Influence of File Size Distribution on Legacy LAN QoS Parameters

1. Influence of File Size Distributionon Legacy LAN QoS Parameters Nikolaus Färber Nov. 15, 2000

2. Outline • Network topology • Qos parameter voice • Traffic model and QoS parameter data • PDF of file size • Uniform • Log-Normal • Tradeoff QoS voice vs. data • Tradeoff delay vs. loss as before

3. Topology: N to N Communication • Voice received from WAN • Each terminal sends/receives data to/from every other terminal • Balanced N to N communication • N=16 • W={1, 2, 4, 8, 16, 32, 64} • l = {0.1, 0.2, 0.3, 0.4, 0.5} R0 = 10 Mbps T2 A1 100 KByte/port, drop tail A2 WAN R … S AN QoS provided

4. N 1 N S | di – di+1| = i=1 loss delay QoS Parameter Voice • Average Voice Jitter • Reasonable quantity to predict performance of adaptive playout scheduling • More complete (but less compact) description of voice quality is possible by plotting tradeoff delay vs. loss

5. N-1 Bi Wi = R0 l S Bi R = S Ti Traffic Model and QoS Par. Data • Random file size Bi distributed according to fB(B) • 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 • Qos parameter data: “Data goodput”:

6. File Size Distribution PB(B) • Assumed so far: Uniform (4-512 packets of 1480 byte) • Literature [Barford 98, Paxson 95, Douceur 99, Arlitt 99] • File system: Log-Normal, Log-Normal Body/Pareto Tail • Network: Log-Normal, Pareto • Pareto: • Log-Normal: (“heavy tailed”)

7. Workload of 1998 World Cup • M. Arlitt, T. Jin, “Workload Characterization of the 1998 World Cup Web Site”, HP Lab. Tech. Report, September 1999. • http://www.hpl.hp.com/techreports/1999/HPL-1999-35R1.html • Result of 1.35 billion requests during 1 month Log-Normal m = 10.13 s = 2.19

8. Comparison of used PDFs • = 3.6 103 s = 1.2 104 • = 3.8 105 s = 2.2 105 prob. file size [byte] prob. log2(File size)

9. l = 0.5 W=64 32 16 0.4 average voice jitter [ms] 8 0.3 4 0.2 1 2 0.1 data goodput [Mbps] QoS Tradeoff, PB(B) Uniform • N = 16, l = {0.1, 0.2, 0.3, 0.4, 0.5} x W = {1, 2, 4, 8, 16, 32, 64}

10. QoS Tradeoff, PB(B) Log-Normal • N = 16, l = {0.1, 0.2, 0.3, 0.4, 0.5} x W = {1, 2, 4, 8, 16, 32, 64} 32 l = 0.5 W=64 16 8 0.4 average voice jitter [ms] 0.3 4 0.2 2 1 0.1 data goodput [Mbps]

11. Uniform vs. Log-Normal PDF • In general similar behavior • Average jitter decreases monotonically with window size • Maximum goodput at low-medium window size (W = 4-16) • High variation of goodput at low loads • High variation of jitter at high loads • Longer average file size (uniform) results in reduced average voice jitter • For given scenario W=4 gives good performance at all loads • Why? • BxD = WxN increase with load?

12. Delay vs. Loss at 10% Load loss W = {1, 2, 4, 8, 16, 32, 64} delay [ms]

13. Delay vs. Loss at 20% Load loss W = {1, 2, 4, 8, 16, 32, 64} delay [ms]

14. Delay vs. Loss at 30% Load loss W = {1, 2, 4, 8, 16, 32, 64} delay [ms]

15. Delay vs. Loss at 40% Load loss W = {1, 2, 4, 8, 16, 32, 64} delay [ms]

16. Delay vs. Loss at 50% Load loss W = {1, 2, 4, 8, 16, 32, 64} delay [ms]

17. Conclusions and Future Work • Different file size distributions results in • Same general behavior • Different quantitative behavior (average voice jitter) • Fixed value for window size may not be too bad • Compare Delay-Loss curves for • Reduced TCP window size • Adaptive playout • Further refinement of traffic model