Commit 1e07381f authored by Leigh B. Stoller's avatar Leigh B. Stoller
Browse files

More text describing physical nodes and selecting the nodes you want.

parent 7de2131e
......@@ -7,6 +7,11 @@
<h2>Emulab Tutorial - Using Wireless Nodes</h2>
<font size=+1>
Creating an Experiment with Wireless Capable Nodes:</font>
Some Emulab nodes may contain wireless interfaces, and those nodes may
be scattered around at various locations. To find out where those
nodes are located and what their node IDs are, see the <a
......@@ -74,6 +79,14 @@ A few points should be noted:
create an experiment that uses more links (wired or wireless) on a
node, the experiment will fail to map.
<li> In the example above, we let Emulab decide what wireless nodes to
use for the lan. This is not an ideal approach, as Emulab does
not currently track the connectivity of nodes, and so might pick
a set of nodes (randomly) that cannot communicate with each
other. See the section below on <a href="#ChoosingNodes">choosing
your nodes</a> for more information on how to overcome this
<li> You must specify which node is to act as the <em>access point</em> for
the lan. Rather then using dedicated access points, Emulab's
implementation of wireless lans uses the interface's capability to
......@@ -81,6 +94,8 @@ A few points should be noted:
access point should obviously be within range of all of the nodes in
the lan. There is currently no automated mechanism to pick the access
point for you, but one is planned for the future.
Also planned for the future is to support <em>ad-hoc</em> mode on
the cards.
<li> Wireless lans allow a number of configuration parameters to be
specified, either for the lan as a whole, or for individual members of
......@@ -166,4 +181,58 @@ XMLRPC interface: link_config proj=myproj exp=myexp
src=nodew1 link=lan0 "params={'txpower': 50}"
<a NAME="ChoosingNodes"></a>
<font size=+1>
Choosing Physical Nodes:</font>
As mentioned above, Emulab's default mapping of nodes in your virtual
topology, to physical nodes with wireless interfaces, does not
currently take into account physical connectivity (walls, floors,
electrical conduits, etc. all conspire to make it possible that two
wireless nodes 50 apart from each other will not actually be able to
communicate with each other). We <b>are</b> planning to add this
capability in the future, but in the meantime it is mostly up to you
to choose nodes that make sense for your topology. You might end up
having to make some trial and error runs, trying to find the right
set of nodes (including setting the accesspoint to different nodes in
a lan) before you get a working set.
To assist in this chore there are two Emulab specific NS extensions
you can use in your NS file. The first is to use <tt>tb-fix-node</tt>
for all (or some) of the nodes in your lan. Using the
<a href=>wireless floormaps</a>
choose which nodes you want, and then in your NS file:
set nodew1 [$ns node]
set nodew2 [$ns node]
set nodew3 [$ns node]
set nodew4 [$ns node]
tb-fix-node $nodew1 pc222
tb-fix-node $nodew2 pc223
tb-fix-node $nodew3 pc224
tb-fix-node $nodew4 pc225 </code></pre>
Keep in mind that the physical nodes you choose must be free when you
swap in your experiment! The second approach is to use the
<tt>tb-use-physnaming</tt> extension.
tb-use-physnaming 1
set pc222 [$ns node]
set pc223 [$ns node]
set pc224 [$ns node]
set pc225 [$ns node] </code></pre>
which says that whenever a node is named by an existing physical node
in the testbed, do an implicit fix-node. This saves a little bit of
typing, and in some cases might be easier to manage.
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