1	High Performance WAN Testbed Experiences & Results Les Cottrell – SLAC Prepared for the CHEP03, San Diego, March 2003 http://www.slac.stanford.edu/grp/scs/net/talk/chep03-hiperf.html
2	Outline Who did it? What was done? How was it done? Who needs it? So what’s next? Where do I find out more?
3	Who did it: Collaborators and sponsors Caltech: Harvey Newman, Steven Low, Sylvain Ravot, Cheng Jin, Xiaoling Wei, Suresh Singh, Julian Bunn SLAC: Les Cottrell, Gary Buhrmaster, Fabrizio Coccetti LANL: Wu-chun Feng, Eric Weigle, Gus Hurwitz, Adam Englehart NIKHEF/UvA: Cees DeLaat, Antony Antony CERN: Olivier Martin, Paolo Moroni ANL: Linda Winkler DataTAG, StarLight, TeraGrid, SURFnet, NetherLight, Deutsche Telecom, Information Society Technologies Cisco, Level(3), Intel DoE, European Commission, NSF
4	What was done? Beat the Gbps limit for a single TCP stream across the Atlantic – transferred a TByte in an hour
5	On February 27-28, over a Terabyte of data was transferred in 3700 seconds by S. Ravot of Caltech between the Level3 PoP in Sunnyvale, near SLAC, and CERN. The data passed through the TeraGrid router at StarLight from memory to memory as a single TCP/IP stream at an average rate of 2.38 Gbps (using large windows and 9KByte “jumbo” frames). This beat the former record by a factor of approximately 2.5, and used the US-CERN link at 99% efficiency.
6	How was it done: Typical testbed
7	Typical Components CPU Pentium 4 (Xeon) with 2.4GHz cpu For GE used Syskonnect NIC For 10GE used Intel NIC Linux 2.4.19 or 20 Routers Cisco GSR 12406 with OC192/POS & 1 and 10GE server interfaces (loaned, list > $1M) Cisco 760x Juniper T640 (Chicago) Level(3) OC192/POS fibers (loaned SNV-CHI monthly lease cost ~ $220K)
8	Challenges After a loss it can take over an hour for stock TCP (Reno) to recover to maximum throughput at 1Gbits/s i.e. loss rate of 1 in ~ 2 Gpkts (3Tbits), or BER of 1 in 3.6*10¹²
9	Windows and Streams Well accepted that multiple streams (n) and/or big windows are important to achieve optimal throughput Effectively reduces impact of a loss by 1/n, and improves recovery time by 1/n Optimum windows & streams changes with changes (e.g. utilization) in path, hard to optimize n Can be unfriendly to others
10	Even with big windows (1MB) still need multiple streams with Standard TCP Above knee performance still improves slowly, maybe due to squeezing out others and taking more than fair share due to large number of streams Streams, windows can change during day, hard to optimize
11	New TCP Stacks Reno (AIMD) based, loss indicates congestion Back off less when see congestion Recover more quickly after backing off Scalable TCP: exponential recovery Tom Kelly, Scalable TCP: Improving Performance in Highspeed Wide Area Networks Submitted for publication, December 2002. High Speed TCP: same as Reno for low performance, then increase window more & more aggressively as window increases using a table Vegas based, RTT indicates congestion Caltech FAST TCP, quicker response to congestion, but …
12	Stock vs FAST TCP MTU=1500B Need to measure all parameters to understand effects of parameters, configurations: Windows, streams, txqueuelen, TCP stack, MTU, NIC card Lot of variables Examples of 2 TCP stacks FAST TCP no longer needs multiple streams, this is a major simplification (reduces # variables to tune by 1)
13	Jumbo frames Become more important at higher speeds: Reduce interrupts to CPU and packets to process, reduce cpu utilization Similar effect to using multiple streams (T. Hacker) Jumbo can achieve >95% utilization SNV to CHI or GVA with 1 or multiple stream up to Gbit/s Factor 5 improvement over single stream 1500B MTU throughput for stock TCP (SNV-CHI(65ms) & CHI-AMS(128ms)) Complementary approach to a new stack Deployment doubtful Few sites have deployed Not part of GE or 10GE standards
14	TCP stacks with 1500B MTU @1Gbps
15	Jumbo frames, new TCP stacks at 1 Gbits/s
16	Other gotchas Large windows and large number of streams can cause last stream to take a long time to close. Linux memory leak Linux TCP configuration caching What is the window size actually used/reported 32 bit counters in iperf and routers wrap, need latest releases with 64bit counters Effects of txqueuelen (number of packets queued for NIC) Routers do not pass jumbos Performance differs between drivers and NICs from different manufacturers May require tuning a lot of parameters
17	Who needs it? HENP – current driver Data intensive science: Astrophysics, Global weather, Fusion, sesimology Industries such as aerospace, medicine, security … Future: Media distribution Gbits/s=2 full length DVD movies/minute 2.36Gbits/s is equivalent to Transferring a full CD in 2.3 seconds (i.e. 1565 CDs/hour) Transferring 200 full length DVD movies in one hour (i.e. 1 DVD in 18 seconds) Will sharing movies be like sharing music today?
18	What’s next? Break 2.5Gbits/s limit Disk-to-disk throughput & useful applications Need faster cpus (extra 60% MHz/Mbits/s over TCP for disk to disk), understand how to use multi-processors Evaluate new stacks with real-world links, and other equipment Other NICs Response to congestion, pathologies Fairnesss Deploy for some major (e.g. HENP/Grid) customer applications Understand how to make 10GE NICs work well with 1500B MTUs
19	More Information Internet2 Land Speed Record Publicity www-iepm.slac.stanford.edu/lsr/ www-iepm.slac.stanford.edu/lsr2/ 10GE tests www-iepm.slac.stanford.edu/monitoring/bulk/10ge/ sravot.home.cern.ch/sravot/Networking/10GbE/10GbE_test.html TCP stacks netlab.caltech.edu/FAST/ datatag.web.cern.ch/datatag/pfldnet2003/papers/kelly.pdf www.icir.org/floyd/hstcp.html Stack comparisons www-iepm.slac.stanford.edu/monitoring/bulk/fast/ www.csm.ornl.gov/~dunigan/net100/floyd.html
20	Impact on others