12.1 Overview of the model

Note: This overview is taken largely from the Doxygen for the WifiNetDevice module.

The set of 802.11 models provided in ns-3 attempts to provide an accurate MAC-level implementation of the 802.11 specification and to provide a not-so-slow PHY-level model of the 802.11a specification.

The current implementation provides roughly four levels of models:

• the PHY layer models
• the so-called MAC low models: they implement DCF
• the so-called MAC high models: they implement the MAC-level beacon generation, probing, and association state machines, and
• a set of Rate control algorithms used by the MAC low models

There are presently three MAC high models:

1. a simple adhoc state machine that does not perform any kind of beacon generation, probing, or association. This state machine is implemented by the ns3::AdhocWifiNetDevice and ns3::MacHighAdhoc classes.
2. an active probing and association state machine that handles automatic re-association whenever too many beacons are missed is implemented by the ns3::NqstaWifiNetDevice and ns3::MacHighNqsta classes.
3. an access point that generates periodic beacons, and that accepts every attempt to associate. This AP state machine is implemented by the ns3::NqapWifiNetDevice and ns3::MacHighNqap classes.

The MAC low layer is split into three components:

1. ns3::MacLow which takes care of RTS/CTS/DATA/ACK transactions.
2. ns3::DcfManager and ns3::DcfState which implements the DCF function.
3. ns3::DcaTxop which handles the packet queue, packet fragmentation, and packet retransmissions if they are needed.

There are also several rate control algorithms that can be used by the Mac low layer:

• ns3::ArfMacStations
• ns3::AArfMacStations
• ns3::IdealMacStations
• ns3::CrMacStations
• ns3::OnoeMacStations
• ns3::AmrrMacStations

The PHY layer implements a single model in the ns3::WifiPhy class: the physical layer model implemented there is described fully in a paper entitled "Yet Another Network Simulator".

In ns-3, nodes can have multiple WifiNetDevices on separate channels, and the WifiNetDevice can coexist with other device types; this removes an architectural limitation found in ns-2. Presently, however, there is no model for cross-channel interference or coupling.

The source code for the Wifi NetDevice lives in the directory src/devices/wifi.

Figure 12.1: Wifi NetDevice architecture.

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