Showing papers on "Transmission delay published in 2009"

Transparent provisioning of services over a network

Abstract: An apparatus and method for enhancing the infrastructure of a network such as the Internet is disclosed. A packet interceptor/processor apparatus is coupled with the network so as to be able to intercept and process packets flowing over the network. Further, the apparatus provides external connectivity to other devices that wish to intercept packets as well. The apparatus applies one or more rules to the intercepted packets which execute one or more functions on a dynamically specified portion of the packet and take one or more actions with the packets. The apparatus is capable of analyzing any portion of the packet including the header and payload. Actions include releasing the packet unmodified, deleting the packet, modifying the packet, logging/storing information about the packet or forwarding the packet to an external device for subsequent processing. Further, the rules may be dynamically modified by the external devices.

Transparent provisioning of network access to an application

Abstract: An apparatus and method for enhancing the infrastructure of a network such as the Internet is disclosed. A packet interceptor/processor apparatus is coupled with the network so as to be able to intercept and process packets flowing over the network. Further, the apparatus provides external connectivity to other devices that wish to intercept packets as well. The apparatus applies one or more rules to the intercepted packets which execute one or more functions on a dynamically specified portion of the packet and take one or more actions with the packets. The apparatus is capable of analyzing any portion of the packet including the header and payload. Actions include releasing the packet unmodified, deleting the packet, modifying the packet, logging/storing information about the packet or forwarding the packet to an external device for subsequent processing. Further, the rules may be dynamically modified by the external devices.

Aggregation with fragment retransmission for very high-speed WLANs

Abstract: In upcoming very high-speed wireless LANs (WLANs), the physical (PHY) layer rate may reach 600 Mbps. To achieve high efficiency at the medium access control (MAC) layer, we identify fundamental properties that must be satisfied by any CSMA-/CA-based MAC layers and develop a novel scheme called aggregation with fragment retransmission (AFR) that exhibits these properties. In the AFR scheme, multiple packets are aggregated into and transmitted in a single large frame. If errors happen during the transmission, only the corrupted fragments of the large frame are retransmitted. An analytic model is developed to evaluate the throughput and delay performance of AFR over noisy channels and to compare AFR with similar schemes in the literature. Optimal frame and fragment sizes are calculated using this model. Transmission delays are minimized by using a zero-waiting mechanism where frames are transmitted immediately once the MAC wins a transmission opportunity. We prove that zero-waiting can achieve maximum throughput. As a complement to the theoretical analysis, we investigate the impact of AFR on the performance of realistic application traffic with diverse requirements by simulations. We have implemented the AFR scheme in the NS-2 simulator and present detailed results for TCP, VoIP, and HDTV traffic. The AFR scheme described was developed as part of the IEEE 802.11n working group work. The analysis presented here is general enough to be extended to proposed schemes in the upcoming 802.11n standard. Trends indicated in this paper should extend to any well-designed aggregation schemes.

Performance and reliability of DSRC vehicular safety communication: a formal analysis

Abstract: IEEE- and ASTM-adopted dedicated short range communications (DSRC) standard toward 802.11p is a key enabling technology for the next generation of vehicular safety communication. Broadcasting of safety messages is one of the fundamental services in DSRC. There have been numerous publications addressing design and analysis of such broadcast ad hoc system based on the simulations. For the first time, an analytical model is proposed in this paper to evaluate performance and reliability of IEEE 802.11a-based vehicle-to-vehicle (V2V) safety-related broadcast services in DSRC system on highway. The proposed model takes two safety services with different priorities, nonsaturated message arrival, hidden terminal problem, fading transmission channel, transmission range, IEEE 802.11 backoff counter process, and highly mobile vehicles on highway into account. Based on the solutions to the proposed analytic model, closed-form expressions of channel throughput, transmission delay, and packet reception rates are derived. From the obtained numerical results under various offered traffic and network parameters, new insights and enhancement suggestions are given.

