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CprE 458/558: Real-Time Systems

CprE 458/558: Real-Time Systems. Real-Time Networks – WAN Channel establishment. QoS metrics: types of constraint. Metrics and their nature End-to-end delay: additive metric, path metric Delay jitter: additive metric, path metric Bandwidth: convex (min), link metric

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CprE 458/558: Real-Time Systems

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  1. CprE 458/558: Real-Time Systems Real-Time Networks – WAN Channel establishment CprE 458/558: Real-Time Systems (G. Manimaran)

  2. QoS metrics: types of constraint Metrics and their nature • End-to-end delay: additive metric, path metric • Delay jitter: additive metric, path metric • Bandwidth: convex (min), link metric • Packet loss: multiplicative, path metric Theorem: A problem with two or more path constraints is NP-Complete, assuming the constraints are independent and the values are real. CprE 458/558: Real-Time Systems (G. Manimaran)

  3. QoS routing problem instances Given a graph G(V,E), with each edge labeled with (cost, delay, available bw). • Bandwidth-constrained least-cost routing • Polynomial time problem • Solution: shortest path algorithm with suitable modification • Delay-constrained, bandwidth constrained, least-cost routing • NP-complete problem • Heuristics exists CprE 458/558: Real-Time Systems (G. Manimaran)

  4. Channel establishment – QoS routing • Source Routing • Source computes the routing path • Obtaining global state is difficult • Not scalable • Distributed Routing (hop-by-hop) • Each node decides what is the next hop • Lack of global knowledge  inferior paths • Scalable • Hierarchical Routing • Based on aggregate state information • Scalable (works well for inter-domain routing) • Compromise between source and distributed routings CprE 458/558: Real-Time Systems (G. Manimaran)

  5. Choose the entire path from source to destination Source Routing Connection 1 1 S D • The source has the entire network state information (cost, delay, etc.. of each edge) CprE 458/558: Real-Time Systems (G. Manimaran)

  6. Distributed / Hop-by-hop Routing Connection 1 1 S D CprE 458/558: Real-Time Systems (G. Manimaran)

  7. Hierarchical Routing S D CprE 458/558: Real-Time Systems (G. Manimaran)

  8. Hierarchical Routing Routing based on precise state 1 Routing based on aggregate state S Routing based on precise state D CprE 458/558: Real-Time Systems (G. Manimaran)

  9. QoS Source Routing Choose the path from source to destination that satisfies the QoS requirements based on some heuristic function Connection 1 With some QoS requirements 1 S D • The source has the entire network state information (cost, delay, etc.. of each edge) CprE 458/558: Real-Time Systems (G. Manimaran)

  10. QoS Hop-by-hop Connection setup No outgoing edge satisfies the required QoS Therefore, back off Connection 1 With some QoS requirements 1 S D CprE 458/558: Real-Time Systems (G. Manimaran)

  11. Channel establishment – Resource reservation • Once a feasible path is found, resources such as bandwidth, buffers are reserved along the path • Resource Reservation Protocol (RSVP) • Receiver-driven protocol • Supports multicast as well as unicast • Provides different type of reservation styles CprE 458/558: Real-Time Systems (G. Manimaran)

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