Internet Measurement Methods

March/7/2005 Hanoch Levy, CS, TAU 1

Internet Measurement Methods

Workshop on QoSHanoch Levy

March 2005

To Start 23/3/05To Start 23/3/05


• A talks to B. • A wants to know how

well it goes. • How well it will go?

A

B

DC

The objective:


Performance Measures

• Delay: – The time it takes a packet to go from A to B.

• Loss: – Will the packet arrive or not? – What fraction of packets will get lost.

• Jitter: – What is the variability of the delay?

• Bandwidth (rate): [ “bandwidth” taken from EE]– At what rate can I transfer my bits to the destination?


What are typical performance measures

• Look at: http://special.matrixnetsystems.com/ratings/index.asp

• Round trip delay: 40ms – 700 ms• Loss: 0% - 12%

– Goes down on terrestrial links, yet high on wireless

• Jitter: 10ms, 30 ms 100 ms.• Bandwidth: depends.

http://special.matrixnetsystems.com/ratings/index.asp

http://special.matrixnetsystems.com/ratings/index.asp


The causes for problems


The causes for problems

• Sources for delay: Packets have to: – Traverse links: Propagation delay

• Function of distance – roughly speed of light, 0.1-0.2 sec around the globe

– Be transmitted: Transmission delay• Packet size / line rate

– Wait on line: Queueing delay• Number of packets * packet size/line rate

• Sources for loss: – Queue is full– Noisy line (quite uncommon today except for wireless)


Who is Who + references

• IETF: the standardization body of Internet. • IPPM = IP Performance Metrics: a working group

of measurements under IETF. • http://www.ietf.org/html.charters/ippm-charter.ht

ml• In there: find drafts for measuring:

– Delay– Loss– Delay variation (jitter).

http://www.ietf.org/html.charters/ippm-charter.html

http://www.ietf.org/html.charters/ippm-charter.html


References (2)

• Conferences: – INFOCOM – SIGCOMM – SIGMETRICS


Performance Measures and applications (1)

• Applications differ in the quality measures they require• Voice:

– Send a packet every 30 ms. – Packets must arrive at “real time” (<200 msec)– If don’t arrive makes no sense!– If arrive irregularly – confuse recipient!– Lost packets are OK if not often. major quality factors:

• Delay• Loss• Jitter


Applications (2): FTP

• FTP: File transfer protocol

• Want the file to transfer as soon as possible

• Packet delay: not important:

• Packet Loss: Directly – not important

• Packet jitter: not important

• Bandwidth: Important! (loss indirectly).


Applications (3)

• Web:– Want your page to make it in a few seconds

• SEMI real time.

• Network delay – is not major factor (since it is anyhow less than a second).

• Losses -- a factor can slow down the transfer

• “Bandwidth” (how much bandwidth is available)


Bandwidth Measurement

• The route to destination consists of routers and links.

• The delay incurred on the path:

• Where q_i = queueing delay

• l_i = latency • S/b_i = transmission delay (S=pckt size)

ni

1ii

qi

li

b

ST



• Path Capacity bandwidth (PCB):• Min_i (b_i) • Interpretation: If the pipes were in my hands –

how much could I push? • Path Available Bandwidth (PAB):• Min (b_i-c_i) where c_i is the cross traffic. • Interpretation: how much BW can (will) I get.


Bandwidth Measurement (3) : Packet pair

• Send a packet pair (two packets back to back) on the route

• Property: the arrival time difference is equal to the transmission delay over the bottleneck (S. Keshav 91 ):

)/(max01iinn bStt

)/()(min 01nnii ttSb


Bandwidth Measurement (4) : Packet pair: Explanation

Bandwidth

Time

Bottleneck Link


Bandwidth Measurement (5) : Packet pair: Conditions

• The routers on the path are store and forward

• The two packets are sent sufficiently close to one another

• Both packets take the same route to the destination.

• There are no multi-channel links.

• There is no cross traffic!


Bandwidth Measurement (5) : Packet pair

• If no cross traffic: Measures PCB

• If there is cross traffic and routers use Fair Queueing measures PAB

• Fair Queueing: – Will explain in the sequel– More or less divides the channel to “pieces”

where each application gets it share of the channel.


Bandwidth Measurement : What we want on the project

• Want to get the route where one can push the data as much as possible.

• Want the route with the highest Available BW:– Better a pipe of 100MByte with 30Mbyte avail

than 200MB with 20 avail



• Carter and Mark E. Crovella 96• Bprobe: pairs of packets sent for a roundtrip• Use echo packets (ICMP) by the sender• Send several pairs• Use histograms to clean those affected by

cross traffic• Measures PCB • Measures round-trip BW • Does not need receiver cooperation


A histogram C&C


Another histogram



• Carter and Mark E. Crovella 96• Cprobe: Send a train of packets • Measures PAB (avail BW)• Again: packets are ICMP Does not require target cooperation Measures only the round trip BW • Train length: used several trains of 8 packets• Do ICMP represent real traffic?

