Capacity Planning for Internet Service Networks
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Capacity Planning for Internet Service Networks Geoff Huston NTW Track4
Transcript of Capacity Planning for Internet Service Networks
Capacity Planning forInternet Service
Networks
Geoff HustonNTW Track4
Issues
TCP/IP Protocol BehaviorIssuesUsage ProfileCapacity GuidelinesGrowth Levels
Planning Issues
Understand the domain of operationtechnical issuesmarket issuescompetitive issuesregulatory issues
TCP/IP Protocol Issues
TCP/IP is NOT a flow damped protocolend to end flow managementsliding window protocoladaptive flow rate designed to probe and use max available end to end bandwidthonly limited by end system buffering size ⌧bandwidth x delay
system buffers are getting larger as OS vendors come to understand the problem
TCP/IP Protocol Issues
TCP/IP Data Flow Rate AdaptationTCP/IP Data Flow Rate Adaptation
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Steady State Available BandwidthRate overflow loading into network queues
TCP/IP Protocol Issues
No network-based flow control mechanismNetwork-based packet loss signals end systems to collapse transmission window sizeVarying window size allows adaptive flow metrics to adapt to changing maximum available capacitySustained insufficient capacity leads to congestion induced collapse of data throughput
TCP/IP Protocol Issues
Many simultaneous TCP sessions interact with non-predictive non-uniform load (ftp://thumper.bellcore.com/pub/dvw/sigcom93.ps.Z)
Peaks start to synchronize with each otherBuffering evens out individual flows, but buffers themselves behave with fluctuating loadBuffering adds latency
TCP/IP Protocol Issues
TCP/IP efficiency under congestion loadTCP/IP efficiency under congestion load
Traffic Level
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33% 66%
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66% Congestive Collapse -
The slide to miseryand packet loss
TCP/IP Protocol Issues
TCP vs UDPUDP-based applications
Internet Phone, Video, Workgroup
UDP Issuesno flow control mechanismsustained use forces precedence over TCP flowsincreasing use of flow bandwidth negotiated protocols for these applications (RSVP)
TCP/IP Protocol Issues
Damping network capacity is not a demand management toolNetwork capacity must be available to meet peak demand levels without congestion loss
Usage Profile
Two major Internet use profiles:Business use profile⌧peak at 1500 - 1600⌧plateau 1000 - 1730
Residential dial profile⌧peak at 2030 - 2330⌧plateau 1900 - 2400
Usage Profile
Distance profiles12% Local18% Domestic Trunk70% International
Traffic mix due to:Distance invisible applications without user controlDistance independent user tariff
Capacity Guidelines
Link UtilisationAverage weekly traffic level set to 50% of available bandwidth.
Core network capacity should be dimensioned according to aggregate access bandwidth
Link Usage Profile - optimal
peak loading less than 10% timegreater than 50% loading for 50% timetraffic bursting visible
Link Usage Profile - overloaded
90% peak loading for 45% time60% peak loading for 60% timeno burst profile at peak loadsimbalanced traffic (import based)
visible plateau traffic load signaturesmall load increases cause widening plateau
Link Usage Profile - saturated
Overall Growth Levels
Two growth pressures:serviced populationthe changing Internet service model⌧more network-capable applications⌧using more bandwidth
Overall Growth Levels
For a constant service model the growth curve will exhibit demand saturation
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Overall Growth Levels
For a changing service model the saturation point will moveMore intense network use by increasingly sophisticated applications
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Technology shift
How to plan
Generate a market demand modelforecast the number of services in operation⌧existing services⌧growth rate⌧market capture level (competitive position)
forecast the average demand per service⌧dial access, leased line⌧web, ftp, usenet⌧caching trends⌧new Internet services
How to plan
demand models are typically very uncertain indicators
high level of uncertainty of externalitieshighly dynamic competitive positionpoorly understood (and changing) service demand model
How to plan
Forward extrapolationassume existing traffic follows a general growth modelforward extrapolat the growth model
Good for short term planning (12 months)Cannot factor
latent demandmarket price sensivity
Trend forecasting
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Total CapacityDaily Traffic INDaily Traffic OUT
historical usage vs capacity data
Growth Trends
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inoutTrend - highTrend - midTrend - Low97/98 bandwidth
Planning
undertake demand and trend forecast modelsconstantly review the model against generated usage datarecognise that the larger the capacity you need the longer the lead time to purchase itrecognise that the bigger the purchase the greater the requirement for capital
