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Scalable Network Path Emulation
Shilpi Agarwal, Joel Sommers, Paul BarfordUniversity of Wisconsin-Madison
http://wail.cs.wisc.edu
simulationlaboratory emulation
in situ
strengths accessibilityexperimental
control; system realism
realism(โit is what it isโ)
challenges realism (everything)
realism of traffic, topology, and
link/path conditions
experimental control
examples ns-2, Opnet, GloMoSim
WAIL, DETER, Emulab Planetlab, RON
Internet testbeds
2
network emulation packet delays, bandwidths, loss characteristics,
assuming some topologyModelNet
packet-oriented latency, loss,
duplication, reordering
path emulationDummynet, NIST net
link emulation bit-oriented propagation delay and
errors
Adtech SX-14A spool of optical fiber (!)
A taxonomy of emulation systems
3
Emulation challenges for todayโs testbeds
โข Scale to many physical routers, links, and end hosts
โข Implies need for flexibility in configuration options
โข Scale to Gigabit+ links
โข Cost effectiveness (free software, commodity hardware)
โข No existing software-based link or path emulator satisfies all these requirements
4
WAIL: an example of a modern testbed
> 50 routers (hundreds of interfaces)> 200 workstations
5
NetPath: a scalable network path emulator
โข Foundations and design principles of NetPath
โข Modify Click modular router โ run on commodity hardware
โข Eliminate unnecessary packet processing
โข Push functionality as close to hardware as possible
โข Exploit hardware capabilities where possible
โข Support a variety of topological and network configurations
6
NetPath with a single emulated path
poll device receive and timestamp packets
queue buffer packets in system memory
delay delay packets for specified time; perform reordering and errors
addressing decide how/where packet should be forwarded
to device transmit packet in egress interface
7
NetPath with multiple emulated paths
8
queue
delay
addressing
poll device
todevice
classify
scheduler
queue
delay
addressing
. . .
. . .
Classifying and scheduling are only
additional overheads.
Exploiting system memory for high performance
9
โข Basic Click elements do not enable full use of memory resources
โข Packets are dropped as a result
โข NetPath provides new Click elements to take advantage of system resources
โข Use available system RAM โ BigQueue
โข Use disks as backing store for long delays โ DiskQueue
โข Use a pair of disks to hide disk access latency โ ODQM (opportunistic disk queue management)
Options for topological configuration
โข Direct interposition
โข Layer 2 โ virtual interposition
โข Additional Click elements to optimize VLAN tag rewriting
โข Layer 3 โ interposition via IP routing
โข Leverage existing Click configuration tools
10
Results overview
โข Accuracy & precision of NetPath over a range of operating conditions is close to a hardware-based platform
โข NetPath significantly outperforms other emulation systems
โข NetPath modifications to Click significantly improve performance over out-of-the-box Click elements
โข NetPath can accurately & precisely support simultaneous emulation over several paths
11
Comparison with a hardware-based reference
offered load (kpps)
NetPath Adtech SX-14
50 10.03 (0.01) 9.99 (0.00)
100 10.03 (0.01) 9.99 (0.00)
150 10.04 (0.01) 9.99 (0.00)
200 10.05 (0.01) 9.99 (0.00)
250 10.06 (0.01) 9.99 (0.00)
300 10.09 (0.03) 9.99 (0.00)12
Using available system RAM for packet buffers
13
Using available system RAM enables longer delays at higher packet rates.
50 100 150 200 250 300
020
0040
0060
0080
00
offered packet rate (Kpps)
max
imum
pro
paga
tion
dela
y (m
illise
cond
s)
BigQueueQueue
Accuracy of probabilistic delay emulation
14
NetPath can provide high accuracy, buthead-of-line blocking can be a problem.
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
10 20 30 40 50
0.0
0.2
0.4
0.6
0.8
1.0
delay (milliseconds)
cum
ulat
ive fr
actio
n
โ generated delaymeasured delay (1 Kpps)measured delay (10 Kpps)
โ โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
โโโโโโโโโ
10 20 30 40 500.
00.
20.
40.
60.
81.
0delay (milliseconds)
cum
ulat
ive fr
actio
n
โ generated delaymeasured delay (1 Kpps)measured delay (10 Kpps)
Comparison of emulation systems
offered load (Kpps)
NetPath NIST net Dummynet Modelnet
4010.04 (0.01)
10.14 (0.03)
10.00 (0.35)
10.06 (0.13)
8010.04 (0.01)
10.52 (0.40)
10.23 (0.46)
10.10 (0.20)
12010.04 (0.01)
12.75 (0.84)
29.08 (1.68)
10.56 (0.45)
16010.04 (0.01)
16.47 (1.96)
399.00 (3.50)
-failure-
15
Packet drops are a problem with previous emulators
16
NetPath accurately emulates delay without introducing packet loss for much higher rates than other emulators.
โ โ โ โ โ โ โ โ โ โ โ โ โ โ โ โ โ โ โ โ
0 50 100 150 200
020
4060
80
offered packet rate (Kpps)
pack
et lo
ss p
erce
ntag
eโ NetPath
NIST netDummynetModelnet
Scaling to multiple paths
0
87.5
175.0
262.5
350.0
1 2 3 4 5 6 7 8 9 10Max
imum
loss
-free
forw
ardi
ng r
ate
(Kpp
s)
Number of paths
17
NetPath enables more efficient use of resources. Slight performance degradation is due to scheduling overhead.
Summary and conclusions
18
โข NetPath provides accurate path emulation capabilities for modern laboratory testbeds
โข Suitable for analysis of delay-sensitive protocols
โข Scalability to multi-link scenarios means that laboratory resources can be more efficiently used
โข A variety of supported configuration scenarios means that NetPath can be used in a wide variety of lab settings
โข Software will be available at http://wail.cs.wisc.edu/