SIGCOMM 2002 New Directions in Traffic Measurement and Accounting Focusing on the Elephants, Ignoring the Mice Cristian Estan and George Varghese University of California, San Diego

SIGCOMM 2002 Talk outline Problem definition Sample and hold Multistage filters Validation, measurements Conclusions

SIGCOMM 2002 Traffic analysis today Router Fast link Measurement module Sampled packets Workstation Large raw data Collection and analysis software Concise analysis results Offline analysis

SIGCOMM 2002 Our research agenda Router Real-time analysis Is it doable? Is it better? Fast link Measurement module Concise analysis results

SIGCOMM 2002 What is traffic analysis used for? Network planning: need to know traffic between pairs of networks (traffic matrix) Accounting: usage based billing Detecting DoS attacks: flood attacks Application characterization: breaking up the traffic based on port numbers …

SIGCOMM 2002 Common abstractions Packets are grouped together into streams based on header fields  Traffic matrix – by source and destination AS  DoS attacks – by destination IP address Measuring large streams (this paper) Estimating the number of active streams (poster) …

SIGCOMM 2002 Why is measuring streams hard? Cheap memories (DRAM) are too slow to count all packets Fast memories (SRAM) are too small to keep counters for all streams Opportunity: elephants matter, mice don’t Problem: usually we don’t know in advance which streams are large

SIGCOMM 2002 Problem definition Given a fixed definition for streams, measure large streams accurately  Large = above 1% of link capacity over a 1 minute interval Assumptions  Mice don’t matter  Accuracy of results important

SIGCOMM 2002 Talk outline Problem definition Sample and hold Multistage filters Validation, measurements Conclusions

SIGCOMM 2002 How does sample and hold work? stream memory stream1 1 Sample Insert

SIGCOMM 2002 How does sample and hold work? stream memory stream1 1stream1 2 Update

SIGCOMM 2002 How does sample and hold work? stream memory stream1 2 stream2 1 Sample Insert

SIGCOMM 2002 Why is sample & hold better? uncertainty Sample and hold Ordinary sampling

SIGCOMM 2002 Comparing the relative error of the estimate for a stream at 1/F of the link bandwidth Memory limited to M entries How much better is it? Measure Ordinary sampling Sample and hold Error √ F/MF/M Memory accesses 1/S1

SIGCOMM 2002 Talk outline Problem definition Sample and hold Multistage filters Validation, measurements Conclusions

SIGCOMM 2002 Multistage filters Characteristics: No large stream is ever omitted Very few entries are used by small streams Better performance but implementation and tuning is more complex

SIGCOMM 2002 How do multistage filters work? stream memory Array of counters Hash(Pink)

SIGCOMM 2002 How do multistage filters work? stream memory Array of counters Hash(Green)

SIGCOMM 2002 How do multistage filters work? stream memory Array of counters Hash(Green)

SIGCOMM 2002 How do multistage filters work? stream memory

SIGCOMM 2002 How do multistage filters work? stream memory Collisions are OK

SIGCOMM 2002 How do multistage filters work? stream memory stream1 1 Insert Reached threshold

SIGCOMM 2002 How do multistage filters work? stream memory stream1 1

SIGCOMM 2002 How do multistage filters work? stream memory stream1 1 stream2 1

SIGCOMM 2002 Stage 2 How do multistage filters work? stream memory stream1 1 Stage 1

SIGCOMM 2002 Conservative update Gray = all prior packets

SIGCOMM 2002 Conservative update Redundant

SIGCOMM 2002 Conservative update

SIGCOMM 2002 Talk outline Problem definition Sample and hold Multistage filters Validation, measurements Conclusions

SIGCOMM 2002 Validation Analytical evaluation Comparison of analytical results to measured performance Comparison of full measurement devices using different algorithms

SIGCOMM 2002 On traces, algorithms much better than analysis predicts Number of stages Percentage of small streamspassingfilter (log scale) TheoryZipfActual Conservativeupdate

SIGCOMM 2002 Measurement results Setup: OC48 trace, 100,000 TCP flows, 5 second intervals, ordinary sampling - unlimited memory, sampling 1 in 16 our algorithms - 1Mbit, adapting parameters to keep it around 90% full Large streams (above 0.1%): ordinary sampling has an error of 9% sample and hold 0.075%, multistage filter 0.037%

SIGCOMM 2002 Talk outline Problem definition Sample and hold Multistage filters Validation, measurements Conclusions

SIGCOMM 2002 Our contributions Abstraction:  Real-time packet analysis abstractions can help systematize router implementations.  While the notion of elephants and mice is inherent in earlier work, we abstracted measurement of large streams - it can be used by many applications.

SIGCOMM 2002 Our contributions (2) Algorithms:  Sample and hold is a simple and efficient algorithm for identifying and measuring large streams.  Multistage filters with conservative update perform better but are more complex.  Both can be used for real-time as well as offline analysis.

SIGCOMM 2002 Our contributions (3) Validation:  Theoretical results that make no assumptions on traffic distribution  Simulations on traces are orders of magnitude better  Preliminary hardware design (John Huber) indicates feasibility at OC192 speeds

SIGCOMM 2002 Thank you!

SIGCOMM 2002 Optimizations to sample and hold Preserving entries: Keep large entries from one measurement interval to the next  Reduces error by a factor of 6 Early removal: Quickly remove entries that do not accumulate much traffic  Reduces memory usage by 25%

SIGCOMM 2002 Optimizations to multistage filters Preserving entries: Keep large entries from one measurement interval to the next  Reduces error by a factor of 5 Shielding: Large streams identified in previous intervals don’t pass through the filter  Reduces memory usage by up to 70%