When it comes to wireless, not all APs are made the same. The most popular type of APs either follow a centralized architecture or a decentralized architecture. Today I will be discussing autonomous APs vs lightweight APs.
Autonomous AP – Autonomous APs follow a “decentralized architecture,” where each AP can function independently. An autonomous AP is a standalone AP that manages all of its own configuration, management, control plane, and operational functions without the need for a central WLC (Wireless LAN Controller.) In this decentralized architecture, the management plane (configuration, administration, SNMP, Syslog), the control plane (client authentication, association, roaming decisions, RF management) and data plane (forwarding client traffic) all reside locally at the AP itself. Because there is no central controller (WLC), each AP must be configured and managed individually. This means if a company site requires 50 APs, each AP must be configured either through a web GUI, CLI, or ssh connections. As you can assume, this limits scalability as opposed to its counterpart “lightweight APs”.”
Lightweight APs – Lightweight APs follow more of a centralized network. Lightweight APs depend on the WLC (Wireless LAN Controller) for most of its configuration, management, and control plane functions. Unlike the autonomous AP, it does not operate independently but is a part of a centralized configuration in which the WLC acts as the “brain” of the network.
Lightweight APs primarily handle the time sensitive wireless functions such as transmitting and receiving RF traffic, sending and processing ACKs, sending beacon frames and probe responses, and encrypting/decrypting traffic. The WLC manages centralized functions such as security and QOS policy, WLAN configuration, roaming, transmit power levels, channel assignments and overall network management.
Split MAC- This centralized architecture is typically called a “Split MAC Architecture,” which is a wireless network design in which the responsibilities of the 802.11 MAC layer (beacons, authentication, security policy) are divided between the WLC and lightweight APs.
Lightweight AP
- Beacon transmission
- Probe responses
- ACK
- Encryption/decryption
- RTS/CTS
- Frame retransmissions
WLC
- Authentication decisions
- Association management
- Roaming management
- RF management
- Transmit Power Level
- Channel Assignment
- WLAN policies
- Security and QoS policies
CAPWAP – In order to transport traffic between the WLC and lightweight APs, a protocol called CAPWAP (Control and Provisioning Wireless Access Points ) is used. This protocol enables the WLC and lightweight APs to exchange communication by using two tunnels: the data tunnel and a control tunnel.
Control Tunnel – A control tunnel is a dedicated communication channel used by the WLC and lightweight APs to exchange configuration, management and operational (example: number of connected clients) information. Operating over UDP port 5426, the control tunnel carries administrative traffic such as firmware updates, security and QOS policy changes, RF management traffic and real time operational statistics such as client association status or number of connected clients. Because this traffic mostly consists of sensitive management traffic, this tunnel uses DTLS (Datagram Transport Layer Security) by default. This helps ensure that management communications between the WLC and lightweight AP cannot be intercepted or modified.
Data Tunnel – A data tunnel is a communication channel used to carry client traffic between the WLC and Lightweight AP when the AP is operating in local mode with centralized data forwarding. Unlike the control tunnel, it is not encrypted by default and carries actual client traffic such as web browsing traffic, file downloads, emails, voice traffic and video streaming.
Leave a Reply