画像情報特論 (5) - waseda universitykatto/class/18...tfrc and its variants 画像情報特論...
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TFRC and its Variants
画像情報特論 (5)Advanced Image Information (5)
情報理工・情報通信専攻 甲藤二郎
E-Mail: [email protected]
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Protocol Transition90 95 00 05 10
VoIP
Streaming
Broadcast
RTP/UDP
RTP/UDP
RTP/IP-multicast
CDN
Proprietary: Skype (P2P), LINE, …Mbone experiment
standardization (IETF, ITU-T)
HTTP/TCP
15
TCP or UDP
MPEG2-TS MNT ?
MPEG-DASH
WebRTC
NGN
TFRC
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TCP Equations→ TFRC
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TCP Modeling
• TCP-Reno Equivalent Ratecwnd
n
w
w/2
0w/2 RTT round
⋅=
=
pRTTPSR
wp
23
38
2
)321(8
333
2 2, ppbptbpRTT
PSR
lossRTO
loss
+⋅⋅+=
with timeout consideration
w: cwnd when packet is lostp: PLRRTT: round trip timeR: equivalent rateb: # of delayed ACKs
R
TCP-Reno
J.Padhye et al: “Modeling TCP Throughput: A Simple Model and its Empirical Validation”, ACM SIGCOMM 1998.
packet loss time out
PS: packet size
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TCP Westwood
• Duplicate ACKs
• Timeout
• multiple versions according to FSE estimation methods
ssthreshcwndssthrehcwndifRTTFSEssthresh
=>=
)(* min
1* min
==
cwndRTTFSEssthresh
2/cwndssthresh =in TCP-Reno case
FSE: Fair Share Estimates
C.Casetti et al: “TCP Westwood: Bandwidth Estimation for Enhanced Transport over Wireless Links”, ACM MOBICOM 2001.
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Performance tools
• Active probing (high accuracy)– uses probe packets
• pathchar, pchar, …• iperf, netperf
• Inline measurement (low accuracy)– uses application data packets
• TCP-Westwood
https://www.caida.org/tools/taxonomy/perftaxonomy.xml
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Bandwidth Share Estimation
C.Casetti et al: “TCP Westwood: Bandwidth Estimation for Enhanced Transport over Wireless Links”, ACM MOBICOM 2001.
tk-1
tk
b(1)
dk/b(2)
∆tk
sender receiver
Bandwidth share: ( ))(min jbbj
=TCPW-BE
bdttt k
kkk ≈−=∆ −1
b(2) b(3)
tk: ack arrival time of the k-th packet
dk: size of the k-th packet
k
kk t
db∆
≈
moving average:
“packet pair”
FSEbk →ˆ
RTTk-1
slow fastfast
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Rate Estimation(reference) TCP-Vegas
minmin
RTTRTTcwnd
RTTcwnddiff ⋅
−=
expect rate actual rate
TCPW-RE:
Td
RE jk∑= cwnd ⇒ S=Σdj
RTT⇒ T= Σ∆tj
moving average: RTTnT ⋅=
T
(e.g. n=4)FSEER k →ˆ
∑∑∆
≈j
jk t
dER̂
M.Gerla et al: “TCP westwood with adaptive bandwidth estimation to improve …”, Comp. & Comm., 2004.
∆tj
“packet train”
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Comparison of BSE and RE
• BSE tends to overestimate (due to burstiness)• RE tends to underestimate when losses occur
solid: BSE, dashed: RE, red: fair share, green:capacity
M.Gerla et al: “TCP westwood with adaptive bandwidth estimation to improve …”, Comp. & Comm., 2004.
without error with error
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Adaptive Bandwidth Share Estimation
• BSE: overestimation, RE: underestimation• difference lies in sampling period T
• large T when congested (BSE), small T when not congested (RE)
⋅−⋅=
cwndRTThTRTTTTk
minmin
ˆ1,max
actual rate
cwndRTThT <⋅ minˆ congested larger Tk
TCPW-ABSE:
Tmin : ACK arrival interval
多数のパケットを送っても実レートが上がらない
M.Gerla et al: “TCP westwood with adaptive bandwidth estimation to improve …”, Comp. & Comm., 2004.
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TFRC and its variants
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TFRC (RFC 3448)• TCP-Friendly Rate Control
– calculate TCP-Reno equivalent rate by observing RTT and PLR p
– assume real-time applications (voice, video, or game) by RTP/UDP or DCCP
M.Handley et al: “TCP Friendly Rate Control (TFRC): Protocol Specification”, IETF RFC 3448, 2003.
)321(8
3343
2 2ppbpRTTbpRTT
PSRTFRC
+⋅⋅⋅+=
RTOt TCP retransmission timeoutb=1: delayed ACK (recommended)
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Disadvantage of TFRC
• inherits TCP-Reno’s weak points– causes vacant capacity when buffer size
is smaller than BDP (due to window halving)
– causes unnecessary window decrease when PLS is high (e.g. wireless networks) ⇒ LDA
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LDA (1)
• Loss Differentiation Algorithm– Congestion loss OR Wireless error loss
S.Cen et al: “End-to-end differentiation of congestion and wireless losses”, IEEE/ACM Trans. Networking, 2003.
ROTT: Relative One-way Trip Time
Spike algorithm ZigZag algorithm
( )( )
3/1,2/1minmaxmin
minmaxmin
==
−⋅+=
−⋅+=
βα
β
α
rottrottrottBrottrottrottB
spikeend
spikestart
“TFRC Wireless”
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LDA (2)
• Simulation results
S.Cen et al: “End-to-end differentiation of congestion and wireless losses”, IEEE/ACM Trans. Networking, 2003.