Discovering path maximum transmission unit size

Abstract: Intermediate network devices, such as routers, are configured to discover a maximum transmission unit (MTU) for a path between two network endpoints by removing data from packets when the packet size exceeds a link MTU to a next hop. An example intermediate network device includes a forwarding engine to determine an interface card through which to forward a received packet and to determine a link MTU for a link corresponding to the interface card, wherein the received packet comprises a header and a payload, the header indicating not to fragment the packet, and a PMTU determination module to determine whether a size of the received packet exceeds the link MTU, and to remove a portion of data from the payload of the packet, discard the removed portion, and adjust the header of the packet according to the removed portion when the size of the received packet exceeds the link MTU.

Selected mapping without side information for PAPR reduction in OFDM

Abstract: Selected mapping (SLM) is a technique used to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. SLM requires the transmission of several side information bits for each data block, which results in some data rate loss. These bits must generally be channel-encoded because they are particularly critical to the error performance of the system. 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 several OFDM systems using either QPSK or 16-QAM modulation, we show that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output provided that the number of subcarriers is large enough.

Delay aware link scheduling for multi-hop TDMA wireless networks

Abstract: Time division multiple access (TDMA) based medium access control (MAC) protocols can provide QoS with guaranteed access to the wireless channel. However, in multi-hop wireless networks, these protocols may introduce scheduling delay if, on the same path, an outbound link on a router is scheduled to transmit before an inbound link on that router. The total scheduling delay can be quite large since it accumulates at every hop on a path. This paper presents a method that finds conflict-free TDMA schedules with minimum scheduling delay. We show that the scheduling delay can be interpreted as a cost, in terms of transmission order of the links, collected over a cycle in the conflict graph. We use this observation to formulate an optimization, which finds a transmission order with the min-max delay across a set of multiple paths. The min-max delay optimization is NP-complete since the transmission order of links is a vector of binary integer variables. We devise an algorithm that finds the transmission order with the minimum delay on overlay tree topologies and use it with a modified Bellman-Ford algorithm, to find minimum delay schedules in polynomial time. The simulation results in 802.16 mesh networks confirm that the proposed algorithm can find effective min-max delay schedules.

Energy efficiency in wireless sensor networks using sleep mode TDMA scheduling

Abstract: Power saving is a very critical issue in energy-constrained wireless sensor networks. Many schemes can be found in the literature, which have significant contributions in energy conservation. However, these schemes do not concentrate on reducing the end-to-end packet delay while at the same time retaining the energy-saving capability. Since a long delay can be harmful for either large or small wireless sensor networks, this paper proposes a TDMA-based scheduling scheme that balances energy-saving and end-to-end delay. This balance is achieved by an appropriate scheduling of the wakeup intervals, to allow data packets to be delayed by only one sleep interval for the end-to-end transmission from the sensors to the gateway. The proposed scheme achieves the reduction of the end-to-end delay caused by the sleep mode operation while at the same time it maximizes the energy savings.

Packet switch and switching method for switching variable length packets

Abstract: A packet switch for switching variable length packets. Each output port interface of the packet switch includes a buffer memory, a transmission priority controller, and a packet readout controller. The buffer memory stores transmission packets. The transmission priority controller classifies, based on a predetermined algorithm, transmission packets passed from a packet switching unit into a plurality of queue groups to which individual bandwidths are assigned respectively, and queues the transmission packets in the buffer memory so as to form a plurality of queues according to transmission priority in each of the queue groups. The packet readout controller reads the transmission packets from each of the queue groups in the buffer memory according to the order of transmission priority of the packets while guaranteeing the bandwidth assigned to the queue group.

