Showing papers on "Transmission delay published in 2003"

IEEE 802.11 packet delay-a finite retry limit analysis

Abstract: The contribution of this paper is on the study of packet delays for the IEEE 802.11 wireless local area network DCF MAC protocol. A method is presented capable of taking into account retransmission delays with or without retry limits. We present an analytical model based on a Markov chain which allows us to derive closed form expressions for the packet delays, the probability of a packet being discarded when it reaches the maximum retransmission limit and the average time to drop such a packet for the basic and RTS/CTS access mechanisms. The results presented are for standard protocol parameters versus the number of contention stations. Finally, the accuracy of the analytical model is verified by simulations.

Dynamic power allocation and routing for satellite and wireless networks with time varying channels

Abstract: Satellite and wireless networks operate over time varying channels that depend on attenuation conditions, power allocation decisions, and inter-channel interference. In order to reliably integrate these systems into a high speed data network and meet the increasing demand for high throughput and low delay, it is necessary to develop efficient network layer strategies that fully utilize the physical layer capabilities of each network element. In this thesis, we develop the notion of network layer capacity and describe capacity achieving power allocation and routing algorithms for general networks with wireless links and adaptive transmission rates. Fundamental issues of delay, throughput optimality, fairness, implementation complexity, and robustness to time varying channel conditions and changing user demands are discussed. Analysis is performed at the packet level and fully considers the queueing dynamics in systems with arbitrary, potentially bursty, arrival processes. Applications of this research are examined for the specific cases of satellite networks and ad-hoc wireless networks. Indeed, in Chapter 3 we consider a multi-beam satellite downlink and develop a dynamic power allocation algorithm that allocates power to each link in reaction to queue backlog and current channel conditions. The algorithm operates without knowledge of the arriving traffic or channel statistics, and is shown to achieve maximum throughput while maintaining average delay guarantees. At the end of Chapter 4, a crosslinked collection of such satellites is considered and a satellite separation principle is developed, demonstrating that joint optimal control can be implemented with separate algorithms for the downlinks and crosslinks. Ad-hoc wireless networks are given special attention in Chapter 6. A simple cell-partitioned model for a mobile ad-hoc network with N users is constructed, and exact expressions for capacity and delay are derived. End-to-end delay is shown to be O(N), and hence grows large as the size of the network is increased. To reduce delay, a transmission protocol which sends redundant packet information over multiple paths is developed and shown to provide O( N ) delay at the cost of reducing throughput. A fundamental rate-delay tradeoff curve is established, and the given protocols for achieving O(N) and O( N ) delay are shown to operate on distinct boundary points of this curve. In Chapters 4 and 5 we consider optimal control for a general time-varying network. A cross-layer strategy is developed that stabilizes the network whenever possible, and makes fair decisions about which data to serve when inputs exceed capacity. The strategy is decoupled into separate algorithms for dynamic flow control, power allocation, and routing, and allows for each user to make greedy decisions independent of the actions of others. The combined strategy is shown to yield data rates that are arbitrarily close to the optimally fair operating point that is achieved when all network controllers are coordinated and have perfect knowledge of future events. The cost of approaching this fair operating point is an end-to-end delay increase for data that is served by the network. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

Bilateral teleoperation over the internet: the time varying delay problem

Abstract: This paper addresses the problem of time-varying communication delay in force reflecting bilateral teleoperation. The problem is motivated by the increasing use of the Internet as a communication medium where the time delay is variable depending on factors such as congestion, bandwidth, or distance. The well-known scattering formalism introduced in 111 preserves passivity of the communication channel in general only for constant transmission delay. We demonstrate how to recover both passivity and tracking performance using a modified control architecture that incorporates timevarying gains into the scattering transformatioil and feedforward position control. Experimental results using a single-degree of freedom master/slave system are presented

A scheduling algorithm for QoS support in IEEE802.11 networks

Abstract: This article presents a scheduling algorithm for the IEEE 802.11e hybrid coordination function under definition by the IEEE 802.11e task group. HCF can be used to provide IP quality of service guarantees in IEEE802.11e infrastructure WLANs. The enhanced distributed coordination function is mainly used for data transmission without QoS guarantees, but can also be used to decrease the transmission delay of QoS-sensitive traffic. Scheduling of queued packets follows a delay-earliest-due-date algorithm. The proposed algorithm is compatible with the link adaptation mechanisms implemented in commercial WLANs, as it limits the amount of time during which the stations control the wireless medium. The performance of the algorithm is evaluated through computer simulation and compared with the reference scheduler presented by the IEEE 802.11e task group.

