Bandwidth Metrics and Measurement Tools

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Bandwidth Metrics and Measurement Tools

• Xin, Lu
• High-Performance Computing Group
• Computer Science University of Windsor

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Bandwidth Metrics

• NMWG divide bandwidth into four sub-metrics
• Bandwidth Capacity
• Achievable Bandwidth
• Available Bandwidth
• Bandwidth Utilization

FOR MORE INFO...
http//www-didc.lbl.gov/NMWG http//www-didc.lbl.g
ov/NMWG/docs/measurements.pdf
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Other Metric Terms

• Throughput
• Throughput is the same as achievable bandwidth.
• Bulk Transfer Capacity (BTC)
• Defined by RFC 3148
• BTC data_sent / elapsed_time
• The throughput of a persistent TCP transfer.
• Each of these metrics can be used to describe
• the entire path (end-to-end) as well as paths
• link (hop-by-hop)characteristics.

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Bandwidth Capacity vs. Achievable Bandwidth

• Capacity is the maximum amount of data per time
  unit that the link or path has available, when
  there is no competing traffic.
• Achievable bandwidth is the maximum amount of
  data per time unit that a link or path can
  provide to an application, given the current
  utilization, the protocol and operating system
  used, and the end-host performance capability and
  load. (Throughput )
• Reference 2

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Bandwidth Capacity vs. Achievable Bandwidth Cont.

• If a path consists of several links, the link
  with the minimum transmission rate determines the
  capacity of the path.
• While the link with the minimum unused capacity
  limits the achievable bandwidth. i.e. at
  high-speed networks, hardware configuration or
  software load on the end hosts actually limit the
  bandwidth delivered to the application.

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Available Bandwidth vs. Bandwidth Utilization

• Available bandwidth is the maximum amount of data
  per time unit that a link or path can provide,
  given the current utilization.
• Utilization is the aggregate capacity currently
  being consumed on a link or path.
• Available Bandwidth
• Bandwidth Capacity Bandwidth Utilization
• Reference 2

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BTC vs. Available Bandwidth

• Available Bandwidth is the amount of usable
  bandwidth without affecting cross-traffic,
  whereas, the BTC is measured by sending as much
  packets as possible, limiting other traffic.
• BTC is simulating steady state persistent
  flow, taking considerable time and overhead.

FOR MORE INFO...
RFC 3148 A Frame Work for Defining Empirical
Bulk Transfer Capacity Metrics
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BTC vs. Available Bandwidth Cont.

• The BTC definition assumes an ideal TCP
  implementation, actually, this doesnt exist,
  and what BTC measured is the variant of
  achievable bandwidth.

FOR MORE INFO...
RFC 3148 A Frame Work for Defining Empirical
Bulk Transfer Capacity Metrics
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Passive vs. Active measurement

• Active measurement means that the tool actively
  sends probing packets into the network.
• Passive measurement tools monitors the passing
  traffic without interfering.
• Passive measurement is appreciated, however, less
  reliable than active, as it cant extract any
  data pass through it.

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Receiver-based vs. Sender-based techniques

• Receiver-based (end-to-end) techniques usually
  use the one-direction TCP stream to probe the
  path bandwidth.
• Sender-based (echo-based) techniques force the
  receiver to reply the ICMP query, UDP echo or
  TCP-FIN.

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Sender-based technique

• Advantage
• Flexible deployment.
• Clock neednt synchronized at two ends.
• Disadvantage
• ICMP and UDP echo packets usually be rate-limited
  or filtered out by some routers.
• Round-trip is much more possibility influenced by
  cross-traffic than that of one-way delay
• Response packets may come back through a
  different path

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Receiver-based technique

• Advantage
• More accurate than sender-based technique.
• Disadvantage
• Difficult to deployment.
• The clock have to be synchronized at two ends.

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Bandwidth Measurement Technology

• Packet Dispersion technology
• packet pair and packet train
• Self-Loading Periodic streams (SLOPS)
• Variable Packet Size (VPS) technology
• VPS even/odd
• Tailgating technique

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Packet Dispersion Technique

• Sender sends two same-size packets back-to-back
  from source to sink.
• The packets will reach the sink dispersed by the
  transmission delay of the bottleneck links if
  there is no cross traffic.
• Measuring the dispersion can infer the
  bottleneck link bandwidth capacity.
• Note Bottleneck link can refer to the link with
  smallest transmission rate, its also can refer
  to the link with minimum available bandwidth. We
  refer the bottleneck link to the first case.

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Packet Dispersion Technique Cont.

• Bottleneck bandwidth packet size/ t

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Packet Dispersion Technique Cont.

• If sender sends the packets as one observation
  sample more than two, called packet train.
• Tools usually apply robust statistical filtering
  techniques to find valid samples.

