Showing papers on "Transmission delay published in 2008"

Secure network switching infrastructure

Abstract: Use of a centralized control architecture in a network. Policy declaration, routing computation, and permission checks are managed by a logically centralized controller. By default, hosts on the network can only route to the network controller. Hosts and users must first authenticate themselves with the controller before they can request access to the network resources. The controller uses the first packet of each flow for connection setup. When a packet arrives at the controller, the controller decides whether the flow represented by that packet should be allowed. The switches use a simple flow table to forward packets under the direction of the controller. When a packet arrives that is not in the flow table, it is forwarded to the controller, along with information about which port the packet arrived on. When a packet arrives that is in the flow table, it is forwarded according to the controller's directive.

Master–Slave Current-Sharing Control of a Parallel DC–DC Converter System Over an RF Communication Interface

Abstract: Using analog wireless communication, we demonstrate a master-slave load-sharing control of a parallel dc-dc buck converter system, thereby eliminating the need for physical connection to distribute the control signal among the converter modules. The current reference for the slave modules is provided by the master module using radio-frequency (RF) transmission, thereby ensuring even sharing of the load current. The effect of delay due to RF transmission on system stability and performance is analyzed, and regions of operation for a stable as well as satisfactory performance are determined. We experimentally demonstrate a satisfactory performance of the master-slave converter at 20-kHz switching frequency under steady state as well as transient conditions in the presence of a transmission delay. The proposed control concept, which can potentially attain redundancy that is achievable using a droop method, may lead to more robust and reconfigurable control implementation of distributed converters and power systems. It may also be used as a (fault-tolerant) backup for wire-based control of parallel/distributed converters.

Virtualized application acceleration infrastructure

Abstract: In one example embodiment, a system and method is illustrated that includes processes a first data packet using a first operating system, the first data packet received from a first network. A second operation is shown that processes a second data packet using a second operating system, the second data packet received from a second network. Further, an additional operation is shown that determines a route associated with the first data packet and the second data packet, the route including at least one of a logical route or physical route. Moreover, an operation is shown that parses the first data packet into at least one first logical segment, and parsing the second data packet into at least one second logical segment. An operation is shown that transmits the first logical segment and the second logical segment as at least one data packet across the WAN.

Modeling queueing and channel access delay in unsaturated IEEE 802.11 random access MAC based wireless networks

Abstract: In this paper, we present an analytic model for evaluating the queueing delays and channel access times at nodes in wireless networks using the IEEE 802.11 Distributed Coordination Function (DCF) as the MAC protocol. The model can account for arbitrary arrival patterns, packet size distributions and number of nodes. Our model gives closed form expressions for obtaining the delay and queue length characteristics and models each node as a discrete time G/G/1fs queue. The service time distribution for the queues is derived by accounting for a number of factors including the channel access delay due to the shared medium, impact of packet collisions, the resulting backoffs as well as the packet size distribution. The model is also extended for ongoing proposals under consideration for 802.11e wherein a number of packets may be transmitted in a burst once the channel is accessed. Our analytical results are verified through extensive simulations. The results of our model can also be used for providing probabilistic quality of service guarantees and determining the number of nodes that can be accommodated while satisfying a given delay constraint.

DFR: Directional flooding-based routing protocol for underwater sensor networks

Abstract: Unlike terrestrial sensor networks, underwater sensor networks (UWSNs) have different characteristics such as a long propagation delay, a narrow bandwidth and high packet loss. Hence, existing path setup-based routing protocols proposed for terrestrial sensor networks are not applicable in the underwater environment. For example, they take much time when establishing a path between source and destination nodes due to the long propagation delay. In addition, the path establishment requires much overhead of control messages. Moreover, the dynamic and high packet loss degrades reliability, which invokes more retransmissions. Even though exiting routing protocols such as VBF were proposed to improve the reliability, they did not take into account the link quality. That is, there is no guarantee that packets reach the sink safely especially when a link is error-prone. In this paper, we therefore propose a directional flooding-based routing protocol, called DFR. Basically, DFR relies on a packet flooding technique to increase the reliability. However, the number of nodes which flood a packet is controlled in order to prevent a packet from flooding over the whole network and the nodes to forward the packet are decided according to the link quality. In addition, DFR also addresses a well-known void problem by allowing at least one node to participate in forwarding a packet. Our simulation study using ns-2 proves that DFR is more suitable for UWSNs especially when links are prone to packet loss.