Wireless video transmission system

Abstract: A transmission system suitable for video where a sender encodes video for transmission to a receiver at an adjustable date rate The data rate may be adjusted using a delay constraint that constrains the expected delay of transmitted packets The expected delay may be measured from a time that a transmitter encodes a packet to a time that a receiver decodes a packet

An introduction to optical burst switching

Abstract: Optical burst switching is a promising solution for all-optical WDM networks. It combines the benefits of optical packet switching and wavelength routing while taking into account the limitations of the current all-optical technology. In OBS, the user data is collected at the edge of the network, sorted based on a destination address, and grouped into variable sized bursts. Prior to transmitting a burst, a control packet is created and immediately sent toward the destination in order to set up a bufferless optical path for its corresponding burst. After an offset delay time, the data burst itself is transmitted without waiting for a positive acknowledgment from the destination node. The OBS framework has been widely studied in the past few years because it achieves high traffic throughput and high resource utilization. However, despite the OBS trademarks such as dynamic connection setup or strong separation between data and control, there are many differences in the published OBS architectures. In this article we summarize in a systematic way the main OBS design parameters and the solutions that have been proposed in the open literature.

Detecting network denial of service attacks

Abstract: A method for detecting a suspicious packet flow in a packet-switched network comprises the computer-implemented step of receiving a first packet in which the SYN bit but not the ACK or RST bit of the packet's TCP header is set. If a specified first time has elapsed, a packet counter associated with the destination address of the flow is incremented. A determination as to whether the packet counter is greater than a specified threshold values is made. If the packet counter is greater than the threshold value, a notification message is generated. In one embodiment, information identifying a packet flow is aggregated to an aggregation cache based on the destination address of the flow.

Measurement and analysis of single-hop delay on an IP backbone network

Abstract: We measure and analyze the single-hop packet delay through operational routers in the Sprint Internet protocol (IP) backbone network. After presenting our delay measurements through a single router for OC-3 and OC-12 link speeds, we propose a methodology to identify the factors contributing to single-hop delay. In addition to packet processing, transmission, and queueing delay at the output link, we observe the presence of very large delays that cannot be explained within the context of a first-in first-out output queue model. We isolate and analyze these outliers. Results indicate that there is very little queueing taking place in Sprint's backbone. As link speeds increase, transmission delay decreases and the dominant part of single-hop delay is packet processing time. We show that if a packet is received and transmitted on the same linecard, it experiences less than 20 /spl mu/s of delay. If the packet is transmitted across the switch fabric, its delay doubles in magnitude. We observe that processing due to IP options results in single-hop delays in the order of milliseconds. Milliseconds of delay may also be experienced by packets that do not carry IP options. We attribute those delays to router idiosyncratic behavior that affects less than 1% of the packets. Finally, we show that the queueing delay distribution is long-tailed and can be approximated with a Weibull distribution with the scale parameter a=0.5 and the shape parameter b=0.6 to 0.82.

Network interconnection apparatus network node apparatus and packet transfer method for high speed large capacity inter-network communication

Abstract: A packet transfer scheme in a network system capable of realizing a high speed, large capacity inter-network communication under an internet environment. A network interconnection apparatus (router) has a memory for storing a correspondence relationship between a virtual connection used in receiving a packet from one logical network and a virtual connection used in transmitting a packet to another logical network, and a transfer at a datalink layer is carried out according to the registered correspondence relationship, to effectively form a bypass pipe capable of transferring a packet by an datalink layer level processing alone over a plurality of networks from the transmission terminal to the destination terminal, so that a high speed packet transfer between networks can be realized.

