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Can We Multiplex ACKs
without Harming the
Performance of TCP?
CCNC 2014, The 11Th Annual IEEE Consumer Communications & Networking Conference
January 10-13 Las Vegas, Nevada USA
Jose Saldana, Julián Fernández-Navajas, José Ruiz-Mas
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Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Index
1. Introduction
2. Tests and results
3. Conclusions
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Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Index
1. Introduction
2. Tests and results
3. Conclusions
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Introduction
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Increase of emerging real-time services
They use small packets
This is modifying the traffic mix present
on the Internet
Inefficiency of the packets
IPv6 makes the problem even worse
VoIP packets
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Introduction
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
TCRTP (RFC4170) improves the efficiency
of VoIP. It uses three layers:
Header compression
Multiplexing
Tunneling
IP network
MUX DEMUX .
.
.
.
.
.
RTP RTP multiplexing RTP
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Introduction
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Advantage: Bandwidth and pps savings
At the cost of an additional multiplexing delay
Inter - pkt time
. . .
. . .
Native VoIP
traffic
Optimized
traffic
Inter - pkt time Inter - pkt time
. . .
. . .
. . .
. . .
. . .
. . .
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Introduction
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
TCM-TF*: Proposal for multiplexing other traffic
flows, including UDP (non-RTP) and TCP
*draft-saldana-tsvwg-tcmtf-05
IP IP IP
No compr. / ROHC / IPHC / ECRTP
PPPMux / Other
GRE / L2TP
IP
Compression layer
Multiplexing layer
Tunneling layer
a) TCRTP
Network Protocol
UDP
RTP
payload
UDPTCP
payloadpayload
ECRTP
PPPMux
L2TP
IP
IP
UDP
RTP
payload
b) TCMTF
MPLS
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Introduction
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
TCP video traffic: 69% of all consumer Internet traffic
in 2017.
When downloading a video, a computer may
generate some hundreds of ACKs per second, during
some tens of seconds.
In some scenarios (e.g. the aggregation network of an
operator) high numbers of long-term flows of ACKs
share a common path.
Header compression ratio of ACKs: from 40 to 7 or 8
bytes (savings of 80%).
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Introduction
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Is it a good idea to compress and multiplex these
flows?
Would the multiplexing delay degrade the
performance of TCP?
Sawtooth-shaped delay
PE
PE time
Added
delay
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Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Index
1. Introduction
2. Tests and results
3. Conclusions
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Dumbbell scenario in ns2
A sawtooth-shaped delay is added to the ACKs B-B’
What is the effect? We use TCP Tahoe (the most
basic one) in order to more clearly see the effect
First tests: separate A-A’ and B-B’
A
B
N M
A’
B’
O
P ACK mux (PE)
FTP
FTP
ACK
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
0
2
4
6
8
10
30 35 40 45 50 55 60Ban
dw
idth
[M
bp
s]
simulated time [s]
Throughput (RTT = 80 ms)
0
2
4
6
8
10
30 35 40 45 50 55 60Ba
nd
wid
th [
Mb
ps]
simulated time [s]
Throughput (RTT = 80 ms, mux period 50 ms)
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
0
2
4
6
8
10
30 35 40 45 50 55 60Ban
dw
idth
[M
bp
s]
simulated time [s]
Throughput (RTT = 80 ms)
0
2
4
6
8
10
30 35 40 45 50 55 60Ba
nd
wid
th [
Mb
ps]
simulated time [s]
Throughput (RTT = 80 ms, mux period 50 ms)
avg 9.24 Mbps window reset
every ~7 sec
avg 8.04 Mbps
(12% reduction)
window reset
every ~9,5 sec
ACKs arrive
in bursts
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
0
50
100
150
200
250
0 10 20 30 40 50 60 70 80
Win
do
w s
ize
simulation time [s]
Window size
no PE
PE=50ms
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
0
20
40
60
80
100
120
140
Win
do
w s
ize
Window evolution. One period
no PE
PE=50ms
Slow start
ends later
Window size
increases
more slowly
The period
between
window
resets
increases
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Second tests: A-A’ and B-B’ share the bottleneck
Are multiplexed flows in clear disadvantage?
We will use four different TCP variants:
Tahoe
Reno
New Reno
SACK
Results: Throughput difference between
multiplexed and non-multiplexed flows
A
B
N M
A’
B’
O
P ACK mux (PE)
FTP
FTP
ACK
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Results: Throughput difference between
multiplexed and non-multiplexed flows
Multiplexing Period PE [ms]
TCP 5 10 15 20 25
Tahoe 4.91 % 10.05 % 31.67 % 7.88 % 49.74 %
Reno 5.95 % 17.78 % 48.62 % 24.29 % 61.92 %
New
Reno 4.82 % 12.95 % 30.52 % 16.70 % 52.87 %
SACK 2.27 % 12.70 % 20.62 % 14.75 % 50.90 %
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Results: Throughput difference between
multiplexed and non-multiplexed flows
Multiplexing Period PE [ms]
TCP 5 10 15 20 25
Tahoe 4.91 % 10.05 % 31.67 % 7.88 % 49.74 %
Reno 5.95 % 17.78 % 48.62 % 24.29 % 61.92 %
New
Reno 4.82 % 12.95 % 30.52 % 16.70 % 52.87 %
SACK 2.27 % 12.70 % 20.62 % 14.75 % 50.90 %
With PE=5 ms
the difference
is small
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Results: Throughput difference between
multiplexed and non-multiplexed flows
Multiplexing Period PE [ms]
TCP 5 10 15 20 25
Tahoe 4.91 % 10.05 % 31.67 % 7.88 % 49.74 %
Reno 5.95 % 17.78 % 48.62 % 24.29 % 61.92 %
New
Reno 4.82 % 12.95 % 30.52 % 16.70 % 52.87 %
SACK 2.27 % 12.70 % 20.62 % 14.75 % 50.90 %
With PE=10 ms
the difference
becomes higher
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Results: Throughput difference between
multiplexed and non-multiplexed flows
Multiplexing Period PE [ms]
TCP 5 10 15 20 25
Tahoe 4.91 % 10.05 % 31.67 % 7.88 % 49.74 %
Reno 5.95 % 17.78 % 48.62 % 24.29 % 61.92 %
New
Reno 4.82 % 12.95 % 30.52 % 16.70 % 52.87 %
SACK 2.27 % 12.70 % 20.62 % 14.75 % 50.90 %
Below 10 ms the
difference may
become
unacceptable
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
0
2
4
6
8
10
900 910 920 930 940 950 960 970 980 990 1000
Th
rou
gh
pu
t [M
bp
s]
Simulation time
Throughput (SACK) no PE
PE=5 ms
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Tests and Results
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
0
2
4
6
8
10
900 910 920 930 940 950 960 970 980 990 1000
Th
rou
gh
pu
t [M
bp
s]
Simulation time
Throughput (Reno) no PE
PE=25 ms
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Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Index
1. Introduction
2. Tests and results
3. Conclusions
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Conclusions
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Suitability of traffic optimization, based on header
compression and multiplexing, to the flows of ACKs
The expected bandwidth savings are huge because of
the absence of payload
Counterpart: throughput reduction when an
optimized flow shares a bottleneck with a non-
optimized one
The impairments can be maintained in tolerable
limits, by setting an upper bound on the period
Further study this trade-off between bandwidth
saving and throughput reduction
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Thank you very much!
Jose Saldana, Julián Fernández-Navajas, José Ruiz-Mas