Specifications

Chapter 5
Traffic Generation
The network tester generates traffic according to a traffic description table that is loaded
into the network cards before a test is started. By network traffic we understand a stream
of packets. The way the packets are related inside the stream depends on the application,
but in general we c an specify some statistical parameters that characterize the traffic.
Our traffic generator produces the packet stream according to a specified traffic pattern
description.
The traffic generator takes this description as an input and produces at the output a set
of packet descriptors. A packet descriptor is a group of some fields that characterize one
network packet. These fields can be: Source, Destination, Packet size, Inter packet time and
so on. These fields are all that we need to build a complete network packe t. The additional
fields inside a packet (like checksum or length) are computed using this information.
5.1 Traffic profiles
Various types of traffic profiles (or traffic pattern descriptions) can be used. We can have
CBR traffic (Constant Bit Rate), bursts of packets, Poisson traffic, random, round robin or
any kind of combination of those. The user can c reate also his own custom traffic profiles.
The pattern description is specified by giving the statistical distribution for each of the
fields inside a packet descriptor (packet size, destination, inter packet time, etc). Then
the program generates random packets that have the required statistical characteristics. In
this way many kind of applications can be simulated and many types of traffic profiles are
possible. The distributions for different fields of the packet can be independent or correlated
such that some fields app ear in pairs.
The output of the traffic generator is used to program the network cards to generate packets
according to the specifications. The Figure 5.1 shows a block diagram of the whole system.
At the end of the chain we have the post-processing software that will program the net-
working hardware to generate the traffic. Different post-proce ss ing software can produce
output for various types of hardware (network cards). Finally the network hardware is
programmed to generate the required traffic.
The fields inside a packet descriptor are shown in the following table:
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