+++ /dev/null
-.. _models:
-
-The SimGrid Models
-##################
-
-.. todo::
-
- - Main existing models (contention, cste, LM07)
- - Main concepts (Routing, LMM) + link to the papers
- - How to switch on the command line
-
-.. _understanding_lv08:
-
-The default TCP model
-*********************
-
-When simulating a data transfer between two hosts, you may be surprised
-by the obtained simulation time. Lets consider the following platform:
-
-.. code-block:: xml
-
- <host id="A" speed="1Gf" />
- <host id="B" speed="1Gf" />
-
- <link id="link1" latency="10ms" bandwidth="1Mbps" />
-
- <route src="A" dst="B">
- <link_ctn id="link1" />
- </route>
-
-If host `A` sends `100kB` (a hundred kilobytes) to host `B`, one could expect
-that this communication would take `0.81` seconds to complete according to a
-simple latency-plus-size-divided-by-bandwidth model (0.01 + 8e5/1e6 = 0.81).
-However, the default TCP model of SimGrid is a bit more complex than that. It
-
-accounts for three phenomena that directly impact the simulation time even
-on such a simple example:
-
- - The size of a message at the application level (i.e., 100kB in this
- example) is not the size that will actually be transferred over the
- network. To mimic the fact that TCP and IP headers are added to each packet of
- the original payload, the TCP model of SimGrid empirically considers that
- `only 97% of the nominal bandwidth` are available. In other words, the
- size of your message is increased by a few percents, whatever this size be.
-
- - In the real world, the TCP protocol is not able to fully exploit the
- bandwidth of a link from the emission of the first packet. To reflect this
- `slow start` phenomenon, the latency declared in the platform file is
- multiplied by `a factor of 13.01`. Here again, this is an empirically
- determined value that may not correspond to every TCP implementations on
- every networks. It can be tuned when more realistic simulated times for
- short messages are needed though.
-
- - When data is transferred from A to B, some TCP ACK messages travel in the
- opposite direction. To reflect the impact of this `cross-traffic`, SimGrid
- simulates a flow from B to A that represents an additional bandwidth
- consumption of `0.05`. The route from B to A is implicitly declared in the
- platform file and uses the same link `link1` as if the two hosts were
- connected through a communication bus. The bandwidth share allocated to the
- flow from A to B is then the available bandwidth of `link1` (i.e., 97% of
- the nominal bandwidth of 1Mb/s) divided by 1.05 (i.e., the total consumption).
- This feature, activated by default, can be disabled by adding the
- `--cfg=network/crosstraffic:0` flag to command line.
-
-As a consequence, the time to transfer 100kB from A to B as simulated by the
-default TCP model of SimGrid is not 0.81 seconds but
-
-.. code-block:: python
-
- 0.01 * 13.01 + 800000 / ((0.97 * 1e6) / 1.05) = 0.996079 seconds.
-
-.. _model_ns3:
-
-ns-3 as a SimGrid model
-***********************
-
-You can use the well-known `ns-3 packet-level network simulator
-<http://www.nsnam.org>`_ as a SimGrid model, for example to investigate the
-validity of your simulation. Just install ns-3 and recompile SimGrid
-accordingly.
-
-The SimGrid/ns-3 binding only contains features that are common to both systems.
-Not all ns-3 models are available from SimGrid (only the TCP and WiFi ones are),
-while not all SimGrid platform files can be used in conjunction ns-3 (routes
-must be of length 1). Also, the platform built in ns-3 from the SimGrid
-description is very basic. Finally, communicating from a host to
-itself is forbidden in ns-3, so every such communication completes
-immediately upon startup.
-
-
-Compiling the ns-3/SimGrid binding
-==================================
-
-Installing ns-3
----------------
-
-SimGrid requires ns-3 version 3.26 or higher, and you probably want the most
-recent version of both SimGrid and ns-3. While the Debian package of SimGrid
-don't have the ns-3 bindings activated, you can still use the packaged version
-of ns-3 by grabbing the ``libns3-dev ns3`` packages. Alternatively, you can
-install ns-3 from scratch (see the `ns-3 documentation <http://www.nsnam.org>`_).
-
-Enabling ns-3 in SimGrid
-------------------------
-
-SimGrid must be recompiled with the ``enable_ns3`` option activated in cmake.
-Optionally, use ``NS3_HINT`` to tell cmake where ns3 is installed on
-your disk.
