers must assign a master controller for each networking devices. Most previous studies, however, did not consider the characteristics of DCNs. Thus, they are not suitable to operate in DCNs. In this paper, we propose HeS‐CoP, a heuristic switch‐controller placement scheme for distributed SDN controllers in DCNs. With the control traffic load and CPU load, HeS‐CoP decides when our scheme should be performed in DCNs. To show the feasibility of HeS‐CoP, we designed and implemented an orchestrator that contains our proposed scheme and then evaluated our proposed scheme. As a result, our proposed scheme well distributes the control traffic load, decreases the average CPU load, and reduces the packet delay.     

Stability analysis of an adaptive packet access scheme for mobile communication systems with high propagation delays

In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time‐Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot‐code resource. This protocol is named Adaptive Time Code‐Packet Reservation Multiple Access (ATC‐PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)‐Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High‐Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC‐PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC‐PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd.     

Analysis of Priority R‐ALOHA (PR‐ALOHA) protocol

With the exception of required time synchronization, the Reservation‐ALOHA (R‐ALOHA) protocol is simple to implement and suitable for medium access control in ad hoc wireless networks. In this paper, we propose an innovative protocol, referred to as Reservation ALOHA with priority (PR‐ALOHA) that provides differentiated services on the basis of traffic priority. To date, the carrier sense multiple access/collision avoidance (CSMA/CA) protocol has been widely used for this purpose by employing an interframe spacing (IFS) for priority service, that is, nodes ready for packet transmissions are required to wait for an IFS amount of time, where a shorter IFS is used to gain faster access to the radio channel. However, sensing and collision avoidance mechanisms make CSMA/CA unsuitable for delay‐sensitive applications, that is, congested scenarios with high traffic. In contrast, the proposed PR‐ALOHA protocol may be considered a good candidate for such applications. In this paper, the performance of the PR‐ALOHA protocol is investigated analytically and by simulation. Its comparison with regular R‐ALOHA is also carried out. Modeling and simulation results of PR‐ALOHA show that PR‐ALOHA improves the performance of high‐priority traffic with limited effect on normal network traffic. Thus, PR‐ALOHA may be useful in vehicular communications, where traffic may be separated into emergency messages having high priority and multimedia messages having low priority. Copyright © 2013 John Wiley & Sons, Ltd.     

MLAS: Multiple level authentication scheme for VANETs

The vehicular ad hoc network (VANET) is an emerging type of network which enables vehicles on roads to inter-communicate for driving safety. The basic idea is to allow arbitrary vehicles to broadcast ad hoc messages (e.g. traffic accidents) to other vehicles. However, this raises the concern of security and privacy. Messages should be signed and verified before they are trusted while the real identity of vehicles should not be revealed, but traceable by authorized party. Existing solutions either rely too heavily on a tamper-proof hardware device, or do not have an effective message verification scheme. In this paper, we propose a multiple level authentication scheme which still makes use of tamper-proof devices but the strong assumption that a long-term system master secret is preloaded into all tamper-proof devices is removed. Instead the master secret can be updated if needed to increase the security level. On the other hand, messages sent by vehicles are classified into two types – regular messages and urgent messages. Regular messages can be verified by neighboring vehicles by means of Hash-based Message Authentication Code (HMAC) while urgent messages can only be verified with the aid of RSUs nearby by means of a conditional privacy-preserving authentication scheme. Through extensive simulation, we show that our multiple level authentication scheme is much more efficient that those RSU-aided authentication scheme as long as the proportion of urgent messages is less than 100%. The verification delay required can be up to 110 times smaller than other protocols. Our implementation shows that batch verification may not be as efficient as expected. In case without batch verification, the verification delay required by our scheme can even be up to 173 times smaller.