To test the adaptability of network-aware applications, a toolkit is
required, to generate network traffic and watch the application's reactions.
While several network simulation products exist, this toolkit should act
as an emulator, producing real application-level data traffic on a network.
In addition, off-line analysis of experiments should be possible.
There are three basic requirements for the emulation part of the toolkit
to be met; first, it must be possible to designate several nodes of a network
as source or sink. Nodes should act as applications, producing or consuming
network traffic of a certain kind. The second point is the generation of
realistic application-level traffic of different types. Finally, sent and
received data are to be traced carefully by all nodes for evaluation reasons.
Experiments are prepared in specification files, by description of start-
and end-nodes of various sessions of different types. Three different traffics
on the application-level are supported by the toolkit. These are Telnet,
FTP and Constant Bit Rate (CBR). The statistical properties
of synthetic Telnet and FTP traffic are modeled by using tcplib,
a free available library of TCP traffic characteristics. The behavior of
CBR applications is to be specified by the user.
Time and size of sent or received data packets is logged in files by all
applications. These files are used to calculate delay times or
round trip times of packets, and bandwidths or loss
rates of applications. After calculations are completed, user defined
graphical output is produced for evaluation and analysis of an experiment.
Apart from the description of the developed software several experiments
are presented and interpreted. They are illustrating capabilities and limits
of the toolkit. One possible use of the toolkit in testing network-aware
applications is to run in parallel an experiment and the application that
is to be tested.