Net4sat wiki

To assess the delay in a deployed network, one may easily exploit the results given by the ICMP ping command. However, this measure may not reflect the actual delay that applications may face. To properly measure the delay in a given infrastructure, we recommend to compare the results of various delay measurements jobs. Depending on the targeted evaluation (application level, transport level, network level, etc.), one measure may be more relevant than one other.

The most common way to assess delay in a deployed network remains to use round-trip time metric. Our choice is to use two tools one at ICMP level (fping) and one at UDP level (d-itg) to enforce the measurement.

However, this value may not reflect the real situation of the network of interest if the links from test host and to test host are unbalanced. To obtain this unbalanced delay assessment and better understanding of the tested network, one may use one-way delay tool which provides delay values on each link. The tool owping (composed of two jobs: owamp-client and owamp-server) is provided by OpenBACH in the One Way Delay reference scenario.

This scenario provides a delay diagnostic of a deployed network. It is assumed that the network is stable. The diagnostic allows to sequentially assess different delay metrics (RTT)

The purpose of this scenario is to compare delay results obtained from jobs: fping and d-itg (RTT).

• fping measures the RTT delay (in ms) using the ICMP protocol (i.e. time since ICMP request sent until ICMP response received)

• d-itg measures the RTT delay (in ms) using the an UDP connection (i.e. time since d-itg sender the packet until d-itg sender receive the same packet from d-itg receiver).

D-itg and fping (which are persistent jobs) are launched during the duration time (default 10).

Two approaches are used to analyse the delay:

• The default first one considers a sequential launch of the two jobs in order to avoid any overload caused by the injected test packets (active measurement methods).
• The second one considers a parallel/simultaneous launch of the two jobs

The scenario proposed herein will then:

• Launch subscenarios delay_simultaneous or delay_sequential as subscenarios (allowing to compare the RTT measurement of fping, d-itg).
• Launch two postprocessing jobs to compare the time-series and the CDF of the delay measurements.

These scenarios have been written using the scenario builder.

The scenario is available in network_delay . It uses helpers (see API scenario manual for more information on helpers), and subscenarios delay_sequential and delay_simultaneous.

You must already have a project (i.e. “your_project”), two entities in the project (a server and a client), the d-itg_send/fping jobs installed in the client and d-itg_recv job installed in the server. You also need to install histogram and time-series jobs on the “your_entity”.

The executor script executor_network_delay will allow to launch it as follows.

python3 executor_network_delay.py PROJECT_NAME --client-entity your_client_entity --server-entity your_server_entity --client-ip your_client_ip --server-ip your_server_ip  --post-processing-entity your_entity run

By default, it launches the scenario with the sequential methodology. If you want to launch the simultaneous one, you should add “–simultaneous” to your arguments.

By default, it launches the scenario for a duration of 10 seconds. If you want to change the duration, you should add “–duration duration_in_sec”

Alternatively, it can create a JSON file that could be imported to the OpenBACH web interface:

python3 executor_network_delay.py PROJECT_NAME --client-entity your_client_entity --server-entity your_server_entity --client-ip your_client_ip --server-ip your_server_ip --post-processing-entity your_entity build .

An example of the type of results that this scenarios is capable of plotting is shown below:

The plots can be downloaded from the OpenBACH web interface: go to the scenario instance, click on export CSV, check the histogram and time-series boxes and click on Download.