Side_1_360

The VoIP is a specialisation of the CBR module

where the stream of packets has random breaks.

Both the time between breaks and the break

duration follow a negative exponential distribu-

tion. The VoIP module was created to model

silence suppression in an audio stream as intro-

duced and described in [Brad69].

2.2.1.5 Overview of Interface Modules

In Table 1 is given an overview of the current

set of interface modules. New modules will be

developed as requested by new models in new

traffic scenarios.

2.2.2 Example of a User Behaviour Model

In Section 2.1 the modelling framework of Gen-

Syn was described. The two-layered modelling

consists of a flexible and scalable state diagram

approach for describing the user-behaviour and

the interface modules described in the previous

sections. This means that on top of the interface

modules that were introduced in the previous

section many source models can be described.

In [Heeg01] descriptions can be found of an FTP

client that uses the FTP module and a voice

model that uses either the VoIP (for modelling

of silence suppression) or the CBR module. In

[Heeg00] models of a web and video server are

given.

In this section a model that combines the FTP

and voice models from [Heeg01] will be briefly

described to demonstrate another aspect of the

flexibility of the GenSyn framework, namely the

ability to use more than one interface module in

the same model. First the descriptions of the

FTP and voice models from [Heeg01] are

repeated before the complete combined model is

given.

2.2.2.1 The FTP Client

The overall model of the FTP clients describes

the user behaviour within and between sessions

by the 3-state model in Figure 8. A session is

essentially the same as the web sessions defined

in [Vic98] as a sequence of packets with less

than 30 minutes between two consecutive file

requests. The following states are defined:

• Idle– the user is in-between sessions.


• Read– the user reads the downloaded web
  page or a file and considers what to do next,
  download another one, or close the session?


• Download– the user opens a connection to a
  url address, randomly selected from a list of
  addresses, and downloads this page or file. In
  the web interface module the page is parsed
  and all corresponding image files and applets
  are downloaded.

Module Protocol Source Source Destination Destination Packet Packet Send

IP port IP port size interarrival period

Mpeg Udp Fixed, Random, Random Parameter Frame size Frame Random,

given uniform from IP from is interarrival neg. exp.

by the in (25000, address parameter parameter is parameter distributed

machine 30000] list file from from

parameter parameter

file file

Cbr Udp Fixed, Random, Random Parameter Parameter Parameter Random,

given uniform from IP from from from neg. exp.

by the in (30000, address parameter parameter parameter distributed

machine 35000] list file file file

VoIP Udp Fixed, Random, Random Parameter Parameter Parameter Random,

given uniform from IP from from from neg. exp.

by the in (20000, address parameter parameter parameter distributed

machine 25000] list file file file

Web http-tcp Fixed, Random, Random Fixed, Parameter, Variable, Variable,

given given from 80, 90 file size given constrained

by the by http url list is given by tcp/ip by the

machine by web behaviour network

page size and

in url list servers

FTP http-tcp Fixed, Random, Random Fixed, Parameter, Variable, Variable,

given given from 80, 90 file size given constrained

by the by http file list is given by tcp/ip by the

machine in file list behaviour network

and

servers

Table 1 Characteristics of
the current available set of
interface modules