One-way Delay Research Articles

One-way delay estimation and its application

Delay estimation is a difficult problem in computer networks. Accurate one-way delay estimation is crucial because it serves a very important role in network performance and thus application design. RTT (Round Trip Time) is often used as an approximation of the delay, but because it is a sum of the forward and reverse delays, the actual one-way delay cannot be estimated accurately from RTT. To estimate one-way delay accurately, this paper proposes a new scheme that analytically derives one-way delay, forward and reverse delay, respectively. We show that the performance of TCP can improve dramatically in asymmetric networks using our scheme. A key contribution of this paper is that our one-way delay estimation is much more accurate than RTT estimation so that TCP can quickly find the network capacity in the slow start phase. Since RTT is the sum of the forward and reverse delays, our scheme can be applied to any protocol that is based on RTT.

SRAMT: a hybrid sender and receiver-based adaptation scheme for TCP friendly multicast transmission

In this paper, we describe a hybrid sender and receiver-based adaptation scheme for multicast transmission of multimedia data, which we call SRAMT (Sender–Receiver based Adaptation scheme for Multicast Transmission). The most prominent features of SRAMT are its distributed (to sender and receivers) transmission rate estimation algorithm and its innovative RTT (Round Trip Time) estimation algorithm based on one-way delay measurements. With the use of SRAMT, we ensure that sender will transmit TCP friendly traffic and receivers with different capabilities (in terms of available bandwidth) are able to receive the multimedia information. We evaluate SRAMT through a number of simulations and compare it with other schemes available to the literature. Main target of the simulations was the examination of SRAMT behavior to a heterogeneous group of receivers and its behavior against TCP connections.

HMM delay prediction technique for VoIP

This paper proposes a new algorithm for predicting audio packet playout delay for voice conferencing applications that use silence suppression. The proposed algorithm uses a hidden Markov model (HMM) to predict the playout delay. Several existing algorithms are reviewed to show that the HMM technique is based on a combination of various desirable features of other algorithms. Voice over Internet protocol (VoIP) applications produce packets at a deterministic rate but various queuing delays are added to the packets by the network causing packet interarrival jitter. Playout delay prediction techniques schedule audio packets for playout and attempt to make a reasonable compromise between the number of lost packets, the one-way delay and the delay variation since these criteria cannot be optimized simultaneously. In particular, this paper will show that the proposed HMM technique makes a good compromise between the mean end-to-end delay, end-to-end delay standard deviation and average packet loss rate.

End-to-end available bandwidth: Measurement methodology, dynamics, and relation with TCP throughput

The available bandwidth (avail-bw) in a network path is of major importance in congestion control, streaming applications, quality-of-service verification, server selection, and overlay networks. We describe an end-to-end methodology, called self-loading periodic streams (SLoPS), for measuring avail-bw. The basic idea in SLoPS is that the one-way delays of a periodic packet stream show an increasing trend when the stream's rate is higher than the avail-bw. We have implemented SLoPS in a tool called pathload. The accuracy of the tool has been evaluated with both simulations and experiments over real-world Internet paths. Pathload is nonintrusive, meaning that it does not cause significant increases in the network utilization, delays, or losses. We used pathload to evaluate the variability ("dynamics") of the avail-bw in Internet paths. The avail-bw becomes significantly more variable in heavily utilized paths, as well as in paths with limited capacity (probably due to a lower degree of statistical multiplexing). We finally examine the relation between avail-bw and TCP throughput. A persistent TCP connection can be used to measure roughly the avail-bw in a path, but TCP saturates the path and increases significantly the path delays and jitter.

On synchronization techniques: performance and impact on time metrics monitoring

AbstractThe paper presents an experimental comparison of device synchronization strategies to monitor quality of service (QoS) time metrics, such as the one‐way delay and the delay variation. The compared strategies are based on global positioning system (GPS), public Internet network time protocol (NTP) servers and ad hoc GPS‐based NTP servers with different treatments of the NTP traffic. The presented experimental results allow to quantitatively evaluate the level of performance achievable using each synchronization technique. Finally, considering a satellite test bed, we focus our analysis on two relevant aspects of time metrics monitoring: the impact of the synchronization errors on the metrics observation and the different values that can be measured when a metric is monitored at the application or data link level. Copyright © 2003 John Wiley & Sons, Ltd.

Analytical derivation of one-way delay

Delay estimation is a difficult problem in computer networks. Round trip time (RTT) is often used as an approximation of the delay but, because it is a sum of the forward and reverse delays, the actual one-way delay cannot be estimated accurately from RTT. Accurate one-way delay estimation becomes crucial because it serves a very important role in network and application design. A new scheme is proposed for estimating one-way delay. One-way delay, and forward and reverse delay are analytically derived.

