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Simulation help: Defining traffic

This is the screen where you will define the traffic in your simulation. Each traffic type you define here has a set of properties. There is (apart from memory limitations) no limit on the number of traffic types you can define, but please bear in mind that each traffic type is independently generated (Even more if multiple sources are selected) so defining a lot of different traffic type will make your simulation terribly slow.
Also, only 10 different priorities (or types) are supported, so multiple flows with the same priority will become indistinguishable. Finally, the graph on the "results" screen cannot show more than 6 different traffic types. If you want to show more, the bars and the legend will cross each other. Of course, the numerical results on the Java-console are still readable and usable.

There are four buttons on this sheet, which can be used to navigate through the traffic types that are defined. Next and previous take you to respectively the next and previous traffic type in the list, while delete removes the current one and takes you to the next. If you delete the last definition in the list, you will be taken to the previous. You cannot delete a traffic description if it is the last one in the list.
Finally, new will create a new (default) traffic description for you. The default traffic type for a new traffic description depends on its position in the list.

The parameters of each traffic type are described in the table below. The table has the same order as the controls in the applet.

Name of parameter

Use of parameter

Traffic class

The type of traffic this source will generate. The types are derived from the IEEE 802.1D Standard, and are explained below. Which effective priority a traffic type receives depends on the queue used.

Average rate

The number of bytes this source will generate on the average. This is the effective rate of this traffic source(s). If you choose to use multiple sources, the inter-arrival time is adjusted automatically

Inter arrival time distribution

The probability distribution function that will be used to randomly determine the times that packets arrive.

Packet size

Which size will your packets be? Choose an appropriate type of traffic, or choose a fixed size. The predefined types are explained below.

Number of independent sources.

How many independent traffic sources will be used to generate this traffic. Increasing this number will not increase the total traffic volume

Burst length distribution

If the traffic flow is modulated by bursts, this allows you to choose the distribution of the burst length and silence times.

Average time on

What the average length of a burst is.

Average time off

The average silent time between burst If this is zero, burst modulation will be effectively off!

Packet Sizes


Packet size distribution


Half of the packets is large (1500 bytes), because downloads are usually larger than a few packets. The other half of the packets are small to represent the flow control packets used by TCP.


A mix of packet sizes, especially a part of smaller (600 byte) packets.


A mix of HTTP and FTP that resembles the packet sizes found in actual measurements.

Traffic Types

Name and abbreviation


NC, Network Control

Necessary to keep network operational. Should have lowest possible delay and loss probability.

VO, Voice

The traffic resulting from people making voice calls over the data-network. Should have a low delay and, depending on the encoder used a reasonable low loss.

VI, Video

Video-conferencing, remote instruction. Most video-coders are very sensitive to loss. Delay is somewhat less important than in voice calls, especially for non-interactive applications. (e.g. Video on Demand)

CL, Controlled Load

Important applications. Amount of necessary bandwidth can be planned in advance. This traffic receives a relatively better service in exchange for less flexibility in the bandwidth used.

EE, Excellent Effort

CEO Quality. Better than normal (Best Effort)

BE, Best Effort

Normal LAN Quality. No special measures taken to improve performance; should be as good (or bad) as it is now.

BK, Background

Bulk transfer. Applications not important enough to let them impact any other application of the network. This traffic may use surplus bandwidth

Traffic types not in the 802.1D standard

Name and abbreviation


XS, Excess

Data in exceeding the terms of any contract. Served or stored only when no other traffic is available. (Not even background).

CL-, Less Controlled Load

Defined to use an otherwise unused priority in LDoLL Extended. Somewhat less than Controlled Load.

UC, Uncontrolled Load

Like Less Controlled load, only even less less.

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