Efficient available bandwidth estimation for network paths

Abstract: For estimating the available bandwidth along a network path,a novel active probing methodology COPP(chirp of packet paris)is presented combining self-induced congested principle with packet pair technique.After a sequence of packet pairs with gradually reduced intra-pair spacing was transmitted,COPP process would discover all turning bandwidth.Then every bandwidth was bound with a distinct weight according of the degree of interference of the underlying turning point and its neighbors to yield the final estimate by weighted adding up all turning bandwidth.Based on analysis of inter-packet spacing and one-way delay of single packet in a packet pair,the decision rules for determining whether a packet pair is turning point were shown.We also described the weighting process to obtain different weights for different kinds of turning point and discussed the effect of different thresholds on estimation.Simulation results in several cross traffic conditions indicate that COPP provides accurate estimation with relatively fewer overhead compared to other estimating tools.

Method and apparatus for inter-technology handoff of a user equipment

Abstract: In order to facilitate a handoff of a communication session between a legacy circuit switched network and a packet data network such as a 3GPP LTE, 3GPP2 UMB, or WiMAX network, which communication session is anchored in an IMS Voice Call Continuity Application Server (VCC AS), a Circuit Switched Proxy (CS Proxy) is provided in the packet data network that communicates with a Mobile Switching Center (MSC) of the circuit switched network. The CS Proxy allows the packet data network to communicate with the VCC AS, the MSC to communicate with the packet data network, and the MSC to communicate with the VCC AS via the packet data network, thereby allowing an exchange of handoff-related information between the packet data network and the VCC AS, the packet data network and the circuit switched network, and the circuit switched network and the VCC AS via the packet data network.

Path-quality monitoring in the presence of adversaries

Abstract: Edge networks connected to the Internet need effective monitoring techniques to drive routing decisions and detect violations of Service Level Agreements (SLAs). However, existing measurement tools, like ping, traceroute, and trajectory sampling, are vulnerable to attacks that can make a path look better than it really is. In this paper, we design and analyze path-quality monitoring protocols that reliably raise an alarm when the packet-loss rate and delay exceed a threshold, even when an adversary tries to bias monitoring results by selectively delaying, dropping, modifying, injecting, or preferentially treating packets.Despite the strong threat model we consider in this paper, our protocols are efficient enough to run at line rate on high-speed routers. We present a secure sketching protocol for identifying when packet loss and delay degrade beyond a threshold. This protocol is extremely lightweight, requiring only 250-600 bytes of storage and periodic transmission of a comparably sized IP packet to monitor billions of packets. We also present secure sampling protocols that provide faster feedback and accurate round-trip delay estimates, at the expense of somewhat higher storage and communication costs. We prove that all our protocols satisfy a precise definition of secure path-quality monitoring and derive analytic expressions for the trade-off between statistical accuracy and system overhead. We also compare how our protocols perform in the client-server setting, when paths are asymmetric, and when packet marking is not permitted.

Toward Ideal On-Chip Communication Using Express Virtual Channels

Abstract: Current on-chip networks use a packet-switched design with a complex router at every hop, which imposes significant communication energy, delay, and throughput overhead. we propose reducing energy and delay, and increasing throughput, using express virtual channels. packets traveling along these virtual express lanes, which connect distant nodes in the network, bypass intermediate routers, significantly reducing router overhead.

