Influence of File Size Distribution on Legacy LAN QoS Parameters Nikolaus Färber Nov. 15, 2000

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

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}  = {0.1, 0.2, 0.3, 0.4, 0.5} T2 S R A1A1 ANAN A2A2 QoS provided WAN … R 0 = 10 Mbps 100 KByte/port, drop tail

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 = | d i – d i+1 |  i=1 N 1N1N delay loss

Traffic Model and QoS Par. Data Random file size B i distributed according to f B (B) Waiting time in between file transfers: W i = BiBi N-1 R0R0 R 0 = 10 Mbps  = load in [0,1] time B1B1 B2B2 B3B3 W1W1 W2W2 T1T1 T2T2 request serve R =  B i  T i Qos parameter data: “Data goodput”: ?

File Size Distribution P B (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”)

Workload of 1998 World Cup M. Arlitt, T. Jin, “Workload Characterization of the 1998 World Cup Web Site”, HP Lab. Tech. Report, September Result of 1.35 billion requests during 1 month Log-Normal  =  = 2.19

Comparison of used PDFs file size [byte] log 2 (File size) prob.  =  =  =  =

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

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

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?

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

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

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

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

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

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