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Network Emulation

Network Emulation. Mihai Ivanovici Dr. Razvan Beuran Dr. Neil Davies. Quality of Service. What is “quality” for a network / application Quality is “finite” How is it Shared (between different traffic flows) Managed (at the contention points) Delivered (to the application / user)

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Network Emulation

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  1. Network Emulation Mihai Ivanovici Dr. Razvan Beuran Dr. Neil Davies

  2. Quality of Service • What is “quality” for a network / application • Quality is “finite” • How is it • Shared (between different traffic flows) • Managed (at the contention points) • Delivered (to the application / user) • Perceived (by the user) • View points • Local view (at a point in network) • Global view (end to end)

  3. Application outcomes The judgment metric: “application outcomes”

  4. Needed elements • Model of interaction between application and delivered quality from network • Environment for evaluation of existing applications • Capture process to apply to existing / proposed developments  Combine to create a well-defined methodology for assessing application performance

  5. Assessing application performance • In parallel • Measure the network QoS parameters • Assess the UPQ for the application under test

  6. Current emulators • Do exist • Mainly software based • Packet by packet systems • Independent loss and delay applied to packets – unrealistic behaviour • False packet reordering • No intra-stream contention modelled

  7. Why another emulator? • More realistic scenarios • Intra-stream and inter-stream contention • Correlated loss and delay, natural induced jitter • Phase / mode changes in network • Topology or environment changes (e.g. wireless) • More flexibility and control on the degradation models

  8. Why another emulator? (II) • Safety critical / mission critical viewpoint • How the systems operate under various network conditions • It’s not just about “normal” situations • How and when applications fail • Speeds up to 1 Gbps

  9. The hardware platform

  10. How we do it The packet processor The packet path The control path

  11. The architecture

  12. Network in a box • Predictable = reproducible network behaviour and application errors • Regression testing

  13. The “∆Q” concept Total degradation in the network = aggregation of the degradation induced by each sub-network and network element on the way

  14. Intra-stream contention • Competition for resources • Sharing the connection  THROUGHPUT • Entering the queues  LOSS • Leaving the queues  DELAY • How applications react to quality degradation • Model the effects of application behaviour on quality degradation • e.g. burst loss behaviour on TCP/IP

  15. Inter-stream contention • The total amount of degradation is shared between different streams • By use of scheduling mechanisms (e.g. SP, WRR) • Differentially treat the traffic to achieve the best application outcomes

  16. First versions • Fixed delay + one queue • Constant service time • Bandwidth limitation • Fixed delay + one queue • The effect of other traffic flows sharing the same network/path emulated as server vacations

  17. The next step • More sophisticated network models for the “server with vacations” • Aggregation of simple models of “queues” and “wires”

  18. Conclusions • We propose a methodology for assessing application performance • Network emulation • Allows a hybrid test technique • Combines the advantages of simulation and real application/networks testing

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