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Trivia Champ
Trivia Champ
Posts: 6,014
Registered: ‎09-24-2008

Re: Ping/Lag Spikes over wifi


@cglitcher wrote:

This only happens over wifi, never when I'm connected via Ethernet


Please do not tell me to use a wired connection - I'd like to have the mobility wifi provides.

The Simple Answer(TM) is "You want speed and reliability, go wired. You want convenience, go wireless." Pick your poison accordingly.


@cglitcher wrote:

My indoor RF buddy has told me that unlicensed AP radios have to stop all traffic to do a listen sweep every 2 minutes or so in order to comply with an FCC mandate.

Never heard that one before, but 802.11 wifi I'd argue is half-duplex communication. Reason is the 802.11 spec uses a method called
CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) to check when each node can transmit. Wired ethernet also includes a
similar method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection), but that's only for backwards compatibility reasons
-- everything running on wired ethernet has been full duplex for 20+ years now.

Dumb Question(TM), but just how many 802.11 based hosts total do you have in your house? Be aware that the more 802.11 hosts
you got, the longer the CSMA/CA timers may run -- back to the half duplex nature of wifi I mentioned, imagine how well a long conversation
goes in a room of 4+ people, and only 1 person can talk at a time, and everyone fighting for a "slot" to start their piece of the conversation.


"DFS Channel Availability Check
When support for DFS is enabled, it will be necessary for WiFi access points to verify that any radar in proximity is not using DFS frequencies. This process is called Channel Availability Check, and it’s executed during the boot process of an access point (AP) as well as during its normal operations.


If the AP detects that a radar is using a particular DFS channel, then it will exclude that channel from the list of available channels. This state will last for 30 minutes, after which the AP will check again if the channel can be used for WiFi transmissions.


The Channel Availability Check performed during the boot process can take anywhere between 1 and 10 minutes, depending on which country you’re in. For this reason, DFS channels are not immediately available when an AP boots.


As I just wrote, if the AP detects during the boot process that a DFS channel is currently used by a radar, it will mark it as non-available and exclude it from the list of available channels. This process will have little impact on the WiFi clients.


However, if an AP detects, during normal operations, that a radar is using a particular channel that is currently in use, then it may communicate to associated WiFi clients to stop transmitting on that channel. (Please be aware that not all AP vendors may announce a channel change to clients.) The AP will then switch to another available DFS channel within the Channel Move Time, which is generally set to 10 seconds. This behavior will cause connected WiFi clients to be disconnected from the network for a period of time before re-connecting to a different channel.


It’s very important to keep this behavior in mind when enabling the DFS function. WiFi networks that are servicing real-time and mission-critical applications may want to avoid such disconnections caused by DFS frequencies."


link to article



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