End-to-end available bandwidth

The available bandwidth (avail-bw) in a network path is of major importance in congestion control, streaming applications, QoS verification, server selection, and overlay networks. We describe an end-to-end methodology, called Self-Loading Periodic Streams (SLoPS), for measuring avail-bw. The basic idea in SLoPS is that the one-way delays of a periodic packet stream show an increasing trend when the stream's rate is higher than the avail-bw. We implemented SLoPS in a tool called pathload. The accuracy of the tool has been evaluated with both simulations and experiments over real-world Internet paths. Pathload is non-intrusive, meaning that it does not cause significant increases in the network utilization, delays, or losses. We used pathload to evaluate the variability ('dynamics') of the avail-bw in some paths that cross USA and Europe. The avail-bw becomes significantly more variable in heavily utilized paths, as well as in paths with limited capacity (probably due to a lower degree of statistical multiplexing). We finally examine the relation between avail-bw and TCP throughput. A persistent TCP connection can be used to roughly measure the avail-bw in a path, but TCP saturates the path, and increases significantly the path delays and jitter.

A wind-induced delay pattern in SAR interferometry and numerical simulation.

A particular delay pattern in differential synthetic aperture radar (SAR) interferometry is investigated by using upper sounding data and a numerical simulation technique. A JERS-1 pair of a humid windy summer scene and a dry autumn scene produces a large topography-correlated delay pattern. This topography-correlated delay shows linearity to topography that is mainly due to a wet delay. In this study, the static component of the atmospheric delay is calculated by using upper sounding data observed at a neighbouring station from the site. The result shows 14cm oneway delay corresponding to 3, 800m height difference, while 23cm in SAR interferogram, indicating a disagreement with SAR and meteorological data. A reason for this disagreement may be a distance between the site and the meteorological station. After removing the topography-correlated static component from the interferogram, there still remains a dynamic component caused by a wind. A numerical model, MRI-NHM, developed by Meteorological Research Institute, simulates atmosphere and the dynamic delay is evaluated. The simulation produces similar delay patterns of large scale and a wave-shaped pattern induced by a mountain wave. The simulation explains mechanisms to make these patterns. Although there are disagreements such as small-scale delay patterns and the wave length of the mountain wave, the study shows this simulation approach is promising for evaluatine the atmospheric delay, especially dynamic delay.

Large-scale experimental study of Internet performance using video traffic

In this paper, we analyze the results of a seven-month real-time streaming experiment, which was conducted between a number of unicast dialup clients, connecting to the Internet through access points in more than 600 major U.S. cities, and a backbone video server. During the experiment, the clients streamed low-bitrate MPEG-4 video sequences from the server over paths with more than 5,000 distinct Internet routers. We describe the methodology of the experiment, the architecture of our NACK-based streaming application, study end-to-end dynamics of 16 thousand ten-minute sessions (85 million packets), and analyze the behavior of the following network parameters: packet loss, round-trip delay, oneway delay jitter, packet reordering, and path asymmetry. We also study the impact of these parameters on the quality of real-time streaming.

Hop-by-hop versus end-to-end active measurements

In packet-switching networks, some performance characteristics can be estimated by end-to-end active measurements, i.e. sending probe packets from end hosts. There are different end-to-end measurement techniques to estimate one-way delay and different types of bandwidth. Nevertheless they do not always give accurate results, only work under limited conditions and have disadvantages which we summarize based on several research works [3,10,12]. We propose hop-by-hop active measurement methods to measure bandwidth and one-way delay. The concept of proposed hop-by-hop methods is that not only the end hosts, but nodes along a network path are also involved in measurements. In this paper, new necessary services are also proposed, with which we can apply hop-by-hop methods. Our performance evaluation shows that despite having to implement new services in every node, these services help network performance analysts and applications measure bandwidth and one-way delay faster and more accurately. Our work is an attempt to take part in creating and deploying infrastructure to support better measurement on the Internet.

Quality of services for remote control in High Energy Physics experiments: a case study

The development of new advanced applications and the evolution in networking are two related processes which greatly benefit from two-way exchanges and from progress in both fields. In this study we show how mission-oriented networked applications can be effectively deployed for research purposes if coupled to the support of Quality of Service (QoS) in IP networks. QoS is one of the latest research topics in network engineering. In this article we focus on two specific examples of networked applications: remote instrumentation control and remote display of analysis data when applied for the support of experiments in the high energy physics field. In this paper we focus on the application requirements: the availability of a reliable transmission channel, limited one-way delay for timely interactions between servers and clients and fairness in network resources allocation in case of contention. The above-mentioned requirements can be addressed through the support of QoS, i.e. through the differential treatment of packets on the end-to-end data path. Several technologies and protocols for QoS support in packet networks have been devised during the last years by the research community. In this study we focus on the Differentiated Services (diffserv) approach, an architecture characterized by high scalability, flexibility and interoperability. In this paper we identify the application requirements and we quantitatively specify the corresponding service profiles. The diffserv network architecture needed to support the services is defined in terms of functional blocks (policing, classification, marking and scheduling) and of their placement in the network. Finally, for each of them the configuration best suited to remote control support is defined.

