Available bandwidth measurement as simple as running wget D. Antoniades, M. Athanatos, A. Papadogiannakis, P. Markatos Institute of Computer Science (ICS), Foundation for Research & Technology Hellas (FORTH) C. Dovrolis College of Computing, Georgia Institute of Technology Passive and Active Measurement Conference (PAM) 2006 Presented by Ryan 10 July 2006

Outline Introduction Background Measurement Methodology  Tool - abget Validation Measurement

Introduction End-to-end available bandwidth  Routing and traffic engineering  QoS management  Overlay network

Introduction Existing tools and techniques  e.g. pathload, IGI/PTR and Spruce  Requiring access at both ends of the measured path  Based on UDP and ICMP protocols

Introduction New tool – abget  Requiring access only at the receiving host The sender can be any TCP-based server  Working with TCP packets  Similar estimation methodology to pathload

Background The term “available bandwidth”  Several definitions Link capacity Residual bandwidth Achievable bandwidth

Background  Link capacity Maximum data rate a flow that can utilize when there are no other traffic flows sharing the link End-to-end capacity, C  C = min{C 1,C 2,…C N }  C i is the capacity of link i

Background  Residual bandwidth Unutilized capacity of a path End-to-end available bandwidth, U .  where is the unutilized capacity, C i is the capacity and u i (t, t +τ) is the average link utilization (in normalized unit from 0 to 1) in the interval [t, t +τ) of the link i Adopted in this paper (and pathload)

Background  Achievable bandwidth Throughput achievable by a TCP (or TCP- friendly) flow in passing through a network path End-to-end achievable bandwidth, A .  d i (t,t+τ) – the amount of data received in the interval [t, t+τ) by the receiver from sender i Adopted in our research work (many-to-one data flow analysis)

Background pathload – the basic idea  Self-Loading Periodic Streams (SLoPS) A periodic stream consists of K packets sent to the path at a constant rate R If R > A (available bandwidth), the one-way delay (OWD) of successive packets at the receiver show an increasing trend M. Jain and C. Dovrolis, “End-to-End Available Bandwidth: Measurement Methodology, Dynamics, and Relation with TCP Throughput,” IEEE/ACM Transactions on Networking, 11(4): , Aug

Background  Detection of an increasing OWD trend Partition measured (relative) OWDs = D 1, D 2,…,D K into Г= groups of Г consecutive OWDs Compute the median OWD of each group  More robust to outliers and errors Pairwise Comparison Test (PCT) ,  An increasing trend if S PCT > 0.55 if X holds otherwise

Measurement Methodology Iterative algorithm similar to SLoPS in pathload  pathload – the sender transmits periodic UDP packet streams at a certain rate  abget – TCP-based server sends packets based on TCP’s flow control and congestion control How to send packet streams at a certain rate?

Measurement Methodology The basic idea  A limited advertised window, “fake” ACKs  Receiver – acknowledges only one MMS with each ACK and advertises a window of only one MSS  Sender – is forced to send one MMS upon receiving each ACK

Measurement Methodology  To achieve a certain rate R, the “fake” ACKs should be generated periodically with a period T = MSS/R Assumption: ACKs arrived at the sender periodically

Measurement Methodology  Validation

Measurement Methodology  One-Way Delay (OWD) Estimate from the interarrivals of the received packets  s(i) – the time that the sender transmitted the ith packet  r(i) – the time that the receiver got the ith packet  o – the clock offset between the two hosts  t(i) – the interarrival time between packets i and i-1 at the receiver  d(i) – the OWD of packet i  T – the (assumed) constant interarrival time between packets i and i-1 at the sender

Measurement Methodology  OWD Estimation s(i) = s(i-1) + T r(i) = s(i) + d(i) + o t(i) = r(i) – r(i-1)  d(i) = r(i) – s(i) – o = d(i-1) + t(i) - T

Tool – abget abget, using an iterative algorithm  User specifies Probing range, [R min, R max ] Estimation resolution, w Stream length parameter, K Number of streams per probing rate, N  Probing starts at rate R min, gradually increasing the rate in increments of w until R max

Tool – abget  In each iteration Connect to the remote server (web server) and initiates a download operation Start sending K “fake” ACKs (with a period corresponds to the desired probing rate) Estimate the OWDs and compute the S PCT (same as pathload) Repeat the previous process N times

Tool – abget If more than N/2 of the streams are increasing (non-increasing), the corresponding probing rate is higher (lower) than the available bandwidth

Tool – abget  abget reports a variation range [low_bound, high_bound] Low_bound – max probing rate that was estimated as lower than the available bandwidth High_bound – min probing rate that was estimated as higher than the available bandwidth

Validation Parameters Setting  N = 5  K = 50  w = 5Mbps  R min = 0Mbps  R max = 100Mbps  T i = 500ms Measurement Duration ~ 50s

Validation In local testbed  Cross Traffic Constant-rate UDP traffic Realistic traffic trace Web Server Cross Traffic Source Cross Traffic Sink abget Client Capacity ~ 97Mbps

Validation Constant rate UDP trafficRealistic traffic trace

Validation In the monitored network path

Validation From to UoC clientwww.nytimes.comFrom UoC server to Georgia Tech client

Validation Robustness to reverse path traffic  Forward path – L D ~ 1500B  Reverse path – L A ~ 40B  The ratio L D /L A ~ 40  Few paths have such a high degree of available bandwidth asymmetry?

Measurement Measurement in the Internet  Client hosts The University of Crete (UoC), Greece The Georgia Institute of Technology, USA  Web servers (in Germany) (in France)  Measurement is performed every 10 minutes during a 24-hour period

Measurement

Conclusion Available bandwidth measurement tool – abget  Single-end  TCP  Similar to Pathload Validations and Measurements in different network paths

Duration and Overhead Trade-offs between measurement duration, overhead and accuracy  Parameters K – stream length N – number of streams w – estimation resolution T i – idle time between streams [R min, R max ] – probing range

Duration and Overhead  Measurement Duration  Measurement Overhead (in term of rate) idle time between streams No. of streams per each probing rate No. of probing rate K packets transmission time