Wireless LAN 802.11 Service Sets

Lessons Discussion
22

Hello Peter

First of all, you’re asking your question in the right place. The forum is where you can freely post your queries so that we can respond to them here.

As far as terminology goes, a BSS is defined as the coverage delivered by a single physical access point. The BSS has a unique BSSID which is the MAC address of the device, but can have a configurable SSID.

An ESS is defined as the collective coverage delivered by multiple physical access points that have the same SSID. Thus, by definition, an ESS is composed of multiple BSSes with the same SSID but unique BSSIDs. Therefore, the labeling in the diagram is correct. Does that make sense?

As far as “seamless” roaming, what it actually means depends upon the context and the definition of the concept. You are correct that by simply creating the same SSIDs in different BSSes, it will not necessary provide you with roaming without any disruptions. Take a look at this NetworkLessons Note on Wireless Roaming Defined that tells us a little bit more about what “seamless roaming” really means.

I hope this has been helpful!

Laz

23

I noticed there are, at least, 2 different modes, non-infrasctructure and the other is infrasctructure (?) . Non-infra could be repeater, Workgroup Bridge and Outdoor bridge and Infra is a mode that you could change by software ? for example, the several modes that support Cisco APs such as Flexconnect, SE-Connect, Monitor, etc

Wireless is one of my weakest topics , i’d like to dive more in wireless but specific to outdoor such as outdoor bridge to give internet service using Radio Link as last mile. Do you recommend any book about that ?

24

Hello Juan

The terminology used can be confusing. Let me try to clarify.

When it comes to Wi-Fi, there are two implementation modes: Infrastructure mode and ad hoc mode (also called IBSS).

Infrastructure mode uses an AP as a central “hub” to which clients connect. Via that AP they connect to other clients or to other networks, or to the Internet. Infrastructure mode is characterized by the fact that there is dedicated hardware specifically used to connect the client to the “infrastructure.” That hardware is essentially an AP and any other wired or wireless infrastructure used to connect to other networks.

Ad Hoc mode or IBSS mode is used to connect wireless clients directly to each other. Here there is no infrastructure involved. There is just direct one-to-one communication.

Now when it comes to Cisco APs, you can configure them using several Access Point modes (AP modes). This is different than the infrastructure/ad hoc modes mentioned before.

AP modes essentially tell the access point how to operate. These are described in detail in the lesson. Since an AP is being used, all of these involve infrastructure mode.

Concerning the implementation of wireless links for last-mile communication, I don’t have any books to recommend, but there are many resources online for such wireless links, especially from vendors that are well-known for such equipment. They have huge knowledge bases and how-to sections in their online resources that are freely available. I can’t share the names of those vendors here but I’m sure you have some in mind.

I hope this has been helpful!

Laz

1 Like
25

Hello,

Out of curiosity I was thinking about a scenario where the end user hosts would be ARPing for each other’s MAC addresses in an enterprise environment, and the only example I could think of was an ad hoc network. Are there any other ones?

Attila

26

Hello Attila

An ARP request is sent whenever a host needs to discover the MAC address of the next hop, or the destination host in the event the host is in the same subnet.

Now if you have two devices connected to a Wi-Fi network, to the same SSID and the same VLAN, and those devices are on the same subnet, then any communication that is to take place between these two particular wireless clients will require an ARP request.

ARP functions exactly the same way on wireless networks as on wired networks. Imagine that those two same hosts are connected to a switch on the same VLAN via UTP cables. Again, if one host wants to communicate with the other, an ARP request will necessarily be sent.

What applications require this direct client-to-client communication that in turn requires the use of ARP for those devices to communicate? Well, there are several including things like gaming, VoIP, collaboration tools, and even printing to a network printer.

For one wireless client to ask for the MAC address of another wireless client directly using ARP, they both must be on the same subnet.

I hope this has been helpful!

Laz

1 Like
27

I created a lab with two (2) ap. so I had a essid, both AP had same ssid and sam passphrase for wpa2. Roaming did work, sometimes well sometimes not so good. Each AP was a different vendor (cisco AP and sagecom AP from spectrumISP). When the clients leave one ap and come back, are they reassociating or are they simply associating again? I will try wireless debug on the cisco AP and see if I can figure it out.
thanks!

28

Hello @rod.deluhery ,

Debugging this is a good idea. It’s hard to tell how it works exactly because different vendor APs support different standards. For example, here are some of the standards related to roaming:

  • 802.1F
  • 802.11k
  • 802.11r
  • 802.11v

I would enable a debug on both the Cisco AP and your sagecom AP, then roam and see what happens :slight_smile:

Rene

30

What exactly is the difference between using a repeater with multiple radios (one receives AP signal and other transmits to end devices) and a Mesh AP? It sounds like they are doing the exact same thing: one radio connects to an AP wirelessly and another radio connects to the end device: the latter picks up the client traffic and the former forwards it to the AP/Root AP.

31

Hello CJ

Indeed a repeater with multiple radios sounds very similar to a mesh network. Although the mechanism through which they operate is similar, there are some significant differences.

The difference between using a repeater with multiple radios and a Mesh Access Point (AP) lies in their design, functionality, and network architecture. First of all, keep in mind that “mesh” is actually an infrastructure mode while the repeater is an AP mode. The former has to do with larger scale wireless network design while the latter has to do with the mode of a particular device. Although they are similar in operation, the scope of their implementation is different.

A repeater with multiple radios uses one radio to receive the signal from the main AP, and the other to transmit the signal to end devices. This design is a step up from using a single-radio where the same radio has to alternately receive and transmit signals, effectively halving the bandwidth. However, this is still a relatively simple setup aimed only at extending the range of an existing network.

A mesh AP is part of a more sophisticated mesh system. These APs are designed to dynamically communicate with each other and with the main network, creating a mesh-like interconnectivity. Each mesh AP can act as a router, forwarding data to other mesh APs and end devices. They are typically more intelligent in managing network resources, and routing, and can provide better coverage and reliability compared to simple repeaters.

While both systems aim to extend wireless coverage, mesh APs are part of a more advanced, scalable, and efficient network architecture compared to repeaters with multiple radios, which are more suited for simpler, small-scale range extension.

I hope this has been helpful!

Laz

32

Hello, everyone.

I have some questions.

We can also do this with VLANs. The AP connects to the switch with an 802.1Q trunk. Each SSID maps to a different VLAN:

Technically, the SSID doesn’t have to be unique. So we could have 2 SSIDs that would have the exact same name and both could be mapped to a different VLAN, right? Although I doubt we would do that, so I am just asking from a theoretical perspective.

Wikipedia describes a service set the following way:

In IEEE 802.11 wireless local area networking standards (including Wi‑Fi), a service set is a group of wireless network devices which share a service set identifier (SSID)

What if the SSID is different? What if we have 2 SSIDs that map to the same VLAN? Are these two different service sets or not? And is the BSSID incremented for the second SSID?

And my last question is, how does bandwidth work with Wireless? With cabled networks, these networks had a certain speed that they could operate in. If the speed was, say 100 mbits, so was the bandwidth since you could not transmit more than 100 mbits per second. If the capacity of the link was exceeded, it would be buffered.

How does this work with wireless?

//Edit: Two more questions. These AP modes (Repeater, WGB, Outdoor B), are these all for Autonomous APs only?

How does the Outdoor Bridge mode work?

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Outdoor bridge is something that an AP must operate in? Couldn’t we just use a directional antenna here?

Or in other words, what would be the difference if the AP wasn’t operating in out.bridge but had a directional antenna? :grinning_face_with_smiling_eyes:

That’s all, thank you!
David