This section documents a few error model objects, typically associated with NetDevice models, that are maintained as part of the network module:
Error models are used to indicate that a packet should be considered to be errored, according to the underlying (possibly stochastic or empirical) error model.
The source code for error models live in the directory src/packet/utils.
Two types of error models are generally provided. The first are stochastic models. In this case, packets are errored according to underlying random variable distributions. An example of this is the RateErrorModel. The other type of model is a deterministic or empirical model, in which packets are errored according to a particular prescribed pattern. An example is the ListErrorModel that allows users to specify the list of packets to be errored, by listing the specific packet UIDs.
The ns3::RateErrorModel errors packets according to an underlying random variable distribution, which is by default a UniformRandomVariable distributed between 0.0 and 1.0. The error rate and error units (bit, byte, or packet) are set by the user. For instance, by setting ErrorRate to 0.1 and ErrorUnit to “Packet”, in the long run, around 10% of the packets will be lost.
Error models are ns-3 objects and can be created using the typical pattern of CreateObject<>(). They have configuration attributes.
An ErrorModel can be applied anywhere, but are commonly deployed on NetDevice models so that artificial losses (mimicing channel losses) can be induced.
No known limitations. There are no existing models that try to modify the packet contents (e.g. apply bit or byte errors to the byte buffers). This type of operation will likely be performance-expensive, and existing Packet APIs may not easily support it.
The ns-3 spectrum model and devices that derive from it (e.g. LTE) have their own error model base class, found in
The initial ns-3 error models were ported from ns-2 (queue/errmodel.{cc,h})
The base class API is as follows:
Many ns-3 NetDevices contain attributes holding pointers to error models. The error model is applied in the notional physical layer processing chain of the device, and drops should show up on the PhyRxDrop trace source of the device. The following are known to include an attribute with a pointer available to hold this type of error model:
However, the ErrorModel could be used anywhere where packets are used
This model is typically not used with helpers.
The RateErrorModel contains the following attributes:
What kind of data does the model generate? What are the key trace sources? What kind of logging output can be enabled?
Error models are used in the tutorial fifth and sixth programs.
The directory examples/error-model/ contains an example simple-error-model.cc that exercises the Rate and List error models.
The TCP example examples/tcp/tcp-nsc-lfn.cc uses the Rate error model.
No known issues.
The error-model unit test suite provides a single test case of of a particular combination of ErrorRate and ErrorUnit for the RateErrorModel applied to a SimpleNetDevice.
The basic ErrorModel, RateErrorModel, and ListErrorModel classes were ported from ns-2 to ns-3 in 2007. The ReceiveListErrorModel was added at that time.
The burst error model is due to Truc Anh N. Nguyen at the University of Kansas (James P.G. Sterbenz <jpgs@ittc.ku.edu>, director, ResiliNets Research Group (http://wiki.ittc.ku.edu/resilinets), Information and Telecommunication Technology Center (ITTC) and Department of Electrical Engineering and Computer Science, The University of Kansas Lawrence, KS USA). Work supported in part by NSF FIND (Future Internet Design) Program under grant CNS-0626918 (Postmodern Internet Architecture), NSF grant CNS-1050226 (Multilayer Network Resilience Analysis and Experimentation on GENI), US Department of Defense (DoD), and ITTC at The University of Kansas.