3.2 Data Packet Processing
Packets transmitted on a WLAN include management packets and service data packets. Management packets must be transmitted over Control and Provisioning of Wireless Access Points (CAPWAP) tunnels, and service data packets can be transmitted over CAPWAP tunnels or directly.
Management packets transmit management data between an AC and AP. Data packets transmit data STAs and the upper layer network when WLAN users surf on the Internet.
On a WLAN network, packets transmitted between STAs and APs are 802.11 packets. APs are bridges between STAs and the upper layer wired network. They convert 802.11 packets into 802.3 packets and forward 802.3 packets to the wired network.
Management packets and service data packets are marked with different VLAN tags on a WLAN. In the following content, the VLAN tag of management packets is VLAN m, and the VLAN tag of service data packets is VLAN s.
Management Packet Forwarding Process
- When receiving upstream management packets, the AP encapsulates the packets in CAPWAP packets. The switch tags the packets with VLAN m. The AC decapsulates the CAPWAP packets and removes the tag VLAN m.
- When receiving downstream management packets, the AC encapsulates the packets in CAPWAP packets and tags them with VLAN m. The switch removes the tag VLAN m from the packets. The AP decapsulates the CAPWAP packets.
The devices between an AC and AP must be configured to allow VLAN m and transparently transmit packets of VLAN m.
Direct Forwarding of Service Data Packets
- When upstream service data packets in 802.11 format are sent from the STA to the AP, the AP converts the packets into an 802.3 packets, tags the packets with VLAN s, and forwards the packets to the destination.
- When downstream service data packets in 802.3 format reach the AP (the packets are tagged with VLAN s by upstream devices), the AP converts the 802.3 packets into 802.11 packets and forwards them to the STA.
The devices between an AC and AP must be configured to allow service VLAN s and transparently transmit packets of VLAN s.
In direct forwarding mode, an AC is connected to a core or aggregation switch in bypass mode. The AC does not forward service data and only manages APs. If an AC is connected to an upstream switch in inline mode, the AC forwards data packets. In this networking, the AC acts as an aggregation switch.
Tunnel Forwarding of Service Data Packets
- When upstream service data packets in 802.11 format are sent from the STA to the AP, the AP converts the packets into 802.3 packets, tags the packets with VLAN s, and encapsulates them into CAPWAP packets. The upstream switch tags the packets with VLAN m. The AC decapsulates the CAPWAP packets and removes the tags VLAN s and VLAN m from the packets.
- When downstream service data packets reach the AC, the AC encapsulates the packets into CAPWAP packets and tags the packets with VLAN s and VLAN m. The switch removes VLAN m from the packets. The AP decapsulates the CAPWAP packets, removes VLAN s, and converts the 802.3 packets into 802.11 packets.
The management VLAN tag is the outer tag of encapsulated CAPWAP packets. The intermediate devices between the AC and AP only need to transparently transmit VLAN m and do not need to be configured with VLAN s encapsulated in the CAPWAP packets.
All encapsulated data packets are processed and forwarded by the AC, regardless of whether the AC is connected to the upstream switch in inline or bypass mode.
