Transcript capplan
Capacity Planning for Internet Service Networks Geoff Huston NTW Track4 Issues TCP/IP Protocol Behavior Issues Usage Profile Capacity Guidelines Growth Levels Planning Issues Understand the domain of operation technical issues market issues competitive issues regulatory issues TCP/IP Protocol Issues TCP/IP is NOT a flow damped protocol end to end flow management sliding window protocol adaptive flow rate designed to probe and use max available end to end bandwidth only 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 Adaptation Steady State Available Bandwidth Data Flow Rate Rate overflow loading into network queues Time TCP/IP Protocol Issues No network-based flow control mechanism Network-based packet loss signals end systems to collapse transmission window size Varying window size allows adaptive flow metrics to adapt to changing maximum available capacity Sustained 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 other Buffering evens out individual flows, but buffers themselves behave with fluctuating load Buffering adds latency TCP/IP Protocol Issues 66% Congestive Collapse The slide to misery and packet loss 33% Data Throughput TCP/IP efficiency under congestion load 33% Traffic Level 66% TCP/IP Protocol Issues TCP vs UDP UDP-based applications Internet Phone, Video, Workgroup UDP Issues no flow control mechanism sustained use forces precedence over TCP flows increasing use of flow bandwidth negotiated protocols for these applications (RSVP) TCP/IP Protocol Issues Damping network capacity is not a demand management tool Network 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 profiles 12% Local 18% Domestic Trunk 70% International Traffic mix due to: Distance invisible applications without user control Distance independent user tariff Capacity Guidelines Link Utilisation Average 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% time greater than 50% loading for 50% time traffic bursting visible Link Usage Profile - overloaded 90% peak loading for 45% time 60% peak loading for 60% time no burst profile at peak loads imbalanced traffic (import based) Link Usage Profile - saturated visible plateau traffic load signature small load increases cause widening plateau Overall Growth Levels Two growth pressures: serviced population the 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 500 400 300 200 100 0 1 11 21 31 41 51 61 Overall Growth Levels For a changing service model the saturation point will move More intense network use by increasingly sophisticated applications 1200 1000 Technology shift 800 600 400 200 0 1 11 21 31 41 51 61 How to plan Generate a market demand model forecast 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 externalities highly dynamic competitive position poorly understood (and changing) service demand model How to plan Forward extrapolation assume existing traffic follows a general growth model forward extrapolat the growth model Good for short term planning (12 months) Cannot factor latent demand market price sensivity 4/27/97 4/17/97 4/7/97 3/28/97 3/18/97 3/8/97 2/26/97 2/16/97 2/6/97 1/27/97 1/17/97 1/7/97 12/28/96 12/18/96 12/8/96 11/28/96 11/18/96 11/8/96 10/29/96 10/19/96 10/9/96 9/29/96 9/19/96 9/9/96 8/30/96 8/20/96 8/10/96 7/31/96 7/21/96 7/11/96 7/1/96 Trend forecasting historical usage vs capacity data 120000 100000 80000 60000 Total Capacity Daily Traffic IN Daily Traffic OUT 40000 20000 0 23/8/98 27/7/98 30/6/98 3/6/98 7/5/98 10/4/98 14/3/98 15/2/98 19/1/98 23/12/97 26/11/97 30/10/97 3/10/97 6/9/97 10/8/97 14/7/97 17/6/97 21/5/97 24/4/97 28/3/97 1/3/97 2/2/97 6/1/97 10/12/96 13/11/96 17/10/96 20/9/96 24/8/96 28/7/96 1/7/96 Growth Trends 600000 500000 400000 in out Trend - high Trend - mid 300000 Trend - Low 97/98 bandwidth 200000 100000 0 Planning undertake demand and trend forecast models constantly review the model against generated usage data recognise that the larger the capacity you need the longer the lead time to purchase it recognise that the bigger the purchase the greater the requirement for capital