TCP Reno vs. Vegas

1
TCP Reno vs. Vegas
INFOCOM 1999
Jeonghoon Mo Richard La Venkat Anantharam Jean
Walrand
Paper by
Discussion Leader
Jack Meier
Presented by
Manfred Georg
2
Overview

• TCP Reno
• TCP Vegas
• Fairness
• Simulation
• Conclusion

3
TCP Reno

• Slow Start
• Congestion Avoidance (AIMD)?
• Packet Loss
• Window size and Network Buffering

4
TCP Vegas

• Slow Start
• Congestion Avoidence
• Round Trip Delay
• Alpha and Beta
• Rerouting
• Persistent Congestion

5
Vegas Algorithm

• Expected CWND / BaseRTT
• Actual CWND / RTT
• Diff (Expected - Actual) BaseRTT

6
Vegas Algorithm

• Expected CWND / BaseRTT
• Actual CWND / RTT
• Diff (Expected - Actual) BaseRTT

CWND
7
Vegas Algorithm

• Diff (Expected - Actual) BaseRTT

8
Rerouting Vegas

• No Explicit Feedback
• Propagation Delay Changes
• Shorter Delay Detected
• Longer Delay Interpreted as Congestion
• Occasionally update BaseRTT
• BaseRTT min RTT since last update
• If (RTT
• Cause Persistent Congestion?

9
Persistent Congestion

• New Connection Increases Congestion
• BaseRTT updating
• Temporarily causes congestion
• Other connections back off
• All connections get accurate estimate of BaseRTT

10
Fairness

• Reno vs. Reno
• Vegas vs. Vegas
• Reno vs. Vegas

11
Reno Fairness
D. Chiu and R. Jain, Journal of Computer Networks
and ISDN Systems, 1989
12
Vegas Fairness
z(t) total backlog ei(t) ACK received rate
qi(t) backlog in queue
wi(t) window size
qi(t) between a and ß
13
Vegas Fairness
z(t) total backlog ei(t) ACK received rate
qi(t) backlog in queue
wi(t) window size
wi(t) qi(t) ei(t) di )? ei(t) wi(t) / (zi(t
) di)?
e1(t) e2(t) 1
14
Vegas Fairness
Fixed Window Stream
ß
a
15
Vegas Fairness
ß
a
Fixed Window Stream
16
Vegas Fairness
17
Vegas Fairness
70
Delay 12.9ms
80
Delay 18.9ms
18
Vegas Fairness
70
Delay 12.9ms
110
Delay 36.9ms
19
Vegas Fairness
70
Delay 12.9ms
160
Delay 66.9ms
20
Vegas Fairness
70
Delay 12.9ms
400
Delay 186.9ms
21
Simulation

• Vegas vs. Vegas
• Reno vs. Reno
• Reno vs. Vegas

22
Vegas vs. Vegas
23
Reno vs. Reno
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Reno vs. Vegas

• Vegas less than ß packets buffered
• k
• Reno fills the rest (half the time)?
• (B-k)/2
• Vegas to Reno Throughput
• 2k/(B-k)?

25
Reno vs. Vegas
26
Reno vs. Vegas
27
Conclusion

• Rerouting
• Persistent Congestion
• Vegas vs. Vegas Fairness
• Reno vs. Reno Fairness
• Vegas and Reno do not cooperate

28
Thank You
'The time has come,' Jack Meier said,
'To speak of many thing...'