traffic characteristics data traffic voice traffic video traffic delay constraints multimedia...
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Traffic Characteristics
Data trafficVoice trafficvideo traffic
Delay Constraints
Multimedia Traffic
Integrated services
Circuit switching vs. packet switchingTelephone vs. data services
• Circuit switchingDedicated, fixedRealtimePay for distance and time
• Pakcet switchingShared, flexibleNon-realtimePay for amount of data
• QoS guaranteed switching/networkShared and dedicated, flexible and fixedNon-realtime and realtimePay for QoS ⇒⇛=> 인터넷 종량제
Analytic models of data application traffic characteristics
Application variable model parameters mean
telnet responder Log-normal X=4500, σx=7.2 31582
Duration (sec)
Log-normal X=240, σx=7.8 1979
nntp originator Log-normal X=211.5, σx=3 5295
smtp originator Log-normal X=210, σx=2.75 1708
ftp connection Log-normal X=3000, σx=16 140083
Burst size Pareto α=1, k=105.5 ∞
http File size Pareto α=1.1, k=105.5 3478505
Multimedia Traffic
Reference : Vern Paxson, “Empirically-derived analytic models of wide-area TCP connections”
Upper 5% of bursts contribute 90% of the data.
The Log-Normal Distribution
2
2
2
)(
2
1)( y
myy
y
y eyf
)2ln/(xdxdy
Multimedia Traffic
),(~ 2ymyNY
YX 2 XY 2log
mymx 2
YX
21
)(ln2
)/ln(2
ln2
1)(
y
mxx
mX
X x
xxf
X is log2-normal iff i.e.
Geometric mean of X
Geometric standard deviation of X
The Log-Normal Distribution
xm=3000 bytes,
σx=16
Mean=140083 bytes
Multimedia Traffic
Probability density function (pdf) Complementary cumulative density function (cdf)
100 102 104 105
)(xfX xX Pr
Log scale
The Pareto Distribution
pdf heavy-tailed distribution
CDF
Where h is a slow varying function at ∞
Multimedia Traffic
21,0,)/()( kxxkxF C
1)( xkxf X
20),(][)( xhxxXPa
)(lim)( XVarb
x
0,1)(
)(lim
xth
txht
The Pareto Distribution
α=1, k=105.5
Multimedia Traffic
Probability density function (pdf)
Complementary cumulative density function (cdf)
105 106 107
)(xfX xX Pr
Data Traffic Characteristics
Shaped by TCPSlow start and double window size at positive ACK
Loss of a packet restarts the process.
Not suitable to realtime continuous traffic
Self-similarity characteristics
Highly bursty by heavy-tailed distributions of data
Same degree of burstness observed at all time scale
Long range dependency
Slow decay in autocorrelation function
Experienced in both LANs and WANs
No statistical multiplexing gain
Incompatibility to real-time multimedia traffic
Multimedia Traffic
Voice traffic
Multimedia Traffic
Voice Traffic
CBR (Constant Bit Rate)Uncompressed 64 kbps
8000 samples/sec × 8bits/sample
Voice coding standardsMOS (Mean Opinion Score)
ITU-T Rec. Codec Data rate MOS Delay
G.711 PCM 64 kbps 4.4 0.75 ms
G.726 ADPCM 32 kbps 4.2 1 ms
G.728 LD-CELP 16 kbps 4.2 3~5 ms
G.729 CS-ACELP 8 kbps 4.2 10 ms
G.729a CS-ACELP 8 kbps 4.2 10 ms
G.723.1 MP-MLQ 6.3 kbps 3.98 30 ms
G.723.1 ACELP 5.3 kbps 3.5 30 ms
Speech Activity
One speaker talking : 64~73 %Both speakers talking : 3~7 %Both speakers silent : 33~20 %
Multimedia Traffic
SilenceAvg. 1.8 sec
TalkspurtAvg. 1.2 sec
VoIP System and Impairments
Multimedia Traffic
Impairments
Speech quality Delay impairments
Compression Packet Loss Interactivity(<150 ms)
Echo
Delay Jittertalk silence
Packetizer
silence
talkspurt talkspurt
Network
Sender
Depacketizer &Playout buffer
Encoder
Decoder &concealment
Receiver
Voice source
VoIP quality
Multimedia Traffic
Best(very satisfied)
High(satisfied)
Medium(some usersDissatisfied)
Low(many usersDissatisfied)
Poor(nearly alldissatisfied)
Mean Opinion Score(MOS)
Desirable
Acceptable
5.0
4.3
4.0
3.6
3.1
2.6
Speech TransmissionQuality ( user satisfaction )
Video traffic
Multimedia Traffic
Network convergence
Multimedia Traffic
Video people
Network people
Broadcasting,Storage
Circuit switching
Packet switching
Dedicated bitrateFixed rate (CBR)
Shared bitrateVariable rate (VBR)
Video traffic needs merits of both. Dedicated feature of circuit switching Shared feature of packet switching
Leaky bucket model!!
b
r
Bitrate?
MPEG video (Ex: SDTV with Ravg=5Mbps)GOP (500ms, 10Mbps) Frame (30ms, 30Mbps) Macroblock (0.1ms, 100Mbps)
Network (e.g. IETF)Instantaneous transmission speed of any packet is 100Mbps in a 100Mbps LAN Average < Guaranteed < Peak bitrateConstant bitrate(CBR), variable bitrate(VBR)
Multimedia Traffic
10 Mbps5 Mbps
1hr 2hr
VBR Video
SIN CITY
0123456789
1 119 237 355 473 591 709 827 945 1063 1181
Multimedia Traffic
MaxMeanMin Bitrate, R
Distortion
bad
good
Too good
rp
Bitrate
(Mbps)
Time (GOP)
VBR is optimal for compressed video.
