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update manual

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This commit is contained in:
Mirko Banchi
2009-05-01 14:34:27 +02:00
parent 1066eb4764
commit 6bf3f47ea5
1 changed files with 76 additions and 17 deletions
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doc/manual/wifi.texi
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@@ -30,34 +30,55 @@ specification.
The current implementation provides roughly four levels of models:
@itemize @bullet
@item the @strong{PHY layer models}
@item the so-called @strong{MAC low models}: they implement DCF
@item the so-called @strong{MAC low models}: they implement DCF and EDCAF
@item the so-called @strong{MAC high models}: they implement the MAC-level
beacon generation, probing, and association state machines, and
@item a set of @strong{Rate control algorithms} used by the MAC low models
@end itemize
There are presently three @strong{MAC high models}:
There are presently six @strong{MAC high models}, three for non-QoS MACs and three
for QoS MACs.
@itemize @bullet
@item @strong{non-QoS MACs:}
@enumerate
@item a simple adhoc state machine that does not perform any
kind of beacon generation, probing, or association. This
state machine is implemented by the @code{ns3::AdhocWifiNetDevice}
and @code{ns3::MacHighAdhoc} classes.
state machine is implemented by the @code{ns3::AdhocWifiMac} class.
@item an active probing and association state machine that handles
automatic re-association whenever too many beacons are missed
is implemented by the @code{ns3::NqstaWifiNetDevice} and
@code{ns3::MacHighNqsta} classes.
is implemented by the @code{ns3::NqstaWifiMac} class.
@item an access point that generates periodic beacons, and that
accepts every attempt to associate. This AP state machine
is implemented by the @code{ns3::NqapWifiNetDevice} and
@code{ns3::MacHighNqap} classes.
@end enumerate
is implemented by the @code{ns3::NqapWifiMac} class.
@end enumerate
@item @strong{QoS MACs:}
@enumerate
@item a simple adhoc state machine like above but also able to manage QoS traffic.
This state machine is implemented by @code{ns3::QadhocWifiMac} class.
@item a station state machine like above but also able to manage QoS traffic.
Implemented by @code{ns3::QstaWifiMac}.
@item a QoS access point state machine like above implemented by @code{ns3::QapWifiMac}.
@end enumerate
@end itemize
With QoS MAC models is possible to work with traffic belonging to
four different access classes: @strong{AC_VO} for voice traffic, @strong{AC_VI}
for video traffic, @strong{AC_BE} for best-effort traffic and @strong{AC_BK}
for background traffic.
In order to determine MSDU's access class, every packet forwarded down
to these MAC layers should be marked using @code{ns3::QosTag} in order to set
a TID (traffic id) for that packet otherwise it will be considered
belonging to @strong{AC_BE} access class.
The @strong{MAC low layer} is split into three components:
@enumerate
@item @code{ns3::MacLow} which takes care of RTS/CTS/DATA/ACK transactions.
@item @code{ns3::DcfManager} and @code{ns3::DcfState} which implements the DCF function.
@item @code{ns3::DcaTxop} which handles the packet queue, packet fragmentation,
and packet retransmissions if they are needed.
@item @code{ns3::DcfManager} and @code{ns3::DcfState} which implements the DCF and EDCAF functions.
@item @code{ns3::DcaTxop} or @code{ns3::EdcaTxopN} which handle the packet queue,
packet fragmentation, and packet retransmissions if they are needed.
@code{ns3::DcaTxop} object is used by non-QoS high MACs. @code{ns3::EdcaTxopN} is
used by QoS high MACs and performs also QoS operations like 802.11n MSDU
aggregation.
@end enumerate
There are also several @strong{rate control algorithms} that can be used by the Mac low layer:
@@ -96,7 +117,7 @@ to their node must create an instance of a WifiNetDevice, plus
a number of consitutent objects, and bind them together appropriately
(the WifiNetDevice is very modular in this regard, for future
extensibility). At the low-level API, this can be done
with about 20 lines of code (see @code{ns3::WifiHelper::Install} and
with about 20 lines of code (see @code{ns3::WifiHelper::Install}, and
@code{ns3::YansWifiPhyHelper::Create}). They also must create,
at some point, a WifiChannel, which also contains a number of
constituent objects (see @code{ns3::YansWifiChannelHelper::Create}).
