Embedding of a graph metric in Euclidean space efficiently and accurately is an important problem in general with applications in topology aggregation, closest mirror selection, and application level routing. We propose a new graph embedding scheme called Big-Bang Simulation (BBS), which simulates an explosion of particles under force field derived from embedding error. BBS is shown to be significantly more accurate, compared to all other embedding methods including GNP. We report an extensive simulation study of BBS compared with several known embedding schemes and show its advantage for distance estimation (as in the IDMaps project), mirror selection and topology aggregation.

Qo!3 requirements across networks, when the information available for ma:king routing decisions is inaccurate. This uncertainty about the actual stale of a network component arises naturally in a number of different environments, which are reviewed in the paper. The goal of the route selection process is then to identify a path that is most likely to satisfy the QoS re-quirements. For end-to-end delay guarantees, this problem is intractable. However, we show that by decomposing the end-to-end constraint into local delay constraints, efficient and tractable solutions can be established. ‘We first consider the simpler problem of decomposing the end-to-end

This paper investigates the problem of routing flows with Quality-of-Service (QoS) requirements through one or more networks, when the information available for making such routing decisions is inaccurate. Inaccuracy in the information used in computing QoS routes, e.g., network state such as link and node metrics, arises naturally in a number of different environments that are reviewed in the paper. Our goal is to determine the impact of such inaccuracy on the ability of the path selection process to successfully identify paths with adequate available resources. In particular, we focus on devising algorithms capable of selecting path(s) that are most likely to successfully accommodate the desired QoS, in the presence of uncertain network state information. For the purpose of our analysis, we assume that this uncertainty is expressed through probabilistic models, and we briefly discuss sample cases that can give rise to such models. We establish that the impact of uncertainty is minima...

A number of important questions remain concerning the scalability of networks with quality of service guarantees. We consider one of these questions: can QoS routing protocols scale to large networks? To address this question, we evaluate performance of techniques that can reduce QoS routing protocol overhead. We specifically focus on topology aggregation, which can reduce overhead by orders of magnitude. We also investigate the interaction of topology aggregation with other important factors that contribute to performance, such as routing update frequency, routing algorithms, and network configuration. Our experiments are based on simulations of relatively large, structured networks. Among our observations, we find --- contrary to intuition --- that topology aggregationdoes not always have a negativeimpact on routing performance. Aggregation can reduce the routing information fluctuation, increase stability, and thus benefit routing performance. We also propose two new methods of aggr...

In this paper, we investigate the problem of topology aggregation (TA) for scalable, QoS-based routing in ATM networks. TA is the process of summarizing the topological information of a subset of network elements. This summary is flooded throughout the network, and is used by various nodes to determine appropriate routes for connection requests. A key issue in the design of a TA scheme is the appropriate balance between compaction and the corresponding routing performance. The contributions of this paper are twofold. First, we introduce a source-oriented approach to TA, which provides better performance than existing approaches. The intuition behind this approach is that the advertised topologystate information is used by source nodes to determine tentative routes for connection requests. Accordingly, only relevant information to source nodes needs to be advertised. We integrate the source-oriented approach into three new TA schemes that provide different tradeoffs between compaction a...

Abstract In the future, global networks will consist of a hierarchy of subnetworks called domains. For reasons of both scalability and security, domains will not reveal details of their internal structure to outside nodes. Instead, these domains will advertise only a summary, or aggregated view, of their internal structure, e.g., as proposed by the ATM PNNI standard. This work compares, by simulation, the performance of several different aggregation schemes in terms of network throughput (the fraction of attempted connections that are realized), and network control load (the average number of crankbacks per realized connection.) Our main results are: ffl Minimum spanning tree is a good aggregation scheme; ffl Exponential link cost functions perform better than min-hop routing; ffl Our suggested logarithmic update scheme that determine when re-aggregation should be computed can significantly reduce the computational overhead due to re-aggregation with a negligible decrease in performance. 1.

Large networks are often structured hierarchically by grouping nodes into different domains in order to deal with the scaling problem. In such networks, it is infeasible to maintain the detailed network information at every router. Therefore, topology information of domains are summarized before broadcasted. This process is called topology aggregation. Hierarchical routing protocols are then used to find a route among the domains. We study several basic problems associated with hierarchical QoS routing, including (1) how to make QoS-aware topology aggregation, (2) how to represent the aggregated network state, and (3) how to find an end-to-end route based on aggregated information. The novelty in this research is our new network QoS representation which is line segments on the delay-bandwidth plane. We also present a distributed routing mechanism that works with our representation. Our theoretical and simulation results show that the protocol achieves scalability and improved routing p...

and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft " or "work in progress." To learn the current status of any Internet Draft, please check the 1id-abstracts.txt listing contained in the Internet Drafts Shadow Directories on ds.internic.net, nic.nordu.net, ftp.nisc.sri.com or munnari.oz.au. Distribution of this memo is unlimited. This Internet Draft expires on September, 2, 1998. QoS-based routing has been recognized as a missing piece in the evolution

State (topology) aggregation is the notion of reducing nodal as well as link information to achieve scaling in a large network. In this paper, we compare the performance of three different aggregation schemes, namely, the Simple-Node scheme, the Full-Mesh scheme, and the Star scheme, which represent a given group of nodes by a single logical node, a complete graph between border nodes, and a star-like graph connecting all of the border nodes, respectively. We obtain transient performance measures for multi-service networks using our recently developed Z-iteration method [17]. We restrict the set of candidate paths to short length paths as this has been shown to be an effective way to enhance network performance. Our simulation results indicate that under a uniformly distributed workload, the scheme that has more detailed topology information performs much better, as common sense suggests. More interestingly, however, we found that as the workload becomes skewed, i.e., as it concentrat...

Abstract—Routing is a process of finding a network path from a source node to a destination node. The execution time and the memory requirement of a routing algorithm increase with the size of the network. In order to deal with the scalability problem, large networks are often structured hierarchically by grouping nodes into different domains. The internal topology of each domain is then aggregated into a simple topology that reflects the cost of routing across that domain. This process is called topology aggregation. For delay-bandwidth sensitive networks, traditional approaches represent the property of each link in the aggregated topology as a delay-bandwidth pair, which corresponds to a point on the delay-bandwidth plane. Since each link after aggregation may be the abstraction of many physical paths, a single delay-bandwidth pair results in significant information loss. The major contribution of this paper is a novel quality-of-service (QoS) parameter representation with a new aggregation algorithm and a QoS-aware routing protocol. Our QoS representation captures the state information about the network with much greater accuracy than the existing algorithms. Our simulation results show that the new approach achieves very good performance in terms of delay deviation, success ratio, and crankback ratio. Index Terms—Delay-bandwidth sensitive networks, hierarchical routing, QoS routing, topology aggregation. I.