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Bandwidth Estimation: Metrics Mesurement Techniques and Tools By Ravi Prasad, Constantinos Dovrolis, Margaret Murray and Kc Claffy IEEE Network, Nov/Dec 2003. Presented by Sundar P Subramani. Outline. Introduction Metrics Capacity Available bandwidth

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presented by sundar p subramani

Bandwidth Estimation: Metrics Mesurement Techniques and ToolsBy Ravi Prasad, Constantinos Dovrolis, Margaret Murray and Kc ClaffyIEEE Network, Nov/Dec 2003

Presented by

Sundar P Subramani

outline
Outline
  • Introduction
  • Metrics
    • Capacity
    • Available bandwidth
    • TCP throughput and Bulk transfer capacity
  • Bandwidth estimation techniques
  • Taxonomy of tools
  • Conclusion
introduction
Introduction
  • Bandwidth
    • Physical layer – Spectral width of electromagnetic signals
    • Data networks – Data rate
  • In this paper they discuss about the data networks
why b w estimation needed
Why b/w estimation needed?
  • P2P applications form user-level networks based on b/w between them
  • Overlay n/w s configure routing tables based on b/w of the links
  • Service agreements between n/w provider and consumer done based on b/w availability at crucial points of the n/w
why can t snmp be used
Why can’t SNMP be used?
  • Network administrators can read router/switch information using SNMP protocol
  • End-to-end bandwidth estimation cannot be done in the above way
outline1
Outline
  • Introduction
  • Metrics
    • Capacity
    • Available bandwidth
    • TCP throughput and Bulk transfer capacity
  • Bandwidth estimation techniques
  • Taxonomy of tools
  • Conclusion
hops and segments
Hops and segments
  • Segment
    • Links at layer 2
      • Physical point-to-point link
      • Virtual circuit
      • Shared access LAN (ETHERNET, FDDI)
  • Hop
    • Links at layer 3
      • Sequence of segments connected by switches, bridges and other layer 2 devices
  • Path p from s to v
    • Sequence of hops from s to v
capacity
Capacity
  • Transmission rate limited by
    • Capacity of the physical link
    • Speed of the transmitter/receiver hardware
  • Overhead in Layer 2 in terms of encapsulation and framing produces lower rate as far as layer 3 is concerned
capacity1
Capacity
  • Tx time of IP packet of size LL3 in a link of capacity CL2 is
    • Where,

HL2 is the length of the layer 2 header

capacity2
Capacity
  • Capacity of a hop
    • Maximum possible IP layer transfer rate at that hop
    • Maximum layer 2 transfer can occur only with MTU sized packets
    • Bit rate mesured at IP layer transferring MTU sized packets
capacity of a path
Capacity of a path
  • Minimum link capacity determines capacity of the path
  • Where
    • H is the number of hops
    • Ci Is the capacity of the ith hop
problems
Problems
  • Traffic shapers
  • Rate limiters
  • Wireless networks like 802.11
    • Operate at different rates
      • 11, 5.5, 2 or 1 Mbps
      • Definition holds during time at which the capacity remains constant
average utilization
Average utilization
  • At any time
    • Link used fully  utilization =1
    • Not used  utilization =0
  • Avg utilization from time t-α to t is given by
utilization of a link
Utilization of a link

