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Real-Time Systems in Switched LAN: Analysis and Optimization

Explore worst-case channel access time and message path optimization in switched LAN topologies for efficient communication in real-time systems. Learn about CR trees and message admission tests in LAN setups.

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Real-Time Systems in Switched LAN: Analysis and Optimization

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  1. CprE 458/558: Real-Time Systems Switched LAN (SLAN) CprE 458/558: Real-Time Systems (G. Manimaran)

  2. Switched LAN topology Switch Nodes LAN 1 LAN 2 LAN “k” CprE 458/558: Real-Time Systems (G. Manimaran)

  3. LAN 1 LAN 2 Message transmission in SLAN Switch LAN “K” Message path CprE 458/558: Real-Time Systems (G. Manimaran)

  4. LAN 1 LAN 2 Worst case channel access time (WCT) 2. Switching delay (D2) 1. Access the local channel (D1) Switch 3. Access the destination channel (D3) LAN “K” Message path Total delay = D1 + D2 + D3 CprE 458/558: Real-Time Systems (G. Manimaran)

  5. Worst case channel access time (WCT) • WCT = Worst Case (source LAN access delay, D1) + Worst Case (switching delay, D2) + Worst Case (destination LAN access delay, D3) • Worst Case (source LAN access delay, D1): • This is computed for all the outgoing messages (intra-LAN and inter-LAN) • Worst Case (switching delay, D2): • This is computed only for inter-LAN messages • Worst Case (destination LAN access delay, D3): • This is computed at the source. • It is the worst case channel access time of the destination LAN • If the destination is not known, this will be the worst case access channel time for the largest (worst case) LAN CprE 458/558: Real-Time Systems (G. Manimaran)

  6. CR Trees N1 N1 N2 N5 N2 N5 N3 N3 N4 N4 N6 N7 Virtual Nodes (LAN1, LAN3) CR tree for worst-case LAN segment (LAN 2) Worst Case CR (WCCR) tree CprE 458/558: Real-Time Systems (G. Manimaran)

  7. WCT calculation – calculate D1+D2 N1 The worst case channel access time of this modified tree gives the worst case (D2 + D3) N2 N5 N3 N4 N6 N7 Virtual Nodes (LAN1, LAN3) Worst Case CR (WCCR) tree CprE 458/558: Real-Time Systems (G. Manimaran)

  8. Message Admission test Calculate the worst case local channel access time (WC1) Construct the worst case tree assuming the worst-case destination LAN By adding virtual nodes (one per LAN) Calculate the Worst case channel access time of the above constructed Tree and call it WC2 (D – t) ≥ (WC1 + WC2) New message YES Accept NO “t” is current time Reject CprE 458/558: Real-Time Systems (G. Manimaran)

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