 effort, these measures have been ineffective or difficult to deploy. These efforts, however, are necessary steps in our evolution toward ultra- scale networks. Sustaining high performance on a global network is extremely challenging and requires concerted advances in both hardware and protocols. Experiments that achieve high throughput either in isolated environments or with interim remedies that by-pass protocol instability, idealized or fragile as they may be, push the state of the art in hardware. The development of robust and practical protocols means that the most advanced hardware will be effec- tively used to achieve ideal performance in realistic environments. The FAST team is addressing protocol issues head on to develop a variant of TCP that can scale to a multi-gigabit-per-second regime in practical network conditions. This integrated approach combining theory, implementation, and experiment is what makes the FAST team research unique and what makes fundamental progress possible. With the use of standard packet size supported throughout today's networks, TCP presently achieves an average throughput of 266Mbps, averaged over an hour, with a single TCP/IP flow between Sunnyvale near SLAC and CERN in Geneva, over a distance of 10,037km. This represents an efficiency of just THE NEXT INTERNET 27 percent. The FAST TCP sustained an average throughput of 925 Mbps and an efficiency of 95 percent, a 3.5-times improvement, under the same experimental condition. With 10 concurrent TCP/IP flows, FAST achieved an unprecedented speed of 8,609 Mbps, at 88 percent efficiency, which is 153,000 times that of today's modem and close to 6,000 times that of the common standard for ADSL (asymmetric digital subscriber line) connections. The 10-flow experiment set another first in addition to the highest aggre- gate speed over routed paths. High capacity and large distances together cause performance problems. Different TCP algorithms can be compared using the product of achieved throughput and the distance of transfer, meas