Side_1_360

multi-point performance statistics are less com-
putation intensive and can be useful to check
that a certain scenario was run successfully.

4.2.2.2 Point-to-point Performance
The performance from a certain source to a
given destination for a specified type of packets
is investigated by correlating information from
two packet traces. The statistics computed
include:

• Average unidirectional packet loss ratio;


• Average unidirectional throughput (pps and
  bps);


• Unidirectional packet delay
  
  
  • Empirical delay distribution in bins of one
    ms computed over the whole measurement
    period;
  
  
  • Average delay in bins of various sizes as a
    function of time.
  
  
  
  

In addition, various statistics are computed for
the entire measurement period.

Note that point-to-point performance provides
statistics addressing unidirectional performance
including delay and packet loss. However, the
processing is computation intensive and requires
a substantial amount of time for large packet
traces.

5 Closing Comments

The measurement platform developed for QoS
tests of the IP network consists of two main
components; (i) to derive performance measures
like end-to-end packet loss and one-way packet
delay accurate traffic measurements are con-
ducted by external monitors, i.e. dedicated PCs
with a specialized interface card (DAG), and (ii)
a Java based traffic generator (GenSyn) that runs
on a dedicated PC produces synthetic traffic
according to an aggregation of stochastic appli-
cation models. This test bed configuration is a
very flexible platform that opens for doing many

exciting and controlled QoS performance evalu-

ation measurements in an IP network.

5.1 Measurement Probes

The actual measurement instrumentation for

QoS testing of IP networks deploys dedicated

PCs placed at strategic locations that passively

collect measurement data. These PCs are syn-

chronized by GPS.

The measurement probes in the test bed are very

flexible and enables a capturing level down to a

single IP packet if necessary. The monitor set-up

can be used with or without traffic generators,

the GenSyn is only used when the live traffic in

the network is not sufficient or the experiments

require controllable and reproducible traffic

loads. This means that the concepts developed

for this measurement platform can be of interest

also in other communication networks, e.g. the

service production platform, for testing of stabil-

ity, scalability, verification of service quality,

accounting, billing, and network surveillance

systems (OSS).

5.2 Traffic Generators

GenSyn is a Java process that generates IP traf-

fic using a flexible, scalable, stochastic mod-

elling framework for describing the user

behaviour of Internet sources. This stochastic

behaviour model is linked to the underlying pro-

tocol stack and generates real packets into the

network. This is a novel modelling approach that

chooses the best of two world; flexibility and

scalability of composite state models, and accu-

racy in the protocol behaviour by use of the

underlying protocol stack instead of making a

model of it.

5.2.1 GenSyn Modelling Framework

The modelling framework itself is flexible and

prepared for modelling of many different Inter-

net applications. Several model examples are

described in the GenSyn framework, including

web, FTP, VoIP, MPEG video, and constant

packet rate. The models developed are to some

extent parameter controlled and can therefore

easily be changed with respect to the number of

users, state sojourn times, size of packets, time

between packets, IP destination and source

addresses, file and web page locations.

New user behaviour state models using existing

interface modules can be developed without any

changes in the GenSyn implementation.

5.2.2 GenSyn Constraints

The scalability of the generator is limited by the

time granularity and time scheduler of the Java

Runtime Environment (JRE). The portability of

the generator is limited by both the inconsisten-

cies between different versions of Java APIs,

GenSyn availability

A free licence for non-commercial use of

GenSyn can be obtained by sending an

email to: [email protected]. The

licence does not include source code.

Please visit http://www.item.ntnu.no/~poulh/

GenSyn/gensyn.html for further details.

The GenSyn distribution comes with a set of

models and parameter lists with default val-

ues. The interface module parameters are

described in Table 1.