Energy-Efficient Transmissions With Individual Packet Delay Constraints

Abstract: This paper focuses on energy-efficient packet transmission with individual packet delay constraints. The solution presented herein is a generalization of Uysal-Biyikoglu et al. (2002), which considered energy-efficient transmissions for a group of M packets subject to a single transmission deadline. First, the optimal offline scheduler (vis-a-vis total transmission energy) for packet transmissions with individual packet delay constraints is developed. It is shown that when packet inter-arrival times are independent and identically distributed (i.i.d.), the optimal transmission durations of packet m and packet M - m + 1, m isin [1,...,M], M ges 1, are identically distributed. This symmetry property leads to a simple and exact solution of the average packet delay for any i.i.d. inter-arrival times under the optimal offline scheduling. In addition, the packet delay performance for the single transmission deadline model is analyzed and shown to grow monotonically with M and at a rate proportional to radicM. A heuristic online scheduler, which assumes no future arrival information, is also studied and shown to achieve a comparable energy performance to the optimal offline scheduler in a wide range of scenarios. The flexible energy and delay tradeoff provided by the individual delay constraint model is further illustrated via simulations.

Process, voltage, temperature independent switched delay compensation scheme

Abstract: A delay compensation circuit for a delay locked loop which includes a main delay line having a fine delay line comprising fine delay elements and a coarse delay line comprising coarse delay elements, the main delay line being controlled by a controller, the delay compensation circuit comprising: an adjustable fine delay for modeling a coarse delay element, a counter for controlling the adjustable fine delay to a value which is substantially the same as that of a coarse delay element, a circuit for applying a representation of the system clock to the delay compensation circuit, and a circuit for applying the fine delay count from the counter to the controller for adjusting the fine delay line of the main delay line to a value which is substantially the same as that of a coarse delay element of the main delay line.

System and method for multi-services packet network traffic engineering

Abstract: Systems and methods are described that provide network traffic engineering that obviate network over-provisioning by providing QoS to each traffic class. Embodiments dimension switching router LTE schedulers to ensure that each traffic class receives an appropriate QoS in terms of delay, jitter, Packet Loss Ratio and throughput.

Packet forwarding device

Abstract: A power-saving packet forwarding device realizing electric power that accords to the number of lines in which communication is performed and a traffic volume inputted from the lines. A header processing unit with which the packet forwarding device is equipped has a plurality of packet processing circuits for performing a packet processing. A line number decision circuit monitors the number of lines in which communication is performed and a traffic volume inputted from the line, and decides presence or absence of an operation of a packet processing circuit. Based on this decision result, a power supply and a clock of the packet processing circuit that does not need to operate are interrupted, and accordingly power saving of the packet forwarding device is realized.

Control over unreliable networks affected by packet erasures and variable transmission delays

Abstract: This paper describes a novel control strategy aimed at achieving good performance over an unreliable communication network affected by packet loss and variable transmission delays. The key ingredient in the method described here is to use the large data packet frame size of typical modern communication protocols to transmit control sequences which cover multiple data-dropout and delay scenarios. Stability and performance of the resultant scheme are addressed under nominal networked conditions. Simulations verify that the strategy performs exceptionally well under realistic conditions with noise and unmeasured disturbances.

Delay analysis of Ethernet passive optical networks with gated service

Abstract: We analyze the mean packet delay in an Ethernet passive optical network (EPON) with gated service. For an EPON with a single optical network unit (ONU), we derive (i) a closed form delay expression for reporting at the end of an upstream transmission, and (ii) a Markov chain-based approach requiring the numerical solution of a system of equations for reporting at the beginning of an upstream transmission. Reporting at the beginning, which has not been previously examined in detail, achieves significantly smaller delays than reporting at the end of an upstream transmission for a small number of ONUs. Both of these analyses are fundamentally different from existing polling system analyses in that they consider the dependent switchover times of the EPON. We extend the analysis for reporting at the beginning of an upstream transmission to approximate the mean packet delay in an EPON with multiple ONUs and verify the accuracy of the analysis with simulations. Overall, our numerical results indicate that for utilizations up to ~75%, the mean packet delay is close to its minimum of four times the one-way propagation delay.

A novel selected mapping technique for PAPR reduction in OFDM systems

Abstract: Selected mapping (SLM) is a well-known method for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. The main drawback of this technique is that, for each data block, it requires the transmission of several side information bits, which results in some data rate loss. These redundant bits are so critical to the error performance of the system that they need in practice to be protected by a powerful channel code. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of an OFDM system using 16-QAM modulation, it is shown that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output.

