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AF & TCP Testing on LAN

AF & TCP Testing on LAN. Octavio Medina ENSTB / IRISA. AF Testing: Roadmap. Goal of this tests. To check out if AF can be used to control BW sharing among TCP aggregates. To check how TCP is affected by UDP in an AF scenario. To calibrate the parameters of the TCM.

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AF & TCP Testing on LAN

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  1. AF & TCPTesting on LAN Octavio Medina ENSTB / IRISA

  2. AF Testing: Roadmap

  3. Goal of this tests • To check out if AF can be used to control BW sharing among TCP aggregates. • To check how TCP is affected by UDP in an AF scenario. • To calibrate the parameters of the TCM. • No relationship with RTT dependency. • All flows have the same RTT.

  4. Test Topology • Single station generates test flows • UDP background traffic • TCP test flows (differentiated by port no.) • Differentiation is assured by router before bottleneck • Classification/Marking on input interface • Color-based discrimination (WRED) on output iface. TCP Flows 50 Mbps WRED UDP trTCM

  5. Logic Topology TCP: 4 aggregates 10 flows/aggregate TCM tcp aggregate marking tcp tcp 4 Mbps tcp 3 Mbps 50 Mbps WRED 2 Mbps tcp tcp 1 Mbps UDP: single stream @ 0, 15, 30, 45 Mbps. always Red tcp tcp UDP

  6. WRED Configuration • Same as last time random-detect random-detect exp3 random-detect precedence 2 1 20 2 random-detect precedence 4 25 50 10 random-detect precedence 6 63 64 100 0.5 0.1 20 25 50 64

  7. TCM Configuration re rc be bc     • TCM uses 2 token buckets • Tc(rc , bc) • Te(re , be) • Idea: Use rc as reference parameter • Tc(rc , arc) • Te(brc , abrc) • Test to find best valuesof a and b.

  8. Test 0: TCP without AF • BW is shared equally among aggregates • TCP considerably affected by UDP

  9. Test 1: find the right a • a defines the size of the bucket • a = b/r (Ex: r= 500KB/s, a=0.1  b=50KB) (tested from 0.1 to1.0) • Results almost independent of a!

  10. Test 2: find the right b • b defines the behavior of 2nd token bucket • b = Te/Tc

  11. Test 2: find the right b • When b is too small, more red packets are produced. • “Red” bandwidth is shared equally. • Differentiation is reduced in the absence of BG traffic

  12. Test 2: find the right b • When b is too big, differentiation is reduced in high congestion scenarios. • There are too many yellow packets.

  13. Test 2: find the right b • However, increasing the value of b increases the BW obtained by TCP. • Less TCP packets at the same level as UDP (red).

  14. Test 3: test another sharing policy • Test with chose values • a = 0.1 • b = 2.5 tcp aggregate marking tcp tcp 6 Mbps tcp 1.5 Mbps 50 Mbps WRED 1.5 Mbps tcp tcp 1 Mbps Found out that a can not be too big. IOS limits the token size to 200KB. tcp tcp UDP

  15. Test 3: test another sharing policy • Differentiation is more effective when UDP is active (if no UDP, when does WRED start?). • Under congestion, there is good differentiation, but high-rate aggregate fails to obtain desired rate (60%).

  16. Conclusion • TCP can effectively be protected from UDP if flows use different marking. • Application 1. • BW sharing can be controlled at the aggregate level, specially in congested links. • Application 2. • We must be aware that this results were obtained on an homogeneous RTT scenario.

  17. Perspectives • Try smaller values for a. • IOS also limits bucket size to 8KB. • Try other marking schemes • Excess TB before committed TB… • Imagine scenario for testing with different RTTs.

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