Knowing network topology is becoming increasingly important for a number of applications such as server placement (E. Cronin et al., 2002) and traceback of DDoS attacks (D. Song and A. Perrig, 2001), Recent works in modeling the Internet topology and constructing network maps have focused on the connectivity aspect. This paper describes our study on incorporating connectivity, latency, and routing information all into a network map based on a large set of traceroute data. We introduce a model for constructing such a network map. We evaluate our network map based on various Internet routing models proposed in the literature. The evaluation shows that, for those traceroute data that we are able to evaluate, at least 85% of computed hop-counts and latencies are within a factor of two of the actual values. Furthermore, we show that a flat routing model based on hop-count performs as well as more complicated routing models.

Network-overlay construction today assumes two-way communication capability - each host can initiate outgoing connections as well as accepting incoming connections. This is often not true on the current Internet due to several reasons, for example, the use of network address translation (NAT) and firewalls. Our experiments with eDonkey and Gnutella file-sharing systems reveal that as many as 36% of the hosts may be guarded - not accepting incoming connections. This presents a challenge to overlay construction because not all hosts are capable of receiving and forwarding requests. We propose an overlay optimization called e* to help existing overlay protocols overcome the reachability problem. Furthermore, e* builds very efficient overlay networks in terms of latency. Under realistic scenarios involving guarded hosts, e* can reduce the average overlay latency by 28-61% compared with existing protocols.

We describe FAST TCP, a new TCP congestion control algorithm for high-speed long-latency networks, from design to implementation. We highlight the approach taken by FAST TCP to address the four difficulties, at both packet and flow levels, which the current TCP implementation has at large windows. We describe the architecture and characterize the equilibrium and stability properties of FAST TCP. We present experimental results comparing our first Linux prototype with TCP Reno, HSTCP, and STCP in terms of throughput, fairness, stability, and responsiveness. FAST TCP aims to rapidly stabilize high-speed long-latency networks into steady, efficient and fair operating points, in dynamic sharing environments, and the preliminary results are promising.

This paper presents a case study of the 10-Gigabit Ethernet (10GbE) adapter from Intel R . Specifically, with appropriate optimizations to the configurations of the 10GbE adapter and TCP, we demonstrate that the 10GbE adapter can perform well in local-area, storage-area, system-area, and wide-area networks. For local-area, storage-area, and system-area networks in support of networks of workstations, network-attached storage, and clusters, respectively, we can achieve over 7-Gb/s end-to-end throughput and 12-µs end-to-end latency between applications running on Linux-based PCs. For the wide-area network in support of grids, we broke the recently-set Internet2 Land Speed Record by 2.5 times by sustaining an end-to-end TCP/IP throughput of 2.38 Gb/s between Sunnyvale, California and Geneva, Switzerland (i.e., 10,037 kilometers) to move over a terabyte of data in less than an hour. Thus, the above results indicate that 10GbE may be a cost-effective solution across a multitude of computing environments.

Web content providers and content distribution network (CDN) operators often set up mirrors of popular content to improve performance. Due to the scale and decentralized administration of the Internet, companies have a limited number of sites (relative to the size of the Internet) where they can place mirrors. We formalize the mirror placement problem as a case of constrained mirror placement, where mirrors can only be placed on a preselected set of candidates. We study performance improvement in terms of client round-trip time (RTT) and server load when clients are clustered by the autonomous systems (AS) in which they reside. Our results show that, regardless of the mirror placement algorithm used, for only a surprisingly small range of values there is an increase in the number of mirror sites (under the constraint) effective in reducing the client to server RTT and server load. In this range, we show that greedy placement performs the best.

Destination-based forwarding in traditional IP routers has not been able to take full advantage of multiple paths that frequently exist in Internet service provider networks. As a result, the networks may not operate efficiently, especially when the traffic patterns are dynamic. This paper describes a multipath adaptive traffic engineering mechanism, called MATE, which is targeted for switched networks such as multiprotocol label switching (MPLS) networks. The main goal of MATE is to avoid network congestion by adaptively balancing the load among multiple paths based on measurement and analysis of path congestion. MATE adopts a minimalist approach in that intermediate nodes are not required to perform traffic engineering or measurements besides normal packet forwarding. Moreover MATE does not impose any particular scheduling, buffer management, or a priori traffic characterization on the nodes. This paper presents an analytical model, derives a class of MATE algorithms, and proves their convergence. Several practical design techniques to implement MATE are described. Simulation results are provided to illustrate the efficacy of MATE under various network scenarios.

Internet service providers and infrastructural companies often employ mirrors of popular content to decrease client download time and server load. Due to the immense scale of the Internet and decentralized administration of the networks, companies have a limited number of sites (relative to the size of the Internet) where they can place mirrors. Mirrors of popular content are usually replicated on every site to maximize reachability to clients. We study the performance improvements as the number of mirrors increases under different placement algorithms subject to the constraint that mirrors can be placed only at certain locations. Although there are extensive theoretical studies on center placement and, analytical and empirical studies on Web cache placement, we are not aware of any published literature on mirror placement especially in the case of constrained mirror placement. Our results show that increasing the number of mirror sites under the constraint is effective in reducing client download time and reducing server load only for a surprisingly small range of values regardless of the mirror placement algorithm.

There is an increasing need to quickly and efficiently learn network distances, in terms of metrics such as latency or bandwidth, between Internet hosts. For example, Internet content providers often place data and server mirrors throughout the Internet to improve access latency for clients, and it is necessary to direct clients to the nearest mirrors based on some distance metric in order to realize the benefit of the mirrors. We suggest a scalable Internet-wide architecture, called IDMaps, which measures and disseminates distance information on the global Internet. Higher level services can collect such distance information to build a virtual distance map of the Internet and estimate the distance between any pair of IP addresses. We present our solutions to the measurement server placement and distance map construction problems in IDMaps. We show that IDMaps can indeed provide useful distance estimations to applications such as nearest mirror selection.

The IDMaps project aims to provide a distance map of the Internet from which relative distances between hosts on the Internet can be gauged. Many distributed systems and applications can benefit from such a distance map service, for example, a common method to improve user-perceived performance of the Internet is to place data and server mirrors closer to clients. When a client tries to access a mirrored server, which mirror should it access? With IDMaps, the closest mirror can be determined based on distance estimates between the client and the mirrors. In this paper we investigate both graph theoretic methods and ad hoc heuristics for instrumenting the Internet to obtain distance maps. We evaluate the efficacy of the resulting distance maps by comparing the determinations of the closest replica using known topologies against those obtained using the distance maps.