Connectivity and Latency in Large-Scale Wireless Networks with Unreliable Links

Abstract: We study connectivity and transmission latency in wireless networks with unreliable links from a percolation-based perspective. We first examine static models, where each link of the network is functional (active) with some probability, independently of all other links, where the probability may depend on the distance between the two nodes. We obtain analytical upper and lower bounds on the critical density for phase transition in this model. We then examine dynamic models, where each link is active or inactive according to a Markov on- off process. We show that a phase transition also exists in such dynamic networks, and the critical density for this model is the same as the one for static networks under some mild conditions. Furthermore, due to the dynamic behavior of links, a delay is incurred for any transmission even when propagation delay is ignored. We study the behavior of this transmission delay and show that the delay scales linearly with the Euclidean distance between the sender and the receiver when the network is in the subcritical phase, and the delay scales sub-linearly with the distance if the network is in the supercritical phase.

Stability of Networked Control Systems Under a Multiple-Packet Transmission Policy

Abstract: This paper is concerned with stability analysis of discrete-time networked control systems subject to packet loss under a multiple-packet transmission policy with the packet dropping probability of the communication channel bounded from above. Necessary and sufficient conditions for stability are obtained. In addition, the packet dropping margin as a measure of stability robustness of a system against packet loss is defined and its formula is derived. A design method is proposed for enhancing stability robustness subject to the constraint of a set of prescribed nominal closed-loop poles.

Multi-priority Multi-path Selection for Video Streaming in Wireless Multimedia Sensor Networks

Abstract: Video sensors are used in wireless multimedia sensor networks (WMSNs) to enhance the capability for event description. Due to the limited transmission capacity of sensor nodes, a single path often cannot meet the requirement of video transmission. Consequently, multi-path transmission is needed. However, not every path found by multi-path routing algorithms may be suitable for transmitting video, because a long routing path with a long end to end transmission delay may not satisfy the time constraint of the video. Furthermore, each video stream includes two kinds of information: image and audio streams. In different applications, image and audio streams play different roles, and the importance levels are different. Higher priority should be given to the more important stream (either the image stream or the audio stream) to guarantee the using of limited bandwidth and energy in WMSNs. In this paper, we propose a Multi-priority Multi-path Selection (MPMPS) scheme in transport layer to choose the maximum number of paths from all found node-disjoint routing paths for maximizing the throughput of streaming data transmission. Simulation results show that MPMPS can effectively choose the maximum number of paths for video transmission.

Method and apparatus for signaling transmission characteristics in a wireless communication network

Abstract: A wireless network uses an improved frame structure to increase timing acquisition capabilities as well as reduction of spectral lines. In one aspect, the frame packet can be used to communicate the different modes of operation under which the packet was created.

Delay management for distributed communications networks

Abstract: A method for programming the delay for a node in a communication system is disclosed The node receives a selected delay value and a signal path delay value indicating a delay for signals communicated to the node The signal path delay comprises an aggregation of transport delays calculated by each node for segments of the communication system between the node and a host node The method further calculates an additional delay necessary to meet the selected delay value

A Simple Analytical Model for the Periodic Broadcasting in Vehicular Ad-Hoc Networks

Abstract: Nowadays in Europe, USA, Japan and other countries many efforts are being made towards the development and ubiquitous deployment of active vehicular safety systems, which are based on car-to-car and car-to-infrastructure communications. International standard IEEE 802.11p defines low layers protocols for vehicular networks aimed to support Intelligent Transportation Systems (ITS) applications. Periodic broadcasting of short status messages (beacons) is foreseen as one of the key modes, which should be efficiently handled to provide active safety in vehicular networks. This paper presents a simple analytical method to compute the probability of successful message reception and mean message transmission delay in IEEE 802.11p vehicular ad-hoc network with periodic broadcasting of messages. We investigate the influence of beaconing period on the above performance metrics.