Effective Delay Control in Online Network Coding

Abstract: Motivated by streaming applications with stringent delay constraints, we consider the design of online network coding algorithms with timely delivery guarantees. Assuming that the sender is providing the same data to multiple receivers over independent packet erasure channels, we focus on the case of perfect feedback and heterogeneous erasure probabilities. Based on a general analytical framework for evaluating the decoding delay, we show that existing ARQ schemes fail to ensure that receivers with weak channels are able to recover from packet losses within reasonable time. To overcome this problem, we re-define the encoding rules in order to break the chains of linear combinations that cannot be decoded after one of the packets is lost. Our results show that sending uncoded packets at key times ensures that all the receivers are able to meet specific delay requirements with very high probability.

Event-Triggering in Distributed Networked Systems with Data Dropouts and Delays

Abstract: This paper studies distributed networked systems with data dropouts and transmission delays. We propose an event-triggering scheme, where a subsystem broadcasts its state information to its neighbors only when the subsystem's local state error exceeds a specified threshold. This scheme is completely decentralized, which means that a subsystem's broadcast decisions are made using its local sampled data, the maximal allowable transmission delay of a subsystem's broadcast is predicted based on the local information, a subsystem locally identifies the maximal allowable number of its successive data dropouts, and the designer's selection of the threshold only requires information about an individual subsystem and its immediate neighbors. With the assumption that the number of each subsystem's successive data dropouts is less than the bound identified by that subsystem, if the bandwidth of the network is limited so that the transmission delays are always greater than a positive constant, the resulting system is globally uniformly ultimately bounded using our scheme; otherwise, the resulting system is asymptotically stable.

Minimizing End-to-End Delay: A Novel Routing Metric for Multi-Radio Wireless Mesh Networks

Abstract: This paper studies how to select a path with the minimum cost in terms of expected end-to-end delay (EED) in a multi-radio wireless mesh network Different from the previous efforts, the new EED metric takes the queuing delay into account, since the end-to-end delay consists of not only the transmission delay over the wireless links but also the queuing delay in the buffer In addition to minimizing the end-to-end delay, the EED metric implies the concept of load balancing We develop EED- based routing protocols for both single-channel and multi-channel wireless mesh networks In particular for the multi-radio multi- channel case, we develop a generic iterative approach to calculate a multi-radio achievable bandwidth (MRAB) for a path, taking the impacts of inter/intra-flow interference and space/channel diversity into account The MRAB is then integrated with EED to form the metric of weighted end-to-end delay (WEED) As a byproduct of MRAB, a channel diversity coefficient can be defined to quantitatively represent the channel diversity along a given path Both numerical analysis and simulation studies are presented to validate the performance of the routing protocol based on the EED/WEED metric, with comparison to some well- known routing metrics I INTRODUCTION Routing in wireless mesh networks has been a hot re- search area in recent years, with the objective to achieve as high throughput as possible over the network The main methodology adopted by most of the existing work is selecting path based on interference-aware or load-balancing routing metrics to reduce network-wide channel contentions It has been revealed that the capacity of a single-radio multi-hop wireless network can not scale up with the network size, due to the co-channel interference (1)-(3) The multi-radio multi-channel connection has been widely considered as an efficient approach to increase the wireless network capacity (8) Design of efficient routing schemes for multi-radio multi- channel wireless mesh network is much more challenging compared to the single-channel case Many popular multimedia applications, eg, voice over IP, IPTV, and on-line gaming, have strict delay requirement In this paper, we aim at designing a routing metric to minimize the end-to-end delay, considering not only the transmission delay at the medium access control (MAC) layer, but also the queuing delay at the network layer Most of the previous studies focus only on the transmission delay of the packet

Apparatus and methods for forwarding data packets captured from a network

Abstract: In one embodiment, packet forwarding apparatus includes a data packet receiving interface, a data packet forwarding interface, and a configuration interface. The apparatus also includes circuitry that defines a plurality of data packet forwarding paths between the data packet receiving interface and the data packet forwarding interface. The circuitry defines at least one of the plurality of data packet forwarding paths in response to input received via the configuration interface, and the circuitry adaptively reconfigures at least one of the plurality of data packet forwarding paths i) in response to input received via the configuration interface, and ii) while data packets are being received by the packet forwarding apparatus.

