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The Invisible Hand-Off: Why Wi-Fi Roaming Is a Client Decision · Connectivity Without Chaos - The Podcast

• 0:00
  SPEAKER_01: Have you ever watched your phone just inexplicably cling to a single miserable bar
• 0:06
  SPEAKER_01: of weak Wi-Fi while you're standing right next to a brand new router?
• 0:11
  SPEAKER_01: It is honestly completely maddening.
• 0:13
  SPEAKER_00: Oh, it really is.
• 0:14
  SPEAKER_01: Right.
• 0:14
  SPEAKER_01: Right.
• 0:15
  SPEAKER_01: Right.
• 0:36
  SPEAKER_01: Which means this entire deep dive into the hidden mechanics of Wi-Fi roaming is,
• 0:42
  SPEAKER_01: well, is really a look at your device's hidden decision tree.
• 0:45
  SPEAKER_01: And the very first branch of that tree is the trigger threshold.
• 0:48
  SPEAKER_00: Right, the RSSI, or Receive Signal Strength Indicator.
• 0:53
  SPEAKER_00: Your phone or laptop will not even consider looking for a new connection until
• 0:57
  SPEAKER_00: the current signal degrades to a hard-coded point.
• 1:00
  SPEAKER_01: Wait, so it is hard-coded.
• 1:02
  SPEAKER_00: Oh, absolutely.
• 1:03
  SPEAKER_00: And those thresholds are strict, and they vary wildly by manufacturer.
• 1:07
  SPEAKER_00: Apple, for instance,
• 1:08
  SPEAKER_00: has iPhones programmed to trigger a roam when the signal degrades
• 1:12
  SPEAKER_00: to negative 70 dBm.
• 1:14
  SPEAKER_01: Okay, negative 70.
• 1:15
  SPEAKER_00: Yeah.
• 1:16
  SPEAKER_00: But because we're dealing with negative numbers,
• 1:18
  SPEAKER_00: MacBooks actually wait until the signal is notably weaker.
• 1:22
  SPEAKER_00: They wait for negative 75 dBm if we're looking for a new connection.
• 1:25
  SPEAKER_01: Oh wow, and since negative 75 is further from zero,
• 1:28
  SPEAKER_01: that 5 dBm difference explains why laptops act like sticky clients.
• 1:34
  SPEAKER_01: They just hold on to a dying signal
• 1:36
  SPEAKER_00: long after your phone has already jumped ship.
• 1:38
  SPEAKER_00: That is exactly what is happening.
• 1:39
  SPEAKER_01: It is kind of like huddling around a dying campfire on cold night.
• 1:42
  SPEAKER_01: You know there are other fires out there,
• 1:44
  SPEAKER_01: but you won't make the freezing run through the drug to find one
• 1:47
  SPEAKER_01: until your current fire gets so weak that you are actually shivering.
• 1:51
  SPEAKER_00: That is a great way to put it.
• 1:52
  SPEAKER_00: That shiver is the negative 70 dBm trigger.
• 1:56
  SPEAKER_00: And once that shiver hits,
• 1:57
  SPEAKER_00: the device is forced to look around by scanning available channels for
• 2:01
  SPEAKER_00: a new access point.
• 2:02
  SPEAKER_01: But doing that isn't free, right?
• 2:04
  SPEAKER_00: No, not at all.
• 2:05
  SPEAKER_00: To scan the room, the radio actually has to tune away from its current channel.
• 2:09
  SPEAKER_01: Ah, which is exactly why your video call might suddenly stutter or your web page hangs.
• 2:14
  SPEAKER_01: The radio is physically pausing data transfer to actively send out probe requests
• 2:19
  SPEAKER_01: or, you know, passively listen for beacons.
• 2:21
  SPEAKER_00: Right.
• 2:22
  SPEAKER_00: And after that brief pause, the device Hang
• 2:29
  SPEAKER_00: on.
• 2:31
  SPEAKER_01: If my phone ranks these and finds an AP that is just, say,
• 2:38
  SPEAKER_01: one dBm stronger than the current one,
• 2:40
  SPEAKER_01: wouldn't switching immediately cause a nightmare?
• 2:42
  SPEAKER_01: Like if I just lean back in my chair, the signal fluctuates.
• 2:45
  SPEAKER_00: Oh yeah, for sure.
• 2:46
  SPEAKER_01: So my phone would just be constantly bouncing back and forth between the two.
