can we multiplex acks without harming the performance of tcp?
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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
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Index
1. Introduction
2. Tests and results
3. Conclusions
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Index
1. Introduction
2. Tests and results
3. Conclusions
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
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
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
. . .
. . .
. . .
. . .
. . .
. . .
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
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%).
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
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Index
1. Introduction
2. Tests and results
3. Conclusions
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
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)
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
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
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
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
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 %
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
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
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
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
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
Can We Multiplex ACKs without Harming the Performance of TCP? - CCNC 2014
Index
1. Introduction
2. Tests and results
3. Conclusions
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
Thank you very much!
Jose Saldana, Julián Fernández-Navajas, José Ruiz-Mas
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