1. Grid simulation (AliEn) Network data transfer model Eugen Mudnić Technical university Split -FESB

2. 2 Outline  AliEn simulation - AliEnSim  Network data transfer model for the Grid simulation model description model accuracy & performance

3. 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 ...

4. 4 AliEnSim

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7. 7 low efficiency (large RTT & congestion)

8. 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

9. 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

10. 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)

11. 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

12. 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

13. 13 a) Complete transfer is finished during startup phase Data flow can reach only reduced bandwidth allocation Φsli. Di = file size

14. 14 b) Partial transfer during startup phase where D’ i is number of bytes transferred until time t s

15. 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.

16. 16 Network test topology & performance ns-2AGNS 400files/91GByte/1GBps1320 s0.37 s 3800files/853GByte/10G Bps 6180 s1.74 s

17. 17 1GB bottleneck 5ms/10ms/20ms/30ms (fairness) aggregate throughput

18. 18 CE1 RTT=5ms CE2 RTT=10ms CE3 RTT=20msCE4 RTT=30ms throughput

19. 19 10GB bottleneck 5ms/10ms/20ms/30ms aggregate throughput

20. 20 CE1 RTT=5ms CE2 RTT=10ms CE3 RTT=20msCE4 RTT=30ms throughput

21. 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