IEEE 802.11 Model
This page provides an overview of the IEEE 802.11 model for the INET Framework.
An IEEE 802.11 interface (NIC) comes in several flavours, differring in their role (ad-hoc station, infrastructure mode station, or access point) and their level of detail:
- Ieee80211Interface: a generic (configurable) NIC
- Ieee80211Interface with mgmt.typename = Ieee80211MgmtAdhoc: for ad-hoc mode
- Ieee80211Interface with mgmt.typename = Ieee80211MgmtAp or Ieee80211MgmtApSimplified: for use in an access point
- Ieee80211Interface with mgmt.typename = Ieee80211MgmtSta, Ieee80211MgmtStaSimplified: for use in an infrastructure-mode station
NICs consist of four layers, which are the following (in top-down order):
- physical layer (radio)
The physical layer modules (Ieee80211Radio) deal with modelling transmission and reception of frames. They model the characteristics of the radio channel, and determine if a frame was received correctly (that is, it did not suffer bit errors due to low signal power or interference in the radio channel). Frames received correctly are passed up to the MAC. The implementation of these modules is based on the Mobility Framework.
The MAC layer (Ieee80211Mac) performs transmission of frames according to the CSMA/CA protocol. It receives data and management frames from the upper layers, and transmits them.
The management layer performs encapsulation and decapsulation of data packets for the MAC, and exchanges management frames via the MAC with its peer management entities in other STAs and APs. Beacon, Probe Request/Response, Authentication, Association Request/Response etc frames are generated and interpreted by management entities, and transmitted/received via the MAC layer. During scanning, it is the management entity that periodically switches channels, and collects information from received beacons and probe responses.
The management layer has several implementations which differ in their role (STA/AP/ad-hoc) and level of detail: Ieee80211MgmtAdhoc, Ieee80211MgmtAp, Ieee80211MgmtApSimplified, Ieee80211MgmtSta, Ieee80211MgmtStaSimplified. The ..Simplified ones differ from the others in that they do not model the scan-authenticate-associate process, so they cannot be used in experiments involving handover.
The agent is what instructs the management layer to perform scanning, authentication and association. The management layer itself just carries out these commands by performing the scanning, authentication and association procedures, and reports back the results to the agent.
The agent layer is currenly only present in the Ieee80211Interface with mgmt.typename = Ieee80211MgmtSta NIC module, as an Ieee80211AgentSta module. The managament entities in other NIC variants do not have as much freedom as to need an agent to control them.
By modifying or replacing the agent, one can alter the dynamic behaviour of STAs in the network, for example implement different handover strategies.
See the documentation of Ieee80211Mac for features unsupported by this model.
If you are new to 802.11, reading an introductory material before the IEEE standard can help.