Fast flexible filter processor based architecture for a network device

Abstract: A method of filtering data packets in a network device is disclosed. An incoming packet is received from a port and the incoming packet is inspected and packet fields are extracted. The incoming packet is classified based on the extracted packet fields and action instructions are generated. The incoming packet is then modified based on the action instructions. Further, the inspection and extraction includes applying inspection mask windows to any portion of the incoming packet to extract programmable packet fields.

A digitally programmable delay element: design and analysis

Abstract: Variable delay elements are often used to manipulate the rising or falling edges of the clock or any other signal in integrated circuits (ICs). Delay elements are also used in delay locked loops (DLLs). Although, a few types of digitally controlled delay elements have been proposed, an analytical expression for the delay of these circuits has not been reported. In this paper, we propose a new delay element architecture and develop an analytical equation for the output voltage and an empirical relation for the delay of the circuit. The proposed circuit exhibits improved delay characteristics over previously reported digitally controlled delay elements.

Voice and data exchange over a packet based network with timing recovery

Abstract: A signal processing system which discriminates between voice signals and data signals modulated by a voiceband carrier. The signal processing system includes a voice exchange, a data exchange and a call discriminator. The voice exchange is capable of exchanging voice signals between a switched circuit network and a packet based network. The signal processing system also includes a data exchange capable of exchanging data signals modulated by a voiceband carrier on the switched circuit network with unmodulated data signal packets on the packet based network. The data exchange is performed by demodulating data signals from the switched circuit network for transmission on the packet based network, and modulating data signal packets from the packet based network for transmission on the switched circuit network. The call discriminator is used to selectively enable the voice exchange and data exchange.

Prevention of deadlocks and livelocks in lossless backpressured packet networks

Abstract: No packets will be dropped inside a packet network, even when congestion builds up, if congested nodes send backpressure feedback to neighboring nodes, informing them of unavailability of buffering capacity-stopping them from forwarding more packets until enough buffer becomes available. While there are potential advantages in backpressured networks that do not allow packet dropping, such networks are susceptible to a condition known as deadlock in which throughput of the network or part of the network goes to zero (i.e., no packets are transmitted). In this paper, we describe a simple, lossless method of preventing deadlocks and livelocks in backpressured packet networks. In contrast with prior approaches, our proposed technique does not introduce any packet losses, does not corrupt packet sequence, and does not require any changes to packet headers. It represents a new networking paradigm in which internal network losses are avoided (thereby simplifying the design of other network protocols) and internal network delays are bounded.

Performance analysis of a preemptive and priority reservation handoff scheme for integrated service-based wireless mobile networks

Abstract: We propose an analytical model for integrated real-time and non-real-time services in a wireless mobile network with priority reservation and preemptive priority handoff schemes. We categorize the service calls into four different types, namely, real-time and non-real-time service originating calls, and real-time and non real-time handoff service request calls. Accordingly, the channels in each cell are divided into three parts: one is for real-time service calls only, the second is for non-real-time service calls only, and the last one is for overflow of handoff requests that cannot be served in the first two parts. In the third group, several channels are reserved exclusively for real-time service handoffs so that higher priority can be given to them. In addition, a realtime service handoff request has the right to preempt non-real-time service in the preemptive priority handoff scheme if no free channels are available, while the interrupted non-real-time service call returns to its handoff request queue. The system is modeled using a multidimensional Markov chain and a numerical analysis is presented to estimate blocking probabilities of originating calls, forced termination probability, and average transmission delay. This scheme is also simulated under different call holding time and cell dwell time distributions. It is observed that the simulation results closely match the analytical model. Our scheme significantly reduces the forced termination probability of real-time service calls. The probability of packet loss of non-real-time transmission is shown to be negligibly small, as a non-real-time service handoff request in waiting can be transferred from the queue of the current base station to another one.

Medium streaming distribution system

Abstract: A relay apparatus for connecting a communication link with a small delay and a communication link with a large delay, includes a first feedback device (71) for receiving a packet of a media stream transmitted on said link with a small delay, and transmitting information including a packet loss rate over a predetermined period to a transmission source (11), adjusting means (13') for adjusting passage of packets received from said network according to transmission capability of said communication link with a large delay, and a second feedback device (73) for transmitting to said transmission source (11) an acknowledge response about a packet transmitted through said adjusting means (13') to said communication link.