@@ -156,6 +177,44 @@ Note that we haven't actually created any WifiPhy objects yet; we've
just prepared the YansWifiPhyHelper by telling it which channel it is
connected to. The phy objects are created in the next step.
@subsection NqosWifiMacHelper and QosWifiMacHelper
The @code{ns3::NqosWifiMacHelper} and @code{ns3::QosWifiMacHelper} configure an
object factory to create instances of a @code{ns3::WifiMac}. They are used to
configure MAC parameters like type of MAC, values of contention windows and so on.
Setting up a non-QoS MAC layers the object we use is @code{ns3::NqosWifiMacHelper}.
For example the following user code configures a non-QoS MAC sta and changes its default
values for contention window and Aifsn:
@verbatim
NqosWifiMacHelper wifiMacHelper = NqosWifiMacHelper::Default ();
Ssid ssid = Ssid ("ns-3-ssid");
wifiMacHelper.SetType ("ns3::NqstaWifiMac", "Ssid", SsidValue (ssid), "ActiveProbing", BooleanValue (false));
wifiMacHelper.SetDcaParameters ("MinCw", UintegerValue (20), "Aifsn", UintegerValue (3));
@end verbatim
Setting up a QoS MACs we use a @code{ns3::QosWifiMacHelper} instead.
This object could be also used to change default EDCA parameters, and to set a possible MSDU aggregator
for a particular access class in order to use 802.11n MSDU aggregation feature.
A possible user code:
@verbatim
QosWifiMacHelper wifiMacHelper = QosWifiMacHelper::Default ();
wifiMacHelper.SetType ("ns3::QapWifiMac", "Ssid", SsidValue (ssid), "BeaconGeneration", BooleanValue (true),
"BeaconInterval", TimeValue (Seconds (2.5)));
wifiMacHelper.SetEdcaParametersForAc (AC_VO, "MinCw", UintegerValue (2));
wifiMacHelper.SetMsduAggregatorForAc (AC_VO, "ns3::MsduStandardAggregator", "MaxAmsduSize", UintegerValue (3839));
@end verbatim
Call to QosWifiMacHelper::Default () is needed in order to set default EDCA parameters properly for all
access classes. Otherwise we should set them one by one:
@verbatim
QosWifiMacHelper wifiMacHelper;
wifiMacHelper.SetEdcaParametersForAc (AC_VO, "MinCw", UintegerValue (2), "MaxCw", UintegerValue (7),
"Aifsn", UintegerValue (2));
wifiMacHelper.SetEdcaParametersForAc (AC_VI, "MinCw", UintegerValue (7), "MaxCw", UintegerValue (15),
"Aifsn", UintegerValue (2));
...
@end verbatim
@subsection WifiHelper
We're now ready to create WifiNetDevices. First, let's create
@@ -164,12 +223,11 @@ a WifiHelper with default settings:
WifiHelper wifiHelper = WifiHelper::Default ();
@end verbatim
What does this do? It sets the RemoteStationManager to
@code{ns3::ArfWifiManager} and the upper MAC to @code{ns3::AdhocWifiMac}
by default (which can be overridden by other arguments).
Now, let's use the wifiPhyHelper created above to install WifiNetDevices
@code{ns3::ArfWifiManager}.
Now, let's use the wifiPhyHelper and wifiMacHelper created above to install WifiNetDevices
on a set of nodes in a NodeContainer "c":
@verbatim
NetDeviceContainer wifiContainer = WifiHelper::Install (wifiPhyHelper, c);
NetDeviceContainer wifiContainer = WifiHelper::Install (wifiPhyHelper, wifiMacHelper, c);
@end verbatim
This creates the WifiNetDevice which includes also a WifiRemoteStationManager,
a WifiMac, and a WifiPhy (connected to the matching WifiChannel).
@@ -313,6 +371,7 @@ C++ classes and deal with:
@item connection and disconnection to and from an Access Point,
@item the MAC transmission queue,
@item beacon generation,
@item msdu aggregation,
@item etc.
@end itemize