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3/4/2004Hanoch Levy, CS, TAU1 Internet Measurement Methods Workshop on QoS Hanoch Levy Feb 2004.

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Presentation on theme: "3/4/2004Hanoch Levy, CS, TAU1 Internet Measurement Methods Workshop on QoS Hanoch Levy Feb 2004."— Presentation transcript:

1 3/4/2004Hanoch Levy, CS, TAU1 Internet Measurement Methods Workshop on QoS Hanoch Levy Feb 2004

2 3/4/2004Hanoch Levy, CS, TAU2 A talks to B. A wants to know how well it goes. How well it will go? A B D C The objective:

3 3/4/2004Hanoch Levy, CS, TAU3 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: –At what rate can I transfer my bits to the destination?

4 3/4/2004Hanoch Levy, CS, TAU4 What are typical performance measures Look at: index.asp 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.

5 3/4/2004Hanoch Levy, CS, TAU5 The causes for problems

6 3/4/2004Hanoch Levy, CS, TAU6 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 Line rate / packet size –Wait on line: Queueing delay Number of packets * line rate / packet size Sources for loss: –Queue is full –Noisy line (quite uncommon today except for wireless)

7 3/4/2004Hanoch Levy, CS, TAU7 Who is Who + references IETF: the standardization body of Internet. IPPM = IP Performance Metrics: a working group of measurements under IETF. charter.html charter.html In there: find drafts for measuring: –Delay –Loss –Delay variation (jitter).

8 3/4/2004Hanoch Levy, CS, TAU8 References (2) Conferences: –INFOCOM –SIGCOMM –SIGMETRICS

9 3/4/2004Hanoch Levy, CS, TAU9 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

10 3/4/2004Hanoch Levy, CS, TAU10 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).

11 3/4/2004Hanoch Levy, CS, TAU11 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)

12 3/4/2004Hanoch Levy, CS, TAU12 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

13 3/4/2004Hanoch Levy, CS, TAU13 Bandwidth Measurement 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.

14 3/4/2004Hanoch Levy, CS, TAU14 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 propagation delay over the bottleneck ( S. Keshav 91 ):

15 3/4/2004Hanoch Levy, CS, TAU15 Bandwidth Measurement (4) : Packet pair: Explanation

16 3/4/2004Hanoch Levy, CS, TAU16 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!

17 3/4/2004Hanoch Levy, CS, TAU17 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.

18 3/4/2004Hanoch Levy, CS, TAU18 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

19 3/4/2004Hanoch Levy, CS, TAU19 Bandwidth Measurement 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

20 3/4/2004Hanoch Levy, CS, TAU20 A histogram C&C

21 3/4/2004Hanoch Levy, CS, TAU21 Another histogram

22 3/4/2004Hanoch Levy, CS, TAU22 Bandwidth Measurement 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)

23 3/4/2004Hanoch Levy, CS, TAU23 Bandwidth Measurement: Train accuracy Examine the train value against the BW of a real stream

24 3/4/2004Hanoch Levy, CS, TAU24 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!)

25 3/4/2004Hanoch Levy, CS, TAU25 Bandwidth Measurement : Issues (2) 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

26 3/4/2004Hanoch Levy, CS, TAU26 Bandwidth Measurement : Issues (3) 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.

27 3/4/2004Hanoch Levy, CS, TAU27 In case you have Questions 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?

28 3/4/2004Hanoch Levy, CS, TAU28 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, 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.

29 3/4/2004Hanoch Levy, CS, TAU29 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 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.

30 3/4/2004Hanoch Levy, CS, TAU30 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 J. Postel. Internet control message protocol. Request for Comments (Standard) 792, Internet Engineering Task Force, September 1981.

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