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- Introduction (motivation, needs,..)
- Basic principles
- Path characteristics and the examples of packet pair dispersion delays
- Bandwidth estimation
- ABwE versus Iperf
- Conclusions
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- The HEP community is increasingly dependent on networking as internal
cooperation grows (needs transfer huge amount of data between
experimental sites as SLAC,CERN,etc. and home institutes spread over the
world)
- Our main task is to provide the physicists reliable access to the
network (and the integral part of this activity is NETWORK MONITORING)
- We have several monitoring system in operation (active: as ping or
iperf, and passive: reading SNMP counts or using netflows data
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- Network administrators and the users need to know RTT,losses, routing
path, and estimations of available bandwidth to our partners
- Currently we have such information in limited sampling periods.The big
question is. Do we have valid information if we do measurements once per
90 minutes and can we do measurements with tools as Iperf or to transfer
the test files more frequently? Probably no.
- We need a tool that could be used
in continuous mode 24 hours a day 7 days a week which can quickly and
non intrusively detect changes on multiple path
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- Tool based on dispersion techniques which doesn’t pollute Internet (and overload an
entry point to the Internet) with huge amount of testing packets
- Get the result from one path during in a few seconds and produce results
that could be easily preprocessed by graphical tools or enter to other
systems (prediction, warning etc.)
- Easily configurable and manageable from one site
- We evaluated several tools using dispersion techniques but none of them
in their current implementation met our demands.(Some of them were
slow,some of them failed for high capacity paths and some of them were
just technically too complicated).
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- ABwE is based on the simplest way of probing (using only Packet pairs)
- Evaluation is based on detailed technical analysis of how the packets
pass via queuing devices
- Complete path is cascade of queuing devices with different capacities
- The separation of probing packets will happen even if there is no cross
traffic
- The final dispersion PP1 and PP2 is the results of superposition of many
factors
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- Using Netdyn package (package from University of Maryland 1991)
- 20 packets pairs probes for each path
- Probes are repeated with the period 20 msec and once a minute per each
path. Set of 20 probes is called
bunch. The bunch is evaluated as one statistical set of measurements.
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- How to configure Iperf to achieve
maximum performance in
changing environment
- ( difference ~ 10 - 100 %)
- Limitation on the Entry-points to the Internet (SLAC 622Mbits, customer
load (10% - 40% )
- Machine performance (400-550 Mbits)
- Iperf aggressiveness (it suppress bandwidth of other running
applications) and reports all what Iperf transferred
- Synchronization problem to avoid dependency
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- We have demonstrated several network analysis and
- a new method for monitoring ABw
and bottleneck capacity in the range several Mbits to 1000 Mbits
- ABwE is a non intrusive method which can be run in
- a continuous mode 24 hours a
day 7 days a week
- It can detect changes in the path capacity based on heavy traffic and
also discover dramatic changes in routing. The usefulness of ABwE has
been proven several times since last summer
- Unfortunately, ABwE still doesn’t exists as a publicly used tool
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