Time sliced optical burst switching

Abstract: Time Sliced Optical Burst Switching is a proposed variant of optical burst switching, in which switching is done in the time domain, rather than the wavelength domain. This eliminates the need for wavelength converters, the largest single cost component of systems that switch in the wavelength domain. We examine some of the key design issues for routers that implement time sliced optical packet switching. In particular, we focus on the design of the Optical Time Slot Interchangers (OTSIs) needed to effect the required time domain switching. We introduce a novel nonblocking OTSI design and also show how blocking OTSIs can be used to implement the required switching operations. We study the performance of systems using blocking OTSIs and demonstrate that near ideal statistical multiplexing performance can be achieved using even quite inexpensive, blocking OTSI designs. These results suggest that optical technology may one day be able to provide a cost-effective alternative to electronics in packet switching systems.

Methods and systems for firewalling virtual private networks

Abstract: Methods, apparatus, and systems are provided for processing packets between a first and a second network. When a packet is received from the first network, information for routing the first packet is identified. Based on a first set of rules for processing the first packet and the information for routing the first packet, a second packet encapsulated within the first packet is detected. In the first packet, information for routing the second packet is identified based on which a second set of rules for processing the second packet and an index are determined. The second packet is then filtered based on the index, the second set of rules, and the information for routing the second packet. In addition, the index is associated with any additional packets encapsulated within the second packet. The additional packets are also filtered based on the index and the second set of rules.

Path diversity with forward error correction (PDF) system for packet switched networks

Abstract: Packet loss and end-to-end delay limit delay sensitive applications over the best effort packet switched networks such as the Internet. In our previous work, we have shown that substantial reduction in packet loss can be achieved by sending packets at appropriate sending rates to a receiver from multiple senders, using disjoint paths, and by protecting packets with forward error correction. In this paper, we propose a path diversity with forward error correction (PDF) system for delay sensitive applications over the Internet in which, disjoint paths from a sender to a receiver are created using a collection of relay nodes. We propose a scalable, heuristic scheme for selecting a redundant path between a sender and a receiver, and show that substantial reduction in packet loss can be achieved by dividing packets between the default path and the redundant path. NS simulations are used to verify the effectiveness of PDF system.

Packet flow processing in a communication system

Abstract: Method and apparatus for processing packet flows in a communication system. In one embodiment, a resource reservation message includes packet flow parameter information used to determine flow treatment of the associated packet flow. The packet flow mapping is based on the quality of service of the associated packet flow. In another embodiment, a bearer connection is established and monitored for information relating to flow treatment.

Analysis of the parallel packet switch architecture

Abstract: Our work is motivated by the desire to design packet switches with large aggregate capacity and fast line rates. In this paper, we consider building a packet switch from multiple lower speed packet switches operating independently and in parallel. In particular, we consider a (perhaps obvious) parallel packet switch (PPS) architecture in which arriving traffic is demultiplexed overk identical lower speed packet switches, switched to the correct output port, then recombined (multiplexed) before departing from the system. Essentially, the packet switch performs packet-by-packet load balancing, or inverse multiplexing, over multiple independent packet switches. Each lower speed packet switch operates at a fraction of the line rate R. For example, each packet switch can operate at rateR/k. It is a goal of our work that all memory buffers in the PPS run slower than the line rate. Ideally,a PPS would share the benefits of an output-queued switch, i.e., the delay of individual packets could be precisely controlled, allowing the provision of guaranteed qualities of service.In this paper, we ask the question: Is it possible for a PPS to precisely emulate the behavior of an output-queued packet switch with the same capacity and with the same number of ports? We show that it is theoretically possible for a PPS to emulate a first-come first-served (FCFS) output-queued (OQ) packet switch if each lower speed packet switch operates at a rate of approximately 2R/k. We further show that it is theoretically possible for a PPS to emulate a wide variety of quality-of-service queueing disciplines if each lower speed packet switch operates at a rate of approximately 3R/k. It turns out that these results are impractical because of high communication complexity, but a practical high-performance PPS can be designed if we slightly relax our original goal and allow a small fixed-size coordination buffer running at the line rate in both the demultiplexer and the multiplexer. We determine the size of this buffer and show that it can eliminate the need for a centralized scheduling algorithm, allowing a full distributed implementation with low computational and communication complexity. Furthermore, we show that if the lower speed packet switch operates at a rate ofR/k (i.e., without speedup), the resulting PPS can emulate an FCFS-OQ switch within a delay bound.