UW-FLASHR: achieving high channel utilization in a time-based acoustic mac protocol

Abstract: Time-based medium access control (MAC) has potential advantages over FDMA and CDMA approaches in terms of hardware simplicity, energy efficiency, and delay. Unfortunately, the channel utilization of existing TDMA and CSMA acoustic MAC protocols is generally low due to the long propagation delays of acoustic signals. In this work, we argue that several ideas taken from RF protocols, including exclusive channel access, are either unnecessary in acoustic networks or must be redefined. We present and evaluate UW-FLASHR, a time-based MAC protocol which does not require centralized control, tight clock synchronization, or accurate propagation delay estimation. We demonstrate that UW-FLASHR can achieve significantly higher channel utilization than the maximum utilization possible with existing time-based exclusive access MAC protocols, particularly when the ratio of propagation delay to transmission delay is high or data payloads are small.

Reducing Packet Dropping in a Bufferless NoC

Abstract: Networks on chip (NoCs) has a strong impact on overall chip performance. Interconnection bandwidth is limited by the critical path delay. Recent works show that the critical path includes the switch input buffer control logic. As a consequence, by removing buffers, switch clock frequency can be doubled. Recently, a new switching technique for NoCs called Blind Packet Switching (BPS) has been proposed. It is based on replacing the buffers of the switch ports by simple latches. Since buffers consume a high percentage of switch power and area, BPS not only improves performance but also helps in reducing power and area. In BPS there are no buffers at the switch ports, so packets can not be stopped. If the required output port is busy, the packet will be dropped. In order to prevent packet dropping, some techniques based on resource replication has been proposed. In this paper, we propose some alternative and complementary techniques that does not rely on resource replication. By using these techniques, packet dropping and its negative effects are highly reduced. In particular, packet dropping is completely removed for a very wide network traffic range. The first dropped packet appears at a 11.6 higher traffic load. As a consequence, network throughput is increased and the packet latency is kept almost constant.

Joint Rate and Power Adaptation for Type-I Hybrid ARQ Systems Over Correlated Fading Channels Under Different Buffer-Cost Constraints

Abstract: We present a general framework for the computation of the optimal scheduling policies for delay and overflow-constrained joint rate and power adaptations for type-I hybrid automatic-repeat-request systems. This framework can be applied to adaptive resource-allocation problems on correlated flat-fading or frequency-selective fading channels for bursty nonconstant packet arrivals. It is shown that the optimal-rate and powercontrol laws can be obtained by solving the formulated Markov decision process problems. We consider two cases for packet scheduling over wireless channels that are of significant practical importance. In the first case, we assume that the transmitter perfectly knows the channel-state information (CSI) at the beginning of the transmission. The transmitter is also provided with the decoding result for the previous transmission in terms of observation feedback at the end of the transmission. Second, we consider the scheduling problem when the transmitter does not know the CSI at the time of transmission, but it makes the transmission decision based on the history of previous transmissions and corresponding outcomes. In both cases, our objective is to minimize transmission power, and the optimal policies are computed under two different buffer-cost constraints, namely, the average buffer delay and the average packet overflow rate. The results of this paper are of importance for the development of modern wireless standards that support heterogeneous multimedia and Internet traffic with certain application-dependent-delay and packet-dropping requirements.

Energy efficient multi-path communication for time-critical applications in underwater sensor networks

Abstract: Due to the long propagation delay and high error rate of acoustic channels, it is very challenging to provide reliable data transfer for time-critical applications in an energy-efficient way. On the one hand, traditional retransmission-upon-failure usually introduces very large end-to-end delay, thus is not proper for time-critical services. On the other hand, common approaches without retransmission consume lots of energy. In this paper, we propose a new multi-path power-control transmission (MPT) scheme, which can guarantee certain end-to-end packet error rate while achieving a good balance between the overall energy efficiency and the end-to-end packet delay. MPT smartly combines power control with multi-path routing and packet combining at the destination. With carefully designed power control strategies, MPT consumes much less energy than the conventional one-path transmission scheme without retransmission. Besides, since no hop-by-hop retransmission is allowed, MPT introduces much shorter delay than the traditional one-path scheme with retransmission. We conduct extensive simulations to evaluate the performance of MPT. Our results show that MPT is highly energy efficient with low end-to-end packet delays.