ENDE: An End-to-end Network Delay Emulator Tool for Multimedia Protocol Development

Multimedia applications and protocols are constantly being developed to run over the Internet. A new protocol or application after being developed has to be tested on the real Internet or simulated on a testbed for debugging and performance evaluation. In this paper, we present a novel tool, ENDE, that can emulate end-to-end delays between two hosts without requiring access to the second host. The tool enables the user to test new multimedia protocols realistically on a single machine. In a delay-observing mode, ENDE can generate accurate traces of one-way delays between two hosts on the network. In a delay-impacting mode, ENDE can be used to simulate the functioning of a protocol or an application as if it were running on the network. We will show that ENDE allows accurate estimation of one-way transit times and hence can be used even when the forward and reverse paths are asymmetric between the two hosts. Experimental results are also presented to show that ENDE is fairly accurate in the delay-impacting mode.

End-to-end delay analysis of videoconferencing over packet-switched networks

Videoconferencing is an important global application-it enables people around the globe to interact when distance separates them. In order for the participants in a videoconference call to interact naturally, the end-to-end delay should be below human perception; even though an objective and unique figure cannot be set, 100 ms is widely recognized as the desired one-way delay requirement for interaction. Since the global propagation delay can be about 100 ms, the actual end-to-end delay budget available to the system designer (excluding propagation delay) can be no more than 10 ms. We identify the components of the end-to-end delay in various configurations with the objective of understanding how it can be kept below the desired 10-ms bound. We analyze these components step-by-step through six system configurations obtained by combining three generic network architectures with two video encoding schemes. We study the transmission of raw video and variable bit rate (VBR) MPEG video encoding over (1) circuit switching; (2) synchronous packet switching; and (3) asynchronous packet switching. In addition, we show that constant bit rate (CBR) MPEG encoding delivers unacceptable delay-on the order of the group of pictures (GOP) time interval-when maximizing the quality for static scenes. This study aims at showing that having a global common time reference, together with time-driven priority (TDP) and VBR MPEG video encoding, provides adequate end-to-end delay, which is (1) below 10 ms; (2) independent of the network instant load; and (3) independent of the connection rate. The resulting end-to-end delay (excluding propagation delay) can be smaller than the video frame period, which is better than what can be obtained with circuit switching.

Trellis decoding of Reed-Solomon codes in low bit rate speech communications

The residual redundancy that persists in the transmitted parameters of a low bit rate speech coder are exploited to reduce the computational complexity of a Reed-Solomon (RS) trellis decoder. The use of RS codes for mobile telephony provides the opportunity for avoiding channel interleaving and so reduces one-way delay.

Impact of transmission delay in audiovisual communications

AbstractIn this paper, the design and results are presented of an experimental study which was conducted in order to assess subjectively the impact of transmission delay in audiovisual communications. This study was undertaken using two 64 kb/s videotelephones which were connected over links incorporating simulated one‐way circuit propagation delays of 0 ms, 250 ms and 500 ms. From the results obtained it was concluded that audiovisual communication is weakly affected by propagation delay. In general, performance degradation between terrestrial and single‐hop satellite connections was minimal and in most cases statistically insignificant. A subsidiary conclusion is that the presence of the visual cues appears to mitigate the impact of transmission delay in audiovisual communication.

Interconnection networks: Physical design andperformance analysis

This paper considers various physical constraints which influence the design of interconnection networks used in multiprocessor systems. Design expressions are presented for implementing an N log N packet passing interconnection network composed of circuit switched crossbar chip modules. Expressions reflecting chip level and board level pin and area constraints are derived and used to determine the network delay expected at a given clock frequency. Logic and memory delay, signal path delay, clock skew, and clock distribution delay parameters are defined and used to determine the maximum frequency which can be obtained with a given design. An example 2048 × 2048 network design is considered. This example indicates that using aggressive packaging and MOS technology, a clock frequency of about 40 Mhz is achievable. However, even at this frequency, this network would result in a one-way delay (ignoring blocking and hot spot delays) of about 1 μsec. A read operation from memory requiring a round trip would thus require about 2 μsec. This represents considerable slowdown when compared with accessing strictly local memory and appears to be a major problem in the design of network centered multiprocessor architectures.

Prediction of transport protocol performance through simulation

A five-layer simulation model of OSI protocols is described and applied to predict transport performance on a local area network (LAN). Emphasis is placed on time-critical applications typical of a small, flexible manufacturing system. The results predict that, with current technology, OSI protocols can provide 1.5 Mbps throughput, one-way delays between 6 and 10 ms, and response times between 15 and 25 ms. The results also indicate that CSMA/CD is a reasonable access method for time-critical applications on small, factory LANS, if loads of less than 40% are anticipated. For loads between 40% and 70%, a token passing access method provides better performance for time-critical applications.