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Basic question.

In an ad hoc network, two devices, e.g a notebook and a cellphone, if I send a packet from the note to the phone they will talk directly to one another, if in the range. With an addition of an access point, the cellphone won't receive the packet from the note directly anymore? all the packets go to the access point and he forwards it to the phone? I've seen analogies between access point with switch, but one of the latter goals is to replace the CSMA/CD, but, from what I get, CSMA is still the access channel method, whether it is an ad hoc or infrastructure mode. I am confused.

Thanks and sorry my bad engish

  • "I've seen analogies between access point with switch" A WAP is actually more like a hub than a switch because wireless is a shared medium. – Ron Maupin Feb 25 '18 at 20:38
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Apr 1 '18 at 21:20
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With an addition of an access point, the cellphone won't receive the packet from the note directly anymore?

-and-

all the packets go to the access point and he forwards it to the phone?

In essence, the same question, but you are correct. Both the notebook and cellphone will communicate with the AP. The AP would pass traffic from one client device to another (unless it is configured to prevent client to client traffic).

I've seen analogies between access point with switch, but one of the latter goals is to replace the CSMA/CD, but, from what I get, CSMA is still the access channel method, whether it is an ad hoc or infrastructure mode. I am confused.

Your question isn't really clear, but it seems like you are either asking about the AP/switch and media access method and/or why would you want to introduce an AP in between devices when they can talk directly.

Let me start by clarifying that an AP is much more like a hub than a switch when it comes to media access. An AP is a L2 device (like a switch) because of the bridging functionality of the AP. You are correct that CSMA/CA applies both to ad-hoc and infrastructure modes of operation. However using an AP in infrastructure mode provides a number of advantages over ad-hoc mode.

First, in ad-hoc mode, each client must form an ad-hoc connection to each other client. So if you have 20 devices communicating among themselves, each device would have to form a connection to the other 19. With an AP, each client would only have to form a connection to the AP itself.

Second, the AP is the bridge to the wired network (or client devices on a different frequency range - 2.4GHz to 5GHz). If any of the wireless devices need to connect to a device on the wired network (or a different frequency range), something needs to provide that bridge.

Third, the AP provides additional functionality and coordinates the use of the channel by the clients. Ad-hoc networks are generally pretty basic connections and don't provide much more than connectivity.

  • Thanks for the help!! My first two questions, although look similar, were meant to say how one device is prevented to receive a packet from the other device (even to discharge it, although it may have the right MAC adress destination, which makes things even more confusing to me), since it is in the air and in my hypotetical scenario, the only thing that changed is the presence of a WAP, it is easier to picture, at least for me, in a wired network with a switch. – Alex Frei Feb 27 '18 at 20:44
  • @AlexFrei, it may help to look at my answer detailing the four addresses in an 802.11 frame. When the notebook sends the frame destined to the cellphone, the frame will use three addresses: the BSSID of the AP (the receiver address or RA), the MAC of the notebook (the transmitter address and source address or TA/SA), and the MAC of the cellphone (the destination address or DA). The cellphone's radio will only accept wireless frames where it is the RA. – YLearn Feb 27 '18 at 21:41
  • Don't know how many times I googled "to DS and from DS" unfortunately this page didn't show or I overlooked. Very claryfing. I did have difficult, to be honest, to understand what a DS is about, since most of domestic and even small business environment have an AP integrated with a router, DHCP, NAT and so on. A simple cable connecting a AP to a router, or any server is considered a DS, from I what I get. Again, thanks – Alex Frei Feb 27 '18 at 22:13
  • @AlexFrei, in simple terms you can consider the DS as the wired network side of the AP. Even if the AP is built into a router/gateway device, the services offered by the device (gateway, DNS, DHCP, NAT, etc) are all part of the DS. – YLearn Feb 27 '18 at 22:20

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