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Add initial peers in SDP (#105)
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* Add initial peers in SDP

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Co-Authored-By: rsanchez15 <[email protected]>

Co-authored-by: rsanchez15 <[email protected]>
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@EduPonz @rsanchez15
EduPonz and rsanchez15 authored Apr 1, 2020
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75 changes: 60 additions & 15 deletions docs/advanced.rst
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Expand Up @@ -516,14 +516,49 @@ In that case, *eProsima Fast RTPS* understands to calculate well-known port for
Initial peers
=============

These locators are used to know where to send initial discovery network messages. You can set your own locators using
attribute ``rtps.builtin.initialPeersList``. By default *eProsima Fast RTPS* uses as initial peers the Metatraffic
Multicast Locators.
According to the `RTPS standard <https://www.omg.org/spec/DDSI-RTPS/2.2/PDF>`_ (Section 9.6.1.1), each participant must
listen for incoming Participant Discovery Protocol (PDP) discovery metatraffic in two different ports, one linked with a
multicast address, and another one linked to a unicast address (see :ref:`discovery`).
Fast-RTPS allows for the configuration of an initial peers list which contains one or more such address-port pairs
corresponding to remote participants PDP discovery listening resources, so that the local participant will not only
send its PDP traffic to the default multicast address-port specified by its domain, but also to all the address-port
pairs specified in the initial-peers list.

A participant's initial peers list contains the list of address-port pairs of all other participants with
which it will communicate.
It is a list of addresses that a participant will use in the unicast discovery mechanism, together or as an alternative
to multicast discovery.
Therefore, this approach also applies to those scenarios in which multicast functionality is not available.

According to the `RTPS standard <https://www.omg.org/spec/DDSI-RTPS/2.2/PDF>`_ (Section 9.6.1.1), the participants'
discovery traffic unicast listening ports are calculated using the following equation:
7400 + 250 * `domainID` + 10 + 2 * `participantID`.
Thus, if for example a participant operates in Domain 0 (default
domain) and its ID is 1, its discovery traffic unicast listening port would be: 7400 + 250 * 0 + 10 + 2 * 1 = 7412.
By default *eProsima Fast RTPS* uses as initial peers the Metatraffic Multicast Locators.

The following constitutes an example configuring an Initial Peers list with one peer on host 192.168.10.13 with
participant ID 1 in domain 0.

+---------------------------------------------------------+
| **C++** |
+---------------------------------------------------------+
| .. literalinclude:: ../code/CodeTester.cpp |
| :language: c++ |
| :start-after: //CONF_INITIAL_PEERS_BASIC |
| :end-before: //!-- |
+---------------------------------------------------------+
| **XML** |
+---------------------------------------------------------+
| .. literalinclude:: ../code/XMLTester.xml |
| :language: xml |
| :start-after: <!-->CONF_INITIAL_PEERS_BASIC<--> |
| :end-before: <!--><--> |
+---------------------------------------------------------+

.. These locators are used to know where to send initial discovery network messages. You can set your own locators using
.. attribute ``rtps.builtin.initialPeersList``.
.. literalinclude:: ../code/CodeTester.cpp
:language: c++
:start-after: //CONF-INITIALPEERS
:end-before: //!--
.. _whitelist-interfaces:

Expand Down Expand Up @@ -1058,14 +1093,15 @@ The specification splits up the SIMPLE discovery protocol into two independent p
exchange of information in order to discover the RTPS entities contained in each of them, i.e. the writer and
reader Endpoints.

+--------------------------+-----------------------------------------------------------------------+
| Name | Description |
+==========================+=======================================================================+
| `Initial Announcements`_ | It defines the behavior of the RTPSParticipant initial announcements. |
+--------------------------+-----------------------------------------------------------------------+
| `Simple EDP Attributes`_ | It defines the use of the SIMPLE protocol as a discovery protocol. |
+--------------------------+-----------------------------------------------------------------------+

+------------------------------+-----------------------------------------------------------------------+
| Name | Description |
+==============================+=======================================================================+
| `Initial Announcements`_ | It defines the behavior of the RTPSParticipant initial announcements. |
+------------------------------+-----------------------------------------------------------------------+
| `Simple EDP Attributes`_ | It defines the use of the SIMPLE protocol as a discovery protocol. |
+------------------------------+-----------------------------------------------------------------------+
| :ref:`Simple Initial Peers` | A list of endpoints to which the SPDP announcements are sent. |
+------------------------------+-----------------------------------------------------------------------+

.. _`Initial Announcements`:

Expand Down Expand Up @@ -1147,6 +1183,15 @@ Simple EDP Attributes
| :end-before: <!--><--> |
+---------------------------------------------------------+

.. _`Simple Initial Peers`:

Initial Peers
-------------

By default, the SPDP protocol uses a well known multicast address for the participant discovery phase.
With Fast-RTPS, it is possible to expand the list of endpoints to which the participant announcements are sent by
configuring a list of initial peers, as explained in :ref:`initial-peers`.

.. _discovery_static:

STATIC Endpoints Discovery Settings
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