240 research outputs found
On Cyclic Dependencies and Regulators in Time-Sensitive Networks
For time-sensitive networks, as in the context of
IEEE TSN and IETF Detnet, cyclic dependencies are associated
with certain fundamental properties such as improving availability
and decreasing reconfiguration effort. Nevertheless, the
existence of cyclic dependencies can cause very large latency
bounds or even global instability, thus making the proof of the
timing predictability of such networks a much more challenging
issue. Cyclic dependencies can be removed by reshaping
flows inside the network, by means of regulators. We consider
FIFO-per-class networks with two types of regulators: perflow
regulators and interleaved regulators (the latter reshape
entire flow aggregates). Such regulators come with a hardware
cost that is less for an interleaved regulator than for a perflow
regulator; both can affect the latency bounds in different
ways. We analyze the benefits of both types of regulators in
partial and full deployments in terms of latency. First, we
propose Low-Cost Acyclic Network (LCAN), a new algorithm
for finding the optimum number of regulators for breaking all
cyclic dependencies. Then, we provide another algorithm, Fixed-
Point Total Flow Analysis (FP-TFA), for computing end-to-end
delay bounds for general topologies, i.e., with and without cyclic
dependencies. An extensive analysis of these proposed algorithms
was conducted on generic grid topologies. For these test networks,
we find that FP-TFA computes small latency bounds; but, at
a medium to high utilization, the benefit of regulators becomes
apparent. At high utilization or for high line transmission-rates, a
small number of per-flow regulators has an effect on the latency
bound larger than a small number of interleaved regulators.
Moreover, interleaved regulators need to be placed everywhere
in the network to provide noticeable improvements. We validate
the applicability of our approaches on a realistic industrial timesensitive
network
On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks
Flow reshaping is used in time-sensitive networks (as in the context of IEEE
TSN and IETF Detnet) in order to reduce burstiness inside the network and to
support the computation of guaranteed latency bounds. This is performed using
per-flow regulators (such as the Token Bucket Filter) or interleaved regulators
(as with IEEE TSN Asynchronous Traffic Shaping). Both types of regulators are
beneficial as they cancel the increase of burstiness due to multiplexing inside
the network. It was demonstrated, by using network calculus, that they do not
increase the worst-case latency. However, the properties of regulators were
established assuming that time is perfect in all network nodes. In reality,
nodes use local, imperfect clocks. Time-sensitive networks exist in two
flavours: (1) in non-synchronized networks, local clocks run independently at
every node and their deviations are not controlled and (2) in synchronized
networks, the deviations of local clocks are kept within very small bounds
using for example a synchronization protocol (such as PTP) or a satellite based
geo-positioning system (such as GPS). We revisit the properties of regulators
in both cases. In non-synchronized networks, we show that ignoring the timing
inaccuracies can lead to network instability due to unbounded delay in per-flow
or interleaved regulators. We propose and analyze two methods (rate and burst
cascade, and asynchronous dual arrival-curve method) for avoiding this problem.
In synchronized networks, we show that there is no instability with per-flow
regulators but, surprisingly, interleaved regulators can lead to instability.
To establish these results, we develop a new framework that captures industrial
requirements on clocks in both non-synchronized and synchronized networks, and
we develop a toolbox that extends network calculus to account for clock
imperfections.Comment: ACM SIGMETRICS 2020 Boston, Massachusetts, USA June 8-12, 202
Multiplexing regulated traffic streams: design and performance
The main network solutions for supporting QoS rely on traf- fic policing (conditioning, shaping). In particular, for IP networks the IETF has developed Intserv (individual flows regulated) and Diffserv (only ag- gregates regulated). The regulator proposed could be based on the (dual) leaky-bucket mechanism. This explains the interest in network element per- formance (loss, delay) for leaky-bucket regulated traffic. This paper describes a novel approach to the above problem. Explicitly using the correlation structure of the sources’ traffic, we derive approxi- mations for both small and large buffers. Importantly, for small (large) buffers the short-term (long-term) correlations are dominant. The large buffer result decomposes the traffic stream in a stream of constant rate and a periodic impulse stream, allowing direct application of the Brownian bridge approximation. Combining the small and large buffer results by a concave majorization, we propose a simple, fast and accurate technique to statistically multiplex homogeneous regulated sources. To address heterogeneous inputs, we present similarly efficient tech- niques to evaluate the performance of multiple classes of traffic, each with distinct characteristics and QoS requirements. These techniques, applica- ble under more general conditions, are based on optimal resource (band- width and buffer) partitioning. They can also be directly applied to set GPS (Generalized Processor Sharing) weights and buffer thresholds in a shared resource system
FAST Copper for Broadband Access
FAST Copper is a multi-year, U.S. NSF funded project that started in 2004, and is jointly pursued by the research groups of Mung Chiang at Princeton University, John Cioffi at Stanford University, and Alexander Fraser at Fraser Research Lab, and in collaboration with several industrial partners including AT&T. The goal of the FAST Copper Project is to provide ubiquitous, 100 Mbps, fiber/DSL broadband access to everyone in the US with a phone line. This goal will be achieved through two threads of research: dynamic and joint optimization of resources in Frequency, Amplitude, Space, and Time (thus the name 'FAST') to overcome the attenuation and crosstalk bottlenecks, and the integration of communication, networking, computation, modeling, and distributed information management and control for the multi-user twisted pair network
Per-Priority Flow Control (Ppfc) Framework For Enhancing Qos In Metro Ethernet
Day by day Internet communication and services are experiencing an increase in variety and quantity in their capacity and demand. Thus, making traffic management and quality of service (QoS) approaches for optimization of the Internet become a challenging area of research; meanwhile flow control and congestion control will be considered as significant fundamentals for the traffic control especially on the high speed Metro Ethernet. IEEE had standardized a method (IEEE 802.3x standard), which provides Ethernet Flow Control (EFC) using PAUSE frames as MAC control frames in the data link layer, to enable or disable data frame transmission. With the initiation of Metro Carrier Ethernet, the conventional ON/OFF IEEE 802.3x approach may no longer be sufficient. Therefore, a new architecture and mechanism that offer more flexible and efficient flow and congestion control, as well as better QoS provisioning is now necessary
A calculus for stochastic QoS analysis and its application to conformance study
Ph.DDOCTOR OF PHILOSOPH
- …