WLAN standard supports different Network Topologies.
- Infrastructure Network Topology
- Ad-hoc Network Topology
- Wireless Mesh Topology
- P2P Network Topology
In addition to the above, WLAN is also employed in automotive communication and the Automotive Dedicated Short Range Communication topology will be discussed separately later
Infrastructure Topology
An Infrastructure topology is shown below. The area marked by the dashed circle is termed as a Basic Service Set (BSS). All stations connected to an Access point forms a Basic Service Set.
There is another term commonly used – Basic Service Area (BSA). The Basic Service Area is the area covered by an Access Point. The Access Point signal might reach beyond the range of connected devices to it. That coverage area is the BSA.
The MAC address of the Access Point which is broadcast by the Access Point is termed the Basic Service Set Identifier (BSSID) and the human readable name for the BSSID broadcast by the Access Point is termed as Service Set Identifier (SSID).
Fig: WLAN Basic Service Set (BSS)
When multiple Access Points share the same SSID – they form an Extended Sevice Set (ESS)
Fig: An Extended Service Set (ESS)
Ad-hoc Network Topology
The Ad-hoc Topology is a self -contained Peer-to-Peer network. It is shown below
Wireless Mesh Topology
The Wireless Mesh network is an inter-connection of connected nodes which form a self healing network. If one node goes down, a new path is formed to create the mesh network running. The mesh nodes use the 802.11 standards such as 802.11a/b/g/n/ac to speak to one another. One node is connected to the network back-end. A backup mesh node can also be configured to connect to the public gateway in case the primary mesh node goes down. Each mesh node can have users connected to it. Network Traffic load needs to be balanced between the different nodes and efficient routing mechanisms need to be created to provide the fastest route to the public network
Fig: A Wireless LAN Mesh network
P2P Network Topology
A P2P network is a Peer-to-Peer network. One Wireless Station performs the operation of a wireless Master station and it is termed as Group Owner (GO). The Group Owner sends out beacons and is responsible for maintaining the Peer to Peer network. Other wireless stations connect to the Group Owner. The client station is termed as Group Clients (GC). When The Group Owner leaves the network, a group client (GC) will adopt the role of the Group Owner (GO). A Group Owner (GO) device can also join as a Group client (GC) device to another P2P network simultaneously if it support multiple 802.11 radios
Fig: P2P network Topology
In all the above topologies, the Master of the network broadcasts the services and capabilities of the network via a beacon frame. A beacon frame is discussed next