What is Split MAC Architecture
Controller-based wireless systems are built on the Split-MAC (Media Access Control) architecture, a centralized paradigm used in enterprise wireless networks. The division of labor between an Access Point (AP), also known as a Lightweight Access Point (LAP), and a central Wireless LAN Controller (WLC) is defined by this important design idea.
The 802.11 protocol’s functionality is purposefully “split” between these two halves in this architecture. By centralizing the complicated, non-time-critical administrative tasks onto the WLC, this design aims to make the APs lighter, more straightforward devices.
You can also read What is DC Distribution System Definition and Key Functions
Division of Functions
The AP handles real-time tasks, whereas the WLC handles non-real-time management chores. This is how the typical AP operates.
Lightweight Access Point (LAP) Responsibilities (Real-Time Functions)
Time-sensitive operations that need instant communication with wireless clients are handled by the AP; these processes are carried out locally at the AP with very low latency.
Key real-time responsibilities include:
- RF Transmit/Receive.
- Sending Beacons and responding to Probe Requests (timing-critical portions).
- Handling frame acknowledgments (ACKs) and retransmissions.
- MAC layer data encryption and decryption (on the air interface).
- Packet buffering, Queuing, and Fragmentation.
- Processing 802.11 control frames, such as Request to Send / Clear to Send (RTS/CTS).
- Handling frames for clients operating in power save mode.
Wireless LAN Controller (WLC) Responsibilities (Non-Real-Time/Management Functions)
The WLC manages centralised management and control tasks, also known as non-real-time tasks, that don’t need to be completed right away.
Key management responsibilities include:
- Client Authentication (e.g., 802.1x/EAP processing).
- Association Management and Roaming decisions.
- Security Management (e.g., policy enforcement, rogue detection, controlling client access).
- RF Management (such as dynamic power level and channel selection/RRM).
- Configuration and Firmware distribution for all APs.
- Quality of Service (QoS) policies and decisions.
- Translating wireless 802.11 frames to wired 802.3 Ethernet frames.
You can also read What Is BSSID Basic Service Set Identifier And BSSID Vs SSID
Implementation and Data Path
The Control and Provisioning of Wireless Access Points (CAPWAP) protocol is used to implement the Split-MAC architecture.
- Communication: CAPWAP, which uses IP tunnels to transport control messages and client data, is used to link the Lightweight AP (LAP) with the WLC.
- Centralized Control: Without the WLC, the LWAP cannot operate. Upon booting up, an LWAP finds a WLC and establishes a connection to get its configuration.
- Location Flexibility: The AP and WLC can be conceptually and physically separated, even if they are on different IP subnets, through the usage of tunneling.
All client data traffic is centrally switched in the typical split-MAC operation, often known as Local Mode for APs. This implies:
- The LAP receives a frame from a wireless client.
- The frame is sent to the WLC by the LAP after being encapsulated in a CAPWAP Data Tunnel (UDP 5247).
- The frame is processed and decapsulated by the WLC.
- The frame is subsequently sent to the wired network by the WLC.
- Tunneling to and from the WLC is required for even client-to-client traffic on the same subnet.
Benefits
For extensive WLAN installations, this architecture has several benefits:
- It makes network setup and maintenance easier and permits centralised control.
- It guarantees uniform network-wide security and policy enforcement.
- Because the WLC controls the client association state, it makes travelling easy for clients.
You can also read What Is Service Set Identifier SSID? How It Works & Features