\section pf_basics Basic concepts
-Nowadays, the Internet is composed of a bunch of independently managed
-networks. Within each of those networks, there are entry and exit
-points (most of the time, you can both enter and exit through the same
-point); this allows to leave the current network and reach other
-networks, possibly even in other locations.
-At the upper level, such a network is called
-<b>Autonomous System (AS)</b>, while at the lower level it is named
-sub-network, or LAN (local area network).
-They are indeed autonomous: routing is defined
-(within the limits of his network) by the administrator, and so, those
-networks can operate without a connection to other
-networks. So-called gateways allow you to go from one network to
-another, if such a (physical) connection exists. Every node in one network
-that can be directly reached (i.e., without traversing other nodes) from
-another network is called a gateway.
-Each autonomous system consists of equipment such as cables (network links),
-routers and switches as well as computers.
-
-The structure of the SimGrid platform description relies exactly on the same
-concept as a real-life platform (see above). Every resource (computers,
-network equipment etc.) belongs to an AS, which can be defined by using the
-\<AS\> tag. Within an AS, the routing between its elements can be defined
-abitrarily. There are several modes for routing, and exactly one mode must be
-selected by specifying the routing attribute in the AS tag:
+It is certainly very tempting to defining how the information is
+routed in the simulated network in a way that is very similar to how
+it is defined on real network. One would have to define the routing
+tables of each routers interconnections sub-networks, just like in the
+real life. Given the daunting amount of configuration required, we
+could complete the information given by the user with classical
+protocols such as BGP and RIP. Many network simulator take such
+configuration as an input, for good reasons.
+
+This is not the way it goes in SimGrid: the network routing is defined
+in a global and compact way instead. This eases the modeling of very
+large systems, and allows highly optimized datastructures and
+algorithms in the simulator. The proposed description mechanism is
+thus much more convinient and efficient. In addition, it is more
+expressive than the classical solution based on forwarding tables on
+each host and router.
+
+The price to pay is that this representation of networks is very
+specific to SimGrid, so you will have to read further to understand
+it, even if you already know how real networks work.
+
+The central notion here are \b Networking \b Zones. NetZones represent
+network areas in which the routing is done in an homogeneous way.
+Conceptually, netzones generalize from the ideas of local networks
+(such as Ethernet switched networks) and Autonomous System. The
+network as a whole is represented as a single hierarchy of netzones,
+meaning that every netzone is part of another netzone (but the \c
+NetRoot, which is the top-level netzone).
+
+The main goal of the routing module is to provide a list of links
+traversed by a given communication and/or a latency to apply. These
+information are then used by the network model to compute the time
+that this communication takes. This information is retrieved by three
+combined algorithms: intra-zone routing, inter-zone routing, and the
+bypass mechanism.
+
+The <b>intra-zone level</b> is naturally handled by the netzones. Each
+netzone have to specify the routing algorithm it uses for that.
+@ref{FullZone} netzones have complete matrix where matrix(a,b)
+represents the full path (the list of links) between the hosts a and
+b. @ref{FloydZone} apply the Floyd-Warshall algorithm to compute the
+paths. @ref{ClusterZone} model classical switched or hub networks,
+where each component is connected through a private link onto a common
+backbone. Many other routing algorithms are provided to model the
+classical needs, but you can naturally define your own routing if the
+provided ones do not fit your needs.
+
+The <b>inter-zone algorithm</b> is used when the communication
+traverses more than one zone. The overall path goes from the source up
+in the netzones' tree, until the first common ancestor zone, and moves
+down to the destination. It crawls the differing netzones on its path
+according to the user-defined inter-zone routes, moving from gateway
+to gateway.
+
+You can also use the <b>bypass mechanism</b> to specify manually some
+shortcuts that directly provide the list of links interconnecting two
+given processes.
+
\verbatim
-<AS id="AS0" routing="Full">
+<AS id="netzone0" routing="Full">
\endverbatim
\remark
Other supported values for the routing attribute can be found below, Section
\ref pf_raf.
-There is also the ``<route>`` tag; this tag takes two attributes, ``src`` (source)
-and ``dst`` (destination). Both source and destination must be valid identifiers
-for routers (these will be introduced later). Contained by the ``<route>`` are
-network links; these links must be used in order to communicate from the source
-to the destination specified in the tag. Hence, a route merely describes
+There is also the ``<route>`` tag; this tag takes two attributes,
+``src`` (source) and ``dst`` (destination). Both source and
+destination must be valid identifiers for routers (these will be
+introduced later). Contained by the ``<route>`` are network links;
+these links must be used in order to communicate from the source to
+the destination specified in the tag. Hence, a route merely describes
how to reach a router from another router.
\remark
More information and (code-)examples can be found in Section \ref pf_rm.
-An AS can also contain itself one or more AS; this allows you to
-model the hierarchy of your platform.
+A netzone can also contain itself one or more netzone; this allows you to model
+the hierarchy of your platform.
