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Grid simulation (AliEn) Network data transfer model Eugen Mudnić Technical university Split -FESB
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2 Outline AliEn simulation - AliEnSim Network data transfer model for the Grid simulation model description model accuracy & performance
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3 AliEnSim GRID simulation Discrete Event simulation (DES) Simulates AliEn (like) grid data processing/storage It can be used for: planning of resource requirements (network, storage, CPU) identifying system bottlenecks testing system scalability ...
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4 AliEnSim
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7 low efficiency (large RTT & congestion)
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8 Network data transfer model Packet based (ns-2) – accurate, slow for grid simulation, many configuration parameters Fluid based – faster but not satisfactory for the grid simulation, many configuration parameters Approximate-coarse grained model ? Requirements: fast (at least two orders of magnitude faster than ns-2) minimal number of parameters -> assumption of properly configured network satisfactory accurate for the grid simulator -> exhibits most important network limitations
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9 Very simple model Network as a set of links shared by changeable number of data streams CE1 SE1 SE2 SE3 100 MB/s 30MB/s 50 MB/s 30 MB/s 1 GB/s 100 MB/s LAN1 LAN2 LAN3 links with capacity ( C1,..CL ) N streams, every stream has a predefined transfer route ri {1,…,L} Every stream has equal priority Stream bandwidth allocation must conform to: Stream instantaneously allocate available capacity
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10 -3 10 -2 10 10 0 1 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 time[s] MBit/s 0.6ms 1.4ms 2.8ms 4.0ms 5.4ms 16.4ms 60.4ms 200.4ms TCP stream cannot instantaneously allocate available capacity TCP bandwith allocation (BIC)
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11 AGNS- approximate grid network simulation CE1 SE2 SE3 200MB/s RTT=50ms 200MB/s RTT=5ms 1 GB/s 100 MB/s LAN1 LAN2 LAN3 more complicated bandwith allocation alghoritm (not described here) includes TCP unfairness efect includes TCP bandwith allocation dynamic (startup phase) bottleneck
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12 AGNS- slow start approximation Startup phase will be simulated as: delayed start of file transfer limited bandwidth allocation for a small files TCP fairness : data flow allocated bandwidth is a function of streams RTT at the time of data flow start
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13 a) Complete transfer is finished during startup phase Data flow can reach only reduced bandwidth allocation Φsli. Di = file size
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14 b) Partial transfer during startup phase where D’ i is number of bytes transferred until time t s
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15 AGNS- approximative grid network simulation relative aggregate performance metrics will be maintained by data flow bandwidth allocation as a function of its RTT ratio to other concurrent data flows RTT state of the simulator is calculated only 3-times for each transfer !!! Results of AGNS are compared to Ns-2 simulation at aggregate level.
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16 Network test topology & performance ns-2AGNS 400files/91GByte/1GBps1320 s0.37 s 3800files/853GByte/10G Bps 6180 s1.74 s
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17 1GB bottleneck 5ms/10ms/20ms/30ms (fairness) aggregate throughput
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18 CE1 RTT=5ms CE2 RTT=10ms CE3 RTT=20msCE4 RTT=30ms throughput
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19 10GB bottleneck 5ms/10ms/20ms/30ms aggregate throughput
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20 CE1 RTT=5ms CE2 RTT=10ms CE3 RTT=20msCE4 RTT=30ms throughput
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21 simulation using AGNS model is fast it looks enough accurate to exhibit realistic congestion effects of the network traffic should be compared with real measurements Conclusion
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