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Traffic Characteristics

Traffic Characteristics

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Traffic Characteristics

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  1. Traffic Characteristics Data traffic Voice traffic video traffic Delay Constraints Multimedia Traffic

  2. Integrated services • Circuit switching vs. packet switching • Telephone vs. data services • Circuit switching • Dedicated, fixed • Realtime • Pay for distance and time • Pakcet switching • Shared, flexible • Non-realtime • Pay for amount of data • QoS guaranteed switching/network • Shared and dedicated, flexible and fixed • Non-realtime and realtime • Pay for QoS ⇒⇛=> 인터넷 종량제

  3. Analytic models of data application traffic characteristics • Reference : Vern Paxson, “Empirically-derived analytic models of wide-area TCP connections” • Upper 5% of bursts contribute 90% of the data. Multimedia Traffic

  4. The Log-Normal Distribution i.e. X is log2-normal iff Geometric mean of X Geometric standard deviation of X Multimedia Traffic

  5. The Log-Normal Distribution Log scale 100 102 104 105 Complementary cumulative density function (cdf) Probability density function (pdf) Multimedia Traffic

  6. The Pareto Distribution • pdf heavy-tailed distribution • CDF • Where h is a slow varying function at ∞ Multimedia Traffic

  7. The Pareto Distribution 105 106 107 Probability density function (pdf) Complementary cumulative density function (cdf) Multimedia Traffic

  8. Data Traffic Characteristics • Shaped by TCP • Slow 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

  9. Voice traffic Multimedia Traffic

  10. Voice Traffic • CBR (Constant Bit Rate) • Uncompressed 64 kbps • 8000 samples/sec × 8bits/sample • Voice coding standards • MOS (Mean Opinion Score)

  11. Speech Activity • One speaker talking : 64~73 % • Both speakers talking : 3~7 % • Both speakers silent : 33~20 % Silence Avg. 1.8 sec Talkspurt Avg. 1.2 sec Multimedia Traffic

  12. VoIP System and Impairments Impairments Delay impairments Speech quality Compression Packet Loss Interactivity (<150 ms) Echo Voice source talk silence Delay Jitter Depacketizer & Playout buffer Encoder talkspurt talkspurt Decoder & concealment Network Packetizer silence Sender Receiver Multimedia Traffic

  13. VoIP quality Speech Transmission Quality ( user satisfaction ) 5.0 Best(very satisfied) 4.3 High(satisfied) Desirable Acceptable Mean Opinion Score (MOS) 4.0 Medium(some users Dissatisfied) 3.6 Low(many users Dissatisfied) 3.1 Poor(nearly all dissatisfied) 2.6 Multimedia Traffic

  14. Video traffic Multimedia Traffic

  15. Network convergence b r Broadcasting, Storage Video people Dedicated bitrate Fixed rate (CBR) Circuit switching Network people Shared bitrate Variable rate (VBR) Packet switching • Video traffic needs merits of both. • Dedicated feature of circuit switching • Shared feature of packet switching • Leaky bucket model!! Multimedia Traffic

  16. Multimedia Traffic 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 bitrate • Constant bitrate(CBR), variable bitrate(VBR)

  17. VBR Video • VBR is optimal for compressed video. Bitrate (Mbps) Distortion p r bad good Too good Time (GOP) Min Mean Max Bitrate, R Multimedia Traffic

  18. 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)

  19. Double leaky buckets r p b M output input non-realtime traffic Realtime traffic Multimedia Traffic

  20. Resource Allocation for VBR Realtime traffic Non realtime traffic • Resource = bandwidth + buffer (realtime) (non-realtime) • When realtime service needs excess bandwidth, non-realtime service packets are buffered. Multimedia Traffic

  21. 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

  22. 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. Instantaneous bitrate P=p1+p2+p3<Rmax Average bitrate R+NR=r1+r2+r3 +nt1+nr2+nr3 <Rmax KBS (p1,pb1)(r1,b1) FTP : nr1 Realtime (P,PB)(R,B) Non-realtime NR MBC (p2,pb2)(r2,b2) Web : nr2 Fast buffer PB=pb1+pb2+pb3<Brt Slow buffer B=b1+b2+b3 <Bnrt Brt, fast buffer Rmax VOIP (p3,pb3)(r3,b3) Bnrt, slow buffer E-mail : nr3 Multimedia Traffic

  23. Buffer management Data (bytes) Overflow Because of excess feed Available network bandwidth I Maximum buffered data Sum of di + B Underflow Less feed, nothing to decode Available network bandwidth II Buffer B Media data Sum of di t (frame#) Multimedia Traffic

  24. Scheduling (VBR channel) Data (bytes) Optimal schedule A(t) (e) Maximum buffered data W(t) (b) (d) Constant rate schedule (average) Buffer B (c) Media data D(t) δ t (frame#) (a) Multimedia Traffic

  25. Statistical multiplexing of VBR video • As multiplexing more VBRs, peak-to-mean ratio↓ • Multiplexing VBRs  similar to CBR Averaged frame sizes of 1, 2, 4, 8 VBR video streams Multimedia Traffic

  26. b r Leaky bucket for VBR video • Leaky-bucket method • Buffer size (bucket depth) ‘b’ to guarantee no overflow at the drain rate ‘r’ • The more multiplexed, the smoother b r

  27. 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 bandwidth • Satellite in which bandwidth is much costy.

  28. Statistical Multiplexing Gain m 1.2m 2m 1 CBR 0.5 Statistical multiplexing gain n=10 10-1 n=1 10-2 m 10-3 n=10 n=1 CBR

  29. Statistical multiplexing probability N(μ,σ)=N(5Mbps, 1Mbps) N(10Mbps, 1.7Mbps) • Pdf and negative cdf + = 5Mbps 5Mbps 10Mbps normalize N(5Mbps, 0.85Mbps) N(5Mbps, 1Mbps) 1 backward cumulation 0.5 5Mbps 0.5 5Mbps

  30. Statistical multiplexing gain 0.5 gain Log scale Complementary cumulative density function of statistical multiplexed traffic [log scale] Complementary cumulative density function of statistical multiplexed traffic Multimedia Traffic

  31. End-to-end delay components Decoder/ display delay Encoder delay Propagation delay queuing delay • Source of Jitter, • random, function of : • Path in the network • Traffic load and • Characteristics • Scheduling scheme • Packet size • 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 LookAhead Encoding WaitPacketization time Multimedia Traffic

  32. End-to-end Delay Requirements • Hence, the one-way (end-to-end) delay becomes • Toll quality real-time communication needed • Round-trip delay must be in the range 200-300ms • That is, ,where • Amount of jitter allowed 10-50ms, function of • Acceptable end-to-end delay Dmax • Formation time Tf • Propagation delay Multimedia Traffic