– (low priority at routers)


Bandwidth Measurement: Train accuracy

• Examine the train value against the available BW of a real stream


Bandwidth Measurement : Issues (1)

• How large should the train be? – Too small train may not represent reality

– Too large:• Waist “ammunition”

• May affect the BW on the route (if very large!)

• How frequently should we send it? – Too low frequency: What you see now is not what will

happen later (traffic on network changes)

– Too high frequency: • Waist “ammunition”

• May affect the BW on the route (if very large!)



• Should we use ICMP or regular packets?– ICMP: A special IP packet that when sent to destination,

destination returns it right away. – Used to implement ping. – Advantage: Can be used for measurement without

cooperation of other side. – Disadvantages:

• Round-trip and not one-way.• Does not reflect the REAL TRAFFIC• Routers on the route may treat ICMP differently

– Give low priority– Drop



• Should we measure the real transaction?– Reflects the real traffic best– If data is not used at other end – then we

wasting data.

• If we measure the real transaction (FTP, say):– What kind of window should we use to estimate

the BW (mix of control and measurement)


In case you have Questions

• [email protected]• hi, i'm writing from italy, my name is david

• i saw you wrote:

• *******************************************************

• > By the way, I have a question ...

• > What's the difference between a bottleneck b/w and an available b/w?

• > Which of b/w's can "pathchar" give me?

• The available bandwidth along a path between two Internet hosts is

• equal to the bandwidth at the bottleneck. In other words, in the

• context of pathchar, they're the same thing.

• ********************************************************

• yes, but pathchar doen't work with crosstraffic. the vps(variable packet

• size) works

• with a empty link, don't it?


References (1)

• Internetworking with TCP/IP By Douglas E. Comer, Prentice Hall 1995• Van Jacobson. Congestion avoidance and control. In SIGCOMM ’88

Conference Proceedings, pages 314-329, Stanford, CA, USA, August, 1998.

• Van Jacobson. Pathchar - a tool to infer characteristics of Internet paths. Presented at the Mathematical Sciences Research Institute (MSRI); Slides available from ftp://ftp.ee.lbl.gov/pathchar/, April 1997.

• S. Keshav - "Congestion Control in Computer Networks". Ph.D Dissertation.Department of EECS at UC Berkeley, August 1991.

• Vern Paxson. Measurements and Analysis of End-to-End Internet Dynamics. Ph.D. dissertation, University of California, Berkeley, April 1997.

•


References (2)

• Robert L. Carter and Mark E. Crovella. Measuring bottleneck link speed in packet-switched networks. Technical Report TR-96-006, Boston University Computer Science Department, Boston, MA, USA, March 1996.

• Constantinos Dovrolis, Parameswaran Ramanathan, David Moore What Do Packet Dispersion Techniques Measure In Proceedings of IEEE INFOCOM 2001 http://www.cs.utk.edu/~dunigan/pktprb.ps.

• Kevin Lai, Mary Baker, Nettimer: A Tool for Measuring Bottleneck Link Bandwidth, In Proceedings of the USENIX Symposium on Internet Technologies and Systems March 2001

• Kevin Lai and Mary Baker. Measuring link bandwidth using a deterministic model of packet delay. In SIGCOMM 2000 Conference Proceedings, Stockholm, Sweden, August 28-September 01, 2000.

http://citeseer.nj.nec.com/rd/91024091%2C479183%2C1%2C0%2CDownload/http%3AqSqqSqwww.cs.utk.eduqSq%7EduniganqSqpktprb.ps













References (3)

• Allen B. Downey. Using pathchar to estimate Internet link characteristics. In SIGCOMM ’99 Conference Proceedings, pages 241–250, Cambridge, MA, USA, August 31–September 3, 1999. ACM SIGCOMM Computer Communication Review, 29(4).

• W. Jiang, T. F. Williams, Detecting and measuring Asymmetric Links in IP Network, Tech Rep, CUCS-009-99, Columbia University, 1999 http://www.cs.columbia.edu/~wenyu/papers/asym-gi99-ea.ps.

• J. Postel. Internet control message protocol. Request for Comments (Standard) 792, Internet Engineering Task Force, September 1981.

• http://bandwidthplace.com/speedtest/

• Kapoor, Chen, Lao, Gerla and Sanadid, “CAProbe: A simple and accurate capacity estimation technique,” SIGCOMM’ 04, August 2004

http://citeseer.nj.nec.com/rd/91024091%2C500287%2C1%2C0%2CDownload/http%3AqSqqSqwww.cs.columbia.eduqSq%7EwenyuqSqpapersqSqasym-gi99-ea.ps












http://bandwidthplace.com/speedtest/

Internet Measurement Methods

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