- A mobile node consists of network components:
- Link Layer (LL)
- Interface Queue (IfQ)
- the MAC layer
- the PHY layer: the wireless channel that the node transmit and receive signals from
- At the beginning of a wireless simulation,
we need to define the
type
for each of these network components.
- Additionally, we need to define other parameters
like:
- the type of antenna
- the radio-propagation model
- the type of ad-hoc routing protocol used by mobilenodes etc.
- Creating wireless nodes
is also achieved using the
ns_ node
command:
set ns_ [new Simulator] ;# Create a NS simulator object set n1 [ns_ node] ;# Create a WIRELESS node !!!
- However:
-
BEFORE
creating a wireless node
you
MUST
first
select (configure)
the node configuration parameters to
"become" a
wireless node.
- The NS2 command to
select (configure)
node configuration parameters is
node-config
and it is used as follows:
set ns_ [new Simulator] ;# Create a NS simulator object $ns_ node-config \ -llType LL -ifqType "Queue/DropTail/PriQueue" -ifqLen 50 -macType Mac/802_11 -phyType "Phy/WirelessPhy" -addressingType flat or hierarchical or expanded -adhocRouting DSDV or DSR or TORA -propType "Propagation/TwoRayGround" -antType "Antenna/OmniAntenna" -channelType "Channel/WirelessChannel" -topoInstance $topo -energyModel "EnergyModel" -initialEnergy (in Joules) -rxPower (in W) -txPower (in W) -agentTrace ON or OFF -routerTrace ON or OFF -macTrace ON or OFF -movementTrace ON or OFF - The value of most of the parameters are
simple values
- Except for the value of the
-topoInstance
parameters.
- The topology
is a Topography
object that you must create.
Example:
set topo [new Topography] ;# Create a Topography object $topo load_flatgrid 500 500 ;# Make a 500x500 grid topology
- A commonly used
wireless node configuration is:
set ns_ [new Simulator] ;# Create a NS simulator object $ns_ node-config -llType LL -ifqType "Queue/DropTail/PriQueue" -ifqLen 50 -macType Mac/802_11 -phyType "Phy/WirelessPhy" -addressingType flat -adhocRouting DSR or DSDV -propType "Propagation/TwoRayGround" -antType "Antenna/OmniAntenna" -channelType "Channel/WirelessChannel" -topoInstance $topo -agentTrace ON -routerTrace ON -macTrace OFF -movementTrace OFF
- Unlike wired nodes which
connectivity
is determined by
wires
(defined by
duplex-link, see:
click here),
the
connectivity
of wireless nodes is determined by
their
distance
from one another.
- Because
wireless nodes can
MOVE,
their distances
from one another
change over time
- To
keep track
of their
positions
in the
topology grid,
we need to create a
General Operations Director (GOD)
object.
- Quoted from CMU document on the god object:
"God (General Operations Director) is the object that is used to store global information about the state of the environment, network or nodes that an omniscent observer would have, but that should not be made known to any participant in the simulation." - Currently, the God object stores:
- the total number of mobilenodes
- a table of shortest number of hops required to reach from one node to another.
- The next hop information is normally loaded into god object
from movement pattern files, before simulation begins.
That is because calculating this on the fly during simulation runs can be quite time consuming.
- In the first example on wireless networking,
we will keep the example simple and
avoid using movement pattern files
So, we will not provide the God object with next hop information.
(This step will be included in the next example)
- NS Tutorial by Marc Greis (with wireless simulation): click here
- NS by Example (no wireless simulation): click here
- Zhibin Wu's page on Wireless Simulation (good description on internals of NS2): click here or for the local copy: click here