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Networking Performance Analysis: TCP Throughput between NASA GSFC and Alaska

This report presents an analysis of network service parameters for future procurement of network services to Alaska. It includes a baseline assessment of TCP throughput between NASA's Goddard Space Flight Center in Greenbelt, MD, and Alaska. The study identifies end-to-end performance issues, compares SGI and Linux TCP stack performance, and measures performance with varied parameters such as TCP window sizes and buffer lengths. The methodology involved regular testing with Nuttcp, monitoring statistics, and tabulating results to troubleshoot and optimize TCP behavior. Significant findings indicate performance variations affected by window sizes and the necessity of specific optimizations.

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Networking Performance Analysis: TCP Throughput between NASA GSFC and Alaska

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  1. GSFC to AlaskaPerformance Results Tino Sciuto Swales Aerospace ESDIS Network Prototype Lab. NASA GSFC Greenbelt , MD

  2. Motivation • Characterize network service parameters for future purchase of network services to Alaska • Baseline TCP Throughput between NASA’s Goddard Space Flight Center in Greenbelt, MD and Alaska • Identify network as well as end-to-end performance issues • Compare SGI’s with Linux’s TCP stack performance • Measure performance with different parameters • SGI specific like tcp_gofast • Global TCP parameters like, window sizes and buffer length

  3. University Of Alaska Abilene MAX GigaPoP PNW GigaPoP GSFC Research LAN

  4. Test Info • Sender Hosts • SGI • OS IRIX 6.5 • OC-3 ATM NIC with MTU 9180 • End to end MSS was 1460 • SACK enabled • Linux • Red Hat 7.2 • GE NIC with MTU 4470 • End to end MSS was 1460 • SACK enabled • Receiver host: no specific info available • Test tool nuttcp • For IRIX : nuttcp version 3.1.9 • For Linux : nuttcp version 3.1.6 • Test Methodology • At least two minutes test runs every hour. Runs repeated on as needed basis • Wanted to reduce impact on Alaska connection (i.e. would like to continue testing ;-) • Monitored MRTG statistics on routers • Recorded routes, ping avg. and TCP throughput • Varied window and buffer length parameters to identify effects on performance • Tabulated results • Troubleshooting • Started using web100 tool in the last week to study TCP behavior • Many parameters to track (SACK, Retransmittions ….)

  5. SGI Test Results Summary Peak

  6. Linux Test Results Link Capacity ?? Excessive Window Deteriorates Performance

  7. 0.7 * Max Segment Size Bandwidth = Round Trip Time * sqrt[packet loss] Conclusions • Operation of SGI TCP stack not fully understood • Larger nuttcp buffer length results in better performance …? • Without tcp_gofast > RTT even increasing window sizes didn’t help much the SGI host • tcp_gofast essential to obtaining maximum throughput • Web100 for IRIX not available • Linux TCP stack produced expected results • Alaska to Seattle link might be OC-3 • Results seem to indicate a packet loss between E-5 and E-6 when comparing the results with the expected results using the formula Mathis, et. al

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