Packet delay analysis of IEEE 802.11 MAC protocol

Abstract: A new packet delay analysis for the IEEE 802.11b protocol is developed by extending throughput analysis introduced by Bianchi. This analysis is validated by comparison with simulation results using the OPNETTM simulation package. Packet delay results are presented as a function of a number of stations and packet size for basic access and RTS/CTS medium access mechanisms. The proposed analysis identifies when the RTS/CTS mechanism achieves lower packet delay with respect to the basic access mechanism and becomes highly beneficial for the performance of IEEE 802.11 WLANs.

A system for distributing objects to multiple clients

Abstract: A method for updating a subset of a frame of an image is provided. The frame of the image is subdivided into a plurality of tiles. The method initiates with providing a fixed-size queue having a stationary last packet at a bottom of the fixed size queue. Then, a plurality of packets is stored in a time sorted order above the last packet, the plurality of packets corresponding to a frame of an image. Next, an updated packet is received, the updated packet corresponds to a previously received packet of the plurality of packets. Then, the previously received packet is replaced with the updated packet while maintaining the time sorted order. Replacing the previously received packet includes: identifying the previously received packet adjusting any pointers pointing at the previously received packet to point at a packet below the previously received packet; and moving the previously received packet to a top of the fixed size queue. An apparatus and system for distributing packets through a multi point dispatcher between multiple clients is also provided.

High-performance optical-label switching packet routers and smart edge routers for the next-generation Internet

Abstract: This paper discusses the architecture, protocol, analysis, and experimentation of optical packet switching routers incorporating optical-label switching (OLS) technologies and electronic edge routers with traffic shaping capabilities. The core optical router incorporates all-optical switching with contention resolution in wavelength, time, and space domains. It is also capable of accommodating traffic of any protocol and format, and supports packet, flow, burst, and circuit traffic. The edge router is designed to achieve traffic shaping with consideration for quality of service and priority based class-of-service. Simulation results show packet loss rates below 0.3% at load 0.7 and jitter values below 18 /spl mu/s. The traffic shaping reduces the packet loss rate by a factor of /spl sim/5 while adding negligible additional latency. The OLS core routers and the electronic edge routers are constructed including the field-programmable-gate-arrays incorporating the wavelength-aware forwarding and contention resolution algorithms. The experiment shows optical-label-based packet switching with a packet loss rate near 0.2%.

Automatic discovery of network core type

Abstract: Systems and methods for automatically discovering the configuration of network and/or communication facilities are provided The determination generally involves receiving and/or sending at least one test message or packet with special characteristics that normally would be filtered by filtering/forwarding entities in connectionless routed cores, but normally would be forwarded by connectionless communication facilities If the communication facilities do not contain the filtering/forwarding entity, the at least one test packet will be forwarded or passed through the communication facilities If the at least one test packet is filtered or not passed, then at least two scenarios are possible First, the at least one test packet may be filtered and may be silently discarded in which case a determination that the network did not pass the at least one test packet may be made based upon a timeout of a counter Second, the at least one test packet may be filtered and may cause the generation of error or control messages indicating that the at least one test packet is not a proper packet for the network and/or communication facilities

Frame forwarding in a switch fabric

Abstract: A method of forwarding data in a network switch fabric is disclosed. An incoming data packet is received at a first port of the fabric and a first packet portion, less than a full packet length, is read to determine particular packet information including an opcode value. The opcode value allows the fabric to determine the packet type, such a a whether the packet is a broadcast packet, a unicast packet, a multicast packet, etc. Based on the opcode value read, a particular forwarding table of a plurality forwarding tables is read and an egress port bitmap is determined based on entries read from the particular forwarding table. The incoming data packet is then forwarded based on the egress port bitmap. In addition, the architecture of the switch fabric is also disclosed.

