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I want to know why a device can go from AP to AP without interruption. I do ping to a computer and when I connect to other different AP it is not interrupted. Why¿? Thank you in advance

aDoN
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2 Answers2

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Access Points are essentially just relays; when you go from AP to AP you are never leaving the network, so if you do not encounter a physical (layer 1) lack of service somewhere in the middle, you should loose little or no data during the process. This is because there's no layer 3 renegotiation; consecutive access points are generally on different channels and your hardware switches these instantaneously. The OS networking subsystem doesn't have to do anything at all (the device driver may or may not, I don't know).

IP packets (including pings) are atomic, meaning they are either delivered or not. You can't get half a packet; you can get a corrupted packet but that will be dropped == no packet.

Packets can get lost or otherwise fail to reach their destination.

If you were moving rapidly from network to network, when you disconnect from the first one, any packets addressed to you received on that network will be bounced by the router, meaning the sender will be informed via ICMP that you are not there. Ping packets are in pairs; you send one, you get one reply. Actual data transfer is not like that; if you are the sender, you may send quite a few packets before waiting for a reply. For TCP traffic, how many is determined by your congestion window; the system will not send more than that until it receives some acknowledgement.

However, any TCP connections should be properly closed when you properly disconnect. Whether or not they are quickly renegotiated on reconnection depends on the userland software responsible for them. If you disconnect by, e.g., yanking a cable out, the other party will receive an ICMP notification from the network router when it tries to send something, and your userland application will probably receive one from the OS when it does the same.

goldilocks
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  • What if you are connected to AP network 10.0.0.1/24 do a ping to google and during the ping move to an AP on a network 10.0.0.2/24 ¿? Would it be interrupted, because now there is a layer 3 renegotiation, what would happen¿? – aDoN Nov 01 '14 at 13:29
  • Unless the delay between pings is long enough to include the renegotiation you will see them get dropped. – goldilocks Nov 01 '14 at 13:32
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Access points are the equivalent to ethernet switches; they relay packets from one physical segment to another. The difference is that on one side the segment happens to be wireless. Moving from one AP to another is like unplugging an ethernet cord from one port on the switch and into another very quickly. A broadcast packet goes out notifying the switches on the network of the new route to your address and service continues essentially without interruption.

psusi
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