.. _guide-101-networkproximity:

Creating a network proximity service
====================================

.. _guide-networkproximity-overview:

Overview
========

A network proximity service answers queries regarding the network
proximity between hosts. The service accomplishes this by periodically
performing round-trip network transfer experiments between hosts,
keeping a record of observed network transfer times, and computing
network distances.

.. _guide-networkproximity-creating:

Creating a network proximity service
====================================

In WRENCH, a network proximity service is defined by the
:cpp:class:`wrench::NetworkProximityService` class, an instantiation of which
requires the following parameters:

-  The name of a host on which to start the service;
-  A set of hosts names in a vector (``std::vector``), which define
   which hosts are monitored by the service; and
-  Maps (``std::map``) of configurable properties
   (:cpp:class:`wrench::NetworkProximityServiceProperty`) and configurable
   message payloads (:cpp:class:`wrench::NetworkProximityServiceMessagePayload`).

The example below creates an instance that runs on host
``Networkcentral``, and can answer network distance queries about hosts
``Host1``, ``Host2``, ``Host3``, and ``Host4``. The service’s properties
are customized to specify that the service performs network transfer
experiments on average every 60 seconds, that the Vivaldi algorithm is
used to compute network coordinates, and that the message sent to the
service to lookup an entry is configured to be 1KiB:

.. code:: cpp

   auto np_service = simulation->add(
             new wrench::NetworkProximityService("Networkcentral", 
                                          {"Host1", "Host2", "Host3", "Host4"},
                                          {{wrench::NetworkProximityServiceProperty::NETWORK_PROXIMITY_MEASUREMENT_PERIOD, "60"},
                                           {wrench::NetworkProximityServiceProperty::NETWORK_PROXIMITY_SERVICE_TYPE, "VIVALDI"}},
                                          {{wrench::NetworkProximityServiceMessagePayload::NETWORK_DB_LOOKUP_REQUEST_MESSAGE_PAYLOAD, "1024"}});

See the documentation of :cpp:class:`wrench::NetworkProximityServiceProperty` and
:cpp:class:`wrench::NetworkProximityServiceMessagePayload` for all possible
configuration options.