Monitoring link quality in a mobile ad hoc network

Abstract: The mobile ad-hoc network includes a plurality of mobile nodes connected together by a plurality of wireless communication links. The method (FIG. 2) and system for monitoring link quality includes, at each node, recording transmission information for transmissions on links to neighboring nodes (102), calculating a packet error rate for each of the links to the neighboring nodes based upon the recorded transmission information (104), and determining link quality for each of the links to the neighboring nodes based upon the calculated packet error rate (106). The transmission information preferably includes packet size transmitted data, packet size received data, collision data and/or retry data.

Current issues in packet switch design

Abstract: Addressing the ever growing capacity demand for packet switches, current research focuses on scheduling algorithms or buffer bandwidth reductions. Although these topics remain relevant, our position is that the primary design focus for systems beyond 1 Tb/s must be shifted to aspects resulting from packaging disruptions. Based on trends such as increased link rates and improved CMOS technologies, we derive new design factors for such switch fabrics. For instance, we argue that the packet round-trip transmission time within the fabric has become a major design parameter. Furthermore, we observe that high-speed fabrics have become extremely dependent on serial I/O technology that is both high speed and high density. Finally, we conclude that in developing the architecture, packaging constraints must be put first and not as an afterthought, which also applies to solving the tremendous power consumption challenges.

Versatile optical code-based MPLS for circuit, burst, and packet switchings

Abstract: We will present versatile optical code (OC)-based photonic MPLS, so-called OC-MPLS which ranges from circuit switching, burst switching, to packet switching. OC-label is an identifier attached to the data, of which information is mapped onto an optical code, a sequence of optical pulses. The OC-label recognition is performed by the optical correlation between an incoming OC-label and the OC-label entries. Unique to the OC-label processing is that it is analog operation entirely in optical domain, and no optical logic operation is involved, therefore, the processing speed is only limited by the propagation delay in the optical correlator, which is a passive optical device. This is a key to the ultrahigh-speed processing capability. Circuit switching of OC-label switched path (OC-LSP) is characterized by the finer data granularity than the wavelength path of GMPS, resulting in a better bandwidth efficiency. In a one-way reservation protocol of photonic burst switching, the OC-labeled control packet improves the throughput by nearly cutting the offset time between the control packet and the following data burst. OC-labeled header of the packet can enables the ultrafast routing in photonic packet switching. To exploit the ultrafast routing capability, a new packet switch architecture is investigated, in which the longest-prefix match algorithm as well as WDM buffering into the fiber delay lines are introduced.

Influence of channel BER on IEEE 802.11 DCF

Abstract: A new performance model of the IEEE 802.11 protocol is introduced that calculates throughput, average packet delay, packet drop probability and average packet drop time. This model is validated with simulation results using the OPNETTM simulation package. The proposed model predicts 802.11 protocol performance very accurately since it considers both transmission errors and packet retry limits. The effect of errors and network size on the performance of the basic access scheme, in terms of throughput, packet delay, packet drop time and drop probability is explored.

Low latency digital audio over packet switched networks

Abstract: Method and Apparatus for delivering audio signals from a source node to a destination node on a network. The apparatus uses a number of switches that transmit prioritized data on a packet network. The switches are coupled to a number of send/receive nodes for sending and receiving digital audio signals on the data network. The audio packet size and the receive buffers are sized to store a minimum possible number of audio samples to minimize latency in processing audio signals arriving at said receive node, but still ensure audio delivery without interruption due to packet data network delay. An additional feature of the invention is recovery of clock synchronization over the same data network by novel arrangement of transmission of timing packets on the network. By sending a multiplicity of packets at irregular intervals a minimum network transit delay can be determined by each of the receive nodes which allows the receive nodes to filter out packet network transit delay error and maintain accurate local clocks.