Predictive control of networked systems with random delay and data dropout

Abstract: This study is concerned with the stochastic stability analysis of networked control systems with random network delay. A new control scheme termed networked predictive control is proposed. This scheme mainly consists of the control prediction generator and network-delay compensator. The control prediction generator provides a set of future control predictions to make the closed-loop system achieve the desired control performance and the network-delay compensator removes the effects of the network transmission delay and data dropout. The stochastic stability criteria of the closed-loop networked predictive control systems are derived. A numerical example and a practical experiment are given to show the potential of the proposed techniques.

Packet format for a distributed system

Abstract: A method is provided for transmitting a packet including information describing a bus transaction to be executed at a remote device. A bus transaction is detected on a first bus and a network packet is generated for transmission over a network. The network packet includes an opcode describing the type of bus transaction. One or more control signals of the bus transaction map directly to one or more bits of the opcode to simplify decoding or converting of the bus transaction to the opcode. The packet is transmitted to a remote device and the bus transaction is then replayed at a second bus. In addition, the packet includes a data field having a size that is a multiple of a cache line size. The packet includes separate CRCs for the data and header. The packet also includes a transaction ID to support split transactions over the network. Also, fields in the packet header are provided in a particular order to improve switching efficiency.

Synchronization of networks of chaotic units with time-delayed couplings.

Abstract: A network of chaotic units is investigated where the units are coupled by signals with a transmission delay. Any arbitrary finite network is considered where the chaotic trajectories of the uncoupled units are a solution of the dynamic equations of the network. It is shown that chaotic trajectories cannot be synchronized if the transmission delay is larger than the time scales of the individual units. For several models the master stability function is calculated which determines the maximal delay time for which synchronization is possible.

Methods and apparatus for shared layer 3 application card in multi-service router

Abstract: An apparatus and method for enhancing packet transfer in a network using duplicated copy of data packets are disclosed. Upon classifying a data packet in accordance with a set of predefined packet identifiers, the method for enhancing packet transfer, in one embodiment, generates a replicated packet which is substantially similar to the data packet in response to the result of classification of the data packet. The replicated packet is subsequently forwarded to an application component via a route of non-bearer traffic for facilitating parallel processing.

Delay Analysis for Multi-Hop Wireless Networks

Abstract: We analyze the delay performance of a multi-hop wireless network with a fixed route between each source-destination pair. There are arbitrary interference constraints on the set of links that can be served simultaneously at any given time. These interference constraints impose a fundamental lower bound on the delay performance of any scheduling policy for the system. We present a methodology to derive such lower bounds. For the tandem queue network, where the delay optimal policy is known, the expected delay of the optimal policy numerically coincides with the lower bound. We conduct extensive numerical studies to suggest that the average delay of the back-pressure scheduling policy can be made close to the lower bound by using appropriate functions of queue length.

Packet transmission scheduling technique

Abstract: A packet data transmission method of the HSDPA system includes collecting information on the quality of physical channels, a status of the MAC buffer, the priority level of data, the delay of data, and the like, determining the transmission order of data and the size of a data block to be transmitted based on the collected information, and transmitting the data block through the physical layer according to the order of transmissions. Since the HSDPA scheduler takes into account the delay of data, the quality of real-time services can be improved.

A New Backoff Algorithm for IEEE 802.11 Distributed Coordination Function

Abstract: DCF (Distributed Coordination Function) of IEEE802.11 MAC protocols uses binary exponential increasing mechanism, called BEB (Binary Exponential Backoff) algorithm. Due to the lack of a mechanism evaluating the channel condition, it can not tune the value of contention windows adaptively, according to the actual network traffic. By introducing the network allocation vector count in routing protocol to approximate the intensity of surrounding traffic of nodes, the algorithm has been improved, so that the contention windows of backoff mechanism are adjusted reasonably according to the traffic of WLAN. Simulation experiments are done and the results prove that the improved algorithm provides a better channel utilization and reduces the average transmission delay.

