tdctcp - csie.org
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Transcript tdctcp - csie.org
B99705021 李奕德
Abstract
Intro
ECN
in DCTCP
TDCTCP
Performance evaluation
conclusion
TCP
does not fit in datacenter
DCTCP may lower throughput due to small
buffer size
Improved version of DCTCP (called TDCTCP)
Compare to existed algorithm (DCTCP,
TCPNewReno)
TDCTCP may have slightly higher delay but
have much better throughput in general
Abstract
Intro
ECN
in DCTCP
TDCTCP
Performance evaluation
conclusion
Data
1.
2.
flow in datacenter:
large data flow
require high throughput
small data flow
require low latency
Incast problem
TCP:
provide : reliable, ordered byte stream
does not provide: high throughput with
“simultaneously low delay”
Other similar solutions:
DCTCP, TCPNewReno, TDCTCP
Tested
under OMNeT++ simulator
Abstract
Intro
ECN
in DCTCP
TDCTCP
Performance evaluation
conclusion
ECN
mechanism
2-bit used to describe current situation
00: Non ECN-Capable Transport — Non-ECT
10: ECN Capable Transport — ECT(0)
01: ECN Capable Transport — ECT(1)
11: Congestion Encountered — CE
Abstract
Intro
ECN
in DCTCP
TDCTCP
Performance evaluation
conclusion
A.
Modification of Congestion Avoidance
B. Resetting α after Delayed ACK timeout
C. Dynamic Delayed ACK timeout calculation
Modification
of Congestion Avoidance
α = fraction of marked packets in one
congestion window
Indicates current congestion level
= Maximum Segment Size
Indicates the size of data that can be sent
MSS
α after Delayed ACK timeout
delayed ACK timeout: use in TCP to
reduce ACKs send to the sender
When ACK timeout occur:
1. α is not updated
2. Old α remain high and block increment
of window size
α is reset to 0 after every delayed ACK
timeout
Resetting
Set α to 0 when this happen
Dynamic
Delayed ACK timeout calculation
DCTCP: small buffer = small congestion
window
Congestion window reduce to 1, causing ACK
timeouts
Packet
arrival follows an exponential
distribution
Packet loss probability in the network is
small
Use
10 flows to demonstrate
Low variance in window
size
Spend less time in ACK
timeout
Abstract
Intro
ECN
in DCTCP
TDCTCP
Performance evaluation
conclusion
Throughput
Fairness
Delay
Queue
length
Variation in Delay
Variation in Throughput
Environment
Throughput
Better
- single bottleneck, 1Gbps
performance than DCTCP in general
Throughput
Better
- single bottleneck, 10Gbps
than DCTCP under smaller K
Provide same throughput as TCPNewReno in
early stages
Throughput
Better
– multi-bottleneck, 10Gbps
than DCTCP under smaller K
Provide same throughput as TCPNewReno in
early stages
Fairness-
better
single bottleneck, measure in JFI
fairness in every scenario
Fairness-
multi-bottleneck, measure in JFI
Delay-
single bottleneck , 10 Gbps
TCPNewReno
is good except high delay
Delay-
multi-bottleneck , 10 Gbps
Queue
length
TDCTCP
is slightly longer than DCTCP
Variation
in Delay
Variation
in throughput
Abstract
Intro
ECN
in DCTCP
TDCTCP
Performance evaluation
conclusion
Modified
DCTCP => TDCTCP
15% higher throughput than DCTCP
improved fairness compare to DCTCP
provides more stable throughput
queue length is slightly more than that of
DCTCP at 10Gbps
delay is slightly higher than that of
DCTCP
Any questions??