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CprE 458/558: Real-Time Systems

CprE 458/558: Real-Time Systems. Switched LAN (SLAN). Switched LAN topology. Switch. Nodes. LAN 1. LAN 2. LAN “k”. LAN 1. LAN 2. Message transmission in SLAN. Switch. LAN “K”. Message path. LAN 1. LAN 2. Worst case channel access time (WCT). 2. Switching delay (D2).

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CprE 458/558: Real-Time Systems

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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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