A feedback-based adaptive broadcast coding scheme for reducing in-order delivery delay

Abstract: We propose a new feedback-based adaptive coding scheme for a packet erasure broadcast channel. The main performance metric of interest is the delay. We consider two types of delay - decoding delay and delivery delay. Decoding delay is the time difference between the instant when the packet is decoded at an arbitrary receiver and the instant when it arrived at the sender. Delivery delay also includes the period when a decoded packet waits in a resequencing buffer at the receiver until all previous packets have also been decoded. This notion of delay is motivated by applications that accept packets only in order. Our coding scheme has the innovation guarantee property and is hence throughput optimal. It also allows efficient queue management. It uses the simple strategy of mixing only the oldest undecoded packet of each receiver, and therefore extends to any number of receivers. We conjecture that this scheme achieves the asymptotically optimal delivery (and hence decoding) delay. The asymptotic behavior is studied in the limit as the load factor of the system approaches capacity. This conjecture is verified through simulations.

Estimation of a successful beacon reception probability in vehicular ad-hoc networks

Abstract: In vehicular ad-hoc networks (VANETs) beaconing is one of the core communication modes, which is designed to advertise the presence of a car to its neighborhood. For practical applications the delivery of beacons containing the speed, the direction and the position of a car should be organized both timely and successfully. IEEE 802.11p is the most recent developing international standard, which specifies the physical (PHY) and the medium access control (MAC) protocols for car-to-car and car-to-infrastructure communication and is expected to lay the foundation for safety-related and infotainment applications in future VANETs. In previous works, it has been shown that the requirements of safety-related applications for the mean beacon transmission delay could be met for typical cases, but the corresponding probability of a successful beacon reception does not attain the required threshold. In this paper, we present a novel analytical method based on Markov chain for car-to-car communication analysis and investigate the influence of the beacon generation rate on the probability of a successful beacon reception in an IEEE 802.11p-based network.

Deterministically skewing transmission of content streams

Abstract: Described are computer-based methods and apparatuses, including computer program products, for deterministically skewing transmission of content streams. A content stream comprising one or more video frames is received. The content stream is buffered in a buffer, wherein the buffer allows simultaneous read access to the content stream at a plurality of locations. One or more video frames of the content stream are transmitted from the buffer to a first device associated with a first subscriber beginning at a first location in the buffer based on a first transmission delay parameter. One or more video frames of the content stream are transmitted from the buffer to a second device associated with a second subscriber beginning at a second location in the buffer based on a second transmission delay parameter.

Distribution of Packets Among PortChannel Groups of PortChannel Links

Abstract: PortChannel groups are disclosed which include multiple PortChannel links of a PortChannel. Further, the selection of a particular PortChannel group, and possibly a PortChannel link within a selected PortChannel group, for a packet is provided by user-programmable matching of programmed values or rules to data extracted from the packet. In this manner, the forwarding of packets over PortChannel groups can be explicit. Moreover, packets of different flows of a packet session can be caused to be forwarded over a same PortChannel group, possibly leading to a service node for performing one or more applications based on the packets of the flow(s) of a packet session.

Accelerating OpenFlow switching with network processors

Abstract: OpenFlow switching enables flexible management of enterprise network switches and experiments on regular network traffic. We present in this paper a complementary design to OpenFlow's existing reference designs. We apply network processor based acceleration cards to perform OpenFlow switching. We describe the design options and report our experiment results that show a 20% reduction on packet delay and the comparable packet forwarding throughput compared to conventional designs.

