Wireless LAN 802.11 Service Sets

This topic is to discuss the following lesson:


This image has two SSIDs that belong both to VLAN10. Are these suppose to be different VLANs?

Hi David,

That’s right, thanks for letting me know. I fixed this image.


A post was merged into an existing topic: Multicast Routing

Hi Rene,

Regarding the roaming in the ESS section, does that happen automatically or is there some configuration we need to apply on the APs to guarantee this seamless transition?


Hello Luis

By default, a user device which is moving from one BSSID to another with the same SSID, will automatically disassociate with one AP and associate with the other. This is performed by the device itself simply based on the signal strength it detects from each AP. It will use the same credentials (if the network uses a password/authentication) and will connect the user to the network. There is no need for additional configuration of either the user device or the APs, this will take place by default.

In such a case, there will be a small period of time (on the order of several seconds) where there will be no network connectivity, during handoff from one AP to the next. For web browsing or email, that delay is no big deal, and will largely go unnoticed.

Such roaming, however, is unacceptable as far as some real-time services go, such as Voice over IP or videoconferencing. For this purpose, the 802.11r and 802.11k amendments to the Wi-Fi standard were added. Access points that support these amendments are able to seamlessly hand off a user device from one AP to the next without any noticeable disruption of service. In such cases, depending on the vendor, this feature will simply have to be enabled on the APs, and supported by the user device in order for it to function.

I hope this has been helpful!


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Could you please answer the following questions ?

  1. How dose an AP is considered by upper(upstream) network? Is it a switch/bridge(L2) or router(L3)?
    q1. Case 1(home): AP is directly connected to an ISP
    q2. Case 2(soho, enterprise) : AP is connected to a (access)switch of hierarchical swiched network.
    q2.1 How dose an AP is considered by the switch ?
    q2.2 The link between AP and swich should be a trunk ?
    q2.3 AP participates in Spanning tree protocol ?

  2. AP repeater mode- 50% throughput reduction
    In your lesson <Wireless LAN 802.11 Service Sets/3. AP modes/3.1 Repeater>, you say “Since wireless is half-duplex, adding a repeater will reduce your available throughput by about 50%.
    To work around this, some repeaters have two or more radios. They receive on one channel (same as the AP) and retransmit on another”
    q3. Why 50% throughput reduction ?

  3. Repeater mode operation.
    q4. I think repeater wireless should be full duplex(Normal WLAN device is half duplex). It listens from AP and talks to STAs simultaneously or vice versa
    q5. If so, How Repeater knows the timing for downstream(AP to STAs) or upstream(STAs to AP)?
    q6. Reaper mode also does CSMA/CA ?