The role of monitoring enables the strategic management, problem tracking (and thus solving), and informed engineering of both local and wide area networks.
Generally, there are two aspects of network monitoring; that of the performance of network nodes (routers, switches, computers) and the usage (and performance) between the nodes.
It is important to understand both in order to be able to successfully monitor the complete end-to-end path and thus diagnose problems and or reduce the effect of end-to-end congestion.

Our primary projects involve Pinger [Pinger] and IEPM-BW [IEPM-BW] which actively monitor the end-node to end-node network performance patterns across several academic and commercial networks.
SLAC has has over 14 years of experience monitoring computer networks over the wide area.
Currently, this DWMI [DWMI] solution provides network monitoring with regular active and passive measurement methods in order to provide a detail representation (and trends) of Internet usage patterns and performances.
Using monitoring tools such as owamp [OWAMP], ping [PING], traceroute [TRACEROUTE], iperf [IPERF], thrulay [THRULAY], pathchirp [PATHCHIRP] and pathneck [PATHNECK], we have extensively studied the accuracy and effectiveness of numerous network monitoring tools and have collected hundreds of gigabytes of network performance related data.

Of particular interest to us are the extremes of network performance and network performance trends.
Our recent paper [DIGITALDIVIDE] on the digital divide studies the growth of network usage patterns around the world over the last decade of not only the technologically advanced nations, but also that of growing nations.
We have shown that the trends in performance are associated with advances in the underlying technology available to those countries.
We have also published on the effects of traceroute and available bandwidth changes and the effect they have on network performance [ANOMALOUS].

SLAC, in collaboration with other High Energy Physics institutions, hold the previous three consecutive year's record in being able to push the boundaries in network throughput and utilisation with the SuperComputing Bandwidth Challenge.
Our current record stands at over 150Gbps, with the ability to transfer over 1TB of data in 24 hours [SC05].

SLAC has extensive research and real-life experience with both identifying and resolving the host based bottlenecks for high throughput network transfers.
An important limitation to be able to utilise the vast network resources available is often caused by bottlenecks at host end systems.
With the advances in technological hardware such as 10Gbps network interface cards and PCI-X2 more and more emphasis is being put into the performance between network elements as researchers are able to push hardware to their absolutely limits.
Whilst the cost of such hardware is currently out of reach of most scientific projects, it is undeniable that the cost of such technologies will fall, and as such be prevalent in more projects as time goes by.

Low level operating system based parameters such as queue sizes and TCP congestion control algorithms are often the cause of low throughput performances experienced - especially when 10Gbit/sec and beyond network capacities are available end to end.
This is especially apparent when we consider the shared nature of the wide area network where users compete for (sometimes limited) bandwidth.
In particular we have extensively tested and published on the performances of new TCP algorithms that promise to both utilise network resources effectively and fairly.
We have also experimented with UDP-based transport algorithms that can fully utilise lambda and QoS/DiffServ network paths and are currently working closely with BNL to monitor QoS paths effectively.

SLAC is also a leader in the field of new transport applications.
Programs such as bbcp [BBCP] and xrootd [XROOTD] have been proven in both high-performance experiments (at the recent SuperComputing 2005 conference) and in large scale production systems.
As networks become more intelligent with advanced technologies, it will be even more useful to be able to interface with the network services available.
Through close collaboration with both SciDAC projects and internal SLAC initiatives, it shall be possible to integrate the two into one cohesive and effective package.