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Platform
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Dedicated 32-bit low power single board computer
(PC Engines ALIX2c3).
AMD Geode LX 800 (500mhz), 256M memory.
1 gigabyte (or more) 80x flash memory file system.
No rotating media or fans.
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Dedicated high performance computer.
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Operating System and distribution
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Linux 2.6.28.6 (or later) - 32-bit.
Ursaminor Linux
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Fedora 7 - 64-bit.
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Interfaces
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One Ethernet for control.
Two Ethernets for impairments.
All interfaces full or half duplex.
All interfaces 10/100.
Auto MDI/MDI-X (auto crossover)
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One Ethernet for control.
Two Ethernets for impairments.
All interfaces full or half duplex.
All interfaces 10/100/1000.
Auto MDI/MDI-X (auto crossover)
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Fiber optical links
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Supported via external converters.
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Supported via external converters.
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Additional interfaces
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No
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Yes, but special-order chassis may be required.
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Transparency
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Layer 2 bridge with IEEE 802 forwarding table.
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Layer 2 bridge, forwarding defined by impairments.
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Impairment engine
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Netem, a standard Linux kernel module
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IWL impairment server, a real-time multi-threaded process.
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Delay
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Yes
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Yes
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Jitter
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Yes
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Yes (May be highly customized with user-defined jitter distributions.)
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Separate fixed and variable delay components
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No
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Yes
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Jitter Distribution
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Normal (bell curve), Pareto, Paretonormal
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Uniform, Normal (bell curve/Gaussian), piecewise distribution function defined by user.
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User defined jitter distributions
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No
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Yes
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Reordering
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Yes
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Yes, user selectable.
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Add delay/jitter to every Nth packet
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Yes
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Yes, via a plugin
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Hold packets then release all – Dam bursting
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No
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Yes, via a plugin
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IP Fragmentation
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No
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Yes, via a plugin and also part of IP test suite.
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Protocol specific test suites
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No
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Yes
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Maximum packet delay
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About 10 seconds
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More than an hour
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Timer resolution
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1 millisecond
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1 millisecond
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Drop
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Yes
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Yes
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Duplication
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Yes
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Yes
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Corruption
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Yes - Single bit errors may be introduced
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Yes, via a plugin
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Rate Limitation
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Yes, using a token bucket rate limiter.
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Yes, using an algorithm that takes many parameters into account
such as bit propagation delay, link framing overhead, etc.
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Bit-Serial Link Emulation
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No. (For many users the rate limitation feature is sufficient.)
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Yes, using an algorithm that takes many parameters into account
such as bit propagation delay, link framing overhead, etc.
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Modify packet contents?
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No
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Yes
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Protocol specific packet rewriting
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No
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Yes
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User written impairment
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No
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Yes
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Stateful
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No
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Yes, in protocol and user defined impairments.
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Low Frequency changes to individual impairments
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Yes, using a spreadsheet template to define the sequence of impairment steps,
impairment values, and inter-step delay.
Minimum inter-step interval is 1 second.
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Yes. Frequency range from 0.1 second to about two weeks.
Several ways to define the shape of the changes over time:
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Pulse model using linear, sine, and square waveforms for ramp-up and ramp-down.
Ramp-up and ramp-down may have different waveforms.
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User specified list of (X,Y) coordinates.
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User specified mathematical function.
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Burst impairments
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“Correlation” chain in which event probability is partially dependent on proceeding event probability.
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Yes, using a Markov probability chain with modifier based on packet inter-arrival time.
The probability value used to decay the Markov chain is different from the probability used to trigger the burst.
A time window may be used to skew the decay probability.
Algorithm is extension of that used in ITU network impairment model.
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Traffic classification into flows or bands
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Yes
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Yes
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Scriptable
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Yes, using a spreadsheet template to define the sequence of impairment steps,
impairment values, and inter-step delay.
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Yes from Python, Java, Perl, and Bash (shell)
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Can scripts run on other computers (i.e. scripting over the network.)
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No
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Yes
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IEEE tagged VLANs
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Partial support. Tagged ethernet packets are bridged.
However, filters do not operate on tagged packets.
Consequently, when used on a tagged VLAN trunk, all packets are classified
into the default band, Band #5.
All impairments may be applied to tagged packets.
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Yes
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Jumbograms
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No
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Yes
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Intrinsic delay
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Much less than one millisecond
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100 to 150 microseconds
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Throughput
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Packet (Ethernet frame) thoughput varies depending on packet size and
the impairments that are imposed.
- 1500 byte Ethernet packets:
- 8224 packets/second (100% of 100Mbit Ethernet)
in each direction (i.e. full duplex.)
(Delay timing accuracy degrades above 6188 packets/second, 75% of 100Mbit Ethernet.)
- 64-byte Ethernet packets:
- Half duplex (one direction at a time): 26,800 packets/second
- Full duplex (both directions simultaneously): 12,000 packets/second in each direction.
User interface responsivity diminishes at about 75% of these rates.
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25,000 packets/second
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Support