• 2:49
  SPEAKER_00: Yes, you have just described what we call the ping pong problem.
• 2:53
  SPEAKER_00: To prevent your device from constantly tearing down and rebuilding connections
• 2:56
  SPEAKER_00: over minor fluctuations,
• 2:58
  SPEAKER_00: well, manufacturers require a massive upgrade to justify a jump.
• 3:02
  SPEAKER_01: So a tiny improvement won't cut it.
• 3:04
  SPEAKER_00: Exactly.
• 3:05
  SPEAKER_00: Apple demands a new AP be 8 to 12 dBm stronger before it will actually switch.
• 3:10
  SPEAKER_01: Wow, that is a big jump.
• 3:12
  SPEAKER_01: And because jumping is so disruptive,
• 3:14
  SPEAKER_01: the network has to try and help the client out,
• 3:16
  SPEAKER_01: which brings us to the alphabet soup of network amendments.
• 3:21
  SPEAKER_01: 802.11kv and R. Right, the helpers.
• 3:25
  SPEAKER_01: Starting with K or neighbor reports.
• 3:27
  SPEAKER_01: Our sources show the network hands the device a list of nearby APs,
• 3:31
  SPEAKER_01: so it does not have to blindly scan every single channel.
• 3:35
  SPEAKER_00: Yeah, and taking that a step further with 802.1 MNV or BSS transition,
• 3:40
  SPEAKER_00: the network does not just hand you a map, it actually recommends the best route.
• 3:44
  SPEAKER_01: Oh, I see.
• 3:45
  SPEAKER_00: The AP suggests a move to a better access point,
• 3:48
  SPEAKER_00: though, again, the client still makes a final call.
• 3:50
  SPEAKER_01: Right, the client is king.
• 3:51
  SPEAKER_01: And then there is the VIP FastPass, which is 802.109R fast transition.
• 3:56
  SPEAKER_01: It skips the lengthy enterprise authentication handshake.
• 3:59
  SPEAKER_00: Exactly.
• 3:59
  SPEAKER_00: Instead of a disruptive three-second connection drop while you switch APs,
• 4:03
  SPEAKER_00: it cuts the downtime down to mere milliseconds.
• 4:06
  SPEAKER_01: That is a huge difference.
• 4:07
  SPEAKER_01: But since network admins can't force a client to roam even with those protocols,
• 4:10
  SPEAKER_01: they have to create this illusion of control through design.
• 4:14
  SPEAKER_01: Like configurations must be completely identical across the network.
• 4:18
  SPEAKER_00: Yes, matching channel widths and security so all APs look equally attractive.
• 4:23
  SPEAKER_01: Which actually leads to a really counterintuitive trap.
• 4:26
  SPEAKER_01: You would think turning your Wi-Fi transmit power up to maximum would give you
• 4:29
  SPEAKER_01: the best performance.
• 4:31
  SPEAKER_00: Oh, people do that all the time, and that is actually terrible for roaming.
• 4:34
  SPEAKER_01: Wait, really?
• 4:35
  SPEAKER_01: Why?
• 4:35
  SPEAKER_00: Well, if you blast the AP power,
• 4:38
  SPEAKER_00: a client device will never see the signal degrade enough to hit that negative 70
• 4:42
  SPEAKER_00: or 75 dBm trigger.
• 4:44
  SPEAKER_00: It'll just cling to the original AP forever.
• 4:47
  SPEAKER_01: Completely oblivious to the much closer, faster AP right next to it.
• 4:51
  SPEAKER_00: Exactly.
• 4:52
  SPEAKER_00: Never feels the shiver, so it never moves.
• 4:54
  SPEAKER_01: So our devices are constantly negotiating these connections through a maze
• 4:58
  SPEAKER_01: of invisible rules, hidden thresholds, and network assists.
• 5:02
  SPEAKER_01: But at the end of the day, your phone or laptop is entirely autonomous.
• 5:05
  SPEAKER_00: Yeah, it acts in its own self-interest based strictly on how it was programmed.
• 5:09
  SPEAKER_01: Which leaves you with this to mull over.
• 5:11
  SPEAKER_01: If our devices are making all these complex autonomous calculations just to keep
• 5:15
  SPEAKER_01: a simple web page loading smoothly,
• 5:18
  SPEAKER_01: what other invisible decisions are they making in our pockets right now?