-
-.. code-block:: shell
-
- cmake . -Denable_ns3=ON -DNS3_HINT=/opt/ns3 # or change the path if needed
-
-By the end of the configuration, cmake reports whether ns-3 was found,
-and this information is also available in ``include/simgrid/config.h``
-If your local copy defines the variable ``SIMGRID_HAVE_NS3`` to 1, then ns-3
-was correctly detected. Otherwise, explore ``CMakeFiles/CMakeOutput.log`` and
-``CMakeFiles/CMakeError.log`` to diagnose the problem.
-
-Test that ns-3 was successfully integrated with the following (from your SimGrid
-build directory). It will run all SimGrid tests that are related to the ns-3
-integration. If no test is run at all, you probably forgot to enable ns-3 in cmake.
-
-.. code-block:: shell
-
- ctest -R ns3
-
-Troubleshooting
----------------
-
-If you use a version of ns-3 that is not known to SimGrid yet, edit
-``tools/cmake/Modules/FindNS3.cmake`` in your SimGrid tree, according to the
-comments on top of this file. Conversely, if something goes wrong with an old
-version of either SimGrid or ns-3, try upgrading everything.
-
-.. _ns3_use:
-
-Using ns-3 from SimGrid
-=======================
-
-Platform files compatibility
-----------------------------
-
-Any route longer than one will be ignored when using ns-3. They are
-harmless, but you still need to connect your hosts using one-hop routes.
-The best solution is to add routers to split your route. Here is an
-example of an invalid platform:
-
-.. code-block:: xml
-
- <?xml version='1.0'?>
- <!DOCTYPE platform SYSTEM "https://simgrid.org/simgrid.dtd">
- <platform version="4.1">
- <zone id="zone0" routing="Floyd">
- <host id="alice" speed="1Gf" />
- <host id="bob" speed="1Gf" />
-
- <link id="l1" bandwidth="1Mbps" latency="5ms" />
- <link id="l2" bandwidth="1Mbps" latency="5ms" />
-
- <route src="alice" dst="bob">
- <link_ctn id="l1"/> <!-- !!!! IGNORED WHEN USED WITH ns-3 !!!! -->
- <link_ctn id="l2"/> <!-- !!!! ROUTES MUST CONTAIN ONE LINK ONLY !!!! -->
- </route>
- </zone>
- </platform>
-
-This can be reformulated as follows to make it usable with the ns-3 binding.
-There is no direct connection from alice to bob, but that's OK because ns-3
-automatically routes from point to point (using
-``ns3::Ipv4GlobalRoutingHelper::PopulateRoutingTables``).
-
-.. code-block:: xml
-
- <?xml version='1.0'?>
- <!DOCTYPE platform SYSTEM "https://simgrid.org/simgrid.dtd">
- <platform version="4.1">
- <zone id="zone0" routing="Full">
- <host id="alice" speed="1Gf" />
- <host id="bob" speed="1Gf" />
-
- <router id="r1" /> <!-- routers are compute-less hosts -->
-
- <link id="l1" bandwidth="1Mbps" latency="5ms"/>
- <link id="l2" bandwidth="1Mbps" latency="5ms"/>
-
- <route src="alice" dst="r1">
- <link_ctn id="l1"/>
- </route>
-
- <route src="r1" dst="bob">
- <link_ctn id="l2"/>
- </route>
- </zone>
- </platform>
-
-Once your platform is OK, just change the :ref:`network/model
-<options_model_select>` configuration option to `ns-3` as follows. The other
-options can be used as usual.
-
-.. code-block:: shell
-
- ./network-ns3 --cfg=network/model:ns-3 (other parameters)
-
-Many other files from the ``examples/platform`` directory are usable with the
-ns-3 model, such as `examples/platforms/dogbone.xml <https://framagit.org/simgrid/simgrid/tree/master/examples/platforms/dogbone.xml>`_.
-Check the file `examples/cpp/network-ns3/network-ns3.tesh <https://framagit.org/simgrid/simgrid/tree/master/examples/cpp/network-ns3/network-ns3.tesh>`_
-to see which ones are used in our regression tests.
-
-WiFi platforms
-^^^^^^^^^^^^^^
-
-In SimGrid, WiFi networks are modeled with WiFi zones, where a zone contains
-the access point of the WiFi network and the hosts connected to it (called
-station in the WiFi world). Links inside WiFi zones are modeled as regular
-links with a specific attribute, and these links are then added to routes
-between hosts. The main difference When using ns-3 WiFi networks is that
-the network performance is not given by the link bandwidth and latency but
-by the access point WiFi characteristics, and the distance between the access
-point and the hosts.
-
-So, to declare a new WiFi network, simply declare a zone with the ``WIFI``
-routing.
-
-.. code-block:: xml
-
- <zone id="SSID_1" routing="WIFI">
-
-Inside this zone you must declare which host or router will be the access point
-of the WiFi network.
