Bandwidth Metrics and Bandwidth Metrics and Measurement ToolsMeasurement Tools

Xin, Lu

High-Performance Computing Group

Computer Science University of Windsor

Bandwidth MetricsBandwidth 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.gov/NMWG/docs/measurements.pdf

Other Metric TermsOther 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 describethe entire path (end-to-end) as well as path’slink (hop-by-hop)characteristics.

Bandwidth Capacity vs. Bandwidth Capacity vs. Achievable Bandwidth 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]

Bandwidth Capacity vs. Bandwidth Capacity vs. Achievable Bandwidth Cont.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.

Available Bandwidth vs. Available Bandwidth vs. Bandwidth UtilizationBandwidth 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]

BTC vs. Available Bandwidth 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

BTC vs. Available Bandwidth BTC vs. Available Bandwidth Cont.Cont.

The BTC definition assumes an “ideal TCP implementation”, actually, this doesn’t 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

Passive vs. Active measurement 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 can’t extract any data pass through it.

Receiver-based vs. Sender-Receiver-based vs. Sender-based techniquesbased techniquesReceiver-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.

Sender-based techniqueSender-based technique

Advantage: Flexible deployment. Clock needn’t 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

Receiver-based techniqueReceiver-based technique

Advantage: More accurate than sender-based technique.

Disadvantage: Difficult to deployment. The clock have to be synchronized at two

ends.

Bandwidth Measurement Bandwidth Measurement TechnologyTechnologyPacket Dispersion technology

– packet pair and packet train– Self-Loading Periodic streams (SLOPS)

Variable Packet Size (VPS) technology– VPS even/odd– Tailgating technique

Packet Dispersion TechniquePacket 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, it’s also can refer to the link with minimum available bandwidth. We refer the bottleneck link to the first case.

Packet Dispersion Technique Packet Dispersion Technique Cont.Cont.Bottleneck bandwidth = packet size/ t

Packet Dispersion Technique Packet Dispersion Technique Cont.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.

Packet pair vs. packet trainPacket 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 can’t deal with.

Packet train can reduce the limitation of clock resolution.

Sophisticated tools apply both methods in their implementation. i.e. Pathrate

Packet Dispersion Technique Packet Dispersion Technique Cont.Cont.

FOR MORE INFO...

Bprobe and cprobe http://cs-people.bu.edu/carter/tools/Tools.html

Nettest http://www-didc.lbl.gov/pipechar

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

Packet Dispersion Technique Packet Dispersion Technique Cont.Cont.

FOR MORE INFO...

Pathrate http://www.cc.gatech.edu/fac/Constantinos.Dovrolis

Pipechar http://www-didc.lbl.gov/pipechar

SProbe http://sprobe.cs.washington.edu

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

Self-Loading Periodic Self-Loading Periodic Streams(SLOPS)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.

Self-Loading Periodic Streams Self-Loading Periodic Streams Cont.Cont.

FOR MORE INFO...

Pathload http://www.cc.gatech.edu/fac/Constantinos.Dovrolis

Tool Name

Active/

Passive

Method-ology

Protocol Metrics Path/Per-link

pathload Active SLOPS UDP Available bandwidth

Path

Variable Packet Size (VPS) Variable Packet Size (VPS) TechniqueTechnique Step1. Sender set TTL=1, 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 C=1/, is slope of RTT graph.

Set the TTL=2,3…n, repeat the process of step1 to 3, to

Calculate the C=1/ i – i-1

VPS technique cont.VPS technique cont.

Even-odd VPSEven-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 i+1.

Tailgating TechniqueTailgating 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

Tailgating Technique cont.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

(1…n). 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.

VPS TechnologyVPS Technology

Bing http://www.cnam.fn/reseau/bing.html

Clink http://rocky.wellesley.edu/downey/clink/

Pchar http://www.emplyees.org/~bmah/software/pchar

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

VPS Technology Cont.VPS Technology Cont.

Nettimer http://mosquitonet.stanford.edu/~laik/project/nettimer

Pathchar ftp://ftp.ee.lbl.gov/pathchar/

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...

TCP Simulation and Path FloodingTCP 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.

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

TCP Simulation and Path Flooding Cont.TCP Simulation and Path Flooding Cont.

TCP Simulation and Path Flooding Cont.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/

Bandwidth Measurement Tools Bandwidth Measurement Tools Con.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