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Reduced TCP Window Size for Legacy LAN QoS II

Reduced TCP Window Size for Legacy LAN QoS II. Niko F ä rber Sept. 20, 2000. Outline. Summary of previous work Basic idea: Reduce TCP window size for LAN traffic! NS simulation results 10-BASE-T measurements NS simulation for extended LAN topology Worst case scenario

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Reduced TCP Window Size for Legacy LAN QoS II

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  1. Reduced TCP Window Sizefor Legacy LAN QoS II Niko Färber Sept. 20, 2000

  2. Outline • Summary of previous work • Basic idea: Reduce TCP window size for LAN traffic! • NS simulation results • 10-BASE-T measurements • NS simulation for extended LAN topology • Worst case scenario • Is communication between T2s necessary? • NS simulation for simple traffic model • Average case scenario • Bi-directional traffic • Future work

  3. Scenario: Single Switch LAN 10/100 Legacy Switch • Voice is received from WAN • File is loaded from file server • Both have to go through buffer at output port File Server 100 A B Router C WAN bottle neck D 10 QoS provided E T2

  4. Basics Idea • Reduce TCP window size for intra-LAN traffic • No loss in throughput when: NxW = BxD • Set TCP window size according to delay constraint DMAX, e.g., • DMAX = 10 ms • B = 10 Mbps • 1480 Byte packets • N=2 connection • Advertised window in ACK can be modified in T2 without knowledge of sender/receiver W = 4 packets

  5. NS Simulation Results TCP window size 64 KB ftp start voice delay [ms] 3 KB data throughput [Mbps] time [s]

  6. 10-BASE-T Measurements TCP window size 16 KB ftp start voice delay [ms] 4 KB data throughput [Mbps] time [s]

  7. Scenario: 2 Switch LAN • Voice is received from WAN • Files are loaded from Bi to Ai • Appropriate W depends on N! • How bad is mismatch? • Is communication between T2s needed? T2 A1 A2 WAN R … S1 AN S2 QoS provided B1 B2 … BN

  8. Variation of N, W • N={1,2,4,8,16,32} x W={1,2,4,8,16,32,64} N=2 N=1 64 voice delay [ms] 32 16 8 W=1 2 4 data throughput [Mbps]

  9. Variation of N, W - stretched • Similar performance for WxN = const. • For W=4 reasonable performance for N<16 32 16 W=4 8 4 2 N=1 voice delay [ms] WxN=32 data throughput [Mbps]

  10. Scenario: N to N Communication • Voice received from WAN • Each terminal sends/receives data to/from every other terminal • Balanced N to N communication • N=8, W={4, 64} T2 A1 A2 WAN R … S AN QoS provided

  11. N-1 Bi Wi = R0 l S Bi R = S Ti Traffic Model and Measurement • Random file size Bi distributed uniformly within 4-512 packets(1 packet = 1480 Byte) • Waiting time in between file transfers: R0 = 10 Mbps l = load in [0,1] B2 request B1 B3 time W1 W2 serve time T2 T1

  12. Voice Delay • N=8, l=0.3 W = 64 DMAX = 57 ms R = 4.9 Mbps voice delay [ms] W = 4 DMAX = 12 ms R = 5.3 Mbps time [s]

  13. W = 64 voice delay [ms] W = 4 time [s] Voice Delay - Detail • Strong correlation: nice for adaptive play-out control!

  14. Future Work • Refine traffic model and LAN simulation • Implement NS module that acts like T2 • Integrate Networking and Signal Processing parts • Use trace files from NS simulations for adaptive play-out time control • Conjecture: Fixed TCP window is ok, since remaining delay jitter can be controled by adaptive play-out

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