CBR Transmission of VBR Video?
Naturally compressed video is VBR.VBR traffic is better suited to VBR channel.
Double Leaky Bucket
Peak bitrate (p, bp)
Guaranteed bitrate (r, p)
p
bp
rb
Double leaky buckets
Multimedia Traffic
output
input
b
r
M
p
Realtime traffic
non-realtime traffic
Resource Allocation for VBR
Resource = bandwidth + buffer (realtime) (non-realtime)
When realtime service needs excess bandwidth, non-realtime service packets are buffered.
Multimedia Traffic
Non realtime traffic
Realtime traffic
Resource Allocation in a Router
Double leaky bucket for VBR traffic
(peak, buffer1), (guaranteed, buffer2)
One shared egress channel
(peaks of realtime traffics) < (total BW)
(guaranteed of all traffics) < (total BW)
Dual buffer : for peak rate and guaranteed rate
(buffer1`s) < (Realtime Buffer Limit)
(buffer2`s) < (non-Realtime Buffer Limit)
Multimedia Traffic
Multiplexing rt-VBR`s and nrt`s
VBR : peak (p,pb), guaranteed (r, b)Rt-VBR : realtime e.g. VOD, VOIP, video phone etc.nrt : non-realtime e.g. Web, ftp, E-mail, etc.
Multimedia Traffic
KBS (p1,pb1)(r1,b1)FTP : nr1
MBC (p2,pb2)(r2,b2)Web : nr2
VOIP (p3,pb3)(r3,b3)E-mail : nr3
Brt, fast buffer
Bnrt, slow buffer
Rma
x
Instantaneous bitrateP=p1+p2+p3<Rmax
Average bitrateR+NR=r1+r2+r3 +nt1+nr2+nr3 <Rmax
Fast buffer PB=pb1+pb2+pb3<Brt
Slow buffer B=b1+b2+b3 <Bnrt
Realtime (P,PB)(R,B)
Non-realtime NR
Buffer management
Multimedia Traffic
Buffer
B
Data (bytes)OverflowBecause of excess feed
UnderflowLess feed, nothing to
decode
Available network
bandwidth I
Available network
bandwidth II
Maximum buffered data
Sum of di + B
Media dataSum of di
t (frame#)
Scheduling (VBR channel)
Multimedia Traffic
Buffer
B
Data (bytes)
Optimal schedule A(t)
Constant rate schedule (average)
Maximum buffered dataW(t)
Media dataD(t)
t (frame#)(a)
(b)
(d)
(e)
(c)δ
Statistical multiplexing of VBR video
As multiplexing more VBRs, peak-to-mean ratio↓Multiplexing VBRs similar to CBR
Multimedia Traffic
Averaged frame sizes of 1, 2, 4, 8 VBR video streams
Leaky bucket for VBR video
Max Buffer Size by rate
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
2.9 3.2 3.5 3.8 4.1 4.4 4.7
r [Mbps]
b [k
Byte
s]
Original
Merge 2
Merge 4
Merge 8
b
r
Leaky-bucket methodBuffer size (bucket depth) ‘b’ to guarantee no overflow at the drain rate ‘r’The more multiplexed, the smoother
r
b
Statistical Multiplexing of VBR Video Traffics
Multiplexed VBRs becomes CBR-like.Back to the vision of ATM in 1990s Cons : Self-similarity
(mean , deviation )For CBR,
For n VBR`s
30-40% saving in total bandwidthSatellite in which bandwidth is much costy.
0)(
)(
mean
deviation
nn
n
mean
deviation
)(
)(
Statistical Multiplexing Gain
28
CBR
n=10
0.5
1
10-1
10-2
10-3
m
n=1
1.2m 2m
%7.662.1
)2.12(
m
m
Statistical multiplexing
gain
CBR
n=10
n=1
m
Statistical multiplexing
Pdf and negative cdf
29
+ =
5Mbps 5Mbps 10Mbps
N(μ,σ)=N(5Mbps, 1Mbps)
N(10Mbps, 1.7Mbps)
N(5Mbps, 0.85Mbps)
N(5Mbps, 1Mbps)
5Mbps
normalize
backward cumulation
5Mbps
0.5
probability
1
xX Pr
0.5
Statistical multiplexing gain
Multimedia Traffic
Complementary cumulative density function of statistical multiplexed traffic
[log scale] Complementary cumulative density function of statistical multiplexed traffic
gain
Log scale
0.5
End-to-end delay components
Multimedia Traffic
playpathi
ipathi
iif DQPTlTD
)(
Constant, function of:
• Encoding Scheme(frame size, look –ahead)• l : Packet size = k*framesize
Constant, function of:
• Propagation delay = Distance / light speed• Link speed= Packet size / channel speed
Source of Jitter, random, function of :
• Path in the network• Traffic load and Characteristics• Scheduling scheme• Packet size
WaitPacketizationEncoding
time
LookAhead
Encoder delay
Propagation delay
queuing delay
Decoder/ display delay
End-to-end Delay Requirements
Hence, the one-way (end-to-end) delay becomes
Toll quality real-time communication neededRound-trip delay must be in the range 200-300msThat is, ,where
Amount of jitter allowed 10-50ms, function ofAcceptable end-to-end delay Dmax
Formation time Tf
Propagation delay
Multimedia Traffic
edsynchronizDandSQ
edsynchroniznonDandSQPTlTD
iiif
,max
max,2)(
maxDD msDms 150100 max