Wireless last hop Wireless backbone
in Table, • throughput• congestion loss• congestion loss, estimated as wireless loss• wireless loss, estimated as congestion loss
LDA LDA
“TFRC Wireless”
Perform better than original TFRC because LDA behaves similar to delay-based TCP
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VTP (1)
• Video Transport Protocol– LDA (differentiation of congestion loss
and wireless loss ~TFRC Wireless)– rate estimation similar to TCPW-RE (
Achieved Rate)– TCP-Reno emulation (friendliness to
legacy TCP)
G.Yang et al: “Smooth and efficient real-time video transport in the presence of wireless errors”, ACM Trans. MCCAP, 2006.
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VTP (2)
• VTP overview
G.Yang et al: “Smooth and efficient real-time video transport in the presence of wireless errors”, ACM Trans. MCCAP, 2006.
assume Buffer size = BDP
retransmission round
A1=A2: # of packets which can be transmittedduring the retransmission round
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VTP (3)
• VTP’s window control– init: Achieved Rate by TCPW-RE– update: 1 packet increase per RTT
G.Yang et al: “Smooth and efficient real-time video transport in the presence of wireless errors”, ACM Trans. MCCAP, 2006.
kkk RTTRewnd ×=
)(1
1
1
1
11
−
+
+
++ −+
+×=
∆+==
kkk
kk
kk
k
k
kk RTTRTTRTT
RTTRRTTRTT
ewndRTT
ewndR
RateAchived0 =Rk
kk RTTRR 1
1 +=+if no RTT increase,
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VTP (4)
• simulation results
G.Yang et al: “Smooth and efficient real-time video transport in the presence of wireless errors”, ACM Trans. MCCAP, 2006.
VTPTFRC Wireless
(TFRC+LDA)TCP
MULTFRC: use multipleTFRC connections
Perform better than LDA because VTP does not cause vacant link capacity
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VTP (5)
• disadvantage of VTP– assumes only the case that Buffer size =
BDP– no consideration on the vacant capacity
which happens when Buffer size < BDP
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Google Congestion Control(GCC)
G.Carlucci et al: “Analysis and Design of the Google Congestion Control for WebRTC”, ACM MMSys, 2016.
used in Google Hangout and WebRTC, …
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Google Congestion Control• designed for RTP/RTCP content delivery over UDP
– hybrid congestion control by delay-based controller and loss-based controller
• used by Google Hangout and WebRTC in Chrome browser
• one of e2e congestion control algorithms discussed in IETF RMCAT (RTP Media Congestion Avoidance Techniques) WG– NADA (Network Assisted Dynamic Adaptation) – SCREAM (Self-Clocked Rate Adaptation for
Multimedia)– GCC (Google Congestion Control)
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Google Congestion Control
REMB: Receiver Estimated Maximum Bitrate(RTP/RTCP feedback extension)
Ar: expected sending rate calculated by delay-based controller at a receiver sideAs: target sending rate calculated by loss-based controller at a sender side
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Delay-based Controllerm(t): estimated delay gradient at time tby Kalman filterγ(t): threshold to judge three states at time t; “overuse” (m(t) > γ(t)), “underuse” (m(t) < -γ(t)), and “normal” (otherwise)s: one of three statesAr: expected sending rate (feedback to a sender)
𝐴𝐴𝑟𝑟 𝑡𝑡 = �0.85 � 𝑅𝑅𝑟𝑟 𝑡𝑡 − 1 overuse1.05 � 𝐴𝐴𝑟𝑟 𝑡𝑡 − 1 underuse𝐴𝐴𝑟𝑟 𝑡𝑡 − 1 normal
receiving rate in last 500ms
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Loss-based Controller
𝐴𝐴𝑠𝑠 𝑡𝑡 = �(1 − 𝑃𝑃𝑃𝑃𝑅𝑅) � 𝐴𝐴𝑠𝑠 𝑡𝑡 − 1 𝑃𝑃𝑃𝑃𝑅𝑅 > 0.11.05 � 𝐴𝐴𝑠𝑠 𝑡𝑡 − 1 𝑃𝑃𝑃𝑃𝑅𝑅 < 0.02𝐴𝐴𝑠𝑠 𝑡𝑡 − 1 otherwise
RTCP feedback (Ar, PLR)
𝐴𝐴 = min(𝐴𝐴𝑟𝑟 ,𝐴𝐴𝑠𝑠)
PLR: Packet Loss Rate
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Adaptive Threshold
• threshold γ(t) gradually converges to estimated delay gradient |m(t)|
• |m(t)| is gradually controlled to be smaller than threshold γ(t)
𝛾𝛾 𝑡𝑡 = 𝛾𝛾 𝑡𝑡 − 1 + ∆𝑇𝑇 � 𝑘𝑘𝑟𝑟(𝑡𝑡) � 𝑚𝑚(𝑡𝑡) − 𝛾𝛾 𝑡𝑡 − 1
gain
analogous to adaptive filter
time interval
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Single GCC Flow
adaptive threshold contributes to• smaller RTTs (low delay)• smaller PLRs (high QoE)
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GCC vs CUBIC TCP
adaptive threshold contributes to co-existence of GCC flow (over RTP/UDP) with CUBIC TCP flow
starved shared