Reduced TCP Window Size andAdaptive Playout for

Legacy LAN VoIP

Niko Färber, Yi LiangNovember 29, 2000

Outline

Buffer Delay vs. Late Loss Load = 20, 40 % TCP window size = 1, 2, 4, 8, 16, 32, 64 packets Adaptive/Fixed playout

Adaptive playout over time Load = 10, 40% TCP window size = 32 packets

Analysis/Modeling of queuing delay Fd(d) (CDF of delay) n(t), d(t) (n = number of simultaneous transmissions) fn(n) (PDF of simultaneous transmissions) Fd(d | n) (conditional PDF of delay)

Simulation conditions Balanced N-N communication, N=16 hosts, 1 switch File size PDF: Log-Normal Idle time ~ file size 70 KB buffer 10 Mbps Full duplex Drop tail

Load = 20%

buffer delay [ms]

late

loss

[%

]

W = {1, 2, 4, 8, 16, 32, 64}

fixed playout

adaptive playout

Load = 40%

buffer delay [ms]

late

loss

[%

]

W = {1, 2, 4, 8, 16, 32, 64}

fixed playout

adaptive playout

Adaptive Playout, Load = 10%

Adaptive Playout, Load = 10%

Adaptive Playout, Load = 10%

Adaptive Playout, Load = 40%

Adaptive Playout, Load = 40%

Adaptive Playout, Load = 40%

Delay CDF At load link is not used with prob. 1- With 1- prob. voice packets see empty queue

(and therefore experience zero queuing delay) Empirical model for significant delay range

(99 % of packet delays are less than d99)

99

W Nd

R

1-

1

dd99

Fd(d)

dmax

Delay CDF, Load = 10%

d [ms]

Fd(d)

Delay CDF, Load = 20%

d [ms]

Fd(d)

Delay CDF, Load = 30%

d [ms]

Fd(d)

Delay CDF, Load = 40%

d [ms]

Fd(d)

Delay CDF, Load = 50%

d [ms]

Fd(d)

Delay and Simultaneous Txs

t [s]

d(t)

[ms]

n(t)

1

2

3

PDF of Simultaneous Txs

n

f n(n)

Binominal (fn(0) matched)

= 10%, W=32

Cond. Delay PDF, 0 simult. Tx

d [ms]

f d(d

| n=

0)

Cond. Delay PDF, 1 simult. Tx

d [ms]

f d(d

| n=

1)

Cond. Delay PDF, 2 simult. Txs

d [ms]

f d(d

| n=

2)

Cond. Delay PDF, 3 simult. Txs

d [ms]

f d(d

| n=

3)

Mean and Std of Cond. Delay PDF

n

d [ms]

d

d