802.11 handling of multicast and broadcast

Inside the Ethernet there will be broadcast and multicast. Both of these packages are an STA contracted to multiple Sta.

Broadcast and multicast between LAN ports are reliably forwarded when there is no wifi, but it is not the same if WiFi is present.

Power considerations

According to the Protocol, broadcast and multicast are sent to STA at Dtim. The Dtim in the AP is typically one-fold Tim.

When the dtim increases, it is more power-saving because the STA in PS mode wakes up less often. But this can also cause some applications to increase in latency.

When the dtim is reduced, it will be more power-consuming.

Stability

Both broadcast and multicast are sent using the base rate. Multiple tests can be seen, they are sent with 11Mbps CCK rate.

Of course, this is only the AP issued by the broadcast and multicast settings, from the STA sent packets or at a normal rate.

In general, these two packages are not ACK-protected, which means they will be dropped.

For Ethernet, these two packages are basically not lost because the Ethernet is relatively stable. But there is a lot of interference at the WiFi level, causing

Packet loss is serious.

802.11 transparent forwarding

802.11 for the processing of the BC/MC package, it can be understood that the Ethernet is transparent.

When the WiFi client sends the BC/MC packet, the AP forwards the packet, and the following is the process:

1.STA QoS data at normal rates to Ap,ra and TA is the address of STA and AP respectively, SA is the address of STA, DA is BC/MC address. Using pairwise key Encryption

2.AP at the base rate Data,ra is the BC/MC address, TA is the address of the AP, SA is the address of the STA, DA is the BC/MC address, and SA is the address of the STA. Use Group key encryption.

Note that for BC/MC packets, they are encrypted, generally ccmp. The wireless client needs to use group to parse the received packet, and 802.11 also provides a good security.

For both ends of the STA, the 802.11 package converted to Ethernet package, 802.11 levels of things will not be visible, the only difference is the wireless AP LAN port between the BC/MC packet is not easy to lose,

But the BC/MC packet between LAN and Wireless,wireless and wireless is easy to discard. Of course, packets from the wireless STA to the LAN port should not be easily lost, as the QoS data between the unicast is transmitted, with ACK protection.

Other

In the program will involve the IP address and MAC address conversion, in fact, after the completion of the IP address, the protocol stack will help you convert to MAC address.

At this point 802.11 and Ethernet are no different, because this is the IP layer and MAC layer interface considerations.

The Test tool recommends this (open source):

802.11 handling of multicast and broadcast