### Within each AS, the following types of resources exist:
link | \ref pf_link | In SimGrid, (network)links define a connection between two or potentially even more resources. Every link has a bandwidth and a latency and may potentially experience congestion.
cluster | \ref pf_cluster | In SimGrid, clusters were introduced to model large and homogenous environments. They are not really a resource by themselves - technically, they are only a shortcut, as they will internally set up all the hosts, network and routing for you, i.e., using this resource, one can easily setup thousands of hosts and links in a few lines of code. Each cluster is itself an AS.
-%As it is desirable to interconnect these resources, a routing has to be
-defined. The AS is supposed to be Autonomous, hence this has to be done at the
-AS level. The AS handles two different types of entities (<b>host/router</b>
-and <b>AS</b>). However, the user is responsible to define routes between those resources,
-otherwise entities will be unconnected and therefore unreachable from other
-entities. Although several routing algorithms are built into SimGrid (see
-\ref pf_rm), you might encounter a case where you want to define routes
-manually (for instance, due to specific requirements of your platform).
+As it is desirable to interconnect these resources, a routing has to
+be defined. The AS is supposed to be Autonomous, hence this has to be
+done at the AS level. The AS handles two different types of entities
+(<b>host/router</b> and <b>AS</b>). However, the user is responsible
+to define routes between those resources, otherwise entities will be
+unconnected and therefore unreachable from other entities. Although
+several routing algorithms are built into SimGrid (see \ref pf_rm),
+you might encounter a case where you want to define routes manually
+(for instance, due to specific requirements of your platform).
There are three tags to use:
\li <b>ASroute</b>: to define routes between two <b>AS</b>
\subsubsection pf_router <router/>
-%As said before, <b>router</b> is used only to give some information
+As said before, <b>router</b> is used only to give some information
for routing algorithms. So, it does not have any attributes except :
#### Attributes ####
\subsubsection pf_routing_tag_bypassasroute bypassASroute
-%As said before, once you choose
+As said before, once you choose
a model, it (most likely; the constant network model, for example, doesn't) calculates routes for you. But maybe you want to
define some of your routes, which will be specific. You may also want
to bypass some routes defined in lower level AS at an upper stage:
\subsubsection pf_routing_tag_bypassroute bypassRoute
-%As said before, once you choose
+As said before, once you choose
a model, it (most likely; the constant network model, for example, doesn't) calculates routes for you. But maybe you want to
define some of your routes, which will be specific. You may also want
to bypass some routes defined in lower level AS at an upper stage :
(h2) from AS_2 then you'll have to proceed as follows:
\li First, you have to ensure that a route is defined from h1 to the
AS_1's exit gateway and from h2 to AS_2's exit gateway.
-\li Then, you'll have to define a route between AS_1 to AS_2. %As those
+\li Then, you'll have to define a route between AS_1 to AS_2. As those
AS are both resources belonging to AS_Big, then it has to be done
at AS_big level. To define such a route, you have to give the
source AS (AS_1), the destination AS (AS_2), and their respective
defined inside AS_Big. If you choose some shortest-path model,
this route will be computed automatically.
-%As said before, there are mainly 2 tags for routing :
+As said before, there are mainly 2 tags for routing :
\li <b>ASroute</b>: to define routes between two <b>AS</b>
\li <b>route</b>: to define routes between two <b>host/router</b>
-%As we are dealing with routes between AS, it means that those we'll
+As we are dealing with routes between AS, it means that those we'll
have some definition at AS_Big level. Let consider AS_1 contains 1
host, 1 link and one router and AS_2 3 hosts, 4 links and one router.
There will be a central router, and a cross-like topology. At the end
of the crosses arms, you'll find the 3 hosts and the router that will
act as a gateway. We have to define routes inside those two AS. Let
say that AS_1 contains full routes, and AS_2 contains some Floyd
-routing (as we don't want to bother with defining all routes). %As
+routing (as we don't want to bother with defining all routes). As
we're using some shortest path algorithms to route into AS_2, we'll
then have to define some <b>route</b> to gives some topological
information to SimGrid. Here is a file doing it all :
to describe a platform. The main concept is that you have some peers
that are located somewhere: this is the function of the
<b>coordinates</b> of the \<peer\> or \<host\> tag. There's nothing
-complicated in using it, here is an example of it:
+complicated in using it, here is an example:
\verbatim
<?xml version='1.0'?>
<!DOCTYPE platform SYSTEM "http://simgrid.gforge.inria.fr/simgrid.dtd">
<platform version="4">
-<config id="General">
- <prop id="network/coordinates" value="yes"></prop>
-</config>
<AS id="AS0" routing="Vivaldi">
<host id="100030591" coordinates="25.5 9.4 1.4" speed="1.5Gf" />
<host id="100036570" coordinates="-12.7 -9.9 2.1" speed="7.3Gf" />
<!DOCTYPE platform SYSTEM "http://simgrid.gforge.inria.fr/simgrid.dtd">
<platform version="4">
-<config id="General">
- <prop id="network/coordinates" value="yes"></prop>
-</config>
<AS id="AS0" routing="Vivaldi">
<peer id="peer-0" coordinates="173.0 96.8 0.1" speed="730Mf" bw_in="13.38MBps" bw_out="1.024MBps" lat="500us"/>
<peer id="peer-1" coordinates="247.0 57.3 0.6" speed="730Mf" bw_in="13.38MBps" bw_out="1.024MBps" lat="500us" />
