Receiver Driven Bandwidth Sharing for TCP Authors: Puneet Mehra, Avideh Zakor and Christophe De...
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Transcript of Receiver Driven Bandwidth Sharing for TCP Authors: Puneet Mehra, Avideh Zakor and Christophe De...
Receiver Driven Bandwidth Sharing for TCP
Authors: Puneet Mehra, Avideh Zakor and Christophe De Vlesschouwer
University of California Berkeley.Presented at: INFOCOM 2003. Twenty-Second Annual Joint
Conference of the IEEE Computer and Communications Societies.
Overview of the Presentation
MotivationGoalsProposed MethodNS-2 SimulationsConclusion
Motivation
Most Internet traffic is TCP HTTP, FTP, P2P, Multimedia streaming…
In many cases access links are bottleneck Limited Bandwidth (B/W) eg: DSL/Cable < 1.5Mbps User run many apps that compete for B/W
Problem: TCP shares bottleneck B/W according to RTT Not fair to flows with large RTT Doesn’t consider application needs or user prefs!
Example:
INTERNET
BottleneckAccess
Link
=
High RTT
Low RTT
Med. RTT
Video traffic
FTP
P2P
Congestion
Goals
Achieve full utilization of the receiver’s access link (bottleneck).
Satisfy user preferences: -priorities assigned to each flow.Approach: limit throughput of low-
priority flows to provide additional B/W for high-priority ones
Overview of the Presentation
Motivation GoalsProposed MethodNS-2 SimulationsConclusion
TRASTarget Rate
Allocation Sub-System
FCS1Flow Control
System
FCSnFlow Control
SystemσCalculationSub-System
σ
UserPreferences
BWSSBandwidth Sharing System
T1
Tn
Internet
Sendern
Sender1
Rn
Rn
R1
R1
Wn & dn
W1 & d1
For the receiverσ = system target bit-rate
For the nth connectionWn = Advertised Windowdn = Delay in ACK packetsTn = Target RateRn = Measured Rate
1
0
N
iiT
System Overview
.
.
.
.
.
.
System Overview…
Band-Width Sharing System (BWSS) consists of:
a) Flow Control System (FCS) b) Target Rate Allocation Sub-system
(TRAS) c) σ Calculation Sub-system.
FCS1
Flow Control System
T1
R1
d1
W1
For the nth connection W = Advertised Window d = Delay in ACK packets R = Measured Rate P = Packet size in bits Ti = Target Rate mi = minimum bandwidth wi = weight
CalculateTarget Rate –
Measured Rate
MeasureBit-rate and RTT
AdaptReceiver
Window / ACK Delay
Flow Control System
Flow Control System…
Ri < Ti : search for the smallest Wi to achieve (1- α )Ti =< Ri =< (1+ α )Ti
If Ri > (1+α)*Ti then delay the ACKs as decreasing Wi is ineffective.
Aim to minimize delay : otherwise results in unresponsiveness & instability in TCP flow.
)(*
dRTTPWR size
0
2
4
6
8
10
0 2 4 6 8 10 12 14Time (round trips)
Win
dow
size
(seg
men
ts)
Window size limits the data rate : Max Window size = min (cwndmax, receiver’s adv. window)
Receiver’s advertised window
After fast recovery
Example
Slide borrowed from Dr. Nitin Vaidya’s TCP tutorial
RTT and Bandwidth estimation
TCP timestamp option to estimate RTT.Bandwidth estimation relies on
exponentially weighted moving average R α*R + (1-α)*Rø
Ø – bandwidth estimation period, tradeoff between accuracy of estimation and time for convergence.
Target Rate Allocation System
Some apps need minimum guaranteed rate(video), others don’t (ftp)
User assigns each flow: Priority (pi), minimum rate (mi) and weight (wi)
Bandwidth allocation algorithm: Satisfy minimum rate in decreasing order of priority Remaining B/W shared according to weight
T1
User Prefs.
σ
Tn
1
0
1
0iii * w+ m = T N
jj
N
jj
w
m
Prevents starvation of low
priority connection
σ – Calculation SubsystemR1
RN
U = Σi Ri
σ
Goal: Choose σ to maximize link utilization. U = Σi Ri (σ)
Approach: Iteratively increase/decrease σ and measure the impact on utilization
σ < σideal implies under-utilization of the link.If σ > σideal , does it affect the system ?
Overview of the Presentation
MotivationGoalsProposed MethodNS-2 SimulationsConclusion
Example of User PreferencesTime 0: Min. Rate = 0 Kb/s
weights = 1,2,3 for S0-S2Priority -> S0 (max), S2(min)
Time 300: Min Rate = 600 Kb/s
TCP BWSS
Network-Congestion Example
Priorities: increasing from S0-S2Min Rate:S0,S2 – 600Kb/sS1 – 100 Kb/s
Time 400s to 1200s700Kb/s Interfering TCP trafficS2 limited to 300Kb/s
Multimedia Streaming Example
• S0 – Ftp traffic. Low Priority• Min Rate = 700Kb/s
• S1 – Streaming at 450Kb/s• High Priority
• 300Kb/s UDP flow (400s-1000s)
Overview of the Presentation
MotivationGoalsProposed MethodNS-2 SimulationsConclusion
Conclusion
BWSS allows user to allocate link B/W Flexible B/W allocation model Adapts to changing network conditions No changes to TCP/senders/routers
Observation: - works only if desired rate is achievable
under flow’s cwnd- What was receiver window
advertisement actually designed for??
Observation: TCP window management
1
Ack1 win4
2
43 4 5 6 DATA3 ~ 6 win4
Data1 win4
8Ack6 win2
9
10 11 DATA10 ~11 win4
sender
receiver
Questions??