The management, control, and data planes
We’ve covered a lot of detail on RF characteristics up to this point (see prior Wireless Tutorial blog posts from Control Engineering) and briefly touched on the place of wireless in the networking world. We are going to start to "edge into" the science of Wi-Fi in this segment, beginning with the internal segmentation of the various roles each part of a wireless performs; these roles fall into three broad categories called "planes." Consider these planes in the geometrical sense rather than as layers since this introduces some confusion when considering the relationship with the open systems interconnection (OSI) layers previously discussed.
The concept of planes provides a model for the various implementations of WLANs that are present in today’s market. The several vendors do things very differently from one another, and I am studiously avoiding any critique of their methods; all have pros and cons. The plane concept allows designers to properly design and specify a WLAN using the segregation of roles as a framework by which the several different network topologies are implemented. This will become more apparent as we get into the descriptions of roles.
The WLAN is configured in the management plane, which can be thought of as the interface to the wireless network. In a WLAN with several access points (APs) constituting an extended service set (ESS), a means of overall network management is required, just as in a wired network. APs can be configured, provisioned, renamed, or removed from a WLAN using a wireless management system (WMS). No control function is allowed in the AP, typically. The network is also monitored in the management plane. This includes monitoring and acquiring network statistics like client associations and reassociations, actual throughput, and general network operation. AP firmware upgrades are also controlled in this plane.
Routing and client roaming are typically done in the control plane. Discovery of neighboring APs, or the determination of the lowest cost routing between nodes, is done at this plane. While data is passed through the portal or network bridge for transfer into the wireless distribution system (WDS), the control plane facilitates this, controlling the communication end-to-end. All layer 3 routing and layer 2 switching is performed in the control plane. Client device roaming from one BSS to another, hand-off of the client between APs, including the forwarding of any buffered packets, is performed on this plane. Mesh routing and control also resides here.
The data plane is the actual communication channel and resides in the AP. All signaling and front-end data handling is done at this plane. All of the devices in a WLAN at the physical level constitute the components of this plane. In a controller-based network, data is forwarded to the control plane for processing. Autonomous APs handle all data processing and routing locally, straddling all three communication planes. Meshed APs operate on the control and data planes, with overall network operation and monitoring being done on the management plane.
– Daniel E. Capano, owner and president, Diversified Technical Services Inc. of Stamford, Conn., is a certified wireless network administrator (CWNA). Edited by Chris Vavra, production editor, CFE Media, Control Engineering, firstname.lastname@example.org.
www.controleng.com/blogs has other wireless tutorials from Capano on the following topics:
Wi-Fi acronyms, wireless buzzwords, WLAN nomenclature, wireless terms
www.controleng.com/webcasts has wireless webcasts, some for PDH credit.
Control Engineering has a wireless page.