-
-.. code-block:: xml
-
- <prop id="access_point" value="alice"/>
-
-Afterward simply declare the hosts and routers inside the WiFi network. Remember
-that one must have the same name as declared in the property "access point".
-
-.. code-block:: xml
-
- <router id="alice" speed="1Gf"/>
- <host id="STA0-0" speed="1Gf"/>
- <host id="STA0-1" speed="1Gf"/>
-
-Finally, close the WiFi zone.
-
-.. code-block:: xml
-
- </zone>
-
-The WiFi zone may be connected to another zone using a traditional link and
-a zoneRoute. Note that the connection between two zones is always wired.
-
-.. code-block:: xml
-
- <link id="wireline" bandwidth="100Mbps" latency="2ms" sharing_policy="SHARED"/>
-
- <zoneRoute src="SSID_1" dst="SSID_2" gw_src="alice" gw_dst="bob">
- <link_ctn id="wireline"/>
- </zoneRoute>
-
-WiFi network performance
-""""""""""""""""""""""""
-
-The performance of a wifi network is controlled by 3 property that can be added
-to hosts connected to the wifi zone:
-
- * ``mcs`` (`Modulation and Coding Scheme <https://en.wikipedia.org/wiki/Link_adaptation>`_)
- Roughly speaking, it defines the speed at which the access point is
- exchanging data with all stations. It depends on its model and configuration,
- and the possible values are listed for example on Wikipedia.
- |br| By default, ``mcs=3``.
- It is a property of the WiFi zone.
- * ``nss`` (Number of Spatial Streams, or `number of antennas <https://en.wikipedia.org/wiki/IEEE_802.11n-2009#Number_of_antennas>`_)
- defines the amount of simultaneous data streams that the AP can sustain.
- Not all value of MCS and NSS are valid nor compatible (cf. `802.11n standard <https://en.wikipedia.org/wiki/IEEE_802.11n-2009#Data_rates>`_).
- |br| By default, ``nss=1``.
- It is a property of the WiFi zone.
- * ``wifi_distance`` is the distance from the station to the access point. Each
- station can have a specific value.
- |br| By default, ``wifi_distance=10``.
- It is a property of stations of the WiFi network.
-
-Here is an example of a zone changing ``mcs`` and ``nss`` values.
-
-.. code-block:: xml
-
- <zone id="SSID_1" routing="WIFI">
- <prop id="access_point" value="alice"/>
- <prop id="mcs" value="2"/>
- <prop id="nss" value="2"/>
- ...
- </zone>
-
-Here is an example of a host changing ``wifi_distance`` value.
-
-.. code-block:: xml
-
- <host id="STA0-0" speed="1Gf">
- <prop id="wifi_distance" value="37"/>
- </host>
-
-Random Number Generator
------------------------
-
-It is possible to define a fixed or random seed to the ns3 random number
-generator using the config tag.
-
-.. code-block:: xml
-
- <?xml version='1.0'?><!DOCTYPE platform SYSTEM "https://simgrid.org/simgrid.dtd">
- <platform version="4.1">
- <config>
- <prop id = "network/model" value = "ns-3" />
- <prop id = "ns3/seed" value = "time" />
- </config>
- ...
- </platform>
-
-The first property defines that this platform will be used with the ns3 model.
-The second property defines the seed that will be used. Defined to ``time``
-it will use a random seed, defined to a number it will use this number as
-the seed.
-
-Limitations
------------
-
-A ns-3 platform is automatically created from the provided SimGrid
-platform. However, there are some known caveats:
-
- * The default values (e.g., TCP parameters) are the ns-3 default values.
- * ns-3 networks are routed using the shortest path algorithm, using ``ns3::Ipv4GlobalRoutingHelper::PopulateRoutingTables``.
- * End hosts cannot have more than one interface card. So, your SimGrid hosts
- should be connected to the platform through only one link. Otherwise, your
- SimGrid host will be considered as a router (FIXME: is it still true?).
-
-Our goal is to keep the ns-3 plugin of SimGrid as easy (and hopefully readable)
-as possible. If the current state does not fit your needs, you should modify
-this plugin, and/or create your own plugin from the existing one. If you come up
-with interesting improvements, please contribute them back.
-
-Troubleshooting
----------------
-
-If your simulation hangs in a communication, this is probably because one host
-is sending data that is not routable in your platform. Make sure that you only
-use routes of length 1, and that any host is connected to the platform.
-Arguably, SimGrid could detect this situation and report it, but unfortunately,
-this is still to be done.
-
-
-
-.. |br| raw:: html
-
- <br />
