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Protocol Implementation

Protocol Implementation. An Engineering Approach to Computer Networking. Protocol implementation. Depends on structure and environment Structure partitioning of functionality between user and kernel separation of layer processing ( interface ) Environment data copy cost

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Protocol Implementation

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  1. Protocol Implementation An Engineering Approach to Computer Networking

  2. Protocol implementation • Depends on structure and environment • Structure • partitioning of functionality between user and kernel • separation of layer processing (interface) • Environment • data copy cost • interrupt overhead • context switch time • latency in accessing memory • cache effects

  3. Partitioning strategies • How much to put in user space, and how much in kernel space? • tradeoff between • software engineering • customizability • security • performance • Monolithic in kernel space • Monolithic in user space • Per-process in user space

  4. Interface strategies • Single-context • Tasks • Upcalls

  5. Monolithic in kernel

  6. Monolithic in user space

  7. Per-process in user space

  8. Interfaces • Single-context • Tasks • Upcalls

  9. Single context

  10. Tasks

  11. Upcalls

  12. Protocol implementation

  13. Some numbers • 10 Kbps 400 ms • 100 Kbps, 40 ms • 1 Mbps, 4 ms • 100 Mbps, 40 µs • User-to-kernel context switch ~40 µs • Copying the packet ~25 µs • Checksum in software ~40 µs • Scheduling delays ~150 µs (depends on workload) • Interrupt handling ~10-50 µs (depends on the bus) • Protocol processing ~15 -100 µs (depends on protocol complexity)

  14. Rules of thumb • Optimize common case • Watch out for bottlenecks • Fine tune inner loops • Choose good data structures • Beware of data touching • Minimize # packets sent • Send largest packets possible • Cache hints • Use hardware • Exploit application properties

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