Link used 8 out of 20 time slots until T

So the link utilization is 40%

available bandwidth
Available bandwidth
  • Let ui be the average utiliztion of the link i over a period of time
  • Let Ci be the capacity of the hop i
  • Then the available bandwidth during that period
    • Ai = (1 – ui) Ci
  • Available bandwidth along the path
assumptions
Assumptions
  • Link utilization remains constant over the duration of mesurement
    • Reasonable for short intervals
    • Load variations impact the measurement over a long period
  • So available b/w mesurements should be done quickly
    • Since capacity remains constant those measurements need not be made quickly
tcp throughput and bulk transfer capacity
TCP throughput and Bulk transfer capacity
  • TCP throughput depends on various parameters
    • Congestion window
    • RTT
    • Slow start mechanism
    • Capacity and load along the path
  • BTC
    • Maximum capacity obtainable by a TCP connection
difference between btc and available b w
Difference between BTC and available b/w
  • BTC is TCP specific
    • Available b/w is transport protocol independent
  • BTC depends on the how a TCP connection throughput is affected by other flows
    • Available b/w assumes average load remains constant and estimates additional bandwidth
outline2
Outline
  • Introduction
  • Metrics
    • Capacity
    • Available bandwidth
    • TCP throughput and Bulk transfer capacity
  • Bandwidth estimation techniques
  • Taxonomy of tools
  • Conclusion
variable size packet probing
Variable size packet probing
  • Measures capacity of each hop
  • Measure RTT
  • Limit packet propogation by TTL
  • Uses ICMP to measure RTT until that hop
variable size packet probing1
Variable size packet probing
  • RTT includes:
    • Serialization delay
      • Delay to send packet of length L across channel of capacity C = L/C
    • Propogation delay
      • Time taken to traverse the link
    • Queuing delay
      • Delay in routers/Switches
variable size packet probing2
Variable size packet probing
  • Send multiple packets and calculate minimum RTT
    • Assumption: for minimum RTT no queuing delay
  • RTT has two terms
    • Delay independent of packet size = α
    • Based on packet size

where

packet pair dispersion probing
Packet pair dispersion probing
  • Measures end-to-end capacity
problems1
Problems
  • Assumption that no other traffic exists is not real
  • Existing traffic can increase/decrease the estimate
  • Solution?
    • Send multiple pairs and get a statistical estimate
      • Does not always yield a correct estimate
self loading periodic streams
Self-loading periodic streams
  • Measures end-to-end available bandwidth
  • Sends k packets at different rates
  • Receiver notifies the “one way delay trends”
  • If stream rate greater than available b/w
    • One way delay will grow large
  • Else
    • Packets will not make the one way delay large
train dispersion probing
Train dispersion probing
  • Similar to packet pair dispersion probing
  • Instead of sending just two packets send a train of packets
  • Calculate the average dispersion rate
taxonomy of estimation tools per hop capacity estimation tools
Taxonomy of estimation tools Per-hop capacity estimation tools
  • Pathchar
    • First tool to implement
  • Clink
    • On routing instability collects data along all paths
    • Until one path provides statistically significant estimate
  • Pchar
    • Uses linear regression algorithms
taxonomy of estimation tools end to end capacity estimation tools
Taxonomy of estimation tools end-to-end capacity estimation tools
  • BProbe
    • Uses packet pair dispersion
    • Uses variable sized packets to improve efficiency
    • Access needed only in sender side, uses ICMP messages
  • Nettimer
    • Uses sophisticated “kernel density algorithm” to provide better accuracy
  • Pathrate
  • Sprobe
available bandwidth estimation tools
Available bandwidth estimation tools
  • CProbe
    • Measures dispersion of a train of eight maximum sized packets
    • It measures dispersion rate and not available bandwidth
    • Dispersion rate depends on all links of the path and the train’s initial rate
    • Available b/w depends only on tight link of the path
  • Pathload
    • Implements SLoPS
    • Used UDP and requires access at both ends
    • Reports range
      • Center represents the average
      • Range represents values during mesurement period
tcp throughput and btc measurement tools
TCP throughput and BTC measurement tools
  • Treno
    • emulates TCP sends UDP packets to receiver
    • Replies with ICMP port unreachable
    • Does not require access to remote end
    • ICMP rate limited
      • Accuracy of Treno affected
  • Cap
    • More accurate than Treno
    • Uses UDP for TCP data and ACK
    • Requires access at both ends
intrusiveness
Intrusiveness
  • If probe packets comparable to available b/w
  • VPS are non intrusive
    • One packet per RTT
  • PPTD tools create bursts which last only for a very short duration
    • Only a small fraction of available b/w used
  • BTC tools are intrusive
    • They capture all b/w for a specific duration