Resource Congestion Research Articles

Multilayer chip-level global routing using an efficient graph-based Steiner tree heuristic

We present a chip-level global router based on a new, more accurate global routing model for the multilayer macro-cell (building block) technology. The routing model uses a three-dimensional mixed directed/undirected routing graph, which provides not only the topological information but also the layer information. The irregular routing graph closely models the multilayer routing problem, so the global router can give an accurate estimate of the routing resources needed. Route-searching is formulated as the Steiner problem in networks (graph Steiner tree problem). Although the Steiner problem in networks is an NP-hard problem, it can generate better routes than other approaches. Previously published Steiner tree heuristics can not handle the complexity of the modern routing graphs. We developed an improved Steiner tree heuristic algorithm which can take advantage of the features of routing graphs. Tested on industrial circuits, our algorithm yields comparable results while having dramatically lower time and space complexities than the leading heuristics. The efficiency and effectiveness of our algorithm make our global router applicable to large industrial circuits, easily handling multilayer problems consisting of 200 macro cells and 10000 nets. While minimizing the wire length, our global router can also minimize the number of vias or solve the routing resource congestion problems.

Analysis of common‐channel signaling network congestion in the presence of considering various kinds of delay

AbstractCommon channel signaling networks play an important role in providing advanced switching services. With the increase in the degree of the reliability of such switching services on common channel signaling networks, the common channel signaling networks are easily congested, and controlling congestion on these networks has become increasingly important. On the other hand, the network scale has been increasing with the development of the information society. With the increase in the network scale, signal transmission delay and control signal delay have increased, giving adverse effects on congestion control. In this article, the congestion control on common channel signaling networks recommended by CCITT has been analyzed considering the above‐said transmission delay and control signal delay. As a result of this analysis, the above‐said adverse effects could be evaluated quantitatively. A rigorous solution of this model could not be obtained. Thus, a method of analysis by fluid approximation is proposed. In addition, this approximating analytical method is shown to have sufficient practical accuracy in comparison with simulation results. By this analytical method, the rates of blocking of congested resources (signal links, circuits), mean delays, etc., can be easily obtained. As a result of the analysis, it is shown that these delays greatly influence the efficiency of congestion control. Especially, it is shown that the call loss rate shows a great effect; and control parameters must be determined considering these delays in order to satisfy certain standard values by congestion control.

Connections with multiple congested gateways in packet-switched networks part 1

In this paper we explore the bias in TCP/IP networks against connections with multiple congested gateways. We consider the interaction between the bias against connections with multiple congested gateways, the bias of the TCP window modification algorithm against connections with longer roundtrip times, and the bias of Drop Tail and Random Drop gateways against bursty traffic. Using simulations and a heuristic analysis, we show that in a network with the window modification algorithm in 4.3 tahoe BSD TCP and with Random Drop or Drop Tail gateways, a longer connection with multiple congested gateways can receive unacceptably low throughput. We show that in a network with no bias against connections with longer roundtrip times and with no bias against bursty traffic, a connection with multiple congested gateways can receive an acceptable level of throughput.We discuss the application of several current measures of fairness to networks with multiple congested gateways, and show that different measures of fairness have quite different implications. One view is that each connection should receive the same throughput in bytes/second, regardless of roundtrip times or numbers of congested gateways. Another view is that each connection should receive the same share of the network's scarce congested resources. In general, we believe that the fairness criteria for connections with multiple congested gateways requires further consideration.

Estimating the benefits of recreation under conditions of congestion: Comments and extension

The purpose of this paper is to comment on and extend the analysis of a paper by Wetzel. He uses a commonly accepted model of demand for a congested recreational resource and shows how the Clawson method of estimating a recreational demand curve relates to it. Much of his analysis is useful but he errs in his interpretation of the proper value of consumer surplus. In this paper a specific formalization of the demand model is developed for the first time and it is used to show the correct measure of consumer surplus and how to specify the proper level of use for the congested resource.

A feedback-coupled resource allocation policy for multiprogrammed computer systems

An earlier paper on an adaptive workload balancing strategy to achieve efficient resource utilization is extended to include memory cost. The scheme corrects for the imbalance in resource utilization by bringing into play the "Invisible Hand" of classical economics. In this framework, the memory price and the bid, W ij, of each user program U jfor resource R iare calculated adaptively. These prices are not apparent to the users, but they are rather shadow prices determined from the characteristics of user programs, the current resource congestion, and the budget constraints of users. There emerge a set of effective priorities for user programs based on the bid prices, W ij, and these determine the scheduling of programs. An imbalance due to high congestion of some resource will result in a relative decrease of priority for heavy users ofthat resource and a relative increase for light users. Some ideas on an actual implementation scheme are described based on an approximation to the above abstract scheme. It is shown that this approximate scheme will also tend to balance resource utilization.