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Packet pair vs. packet train

• Packet train is more likely to be interfered by
  cross traffic than packet pair.
• Packet train can be used to measure the
  bottleneck link that is multichannel while packet
  pair cant deal with.
• Packet train can reduce the limitation of clock
  resolution.
• Sophisticated tools apply both methods in their
  implementation. i.e. Pathrate

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Packet Dispersion Technique Cont.
Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link
bprobe Active Packet pair ICMP Bandwidth Capacity Path
cprobe Active Packet pair ICMP Bandwidth utilization Path
Netest Active Packet pair UDP Bandwidth capacity Path
FOR MORE INFO...
Bprobe and cprobe http//cs-people.bu.edu/carter/t
ools/Tools.html Nettest http//www-didc.lbl.gov/pi
pechar
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Packet Dispersion Technique Cont.
Pathrate Active Packet pair, packet train UDP Bandwidth capacity Path
Pipechar Active Packet train UDP Available bandwidth Per-link
Sprobe Active Packet pair TCP Bandwidth capacity Path
FOR MORE INFO...
Pathrate http//www.cc.gatech.edu/fac/Constantinos
.Dovrolis Pipechar http//www-didc.lbl.gov/pipecha
r SProbe http//sprobe.cs.washington.edu
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Self-Loading Periodic Streams(SLOPS)

• Sender sends series of packets to the sink at the
  rate of larger than the bottleneck link available
  bandwidth.
• Every packets get a timestamp at sender side.
• Compare the difference of successive packets
  timestamp and their arrival times to infer the
  available bandwidth.
• Rate-adjustment adaptive algorithm to converge to
  the available bandwidth.

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Self-Loading Periodic Streams Cont.
Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link
pathload Active SLOPS UDP Available bandwidth Path
FOR MORE INFO...
Pathload http//www.cc.gatech.edu/fac/Constantinos
.Dovrolis
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Variable Packet Size (VPS) Technique

• Step1. Sender set TTL1, send out the packet, and
  wait for the ICMP TTL-exceeded packet back.
• Step2. Upon receiving ICMP, estimate the RTT.
  Estimate the RTT multiple times for various size
  packets.The minimum RTT of various packets are
  believed to be the valid sample.
• Step3. The first link capacity is C1/b , b is
  slope of RTT graph.
• Set the TTL2,3n, repeat the process of step1 to
  3, to
• Calculate the C1/ bi bi-1

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VPS technique cont.
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Even-odd VPS

• The VPS probing technique is not altered,
  Mathematical trick to improve reliability.
• For each of the probing sizes, divide the set of
  samples into even and odd numbers.
• Calculation is based on even-odd samples. i.e.
  the even sample of link i, the odd sample of link
  i1.

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Tailgating Technique

• Tailgating technique divides into two phrase
• Phase one Like VPS probing, but for entire path
  instead of per link.
• Phase two (tailgating phase) The largest
  possible non-fragmented packet followed by a
  tailgater which is the smallest possible packet
  size (i.e 40 bytes). This causes the smaller
  packet always queue behind the larger packet.
• Reference Kevin Lai, Mary Baker Measuring Link
  Bandwidths Using a Deterministic Model of Packet
  Delay ACM SIGCOMM 2000

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Tailgating Technique cont.

• The following condition should met
• The large packet should not be queued due to
  cross traffic.
• The large packet should have a TTL field set to L
  (1n).
• The tailgater packet should be queued directly
  after the large packet on link L.
• The tailgater packet should not queued after
  having passing link L.

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VPS Technology
Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link
bing Active VPS ICMP Bandwidth capacity, loss, delay Path
clink Active VPS/ even-odd UDP Bandwidth capacity, Loss Path
Pchar Active VPS UDP, ICMP Bandwidth capacity, Loss, delay Per-link
Bing http//www.cnam.fn/reseau/bing.html Clink
http//rocky.wellesley.edu/downey/clink/ Pchar
http//www.emplyees.org/bmah/software/pchar
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VPS Technology Cont.
Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link
Nettimer Active, Passive VPS/tailgating TCP Bandwidth capacity Per-link
pathchar Active VPS/even-odd UDP, ICMP Bandwidth capacity, Loss, delay Per-link
FOR MORE INFO...
Nettimer http//mosquitonet.stanford.edu/laik/pro
ject/nettimer Pathchar ftp//ftp.ee.lbl.gov/pathch
ar/
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TCP Simulation and Path Flooding

• TCP simulation operates at two mode UDP/ICMP
  with low TTL or ICMP echo/reply. It simulates the
  TCP of using slow-start algorithm.
• Path flooding method injects TCP/UDP packets into
  the net as fast as possible within the specific
  time.
• To some degree, both TCP simulation and path
  flooding are associated with Bulk Transfer
  Capacity (BTC)metrics.

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TCP Simulation and Path Flooding Cont.
Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link
TReno Active TCP simulation UDP, ICMP BTC Path
ttcp Active Path flooding TCP, UDP Achievable bandwidth Path
iperf Active Path flooding TCP, UDP Bandwidth capacity, Loss Path
Netperf Active Path flooding TCP, UDP BTC, delay throughput Path
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TCP Simulation and Path Flooding Cont.

• TReno
• http//www.psc.edu/networking/treno_info.html
• Iperf
• http//dast.nlanr.net/Project/Iperf
• Netperf
• http//www.netperf.org/netperf/NetperfPage.html
• ttcp part of OS
• ftp//ftp.arl.mil/pub/ttcp/

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Bandwidth Measurement Tools Con.

• Reference
• 1.http//www.caida.org/tools/
• 2. Bruce Lowekamp, Brain Tierney, Les Cottrell,
  Richard Hughes-Jones, Thilo Kielmann and Martin
  Swany. A Hierarchy of Network Measurements for
  Grid Applications and Services Document (draft)
  Global Grid Forum NMWG Feb 17, 2003.
• 3. Rody Schoonderwoerd Network Performance
  Measurement Tools a comprehensive comparison
  Nov., 2002