Advanced memory device having reduced power and improved performance

Abstract: A memory device including a memory array storing data, a variable delay controller, a passive variable delay circuit and an output driver. The variable delay controller periodically receives delay commands from a first source external to the memory device during operation of the memory device, and outputs delay instruction bits responsive to the received delay commands. The passive variable delay circuit receives a clock from a second source external to the memory device, receives the delay instruction bits from the variable delay controller, generates a delayed clock having a time relation to the received clock as determined by the delay instruction bits, and outputting the delayed clock. The output driver receives the data from the memory array and the delayed clock, and outputs the data at a time responsive to the delayed clock.

Packet-layer transparent packet-switching network

Abstract: Packet forwarding systems and methods allow packet-layer transparent, multi-stage packet forwarding among a set of network access points. Packet forwarding across networks utilizing the invention is directly controllable through the upper-layer nodes, e.g. routers, interconnected by such transparent packet forwarding networks. The systems and methods provide packet-layer routing, switching and forwarding look-up-table free and transparent forwarding of label-encapsulated multi-protocol packet traffic among a set of routers. The invention enables flexible and efficient packet multicast and anycast capabilities along with real-time dynamic load balancing and fast packet-level traffic protection rerouting. The invention replaces the need for packet forwarding look-up-tables in a router interconnect network by a set of rules using which such network forwards packets directly based on their forwarding labels inserted in the packet headers by the routers exchanging packets through said network, thus simplifying network management and equipment implementation, and facilitating optimization of packet traffic flow across communications networks.

Amplify-and-forward cooperative diversity wireless networks: model, analysis, and monotonicity properties

Abstract: This paper models and analyzes the performance of an amplify-and-forward cooperative diversity wireless network. We propose a Markov-based model, which encompasses the following aspects: 1) the transmission using amplify-and-forward cooperative diversity at the physical layer; 2) a flow control pro-tocol, finite and infinite transmitting buffers, and an ARQ-based error recovery mechanism at the radio link layer; and 3) a bursty traffic pattern at the application layer. We derive expressions for packet delivery probability and distribution of packet delivery delay. We numerically quantify improvement in terms of packet delivery probability and packet delivery delay for increasing SNR and/or cooperative nodes. For an additional cooperative node, we quantify the amount of SNR which can be reduced (i.e., SNR saving) without degrading the system performance. Also, the minimum SNR and cooperative nodes which satisfy a probabilistic delay bound are computed. We then derive a sufficient condition that ensures an increase in packet delivery probability. Unlike numerical evaluation of the model, this sufficient condition does not require computation of stationary distribution of the Markov chain. It only involves parameter adjustment at physical, radio link, and application layers, hence substantially reducing the com-putation effort. Based on the developed model, we design a power allocation algorithm, which computes the minimum transmission power under a packet delivery probability constraint. We then use the derived sufficient condition to reduce complexity of the power allocation algorithm.

Mobility increases the connectivity of K-hop clustered wireless networks

Abstract: In this paper we investigate the connectivity for large-scale clustered wireless sensor and ad hoc networks. We study the effect of mobility on the critical transmission range for asymptotic connectivity in k-hop clustered networks, and compare to existing results on non-clustered stationary networks. By introducing k-hop clustering, any packet from a cluster member can reach a cluster head within k hops, and thus the transmission delay is bounded as Θ(1) for any finite k. We first characterize the critical transmission range for connectivity in mobile k-hop clustered networks where all nodes move under either the random walk mobility model with non-trivial velocity or the i.i.d. mobility model. By the term non-trivial velocity, we mean that the velocity of nodes v is Θ(1). We then compare with the critical transmission range for stationary k-hop clustered networks. We also study the transmission power versus delay trade-off and the average energy consumption per flow among different types of networks. We show that random walk mobility with non-trivial velocity increases connectivity in k-hop clustered networks, and thus significantly decreases the energy consumption and improves the power-delay trade-off. The decrease of energy consumption per flow is shown to be Θ(logn/nd}) in clustered networks. These results provide insights on network design and fundamental guidelines on building a large-scale wireless network.